Atkinson-WJ-1967-PhD-Thesis.pdf - Spiral

A

THESIS

entitled

REGIONAL GEOCHEMICAL STUDIES IN COUNTY LIMERICK,

IRELAND, WITH PARTICULAR REeERENCE TO

SELENIUM AND MOLYBDENUM

Submitted for the

degree of

DOCTOR OF PHILOSOPHY

in the

FACULTY OF SCIENCE IN THE UNIVERSITY OF LONDON

By

WARREN JOHN ATKINSON

Royal School of Mines, Imperial College. January, 1967

ABSTRACT

Geochemical studies of an area in Co. Limerick, Ireland, containing Mo and Se-rich Namurian black shales (Clare Shales) show that the metal content of stream sediments sampled at a density of 1-2 samples per sq. mile can be related to patterns in the bedrock and overburden. Anomalous concentrations of Mo and Se in the drainage also reflect the metal content of pasture herbage and afford a means of detecting areas in which toxic or sub-toxic levels in the herbage are related to problems of animal nutrition.

Primary dispersion studies define characteristic minor element patterns for the various bedrock types and investigations are made of the modes of dispersion of Mo, Se and some other metals, in the black shale facies.

Metal patterns in the soils and overburden are described and the dispersion of Mo and Se is shown to be predominantly controlled by the origin of the overburden, the effects of glacia-tion, drainage and the distribution of secondary iron oxides and organic carbon. Particular attention is paid to modes of forma-tion leading to toxic concentrations of Mo and Se in swamp and alluvial soils.

The distribution of Mo and Se in common pasture species is described and it is shown that the Mo content of topsoil, modified by soil 44ction is the major influence on uptake by herbage. However, toxic concentrations of Se in herbage.are re-stricted to Se-rich organic, poorly drained soils with pH greater than 5.5.

Concentrations of Mo and Se in near-surface groundwaters are closely related to the total metal content of the soil profile. Accumulation of Mo and Se in peaty-swamps is attributed to metal introduced in groundwater and fixed by sorption on organic matter and iron oxides. Decomposition of metal-rich organic soils has led to high concentrations of Mo and Se in near-surface groundwater.

Mo and Se precipitate at seepage zones mainly in associa-tion with iron oxides and organic matter respectively, but dispersion downstream in sediments is mainly mechanical. In stream sediments and alluvial deposits, Se only is enriched by sorption on organic carbon which accumulates in calcareous precipitates. The Se content of stream waters can probably be related to the presence of soluble and hence available Se in the catchment soils.

Examples are given of the application of stream sediment reconnaissance to problems of agriculture and geology.

ii

CONTENTS

Page

ABSTRACT

LIST OF TABLES

LIST OF FIGURES

•••

•••

• • •

•••

•••

• • •

••• •••

• • • • • •

• • • • • •

CHAPTER I. INTRODUCTION 1

1. ORIGIN OF THE RESEARCH ... ... 2

(i) Regional Geochemistry ... ... 2 (ii) Regional Biogeochemistry .00 5

2. PREVIOUS WORK ... ... ... 8 (i) Selenium in Relation to Nutrition 8 (ii) Molybdenum in Relation to Nutrition 10

3. PRESENTATION OF THESIS 0.8 • s 4 12

4. ACKNOWLEDGEMENTS .. . 000 006 13

PART A

CHAPTER II. DESCRIPTION OF AREA • • • 15

1. LOCATION ... • • • • • • ... 15

2. GEOLOGY ... me. .06 • • • 15

(a) Pre-Quaternary Geology ... 000 16 (b) Quaternary Geology ... 6.6 21

3. CLIMATE ... ... O.. • • • 26 4. GEOMORPHOLOGY 006 O.. 6.6 27

5. SOILS ... ... • • • ... 28

CHAPTER III. SAMPLING AND ANALYTICAL TECHNIQUES 32

1. FIELD SAMPLING ... 0.0 .00 32

(a) Rocks ... ••• ••• 33 (b) Stream Sediments ••• ••• 33 (c) Soils ... ••• ••• 34 (d) Herbage ••• ••• 35 (e) Natural Waters .00 ••• ••• 36

2. SAMPLE PREPARATION ... 44.

(a) Rocks ... •••

(b) Soils and Sediments •••

(c) Drift ... •••

(d) Peat ... (e) Herbage • • •

3. ANALYTICAL TECHNIQUES 900

.00

•••

•••

•••

• • •

• • •

Page

36

36 36 37 37 37 38

(a) Spectrographic Techniques • • • 38 (b) Selenium • • • • • • 41 (c) Molybdenum • • • 42 (d) Iron ... • • • 43 (e) Copper 044. Os. • • • 43 (f) Zinc ... 4.4 609 • • • 44 (g) Phosphorus • • • 44 (h) Arsenic • • • 44 (i) Sulphate • • • 45 (j) Sulphur GOO .00 • • • 45 (k) Organic Carbon ... 45 (1) Carbonate and Bicarbonate • • • 46

4. MISCELLANEOUS TECHNIQUES • • • • • • 46

(a) pH ... ... .40 00 • 46 (b) Eh ... ... • • • ••• 47 (c) Size Analysis by Wet Dispersion ••• 48 (d) Heavy Liquid Separation ... • • • 50

PART B

CHAPTER IV. THE REGIONAL METAL PATTERNS 44. 51

1. STREAM SEDIMENTS 0.11 • • • 0.6 52

2. BEDROCK ... ... • . • 6.6 57 3. OVERBURDEN ... .64 040 066 61 4. HERBAGE ... 0.. 6.0 468 66

5. DISCUSSION ... • • • ... 68

CHAPTER V. DISTRIBUTION OF METAL IN THE FLYNN'S FARM AREA 40. ... 4.4 72

1. GENERAL DESCRIPTION OF THE AREA 6.1 72

2. STREAM SEDIMENT METAL PATTERNS ... 74

3. NhTAL PATTERNS IN THE SOILS ... ... 77 4. METAL PATTERNS IN PASTURE HERBAGE ... 81

5. DISCUSSION ... 060 004 00. 83

iv

Page

PART C

CHAPTER VI. DISTRIBUTION OF METAL IN THE CLARE SHALES 86

1. VARIATION OF METAL CONTENT WITH LITHOLOGY IN THE CLARE SHALES ... 0.0 0.0 87

2. VERTICAL AND LATERAL DISTRIBUTION OF METAL IN THE CLARE SHALES ... ... 4.. 90

3. MODE OF OCCURRENCE OF METAL IN THE SHALES 96

(i) Relationship Between Sulphur and Selenium 96 (ii) Relationship Between Sulphur and Molybdenum 97 (iii) Selenium and Molybdenum in Relation to

Organic Carbon ... 00. 98 (iv) Selenium and Molybdenum in Relation to

Iron ... 420 000 99 (v) Distribution of Metal in Mineral Fractions 100

SUMMARY OF RESULTS ... 044 107

5. ORIGIN OF MOLYBDENUM AND SELENIUM IN THE CLARE SHALES ••• ••• ••• •••

111

CHAPTER VII. DISTRIBUTION OF METAL IN OVERBURDEN 119

1. RESIDUAL SOILS ... .00 .06 119

(i) Distribution of Metal in the Soil Profiles 120

(a) Molybdenum and Selenium 120 (b) Other Metals 000 004 128

(ii) Size Analysis of Residual Soil Samples 132

(a) Molybdenum and Selenium ... 133

(b) Other Metals .20 000 135

2,. TRANSPORTRD OVERBURDEN ... 000 135

(i) Colluvium •••

•••

•••

138 (ii) Glacial Drift •••

•••

•••

139 (a) Areal Distribution of Metal in Drift 140 (b) Distribution of Metal in Drift Profiles 142 (c) Mechanical Analysis of Drift and the

Distribution of Metal Between Size Fractions 158

(iii)Alluvium .40 .00 166

(a) Distribution of Metal in Profile 167 (b) Size Analysis of Alluvium 0.0 183

220 222 232 233 238 239 240 243

' v

Page

(iv) Peaty-Swamp Deposits • • • • • • 184

(a) Distribution of Metal in Peaty-Swamp Profiles ... 187

(b) Lateral Metal Distribution Patterns in the Peaty-Swamps and Adjacent Over- burden 000 &•• 000

193 (c) Accumulation of Mo and Se in Peaty-

Swamp Soils 198

3. COMPARISON OF -2 mm AND -80 MESH ANALYSES 207

4. SUMMARY OF CONCLUSIONS CONCERNING THE ORIGIN OF MOLYBDENUM AND SELENIUM PATTERNS IN OVER- BURDEN ... 000 ... 00. 209

CHAPTER VIII. METAL DISTRIBUTION IN HERBAGE 213

1. DISTRIBUTION OF MOLYBDENUM, SELENIUM AND COPPER IN SOME COMMON PASTURE SPECIES ... 213

2. FACTORS INFLUUCING METAL UPTAKE BY PLANTS' 219

(a) Metal Content of the Topsoil (b) Soil Reaction ... (c) Eh of the Soil Environment (d) Drainage (e) Organic Matter ... (f) Iron ... solo ...

(g) Sulphate and Phosphate

3. DISCUSSION AND SUMMARY

CHAPTER IX. DISTRIBUTION OF MOLYBDENUM AND SELENIUM IN DRAINAGE ... ... 247

1. GENERAL DESCRIPTION OF FLYNN'S FARM DRAINAGE SYSTEM ... 000 ... 000 247

2. MOLYBDENUM AND SELENIUM CONTENT OF GROUNDWATERS 250

(a) Molybdenum and Selenium in Fackground Areas 250 (b) Groundwaters from Clare Shales 006 251

(c) Groundwaters Draining Drift ... 251

(d) Groundwaters from Peaty-Swamp Deposits 255 (e) Groundwaters from Alluvial Deposits 256 (f) Summary - Molybdenum and Selenium Content

of Groundwaters see ... 258 3. MOLYBDENUM AND SELENIUM CONTENT OF SURFACE WATERS 261

(a) Molybdenum and Selenium Content of Stream

Waters from Background Areas 4.0 261

vi

Page

(b) Distribution of Molybdenum and Selenium in Surface Waters Draining the Flynn's Farm Area ... ... 262

(0) Possible Relationship of Metal Concentrations in Stream Waters to Toxic Soils ... 274

(d) Summary - Molybdenum and Selenium in Stream Waters ... 27? ... ...

4. DISTRIBUTION OF MOLYBDENUM AND SELENIUM IN STREAM SEDIMENTS ... ... ... 278

(a) Molybdenum and Selenium in Sediments from Background Areas 400 WOO 278

(b) Molybdenum and Selenium in Sediments from Flynn's Farm Drainage ... ... 279

(c) Factors Influencing the Metal Content of Stream Sediments 00. 400 281

(i) Mechanical Composition (ii) Physio-Chemical Associations ... (iii) Mode of Occurrence of Molybdenum and

Selenium in Stream Sediments ... (iv) The Distribution of Molybdenum and

Selenium in Bank Soils (d) Summary of Conclusions on the Dispersion

of Molybdenum and Selenium in Stream Sediments • • • • • •

281 282

288

295

304

PART D

CHAPTER X. THE APPLICATION OF REGIONAL GEOCHEMISTRY 308

1. REGIONAL GEOCHEMICAL SURVEYS AND AGRICULTURAL PROBLEMS ... .e. ..• 308

(a) Geochemical Environment Maps 310 (b) Potential Toxic Selenium Occurrences and

Geochemical Environment Maps in Co. Limerick 311

(c) Relationship of Molybdenum Stream Sediment Anomalies to Bovine Hypocuprosis 312

(d) Biogeochemical Reconnaissance in Other Areas 315

2. THE APPLICATION OF REGIONAL GEOCHEMICAL SURVEYS TO GEOLOGICAL MAPPING ... 44. 317

CHAPTER XI. CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH 0.4 0.6 O..

320

LIST OF REFERENCES .... 490 444 .041 329

vii.

LIST OF TABLES

No. Title Page

1 Major Rock Formations in the Area 21

2 Main Glacial Events of the Quaternary Period in Ireland 22

3 Climatic Features of the Area 26

4 Spectrographic Equipment and Conditions 39 5 Wavelengths and Usable Concentration Ranges of

Spectral Lines 40 6 Size Fractions Obtained from Mechanical Analysis 49

7 Metal Contents of Stream Sediments from Different Bedrock Areas 53

8 Metal Content of the Major Rock Types Compared with Average Values for Common Sedimentary Rocks 60

9 Metal Content of Soils and Drift from Different Bedrock Areas 63

10 Regional Distribution of Metal - Comparison of the Mean Metal Contents of Bedrock, Overburden and ' Stream Sediments 69

11 Mean Metal Content of Different Shale Types - Kilcolman Creek Section 89

12 Minor Element Content of the Clare Shales 92

13 Organic Carbon Content of Clare Shale Samples in Relation to the Molybdenum and Selenium Content 99

14 Separation of the Pyrite Fraction from Some Clare Shale Samples 102

15 The Distribution of Minor Elements in Mineral Fractions of the Clare Shales 103

16 Distribution of Molybdenum and Selenium in Residual Soil Profiles 121

17 Other Metal Content of Residual Soil Profiles 129

18 Distribution of Other Metals in Size Fractions of Residual Soils 136

19 Drift Soil Profiles Selected for Study 143

20 Some Physical Characteristics of Elton, Howards- town and Kilrush Series Soils of Drift Origin 144

21 Glacial Drift Profiles in Background Areas. 146

viii

No. Title Page

22 Glacial Drift Profiles with Anomalous Molybdenum and Selenium Contents 148

23 Metal Content of Selected Glacial Drift Profiles 159

24 Distribution of Metal in Size Fractions of Glacial Drift 162

25 Description and Molybdenum and Selenium Content of Alluvial Profiles from Background Areas 168

26 Metal Content of Background Alluvial Profiles 170

27 Profile (BP 28) of Anomalous Alluvium of Pre- dominantly Clare Shale Origin 172

28 Metal Content of Alluvium of Predominantly Clare Shale Origin 173

29 Profile and Molybdenum and Selenium Content of Alluvium of Mixed Limestone and Clare Shale Origin 176

30 Profiles of Anomalous Alluvium of Predominantly Limestone Origin 178

31 General Metal Content of Alluvium of Predominantly Limestone Origin 180

32 Distribution of Metal Between Size Fractions of Alluvium 185

33 Distribution of Molybdenum and Selenium in Peaty- Swamp Profiles from a Background Area 188

34 Profile (BP 6) and Distribution of Molybdenum and Selenium in Peaty-Swamp Deposits, Flynn's Farm Area 189

35 General Metal Content of Peaty-Swamp Soils - Flynn's Farm Selenium Toxic Field 192

36 Comparison of the Metal Content of Peaty and Non- Peaty Soils on the Margin of Peat-Swamp Deposits 197

37 Metal Content of Typical Pasture Species 215

38 Influence of Soil Reaction on Availability of Molybdenum 223

39 Effect of pH on Selenium Uptake by Herbage from Peaty-Swamp Soils 228

40 Relationship Between pH and Selenium Uptake by Red Clover Growing on Alluvial Soils 231

41 Metal Uptake by Plants Under Varying Conditions of Drainage 236

ix

No. Title Page

42 Metal Content of Groundwater from Background Areas 250

43 Molybdenum and Selenium Content of Groundwater from Clare Shale Overburden 251

44 Relationship of Molybdenum and Selenium Content of Groundwater to that of the Soil 253

45 Relationship of Molybdenum and Selenium in Groundwater to Molybdenum and Selenium Content of Alluvium 257

46 Relationship of Molybdenum and Selenium in Groundwater to Molybdenum and Selenium Content of Overburden 260

47 Metal Content of Stream Waters from Background Areas 262

48 Summary - pH, Eh and Bicarbonate Content of Surface Waters Compared to Groundwaters 263

49 Bicarbonate Content of Waters from Non-Limestone Areas 264

50 Comparison of Calculated and Observed Molybdenum and Iron Contents of Stream Waters 268

51 Comparison of Molybdenum and Selenium Content of Flynn's Creek Stream Waters Collected During Two Field Seasons at Similar Sites 276

52 Molybdenum and Selenium Content of Stream Sediments from Background Areas 279

53 Distribution of Metal Between Size Fractions of Stream Sediments 283

54 Comparison of Molybdenum and Selenium Content of Normal Stream Sediment and CaCO

3 Concretions 288

55 Molybdenum and Selenium Content of Stream Sediments in Relation to Organic Carbon and Iron Oxide Content of the Sample 290

56 Blood Copper Values from Dairy Herds Grouped According to Molybdenum Content of Local Stream Sediment 314

x

No.

1

LIST OF FIGURES

Following Page No.

Title

Location of Area, Principal Cities and Locali- ties Mentioned in Text 15

2 Major Roads, Principal Towns and Localities Mentioned in the Regional Study Area 15

3 Simplified Geology of the Area Covered by the Regional Geochemical Survey 16

4 Extent of the Wiechsel Glaciation in Ireland 21

5 Glacial Drift and Overburden Map of the Area 23

6 Topography, Regional Study Area 27

7 Generalized Soil Map of the Area 28

8 Regional Distribution of Molybdenum in Stream Sediments of Tributary Drainage 53

9 Regional Distribution of Selenium in Stream Sediments of Tributary Drainage 54

10 Regional Distribution of Metal in Stream Sediments. Logarithmic Frequency Plots for Molybdenum and Selenium 54

11 Regional Distribution of Metal in Stream Sediments. Logarithmic Frequency Plots for Copper and Vanadium 55

12 Regional Distribution of Molybdenum in Soil and Drift 55

13 Trace Element Content of Major Rock Units 57 14 Regional Distribution of Molybdenum in Rock 58

15 Regional Distribution of Selenium in Rock 58

16 Diagram Illustrating the Mean Values and Range of Metal in the Four Major Rock Types 60

17 Regional Metal Content of Herbage 66 18 Topography and Place Names - Flynn's Farm Area 72

19 Distribution of Molybdenum in Stream Sediment, Soil and Mixed Herbage and Simplified Overburden Map 74

20 Distribution of Selenium in Stream Sediment, Soil and Mixed Herbage and Geology 75

xi

Following No. Title

Page

Distribution of Copper in Stream Sediments and Topsoil - Flynn's Farm Area 76

22 Distribution of Vanadium in Stream Sediments and Topsoil - Flynn's Farm Area 77

23 pH of Topsoil - Flynn's Farm Area 81

24 Thin Sections of Clare Shales 87

25 Stratigraphical Sections of the Clare Shales Showing the Molybdenum and Selenium Content 92

26 Vertical Sections of the South Shelf of the Clare Shale Basin Showing Metal Distribution in Strati- graphic Zones 92

27 Variation of Molybdenum and Selenium Clare Shales 92

28 The Stratigraphic Relationships of Molybdenum : Selenium Ratios in the Clare Shales 93

29 Variation of Molybdenum and Copper in Clare Shales 94

30 Variation of Sulphur - Selenium in Clare Shales 96

31 Variation of Sulphur - Molybdenum in Clare Shales 97

32 Relationship of Molybdenum and Selenium to Iron in Clare Shales 99

33 Size Analysis of Residual Soils 132

34 North-South Section Across South Margin of Peaty- Swamp Area - Flynn's Farm 138

35 Size Analysis of Glacial Drift Samples 161

36 Distribution of Selenium in Alluvium, North-South Section Across Alluvial Flat - Toxic Soil Site B 169

37 Distribution of Molybdenum in Alluvium, North- South Section Across Alluvial Flat - Toxic Soil Site B 169

38 Size Analysis of Alluvium Samples 183

39 West-East Vertical Section Across Mat Margin of Flynn's Toxic Field 187

40 Flynn's Farm Peaty-Swamp Area - Molybdenum and Selenium Content of Ground and Stream Waters 199

41 Stability Fields of Some Ionic Species of Molybdenum Selenium and Iron 201

42 pH-Eh Status of Groundwaters 201

xii

Following No. Title

Page

43 Solubility of Ferric Molybdate at Varying pH 202

44 Relationship Between Molybdenum Content of Topsoil and Pasture Herbage 220

45 Molybdenum Content of Topsoil and Red Clover Under Various Soil pH Conditions 221

46 Relationship Between the Selenium Content of Topsoil and Pasture Herbage 221

47 Relationship between Molybdenum Uptake by Red Clover and Soil Reaction 223

48 Relationship Between Selenium Uptake and Soil Reaction 227

49 pH-Eh Environment of Natural Waters of Study Area 249

50 Relationship Between Metal Content of Soil and Near-Surface Groundwater 252

51 Relationship Between Molybdenum and Selenium in Ground and Surface Waters 252

52 Metal Content of Ground and Stream Waters at the Head of North Creek 265

53 Metal Content of Stream Waters - Flynn's and South Creeks 269

54 Distribution of Molybdenum and Selenium in Stream Waters, Sediments and Bank Soils of Flynn's Creek 270

55 Distribution of Molybdenum and Selenium in Stream Waters, Sediments and Bank Soils of South Creek 271

56 Size Analysis of Stream Sediments 282

57 Distribution of Organic Carbon and Acid Soluble Iron with Reference to the Molybdenum and Selenium Content of Stream Sediment - South Creek 285

58 Relationship of Molybdenum and Selenium to Acid Soluble Iron in Stream Sediments 286

59 Relationship of Molybdenum and Selenium to Organic Carbon in Stream Sediments 286

6o Metal Distribution in Stream Sediments and Bank Soils of Crook Creek 286

61 Metal Content of Stream Sediments at the Head of North Creek 286

Following No. Title Page

62 Stream Bank Cross-Sections Showing Molybdenum and Selenium Content

296

63 Regional Geochemical Environment Map for Selenium 312

64 Location of Dairy Herds Sampled in Relation to Anomalous Molybdenum Stream Sediment Patterns

313

"It is a fact that when they take that road they cannot venture among the mountains with any beast of burden excepting those accustomed to the country, on account of a poisonous plant growing there, which if eaten by them has the effect of causing the hoofs of the animals to drop off. Those of the country, however,'being aware of its dangerous quality, take care to avoid it."

Marco Polo - circa 1275 A.D.

CHAPTER I. INTRODUCTION

The above excerpt from "The Travels of Marco Polo"

is the first recorded instance of what was almost certainly

the accumulation of toxic quantities of Se in plants. Since

then, numerous additional instances of Se poisoning have been

recorded and in general our knowledge of the effects of defi-

ciences or excesses of a large number of metals in plants has

been extended to cover many aspects of agriculture and the

health of human populations as well.

At the same time, but more particularly in recent

years, a vast amount of data on the geochemical distribution

of metals has accumulated, partly from straight geological

studies but also as the result of mineral exploration programmes.

It is estimated (Webb, 1964) that as the result of current world-

wide geochemical surveys involving the sampling of rocks, soils,

herbage, waters and drainage sediments, in the order of

150,000,000 analytical determinations are made each year.

2

In view of the large amount of knowledge that is

accumulating on the geochemical patterns in the upper part of

the earth's crust and on the agricultural and health aspects

of trace element distribution, an obvious problem that arises

is the best means of applyihg the full benefits of the develop-

ing geochemical techniques and data to trace element problems

of agriculture and health. This thesis primarily deals with an

investigation of geochemical mapping techniques applied to the

definition of areas in which abnormal concentrations of trace

elements exist. More specifically, it is concerned with relating

the gbological and geochemical occurrence of excessive concentra-

tions of Se and Mo in the bedrock and soil of an area in Ireland

to the Se and Mo contents of natural herbage by means of regional

stream sediment sampling, as first proposed by Webb (1964).

1. ORIGIN OF THE RESEARCH ssr,onvxan

1122.12221 Geochemistry

In the 1930's the original research by Vernadsky and

Fersman in the U.S.S.R. and Goldschmidt in Scandinavia showed

that anomalous concentrations of metal in soils and plants could

indicate the presence of concealed mineral deposits in the bed-

rock. Since then, and particularly during the last twenty years,

geochemical techniques have advanced rapidly in scale and range

of applications. The dominant impetus to development of the

sampling and analytical methods required has been the needs of

3

the mineral exploration industry.

Geochemical surveys which were intially aimed at the

location of anomalies directly due to mineralisation are now also

employed on a regional scale to delimit by reconnaissance broad

areas or geochemical provinces in which mineral deposits may

occur. More detailed studies are then initiated in these areas.

Regional surveys to disclose broad patterns of metal

distribution related to mineral deposits have involved wide-

spaced sampling of the bedrock, glacial drift, soils, herbage

and waters and sediments of the natural drainage. Although rock

and soil samples may be more closely linked with the metal

content of the bedrock mineral deposits, the present tendency

is to employ stream sediment samples becausel by virtue of their

origini they are more representative of the metal content of the

stream catchment as a whole. It has been shown in many cases

that the presence of mineral deposits located within the catch-

ment is reflected in the metal content of the stream sediments

draining the area (e.g. Case Histories, Chapter 17, Hawkes and

Webb, 1962).

Hawkes et al (1956) showed during the course of a

geochemical mineral reconnaissance carried out in New Brunswick

in 1954 that the background concentrations of base metals in

stream sediments could be related to the distribution of the

principal bedrock units. From this the concept of regional

geochemistry arose in which multi-element analysis of stream

4

sediment samples serves as a means of compiling maps that

reflect the distribution of metals, not only in the drainage

sediments but in the rocks and the bedrock from which they

were ultimately derived. Pioneer studies by Webb et al (1964)

in the Namwala Concession Area, Zambia, in the early 1960's

demonstrated that the overriding control of the metal patterns

in the stream sediment was the bedrock geology. Subsequent

work by Viewing (1962) and James (1964) in Sierra Leone con-

firmed this.

It is true that secondary environmental factors

modify the trace element content of the material as it passes,

during weathering and transport, from rock to soil and thence

to stream sediment. However, the overall bedrock patterns are

retained provided that the drainage takes place along reasonably

well-defined channelways. The greater representivity of stream

sediment samples, compared with rocks and soils which are only

representative of a relatively small area, makes it practical

to map large regions geochemically using widely spaced samples.

Water sampling has the advantage of providing a more homogeneous

sample but is subject to seasonal variations and the influence

of other factors on the composition of natural waters in addi-

tion to problems of analysis and the transport of relatively

bulky samples.

5

(ii) Regional Biogeochemistry

Studies in agriculture and general health have shown

the essentiality of balanced amounts of trace elements to the

well-being of plants, animals and man. Many examples of the

effects of excesses and deficiences of such elements as Co, Cu,

Fe, I, Mn, Mo, Pb, Se and Zn have been recorded (Underwood,

1962; Schutte, 1964).

Although the primary source of trace elements in

the biochemical cycle lies in the bedrock, the actual links

between the metal content of the rock, the soil, water, plants,

and animals are subject to the influence of many factors. Not

only is soil composition dependent on the nature of the bedrock

and the overburden, but it also depends on the mobility of the

elements concerned, the nature and intensity of weathering,

topography and other environmental factors. The soil-plant

relationship is also complicated by other factors in addition

to the total metal content of the soil, in particular the form

of the metal in the soil, interrelationships with other elements,

soil reaction and drainage, the effects of fertilizers, etc.

The assimilation of trace elements by animals is,

of course, influenced by the composition of the herbage they

consume, the relative proportions of the elements in the herbage

being determined by the soil types on which it is grown. The

composition of supplementary feeds, particularly if they are

not of local origin, and drinking water and various physiolo-

gical factors will also affect the proportions of trace

6

elements consumed.

In humans, because of the greater complexity and

variety of diet, in addition to the fact that many populations

move from one geological environment to another, the associa-

tion of health and geology is more tenuous. However, instances

of close relations between human health and trace element

distributions are well known, for example the association of

goitre and widespread I deficiency, F and dental health and

Mo and dental caries in New Zealand.

Many cases of trace element problems in agriculture

have been well-documented. Notable examples of trace element

deficiencies which have been recorded in many parts of the

world are Mn and Mo deficiencies in crops and Cu and Co defici-

ences which affect grazing stock. Cases of toxicity due to

excess concentrations of Cu, Mo and Se in the diet are common.

Trace element problems in plants and animals and the

geochemical distribution of trace elements pointed to an obvious

linkage between the two, in which the areal distribution of

nutrition problems could be associated with the geology and

geochemistry of an area. This led to the recognition of

"biogeochemical provinces" in which work of the Russian

geochemists, Vinogradov (1952,. 1957, 1963), Malyuga (1963) and

Kovalskii (1958, 1960) is particularly noteworthy. Other major

contributions to the biogeochemical field have been made by

Cannon (1960), Warren (1960, 1963, 1965), Griffith (1960),

Hewat and Eastcott (1955) and Pieve (1958).

7

In view of the increasing usage of regional geochemical

stream sediment mapping for

Webb in 1963 suggested that

applied to the detection of

geological and prospecting purposes,

similar techniques could be usefully

biogeochemical provinces or more

localised areas in which deficiencies or excesses of trace

elements were of agricultural significance or involved in pro-

blems of human health. Subsequently, experimental stream

sediment surveys were initiated with the following results

(Webb, 1964):

(a) In Ireland low levels of Co in stream sediments

outlined an area in Counties Wicklow and Carlow in which "pining"

in sheep, due to Co deficient soils, had been previously reported

by the Irish Agricultural Institute.

(b) In England, a preliminary drainage reconnaissance

survey of about 350 squake miles in Devon indicated a hitherto

unsuspected zone of anomalous Mo values in sediment draining an

area of Culm Measures. Local farmers had reported difficulties

in rearing lambs and "scouring" in calves from the area of high

Mo values. The symptoms pointed to a possible occurrence of Mo-

induced Cu deficiency.

(c) In Co. Limerick (Fig. 1 and 2), in an area from

which toxic seleniferous soils accompanied by high Mo values had

been reported by the Irish Agricultural Institute, analysis of

stream sediment samples collected by a mining company during

the course of a prospecting survey (see Acknowledgements)

revealed an extensive area in which anomalous concentrations

of Mo occurred. This area was centred on the toxic Se

8

occurrences and the anomalous Mo patterns showed a certain

degree of correlation with the geology of the area. Cu, a metal

which interacts with Mo in metabolism, accompanied the Mo in a

-roughly-similar but less-proncluw.ed pattern.

It was decided.that_this latter-area_would be suit-

able.for.the present.resparch-which-involves-study of the_bio-

geonhemical features of-Mo_andSe and the application _o-f... _

regional geochemical.surveys to agricultural problems.--Before

proceeding to the-detailscifthe study it- is necesqnry-to give

a brief review of the previous work on Se and Mo in relation

to animal health.

2. PREVIOUS WORK

(i) Selenium in Relation to Nutrition

An extensive literature concerning toxic seleniferous

vegetation associated with Se-bearing rocks and soils has

accumulated mainly since 1930. Most of these reports are

concerned with occurrences in the western United States but

examples have also been recorded from Mexico, Canada, Columbia,

Israel, South Africa, Australia, U.S.S.R. and Ireland.

Comprehensive summaries of these are given by Lakin (in

Anderson et al, 1961) and Rosenfeld and Beath (1964).

Briefly, Se was known to be toxic to animals as early

as 1842 (Moxon, 1937) but prior to 1930 the presence of toxic

quantities of any particular element in certain plants that

grew on soils containing excessive amounts of that element was

9

not accepted as an important factor in animal poisoning.

However, some thirty years ago work by officers of the U.S.

Dept. of Agriculture, particularly at the S. Dakota and

Wyoming Agricultural Experimental Stations, proved that the

symptoms of "alkali disease" and "blind staggers" were due to

high concentrations of Se in certain plants growing in grazing

areas (Byers, 1935; Munsell, 1936).

Further work proved that these plants only grew on

soils containing greater than normal amounts of Se and that

these soils were derived from seleniferous bedrock. Some plants,

often characteristic species and in particular some varieties

of Astragalus sp., accumulated quantities of Se much greater

than other species growing on the same soils. From this the

concepts of "indicator" and "accumulator" plants were formulated.

It was found that a general relationship existed between the

total concentration of Se in the soil and the concentration in

any given species growing on it. However, the form of Se in

the soil varied from relatively insoluble selenite to more soluble,

available selenate, and that only some forms of plant life, the

"accumulatole, were capable of absorbing the less available

forms of the element in toxic quantities, but when these

accumulator plants died and decomposed the element was released

again into the soil in more generally available forms. Such

plants are regarded as "converters" of Se.

10

In general, "indicator", "accumulator" and "converter"

plants are often one and the same species, but it was found

and this is the case in Ireland (Walsh and Fleming, 1952) -

that recognisable "indicator" or "accumulator" species may

not always be present and that toxic concentrations may exist

in the general pasture herbage, including grasses.

In the western U.S. the biogeochemical correlation

.of toxic vegetation with seleniferous soils, known seleniferous

rock horizons and the recognition of "indicator" plant species,

has led to the mapping of seleniferous areas by plant surveys.

Similar methods have also been used for the detection of other

metals associated with Se (Cannon, 1957). The technique is,

of course, dependent on the presence and recognition of suitable

indicator plants. Furthermore, in addition to natural factors

controlling the distribution of individual plants, interpreta-

tion of the results can be particularly difficult in semi-

cultivated areas or where new pasture species have been intro-

duced.

In Ireland, Fleming and Walsh (1957) recorded the

biogeochemical correlation of seleniferous herbage and soils with

Se-bearing shales.

(ii) Molybdenum in Relation to Nutrition

It is now well established (Underwood, 1962) that Mo

is an essential element for plant growth due to its involvement

in the nitrogen cycle and is particularly important for the

11

growth of legumes e.g. clover, where it concentrates in the

nitrogen-fixing nodules (Vinogradova, 1943). As a consequence

of this discovery, many Mo-deficient soils have been located

in various parts of the world and the addition of Mo salts to

the soil have resulted in great improvements to the pasture.

The discovery that Mo is also an essential element in animal

nutrition in its capacity as an ingredient of several enzymes

has naturally augmented interest in Mo deficiency in soils and

herbage.

The toxic effects of excessive amounts of Mo are

more closely related to the subject of the thesis. It has

been established that when present in even moderate excess

in herbage it can cause serious nutritional disorders in live-

stock, especially cattle and to a less extend some other species.

The interaction between Cu and Mo in the animal so that excessive

intake of Mo manifests itself as an Mo-induced Cu deficiency,

has been demonstrated, particularly in Australia and New

Zealand. Inorganic sulphate also plays a part in the relation-

ship by suppressing the effect of Mo on the action of Cu in the

animal. Examples of the biogeochemical relationship between

animal health problems and excessive intake of Mo from herbage

growing on molybdeniferous soils have been reported by Britton

and Goss (1946) and Barshad (1948) in California, Kubota et al

(1961) in Nevada, Cunningham (1950) in New Ze-aland and Marston

(1951) in Australia.

12

One of the earliest and the classic case of this

relationship is the work carried out on the "teart" pastures

of Somerset, England (Ferguson et al, 1943; Muir, 1941; Le

Riche, 1958). It was shown that the disease known as "teartness"

in cattle was due to excessive amounts of Mo in the herbage

growing on molybdeniferous soils. These soils were related

to Mo-bearing shales of the Lower Lias. "Teartness" was not

related to soil type and non-toxic soils only carried normal

amounts of Mo.

Work in Ireland on cases of toxic concentrations of

Se and Mo in herbage has been carried out by workers of the

Irish Agricultural Institute and Dept. of Agriculture. Seleni-

ferous soils and herbage often associated with abnormal con-

centrations of Mo have been recorded in a number of localities

(Walsh et al, 1951; Walsh and Fleming, 1952; Fleming, 1962).

A number of investigations concerned solely with the occurrence

of Mo in soils and herbage have also been undertaken (Walsh et

al, 1952, 1953).

PRESENTATION OF THESIS

The results of the present study follow in four

main sections. Part A is purely descriptive and gives details

of the study area and the techniques employed. In Part B the

regional geochemical patterns are presented empirically with

notes concerning their use in locating abnormal concentrations

13

of metal in herbage. Part C describes the detailed geochemical

investigations of the factors involved in the distribution of

metal in the bedrock, soil, stream sediments, water and herbage.

Finally, the application of geochemical stream sediment recon-

naissance to problems of agriculture and geology are described

in Part D with suggestions for further work.

4. ACKNOWLEDGEMENTS

This work forms part of the continuing programme

in applied biogeochemistry of the Applied Geochemistry Research

Group at Imperial College under the direction of Professor J.S.

Webb. The writer wishes to express his gratitude for help to

all the staff of the group but in particular to his supervisor,

Professor Webb, who initiated the study and helped throughout

with advice and criticism. Also to Mr R.E. Stanton and Dr I.

Nichol for much help and advice in the analytical field and to

Mr I. Thornton for discussion of agricultural problems.

In Ireland the assistance of the Irish Agricultural

Institute was invaluable both at the initiation of the study

and during the course of the investigation. The writer would

like to thank in particular, Dr, T. Walsh, the Director, Mr

G. Fleming of the Dept. of Plant Physiology, Dr Pierce Ryan

and Mr T. Finch of the Soil Survey and Mr D.B.R. Poole of the

Veterinary Research Laboratory. The co-operation of the Irish

Geological Survey is acknowledged and the writer wishes to

thank the Director Mr M, Cunningham and Mr M. O'Meara, also

14

the past Director, Mr M. O'Brien, for helpful discussions.

Thanks are also due to Messrs. Halet, Broadhurst and Ogden

who, on behalf of their clients Messrs. Zenmac Mines and

Tusko Syndicate Limited made available the stream sediment

samples used in the early part of the survey.

The biogeochemical work of the Department is

aided by a Special Research Grant originally awarded by the

Department of Scientific and Industrial Research and now

received from the Natural Environment Research Couhcil. The

writer also wishes to express his gratitude to Rio Tinto-Zinc

Corporation for the financial assistance of a research bursary.

15

PART A

CHAPTER II. DESCRIPTION OF AREA

1. LOCATION

The area selected for regional study comprises about

275 sq. miles situated in Co. Limerick, Ireland, south of the

River Shannon and extending westwards a few miles into Co. Kerry

(Fig. 1): The principal towns, major access roads and localities

mentioned in the text are given in Fig. 2; which also shows the

area of 3 sq. miles chosen for detailed study of metal distri-

bution and dispersion. This area is centred on Flynn's Farm

near the village of Ardagh, where toxic occurrences of Se are

known to occur.

2. GEOLOGY

Detailed descriptions of the geology of Ireland can be

found in the works of Charlesworth (1963), Meehan and Webb (1957),

Nevill (1963) and others. The 3rd Edition of the Geological Map

of Ireland at scale 1:750,000 was published by the Geological

Survey of Ireland in 1962.

The bedrock (pre-Quaternary) geology of the regional

study area is first described, followed by a review of the geo-

chemically important glacial period and recent deposits.

• Buttevant Ballagh

Orchardstown•

Wexford

Belfast

• Enniskillen

••••• ••••%

:•••••••

Mace Hea Galway

• Lisdoonvarna

Batlivor • Naulio

Dublin

*Carlow

Leighlinbridge •

Ballybunnio

Limerick

Cork

0 40 80

miles

FIG.1. LOCATION OF AREA, PRINCIPAL CITIES AND

LOCALITIES NOTED IN TEXT

t4.

FOYNES IS.

ti° gib S

Cliff vxt, et n

°FOYNE

•07%. LOGHILL

SHANAGOLOEN

• ••• •..

• ASIKEATON

CREEVES 3.

DENLEI?

/11).,./ /4 . MAJOR ROADS

• PRINCIPAL TOWNS AND VILLAGES

LIN

RALLYHANILL

/

I.C.OAMAIt

FLYNN'S FARMAD "Mouth Ck.

•

♦

• ..„ RATHKEALNIP..i"

▪ ••• am 40. ▪ 111

GCS.

CAR IGNERRY

•• •

— .0 e •• ........ •riR DAG H

t / I / 1 • .0 /

* i e• / I e• ".... ...• / ...• ...• ...•

‘ •KNOCKADERRY / NEWCASTLE

..---"........ WEST • ../

,

• •

..../ I

.0 • I

STRAN

I 40 • I

ATHEA • • •

I

I I

/ I I

... • . o • / . • " •

....„e ... i ..., O• 4., 40 ..

..• % I

•. / •

KILMEEDV•3

ABBEYFEALE.-

L

0. % lehannegh

• •• • • I

Rellagh\ Sec

..

•

im on ea an re OM On AMA Am MO OM r a OD Am ma /AO

0 2 4 6

miles

FIG. 2. MAJOR ROADS, PRINCIPAL TOWNS AND LOCALITIES •

MENTIONED IN THE REGIONAL STUDY AREA.

16

(a) Pre-Quaternary Geology

As shown in Fig. 3, Old Red Sandstone (O.R.S.) non-

marine sediments occur in the south-east and occupy about 3 per

cent of the area. The O.R.S. apparently rests unconformably on

older Pre-Caledonian structures not exposed in the area. Forming

prominant hills above the surrounding plain, these rocks have the

characteristic purple-red colour of the series and are mainly

represented by fine sandstones, siltstones and shales. Some

greyish-green shales and yellowish sandstones typical of the

uppermost O.R.S. oocur. Charlesworth (1963) describes these

sediments as being accumulated in depressions between mountain

tracts, under freshwater and terrestrial, semi-arid conditions.

The finer, upper O.R.S. sediments present in the area probably

represent lacustrine or lagoonal deposits.

In the Co. Limerick area, the O.R.S. is succeeded

conformably by Carboniferous rocks of the Lower Limestone Shale

series. These shales are about 150 ft in thickness (Charlesworth,

1963) but if present in the study area are concealed by drift.

The area of sub-outcrop is probably small and as fragments are

not readily located in the overlying drift, are of minor geo-

chemical significance.

Carboniferous limestones occupy about 48 per cent

of the area, underlying the mainly drift-covered low-lying

plain in the eastern half of the area. The limestones, including

the basal shale series, are conformable with the O.R.S. and

Glacial striae Carboniferous limestone

Namurian sandstones and siltstones

Clare Shales tiqe:41gli Old Red- Sandstone

ele Limit of glacial drift

* Detailed surve area Figs i8—

=---Th'i*IIIS/110101MOINNIUMMIONW4OWAK. ,===wmwmammulawsmouwwww-mumAmmommmumumumwonnur ==;.inswwwmmatommomocwwww

MMOOMIMIMMIVOMMMONIS,111SMID % --MMOMOWNWWWWWWWOMSNMWMMi% - 41oraNNXIIhi.4141111

Emumiummownwsw mrimmnmwmommmommunril:im

ifiglierral# I t I

1rt [1

111

I1-1

31

--j111 1111111 1.111 .11111 Mil anlinliNi MO in. OM air MO IIMP " lie MI MON gial WI OW OW MOM Mal r". MO

111111111111111=1801 .1111111111111111111111111111111 • NM TWA 111116 willn Er Iv:* memsams 1111111111111111111111111111111— 111111111111111.11111111.11111111WF Eimanas imiu .iararr.maraai

FIG. 3. SIMPLIFIED GEOLOGY OF THE AREA COVERED BY THE REGIONAL GEOCHEMICAL SURVEY. (After Hodson and Le Warne (1961) ' and Irish Geological Survey)

17

probably represent a full sequence of Tournaisean and Visean

stages. Bedded limestones predominate but, in addition to the

shales, oolites and extensively developed and reef limestones

are also present. Some dolomite may also occur but little is

known of its age or origin.

Of possible geochemical significance is the extensive

area of Visean volcanics which mainly outcrop south and south-

east of Limerick city (Gill, in Meenan and Webb, 1957). These

appear to have erupted from a number of small vents and consist

principally of basic and intermediate lavas with some tuff and

agglomerate pyroclastio members. Within the study area, these

volcanics are represented by dark grey to brown coarse tuffs

and agglomerates frequently cemented by a calcareous matrix.

They probably form lenticular deposits interbedded with the

Upper Limestone formations near the village of Kilcolman.

Vent sites or plugs are not recognisable. These rocks occupy

somewhat less than 1 per cent of the study area.

At the close of the Visean a marked change in sedi-

mentation took place. The junction of the Carboniferous

limestones with the overlying Namurian detrital sediments is

non-sequential and marked by an unconformity of mid-Carboniferous,

Sudetian age. The basal rocks of the Namurian in the area,

consist of a sequence of marine black shales which, it will

be shown, are the pre-eminent factor determining the Mo and

Se geochemical patterns in the area. For this reason the

environment to which their deposition is attributed is described

in some detail.

18

Charlesworth (1963) and Hodson and Le Warne (1961)

describe the Namurian as being deposited in a downwarp in the

limestone which extended in a Caledonoid direction from the

Shannon Estuary (the Clare-Limerick basin) near the study area,

across Ireland to the north of Dublin. The extension of this

trough is represented by rocks of similar age in England. The

work of Hodson and Le Warne in Co. Clare and Co. Limerick showed

that the initiation of the trough was Mid-Carboniferous and sub-

sequent to a sedimentary hiatus, but probably followed a pattern

of subsiding tracts in the Lower Carboniferous described by

Lees (1961).

In the study area, the trough had a channel-like

central depressior, closely corresponding to the present

position of the River Shannon, in which the Clare Shales

reached a maximum thickness, flanked to the north (Co. Clare

line of outcrop) and south (Co. Limerick) by sloping shelves.

The form of the basin is the result of differential subsidence

during sedimentation. The line of outcrop of Clare Shales in

the study area (Fig. 3) represents the southern shelf of the

basin. Hodson and Le Warne have shown by mapping stratigraphic

sections and goniatite zones that thinning of the sequence and

overlap of younger horizons takes place southward from near

the centre of the basin at Foynes to Ballagh near the margin.

The basal zone of the Clare Shales, El (Eumorphoceras zone) is

only present in the channel-like centre of the basin, i.e. north

of Foynes on the other side of the Shannon, where the shales

19

are about 1600 ft thick. At Foynes the thickness mapped by

Hodson and Le Warne is about 600 ft, less than half that at

the exact centre of the basin to the north. This represents

the E2

zone, through the H (Homoceras) to the uppermost R1

(Reticuloceras) zones. Moving southwards the shales become

successively thinner until at Ballagh in the south of the study

area, there is not more than 100 ft consisting mainly of the R1

and H zones, the E2 zone being either very thin or absent.

Lithologically the Clare Shales are characteristically

well-bedded black shales, often pyritic and rich in carbonaceous

material. Bullions and nodules, often calcareous or pyritic, are

common at some horizons, particularly on Foynes Island. Siliceous

shales, spongolites (Le Warne, 1963), occur in some areas, inter-

digitating with black shales of equivalent age. These rocks are

made up almost completely of siliceous sponge spicules. In some

areas grey, only slightly carbonaceous shales are present, often

near the top of the sequence.

The "Ribbed Beds" consisting of sandy shales are

present at the top of the Foynes Island section and are included

by Hodson and Le Warne (1961) in the Clare Shales. The fauna is

marine, mainly pelagic forms of goniatites and lamellibranchs.

It is believed that the depositional environment was typical for

black shales, in that circulation in the lower levels of the basin

was limited, resulting in reducing anaerobic conditions.

20

The top of the Clare Shales is marked by an abrupt

change in rock type and sedimentary environment. The black

shales are followed by Namurian non-marine, buff and grey silt-

stones and mudstones with abundant interbedded sandstones. Some

sedimentary coal measures are present. The actual proportion

of sandstone, which constitutes a different geochemical environ-

ment to the argillaceous rocks is not known, but despite the

effects of differential weathering, probably approaches the

ratio established by random sampling, i.e. about 30 per cent

sandstone. Leaf remains are common in the non-marine sediments.

These rocks occupy about 44 per cent of the total study area.

Hodson and Le Warne (1961) consider that the change

from black shales to non-marine, more arenaceous sediments

took place at the same stratigraphic horizon along the length

of outcrop in the area. They use this as a horizontal marker

horizon in the measurement of sections. At some places the

junction is marked by massive sandstones up to 5 ft. thick.

At others it consists of thinner sandstones interbedded with

grey silstones.

The following table summarizes the areal extent of

the major bedrock units that go to make up the primary geo-

chemical environment of the area.

21

Table 1: Major Rock Formations in the Area

Rock Unit Approx. percentage of area covered Environment

Sandstones 13 Namurian

Tuffs

Limestones

Lower Limestone Shales

Old Red Sandstones

44 Non-marine detrital sediments. Some coal measures.

Marine black shale. Organic-rich, reducing.

0.5

Pyroclastic.

48

Chemical-organic, Marine.

Calcareous, detrital.

3 Non-marine, detrital sediments.

Argillites 31

Clare Shales 4

cb) Quaternary Geology

Glacial activity was extremely widespread in Ireland

during the Pleistocene, and extensive deposits of glacial and

fluvio-glacial origin occur in the area. The general Quaternary

succession in Ireland is summarized in the following table which

is based mainly on Mitchell (1957) and Synge and Stephens (1960).

Other workers, in particular Charlesworth (1963) and Nevill (1963),

also record details of this period.

The study area has been affected by both the Saale

and Weichsel glaciations but by far the most extensive deposits

remaining after erosion are of Weichsel origin. Fig. 4 illus-

trates the extent and principal ice-flow directions of the two

major glaciations in Ireland. In the regional study area, the

ground north and east of the terminal moraine was covered by

EASTERN GENERAL (Saale)

Direction of Ice Movement - Saale and Weichsel Glaciations. (After Synge and Stephens 1960)

• Unglaciated areas.

Tipperary Moraine.

Older drift.

Extent of Weichsel Glaciation in Ireland. (After Mitthell1957)

(Synge and Stephens1960) FIG.No.4.

Remarks European Stages Irish Equivalents

Recent Hillwash, swamp deposits and alluvium

Pleistocene.

Weichsel Glaciation

Interglacial Period

Saale Glaciation

Midland General = Last Glaciation

Ardcavan Interglacial Period

Eastern General = Munster General

Main deposits terminated to south by Tipperary Moraine. S.W. Glaciation in West Cork - S.E. Kerry (Refer Fig. 4)

Covered entire country except for a few small areas in south.

Great Interglacial Period

Elster Glaciation

Gort, Co. Galway and Kilbeg, Co. Waterford. Interglacial deposits.

Only limited remnants of drift remain.

Kildromin, Co, Wexford and Kildicomin, Co. Limerick

Table 2: Main Glacial Events of the Quaternary Period in Ireland

23

the Weichsel glaciation. The general composition and type of

the drift is shown in Fig. 5.

Saale deposits, which have been subsequently

destroyed or obscured by the last glaciation over most of the

area, occur as limited remnants in the S.W. as small pockets

in valleys protected from erosion.. The general direction of

ice movement as indicated by striations was east to west, i.e.

from the limestone across the Namurian rocks.

The Weichsel deposits are dominantly boulder clays,

with some minor fluvio-glacial occurrences. Deposits of clayey

gravels are common along the base of the Namurian escarpment that .

terminated the ice sheet in the south of the area, and are possibly

associated with damming by the ice on retreat. The effects of

topography on the extent of the ice sheet are not so pronounced

in the north where the ice transgressed over the basal Namurian,

eroding the escarpment which was probably not so abrupt as in the

south. It penetrated as far south as the village of Carrigkerry

where the terminal moraine, an extension of the Tipperary moraine

shown in Fig. 4, is a prominant feature of the landsoape.

Because of the relatively simple pattern of the

Weichsel ice-sheet in the area, the drift material is generally

readily correlated with the sources of bedrock supply, as noted

by Synge in Finch and Ryan (1966). He states - "the glacial drifts bear a close relationship in composition to the rocks over which they lie. Nevertheless, where ice cross a major geological boundary, there is a 'carry-over' of material from one formation to the other, which becomes progressively more dilute, with distance from the boundary". Over the eastern

half of the area, with the exception of the south-east corner

where O.R.S. fragments are common, aimestone is the dominant

BOULDER CLAY, PREDOM. L IMES TONE

F771

MORAINIC DRIFT DRUMLINS

ALLUVIUM

.PEAT

BOULDER CLAY. PREDOM. NAMURIAN.

BEDROCK MAINLY WITH THIN ROC* WASTE OR DRIFT COVER.

GLACIAL STRIAE .

[-71 \\\N

socT DRIFT PROFILE SITES.

FLuVIO-GLACIAL SAND AND GRAVEL

0 I 2 as 5 1

GLACIAL DRIFT AND OVERBURDEN MAP OF AREA. ( After F.M.Synge.-Irish Geological Survey) FIG. No 5.

24

constituent of the drift. Because of the more or less uniform

south-west direction of movement, Clare Shale and Namurian

detritus is confined to the area west of the escsvpment, the

porportion of Namurian rocks to transported limestone increasing

westwards. Abundant Clare Shale fragments are limited to a

zone "down-ice" from the escarpment, aligned parallel to the

striae direction and terminated by the Carrigkerry moraine.

Ground moraine composed of rock material re-

deposited close to its point of origin is apparently common, as

deduced from the presence of Clare Shale and Namurian drift close

to the nearest available bedrock source of supply. Also much of

the limestone boulder clay may similarly be of local origin.

However, the vast amount of limestone material deposited on the

Namurian areas and the presence of abundant Clare Shale fragments

up to five miles from the nearest outcrop, indicates that much

of the drift has been transported over considerable distances.

In the N.W. section of the area the drift is predominantly

Namurian sandstones and siltstones but also probably includes

muds dredged from the Shannon estuary and geologically similar

Namurian rock material from Co. Clare, north of the river. Erratics,

of rocks not recognised as types of local origin are extremely rare,

but a few granite specimens, possibly of Galway origin and asso-

ciated with the Saale glaciations, have been recorded.

Except for the gravel deposits of fluvio-glacial origin,

which consist of water-sorted sand and gravel beds, the drift is

mainly boulder clay, consisting of partially rounded fragments

25

from sand to boulder size in an abundant matrix of very fine

rock flour. The matrix, where limestone is the dominant

constituent is blue-grey in colour when fresh, weathering to

buff and light brown. Boulder clay of dominantly Clare Shale

origin is dark grey to almost black and the fragments are much

more angular than the limestone. Being less resistant to

mechanical erosion than the limestone the more carbonaceous,

softer shales rapidly break down to form rock-flour, the sili-

ceous types along with the limestone tending to form the bulk

of the coarse material.

In drift of Namurian origin the resistant sand-

stones form the bulk of the coarse material, a greater proportion

of the softer argillaceous rocks presumably tending to grind

away to rock flour.

After the close of the glacial period, the dis-

tribution of more recent deposits was in part controlled by

the post-glacial topography. Erosion of the unconsolidated

drift material resulted in the formation of swamp and lacu-

strine deposits in post-glacial depressions and in alluvium

flanking some of the larger streams, the courses of which were

determined by both glacial and pre-glacial topography.

Extensive peat deposits have formed on both

residual and glacial material, the principal areas occupying

the higher land to the west of the escarpment. Swamp peats

also occupy post-glacial poorly-drained depressions where

they often overly the older lacustrine sediments.

26

3. CLIMATE

Co. Limerick has a relatively mild maritime climate

with moist winters and cool, cloudy summers. The average humidity

is high and the prevailing winds vary from westerly to south-

westerly. Within the regional study area the annual rainfall

varies slightly with relief, the highest fall being recorded in

the western, higher regions.

The following general data on the climatic conditions

of the area (Table 3) are taken from the Irish Soil Survey Bulletin

on Co. Limerick (Finch and Ryan, 1966). Not all the sites where

records have been kept are within the study area but can be taken

to refer to Co. Limerick as a whole.

Table 3: Climatic Features of the Area

Rainfall

Average Monthly and Annual Rainfall 1950-1960, Inches

.Abbeyfeale. (Western part of area)

Highest - Dec. 6.22, Lowest - Apr. 2.41.

Mean Yearly Total - 46.66.

Rathkeale. (Eastern part of area)

Highest - Dec. 5.10, Lowest- Apr. 1.96.

Mean Yearly Total - 37.45

Temperature

Recorded at Pallaskenry, 5 miles east of the study area.

Mean Monthly Temperatures -

Highest - July. 58.9°F, Lowest - Jan. 40.1°F.

27

Table 3 (continued)

Humidity

Recorded at Shannon Airport, about 20 miles east of the study area.

Range 69 to 92 per cent.

Sunshine

Shannon Airport - Average hours per day.

Highest - June 5.95, Lowest - Dec. 1.52.

Frost

Shannon Airport - Average number of days ground frost recorded -

Highest - Feb. 11.7, Lowest - July & Aug. 0.0.

4. GEOMORPHOLOGY

The topography of the area (Fig. 6), which varies

in height from sea level along the River Shannon to 1132 ft. at

Knockanimpaha, is to a large extent controlled by the bedrock

geology.

The "lowland" eastern half of the area consists of flat

to slightly hilly country on the limestone which is mostly masked

by glacial drift. In the S.E. the Old Red Sandstone is marked

by hills that rise above the plain. The drainage is by relatively

slow-moving streams draining north into the River Shannon.

The western "hilly" to mountainous region is separated

from the lowlands by a well-defined escarpment, where the

resistant Namurian sandstones and Clare Shales overly the

Height in Fee t

800 A Spot heights

1:7400

71 200 L

Sea Level

600

0 2 4 6

miles

FIG.6. TOPOGRAPHY,REGIONAL STUDY AREA

28

limestone. The escarpment divides the regional study area on

a north-south line from Foynes on the River Shannon south to

Ballagh. It is highest and most abrupt in the south where it

formed the terminal line of the Weichsel glaciation. In the

north it is less well defined and was transgressed by the ice-

sheet, which probably further contributed to its erosion.

Streams are generally fast flowing. North of the Carrigkerry

moraine in the western half of the area, drainage is northward

into the Shannon. To the south the main streams flow west

into Co. Kerry.

5. SOILS

The soils of the region have been described in

detail by Finch and Ryan (1966) and are classified into the

Great Soil Groups and sub-divided into series. The distri-

7 bution of the more extensive series are shown in Fig. "which

has been adapted from the work of Finch and Ryan.

In the western half of the area the dominant soil

types are gleys; roughly divided between the Kilrush series

in the north and the Abbeyfeale Series in the south. Extensive

tracts of blanket peat also occur over much of this area. The

gley soils are characteristically poorly drained and have

developed under conditions of permanent or intermittent water-

logging. The horizons are usually grey or bluish-grey with

distinctive mottling due to iron staining. In mem cases

organic matter accumulates at the surface in which case the

5 0 1 2 3

MILES

GENERALIZED SOIL MAP OF AREA. ( Adapted from Finch and Ryan-Irish Soil Survey)

ii5BP BROWN EARTH • Ballincurra Series. Miseettaneous soils of limited areal extent.

[0:1•4 in

FR BROWN P00201.1C-Meunteollins Sir. A A Ashvove Complex

GREY-BROWN 1100ZOLIC-Etton Ser.

U11 u A00,10614 Series.

ral Rineanna

V pi Blanket Peat

• • • • .1 • • •

ccm,g, Hostordstown

Kilrush

Shannon

Dreinbanny

FIG.No.7.

29

soils are referred to as humic-gleys. Many of the soils of

the area fall into this class. Both the Kilrush and Abbeyfeale

soils are moderately acid to acid in reaction, pH values within

the profile varying from 5.0 to 5.3 in the non-peaty phase of

the Abbeyfeale series and from 4.4 to 5.8 in the peaty phase.

The pH of the Kilrush series varies from 5.9 to 6.3.. These

data refer to profiles described by the Irish Soil Survey.

The soils of the eastern half of the area are

slightly more complex with extensive development of gleys,

brown-earths and grey-brown podzolic soils on the dominantly

limestone-drift parent material. Gley soils of the Howard-

stown Series occupy much of the southern part extending into the

detailed study area near Ardagh. They are poorly drained soils,

commonly with up to 10 per cent organic matter in the surface

horizon and reaction varies from slightly acid to alkaline.

A profile by the Irish Soil Survey shows an acid toposoil

horizon of pH 5.8 increasing to 8.3 in the lower part of the

lime-rich B horizon.

The other major soils of the eastern part of the

area are the Elton Series, a grey-brown podzolic and the

Ballincurra Series, a brown earth. The latter is a relatively

mature, well-drained mineral soil with a rather uniform profile.

The Ballincurra Series is of high-base status due to its

development from limestone parent material and neutral to

alkaline in reaction (pH 7.7 to 8.0 in a profile by the Irish

Soil Survey). Up to about 5 per cent organic carbon is

30

developed in the topsoil horizon. The grey-brown podzolics

of the Elton Series are developed from limestone drift generally

similar to that of the Ballincurra and Howardstown Series. They

are moderately well-drained and of high base status. Much of

the better drained soils on limestone drift of the detailed

study area belong to this series. There is accumulation of

organic carbont up to several per cent, in the topsoil horizon.

This horizon is slightly acid with a pH of 5.5 which increases

downward to 7.3 in the lower part of the B horizon in the

profile described by the Irish Soil Survey.

Of limited extent, but important from the point of

view of Mo and Se distributionl is the Drombanny Series, described

by the Soil Survey as being of lake alluvial origin and

classified as a humic-gley. This soil type is typical of the

toxic seleniferous soils in the vicinity of Flynn's Farm.

Characteristically it is very poorly drained with an organic-

rich, often peaty, topsoil horizon underlain by a distinctive

marl layer. They are generally neutral to alkaline in reaction

and of very high base status.

6. AGRICULTURE

The agricultural pattern of the area, reflects the

general suitability of the main soil classes.

The gley soils of the Abbeyfeale and Kilrush Series

on the hilly land to the west are poorly drained and of low

nutrient status. They are unsuitable for tillage crops and

31

support small holdings of partly fenced, poor to moderate

grassland. Drainage and liming is required to maintain the

optimum yield. The industry is mostly dairying with cross-

bred cattle.

The limestone soils are more suited to agriculture

and the holdings range in size from about 20 to 40 acres at

the base of the scarp to as much as 200 acres on the more

prosperous undulating land to the east. Dairying is the major

industry, since the soils of the Ballincurra, Elton and

Howardstown Series support good grassland. The Elton Series

have a wide use range and may also carry some cultivated crops.

There is some production of beef cattle and some herds from

the hilly land to the west are fattened on the lowlands. Stud

farms for bloodstock horses are not uncommon and are mainly

situated on the better drained soils of the Elton and Ballincurra

Series.

32

CHAPTER III. SAMPLING AND ANALYTICAL TECHNIQUES

Over 4300 samples were collected during the course

of the survey, of which about 75 per cent were analysed for

up to 17 elements. In addition, about 2700 samples had pre-

viously been analysed during Professor Webb's preliminary

studies in Eire preceeding the selection of the writer's

study area. To date these investigations have yielded in all

approximately 51,000 individual items of analytical data.

The techniques employed for collection, preparation

and analysis of samples are generally similar to those which

had been developed for research in mineral exploration. These

methods can be readily adapted to regional geochemical and

biogeochemical surveys, with minor modifications as described

below.

1. FIELD SAMPLING

Except for waters, samples were collected in water-

resistant kraft paper envelopes with non-contaminating metal

tabs. These are supplied in two standard sizes of 3 x 5 ins

and 11 x 5 ins.

In the case of damp samples, particularly sediments,

initial air-drying to a state adequate for safe transport was

carried out in the field and final drying by electric or

kerosene ovens in the laboratory. Because of the volatile

nature of Se, the oven temperature was limited to not more

33

than 60o (up to 100oC should be safe, with the possible exception

of vegetation samples).

(a) Rocks

Regional rock samples consisted of grab samples

(500-1000 g) taken at random from available outcrops, road

exposures etc. Where the lithology varied in a particular

exposure, an attempt was made to collect representative composite

samples. Weathered material was avoided. Cross sections of the

Clare Shales were chip sampled, the sample length being based

on visible lithological characteristics and corrected for dip

and strike so that throughout the thesis true stratigraphic

widths are quoted. It was considered that chip samples, although

not as accurate as channels, were adequate for the purpose of

this study.

(b) Stream Sediments

Wherever possible, samples were collected from the

active sediment near the centre of the channel, avoiding any

collapsed bank material. To give sufficient fine material for

analysis, fine sands and silts were preferred to coarse material.

Organic or iron-rich samples were avoided except where they

constituted the main sediment type for that locality. The small

sample bags carry about 75 to 100 g of sediment, this normally

produces sufficient minus 80-mesh fraction. for analysis. The

advantage of the kraft paper envelope is that samples can be

dried in the original collection packets.

34

For routine regional surveys the following record

system is recommended:-

1. Sample locations are plotted in the field

directly onto ordnance survey sheets at scales of 1 or 2 miles

to the inch depending on the sampling density. Ordnance survey

sheets also provide a convenient grid reference if automatic

data plotting is to be used (see Nichol et al, 1966). Sample

location points are subsequently transferred to a base map

showing drainage and orientation points only; the sample numbers

are entered on a separate overlay. Both plots are made on trans-

parent paper which allows convenient reproduction of drainage maps

on which metal values can be plotted directly without confusion

from the sample numbers.

2. Records made in duplicate at each sample site

give:- sample no., size of stream, type of sediment (e.g. sand,

silt, organic-rich, calcareous, etc.), the colluvial or alluvial

nature of the bank material, notes on the local agriculture and

any special features such as contamination from mine workings,

etc. The pH of the stream waters are taken using B.D.H. liquid

Universal Indicator.

(c) Soils

Regional soil samples were collected at j- and 1

mile intervals and the detailed grid in the Flynn's Farm area

was sampled on 88o ft. squares. Soil samples (including drift)

were collected using a 1-inch screw auger 3 ft. long graduated

35

at 6 inch intervals. For routine work, 50-100 g samples were

collected at two depths, a "grass-roots" horizon 0-4 inches

and at 18-24 inches in less weathered primary material.

Soil profiles were sampled using a 3-inch 'buoket

auger, 7 ft. in length. Sample intervals down-profile were

based on soil horizon changes; in undifferentiated drift

the sample interval was 1 ft. The bucket auger was capable

of penetrating most soils except where large boulders were

present in drift. Some trouble with recovery was experienced

in soft clays or gravel below the water table.

Bank soils were sampled from vertical channels

after removal of surface vegetation or by horizontal bucket

auger holes. Profile and bank soil samples were generally

500-1000 g in weight.

(d) Herbage

For routine survey purposes grab samples of herbage

weighing about 20-50 g were collected at random around each soil

sample site, approximating to the general forage consumed by

grazing animals. Samples were cut above ground level, avoiding

contamination by root material and soil particles. For the -

investigation of metal uptake, plant material was sampled by

cropping selected species from areas of 100-400 sq. ft. and

where necessary, dividing the material into heads, leaves and

stems.

36

(e) Natural Waters

Water samples were collected in polythene bottles

and filtered on-site through Whatman No. 1 filter paper. Two-

litre samples provided ample material for the analyses required.

pH and Eh readings were made on-site before removal from the

stream or bore hole. CO3

and HCO3 determinations were also

carried out at the time of collection. Groundwaters were

collected from 3 in, bucket auger holes with a glass or alu-

minium ladle. In well-drained hilly areas groundwaters could

only be collected when they came within 7 fti from the surfacey

adjacent to or in topographic depression. Seepage and spring

waters were collected at the point where the flow reached the

surface. Whenever possible, series of samples were collected

over short periods to avoid fluctuations in groundwater level

or composition due to rain.

2. SAMPLE PREPARATION

(a) Rocks

Chip samples were ground to minus 10-mesh in a

small jawcrusheri quartered down to about 5 g, and then pul-

verized in .a Coor's ceramic ball mill to minus 200-mesh. Six

samples can be pulverized simultaneously using this equipment

giving a production rate of 60 samples per man-day.

(b) Soils and Sediments

tt.

Samples for routine analysis were lightly pulverized

37

in a porcelain mortar and sieved to minus 80-mesh.*

Bulk samples were treated in the same way except

that after breaking up the larger aggregates, they were roughly

quartered down prior to pulverizing.

(c) Drift

Samples of boulder-clay were prepared in much the same

manner as for soils including sieving to minus 80-mesh.

(d) Peat

Peat samples required more vigorous crushing in the

mortar before sufficient minus 80-mesh material could be

obtained for analysis. In the case of peaty-soils, which

tended to form very hard aggregates on drying, care had to

be taken to avoid undue fragmentation of mineral particles.

(e) Herbage

After final drying at 60°C in an electric oven,

herbage samples were ground to minus 38-mesh in a Christy Norris

mill. This was considered fine enough to achieve reasonable

representivity.

*The actual mesh size was 82-mesh i.e. 204 microns diameter, which for convenience is referred to as 80-mesh throughout this thesis. The reason for using this mesh size, which passes fine sand, silt and clay, is that it has become standard practice on geochemical surveys and allows the ready comparison of results with observations of other workers.

Agricultural workers more commonly refer to minus 2 mm material, which includes coarse sands. The relationship of the metal content of the two size fractions has been investigated and is discussed in Chapter VII.

38

3. ANALYTICAL TECHNIQUES

A multi-element spectrographic technique is in

routine use at the A.G.R.G. for regional geochemical and bio-

geochemical surveys and this was employed wherever possible.

Colorimetric and other techniques were used in cases where

the spectrographic technique was not applicable.

For routine analyses, accuracy control was main-

tained using the method of Craven (1954, see also A.G.R.G.

Teph. Comm. No. 46, 1963). Control samples constituting a

statistical series were inserted at intervals throughout the

various batches of samples and the precision calculated or

obtained graphically.

The techniques employed are indicated below in

outline only and for details the reader is referred to the references

cited. Any modifications that have been made are, however,

described in full.

(a) Spectrographic Techniques

The semi-quantitative emission spectrographic tech-

nique employed is that described by Nichol and Henderson-

Hamilton (1965). For routine purposes the following elements

are generally determined, Ag, Bi, Co, Cr, Ga, Mn, Mo, Ni, Pb,

Sn, Ti, V, Zn, Zr and sometimes Fe. This method was also used

for Mo determinations alone, on maw rock, soil and stream

sediment samples but was not used for herbage and water samples.

39

In brief, the method entails prior ignition of minus

80-mesh material in a silica crucible at 400-500°C for three

hours to oxidize organic matter and eliminate combined water.

A Li2CO3 buffer is added to the sample to reduce matrix effects

and germanium is added as an internal standard to give a con-

centration of 400 ppm in the final mixture with carbon. The

mixture is homogenized by shaking in a Wig-L-Bug for 30 seconds

and loaded into a carbon electrode. Details of the spectrographic

equipment are given in Table 4 and the wavelengths and useful

ranges of concentration of the elements routinely analysed in

Table 5. This information is taken from Nichol and Henderson-

Hamilton (1965) and Webb et al (1964).

Table 4: Spectrographic Equipment and Conditions

Source Unit Spectrograph Arc Stand Comparator Wavelength Range R Emulsion Anode

Cathode Exposure Gap Arc Current Slit Collimator Step sector

Hilger FS 131 Hilger Large Quartz FR 55 Hilger FS 56 Hilger JS Co,L.90 2800-4950 Ilford N.30 Morganite SG.305 H - 5 mm. carbon, 2.91 mm. diam. crater, 5 mm. deep crater. Morganite SG.305 H - flat ended 20 seconds 3 mms. 12.5 amps 15 µ Internal Two steps giving three intensities in proportion 1.1.1

Table 5: Wavelengths and Usable Concentration Ranges of Spectral Lines

Element Wavelength Range (ppm)

Ag 3382.9 0.2 - 1000 Bi 3067.7 5 - 200 Co 3453.5 5 - 10,000 Cr 4254.3 2 - 1000

2843.2 500 - 10,000 Cu 3274.0 1 - 500

2961.2 500 - 10,000 Ga 2943.6 2 - 10,000 Mn 4034.5 5 - 500

2933.0 500 - 10,000 Igo 3170.3 2 - 10,000 Ni 3414.8 1 - 1000

3050.8 1000 - 10,000 Pb 2833.1 1 - 1000 Sn 2840.0 2 - 10,000 Ti 3377.6 50 - 10,000 V 3185.4 2 - 10,000 Zn 3345.0 50 - 10,000 Zr 3438.2 200 - 10,000

1+0

La

, Estimation of the concentration of each element in

the sample is made visually by comparison of the spectra with

the spectra from a synthetic standard plate. In certain cases

greater precision (in particular for some Mo and Fe determinations)

was obtained by determination of the spectral density by means of

a microphotometer.

Productivity is 26 samples per man-day for 15 elements.

Precision is 135 - 45% at the 95% confidence level.

Because the samples are ignited before being spectro-

graphed, the results for highly organic samples have to be adjusted

for the loss of combustable material. For normal mineral samples

the loss on ignition is not significant.

(b) Selenium

Selenium was determined in soils, sediment, rocks

and herbage by the method of Stanton and McDonald (1965)

using 3,3/-diaminobenzidene after co-precipitation of Se with

As. A 4:1 nitric-perchloric acid attack is used. The method

has a precision of better than 25% at the 95% confidence level

and productivity is 20 to 25 samples per man-day. The lower

limit of detection is about 0.2 ppm Se using a 1 g sample but

this can be extended and the accuracy at the lower levels

increased by use of larger sample weights up to 10 gms. For

waters, the same technique was used on the residue obtained by

evaporating 500 or 1000 ml of sample (with 20 ml of nitric-

perchloric acid mixture added) to fumes.

42

(c) Molybdenum

The Mo content of herbage was determined colorimetri-

cally by a method adapted from North (1956) using zinc dithiol

(see also A.G.R.G., 1962). The techniques used diverged from

the normal A.G.R.G. method by utilizing an acid sample attack

(perchloric and nitric) and extracting the Mo from the residue

after evaporation to dryness by warming with 2N Na2CO3

solution.

This is done in order to eliminate Fe which interferes with the

colour comparison. Precision is ± 25% at the 95% confidence

level and the lower limit of detection is about 0,4 ppm depending

on the sample size and aliquot taken for determination.

Mo in water was initially determined by solvent

extraction from a buffered sample with 8-hydroxyquinolene in

chloroform. The extract is evaporated to dryness with nitric

acid and the Mo then taken up with 2N Na2CO3 as for herbage.

In order to include non-ionic Mo, later analyses were made by

evaporating water samples with a nitric-perchloric acid mixture

to dryness followed by the above procedure from the Na2CO3 stage.

Water samples to be analysed for the three elements

Se, Mo and Fe, were prepared by evaporating 1 to 2 litres with

40 mis of 4:1 nitric-perchloric acid mixture, down to perchloric

acid fumes. The residue was then dissolved in 6N HC1 and aliquots

taken to be treated individually for each element.

43

(d) Iron

Iron in rock samples was determined spectrographically

(Nichol and Henderson-Hamilton, 1965). In soils and sediments,

the amount of Fe present as secondary iron oxides was determined

colorimetrically by extraction with 6N HC1 followed by estimation

with thioglycollic acid. This is a modification of the method

of Sandell (1959) (see also A.G.R.G., 1962). Because of the

highly calcareous nature of many of the samples a greater acid

strength than usual was employed to avoid excessive neutraliza-

tion of the acid.

In waters, total Fe was also determined using

thioglycollic acid, after evaporation of the sample with nitric

and perchloric acid.

The expected precision of the colorimetric method

. + is - 25% at the 95% confidence level.

(e) Copper

Cu in rocks, soils and sediments was determined by

the spectrographic method. For herbage the sample was first

decomposed by nitric-perchloric acid mixture followed by esti-

mation of Cu using 2-2' diquinolyl in amyl alcohol. The method

was adapted from that proposed by Almond (1955) and except for

using the acid mixture instead of KHSO4 in attack, the process

is similar to that described in the A.G.R.G'. (1962). The

expected precision is 1: 25% at the 95% confidence level over

the range 5-2000 ppm.

44

An alternative method used for Cu analysis of

herbage was by atomic absorption using a Perkin Elmer 303

spectrophotometer with a hollow cathode Cu lamp. The samples

were decomposed with a nitric-perchloric acid mixture, evaporated

and made up to volume with water. The solution was sprayed and

the absorption measured at 32478. Unless stated otherwise, the

data for Cu in herbage were obtained by atomic absorption which

gives more consistent results than those obtained by colorimetry.

(f) Zinc

A few colorimetric analyses for Zn in rocks and

sediments were made using dithizone and potassium bisulphate

attack. The method has been described elsewhere (A.G.R.G.,

1962).

(g) Phosphorus

Phosphorus was determined by a method adapted from

Ward et al (1963) involving fusion of the sample with potassium

bisulphate and colour comparison of an ammonium vanadate-

molybdate complex (also refer A.G..R.G.., 1966).

(h) Arsenic

A few arsenic determinations were made on rocks

and stream sediments. The method was the modified Gutzeit

test described by Stanton (1964) and A.G.R.G. (1965).

45

(i) Sulphate

Sulphate analyses of soils and herbage were carried

out using a modification of the method of Scott and Furman (1955)

as detailed in A.G.R.G. (1962). Herbage samples were first

digested in a nitric-perchloric acid mixture and evaporated

to dryness. The residue or soil, as the case may be, is digested

in 1M HC1 and SO4 estimated turbimetrically after precipitation

as BaS04'

(j) Sulphur

Total sulphur was determined by a modification of

the sulphate method. The sample was first fused with a NaOH

and Na202 mixture to oxidize all sulphur minerals, particularly

pyrite, to sulphate. The melt was then leached with water,

filtered and sulphur estimated turbimetrically after precipi-

tation as BaS04'

(k) Organic Carbon

Analyses for organic carbon were based on the method

of Schollenberger (1927) as described in A.G.R.G. (1962). The

sample is oxidised with chromic acid, and organic carbon is

estimated by titration with ferrous ammonium sulphate. Results

are generally lower than those obtained by combustion methods

and the method was not suitable for determination of organic

carbon in the black shales because of the probable presence of

elemental graphitic material.

46

(1) Carbonate and Bicarbonate

These determinations were based on the method of

Scott and Furman (1955) as also described in A.G.R.G. (1962).

The few carbonate analyses of soils and rocks

involved decomposition of the sample with HC1 followed by tit-

ration with NaOH solution.

Carbonate analysis of waters was attempted but it

was found that in almost all waters in the area pH was below

8.35 thus precluding the presence of CO3 ions.

The bicarbonate content of stream and groundwaters

was determined on-site by titration of a 100 ml sample with

HC1 using screened methyl red as an indicator.

4. NiISCFLLANEOUS TECHNIQUES

(a) .pLi

Soils

Soil pH measurements were made in the laboratory

on a soil-water suspension. It has been shown by Huberty and

Hans (1940) that pH values made in this manner are'from 0.5 to

1.4 units higher than those made in the field on freshly

collected material. A 1 g sample was added to 5 ml of freshly

boiled deionized water in a screw top polythene container and

the slurry vigorously agitated for one hour on a mechanical

shaker. The pH was then read on a Pye Model 605 pH meter after

pouring the slurry into a polythene cup surrounding the standard

glass-calomel electrode. The meter was calibrated using pH

1+7

buffer tablets at 4.01 and 9.27 units. It is unfortunate that

this method, the standard one in operation at A.G.R.G., is

different from that used by the National Soil Survey of Ireland,

where the pH is determined on a 2:1 water-soil suspension of

minus 2 mm material. Donovan (1965) gives data on soils ranging

in pH from 6.8 to 8.4 showing that the N.S.S. measurements are

from 0.05 - 0.4 units higher than the A.G.R.G. method. Thus

pH measurements quoted are only relative and may vary slightly

from values taken by other methods.

The pH of natural waters was determined on-site

using a battery-powered pH meter manufactured by Analytical

Measurements Ltd. For groundwaters, the electrode was lowered

down the bore-hole wherever possible, while for stream waters

the electrode was placed several inches below the surface.

(b) Eh

Eh of natural waters was taken in the same manner

as pH using the same instrument but with a platinum electrode

and calibrated by using a standard solution of Eh value equal

to + 0.430 V at 25° with respect to the standard hydrogen

electrode. This solution was made up by dissolving 1.408 g

of potassium ferro-cyanide trihydrate, 1.098 g of potassium

ferri-cyanide and 7.455 g of potassium chloride in 1 litre

of deionized water.

1+8

In the case of groundwaters it was not possible to

exclude air from the bore-hole. The measurements were not

therefore made under truly natural conditions since the redox

equilibrium was upset by exposure to oxygen in the air. However,

the determinations were carried out as soon as possible after

opening up the bore-hole and related groups of measurements

were taken as close as possible in time to one another.

(c) Size Analysis by Wet Dispersion

Soil, drift and sediment samples were dispersik by

the method described by Nicals (1964) and is a modification of

that given in Piper (1950, p. 77-79), In brief, 100 g samples

of minus 2 mm material were dispersed in a solution of "Calgon"

(sodium hexametaphosphate). Separation of particles was achieved

by frequent stirring in a sonic vibrator. The suspension was

transferred to a 1 litre cylinder, made up to volume with water

and the proportion of silt and clay measured after sedimentation

with a Bouyoucous hydrometer. Times of sedimentation and tempera-

ture corrections were given by Piper (1950). Sufficient silt-

plus-clay fraction for analysis was decanted off and evaporated

to dryness. The remaining fine material was removed from the

sand fraction by repeated decantations and the residue dried.

The clean sand fraction was dry-sieved into six size-fractions

and the proportions determined by weighing. For the purpose

of the experiment it was not considered necessary to separate

49

the silt and clay fractions which would have involved lengthy

sedimentation times. The size fractions obtained and their

international standard equivalents are given in the following

table.

Table 6: Size Fractions Obtained from Mechanical Analysis (after Watts, 1960)

Sieve Size

Approx. Aperture International Convention (microns)

-10 mesh 2000 -20 mesh 1075 -38 mesh 520 -82 mesh 204 -125 mesh 107 -197 mesh 53 Silt and Clay 20

2

Coarse sand

Fine sand

I/

Silt Clay

In conventional soil surveys it is customary to

destroy CaCO3 and organic matter prior to mechanical size

analysis. However, this was not possible in the present study

where the object was to determine the distribution of metals in

the different size fractions. Not only would metals have been

extracted during the course of HC1 and H202 digestions but samples

containing an appreciable amount of limestone parent material

would have given entirely misleading size analyses. However,

an important disadvantage of the technique employed is that the

organic matter which acts as a cementing agent was not destroyed.

Consequently, soils from organic surface horizons and sediments

50

draining peaty areas could not be completely separated into

their different size fractions.

It is not known what effect the very dilute calgon

solution has on the distribution of exchangeable metal in the

samples but it is not expected to have achieved any significant

extraction of the total metal content. This method has become

standard practice at the A,G.R.G. and previous work on a variety

of metals has not indicated any serious extraction of metal by

sodium hexametaphosphate.

(d) Heavy Liquid Separation

Pyrite was separated from black shales by crushing

the sample to -80 mesh and removing silt and clay size particles

by decantation. The residue was washed with acetone and then

dry-sieved on a mechanical shaker into three fractions, 82-125,

125-197 and <197 mesh. Separation of the pyrite was obtained

by repeated eezttrifuging using tetra-bromoethane and the purity

of the fractions checked visually under the microscope.

Attempted separation using a Franz isodynamic magnetic separator

was not successful.

51

PART B

CHAPTER IV. THE REGIONAL METAL PATTERNS

As stated previously in the introduction, selection

of the study area of about 275 sq. mi. was initially based on

the recognition of distinct patterns of Mo distribution in the

stream sediments centred on an area of recorded Se toxicity.

To establish the validity of regional stream

sediment reconnaissance as a means of recognising broad patterns

of metal distribution in the natural environments, sampling of

the region as a whole was undertaken prior to any studies of

detailed relationships. The stream sediment coverage was inten-

sified and the original samples which were collected for mineral

exploration purposes, checked by re-sampling. Rocks, soils and

herbage were sampled by means of three widely spaced east-west

traverses and additional samples were also taken either at

random or on a widely-spaced grid in certain critical areas.

This work also enabled background or normal metal values to

be determined well away from the toxic localities where excessive

metal concentrations were known to occur.

To facilitate the comparison of regional metal

patterns in soils and sediments, the background area surrounding

the zones of anomalous Mo content shown in Fig. 8 have been sub-

divided into blocks (A-F) according to the dominant bedrock

type and the extent of drift cover (Fig. 12).

52

1. STREAM SEDIMENTS

In addition to the mean concentration and range of

values for Mo, Se and Cu in sediments from streams draining the

basic rock units of the area (Fig. 12 A-F), available data on

some other elements are also presented in Table 7. The distri-

bution of these elements reflects basic differences in the

bedrock and drift composition but are less directly concerned

with the agricultural aspects of the study.

The geometric value of the mean is used, (a) because

of the approach towards apparent lognormal distribution of the

geochemical data, and (b) because of the logarithmic spacing

of the spectrographic standards against which metal concentra-

tions are estimated. The logarithmic groupings of Mo, Se, Cu

and V values in the frequency plots (Figs. 10 and 11) correspond

to the spacing of the spectrographic standards used for analysis

and are also related to the groupings assigned symbols in Figs.

8, 9 and 12.

(i) Molybdenum

Referring to the histograms given in Fig. 10 most

samples from streams draining the Namurian,Carboniferous and

O.R.S. (areas A, B and C, Fig. 12) contained less than 2 ppm

Mo which is the detection limit of the spectrographic method.

The background level for Mo was therefore established at less

than 2 ppm.

AREAS Mo Se Cu V Pb Ga Ti Ni Co Mn Cr cxZn

A. O.R.S. L.L.'Stone Shale and Basal Limestone

B. Limestone

C. Namurian

n 27 19 27 27 27 27 27 27 27 27 27 27 R <2 0.2-1.0 15-80 20-150 30-120 6-30 1000-5000 15-80 5-20 150-4000 20-100 0-28 M <2 0.54 35 55 66 9.4 2600 45 13.5 950 89 9.0

n 39 40 39 39 39 39 39 39 39 39 39 39 R <2 0.2-2.0 10-60 40-80 10-70 2-10 500-3000 15-70 5-30 150-2000 20-80 0-26 M <2 0.64 29 66 29 5.1 1180 49 8.2 430 44 7.3

n 62 40 62 62 62 62 62 62 62 62 62 62 R <2-4 <0.2-1.2 15-90 30-180 7-60 12-40 1000-7000 40-120 7-90 70-6000 12-250 0-57 M <2 0.3 44 102 21 25 4940 66 30 1240 93 4.0

D. Namurian plus Weichsel drift

• 29 31 29 29 29 29 29 29 29 R <2-7 <0.2-1.2 20-80 80-150 15-180 15-40 4000-7000 60-150 15-90 M 2.6 0.55 53 104 36 24 5300 75 32

29 29 28 900-1% 70-180 2-118 2020 100 11

L. Drift of mixed oriGin incl. Clare Shales. "High Mo Zone"

F. Drift ;•f mixed orit;in incl. Clare Shales "Moderate Mo Zone"

n 67 54 22 22 R 2-200 0.3-21.0 50-300 120-400 M 14.5 2.75 92 187

n 80 46 36 36 R 2-15 0.2-5.0 30-200 80-300 M 5.7 1.2 61 121

32 32 32 32 32 32 32 32 '8-150 4-30 700-8000 60-250 10-60 70-3000 60-5000 4-51 30 13 2970 97 31 960 103 14

Table 7: Metal Contents of Stream Sediments Prom Different Bedrock Areas (Minus 80-mesh traction, values in ppm)

•Areas A-F, refer Fig. 12 n = No. of samples. R • Range of values. M - Geometric Mean.

Mo In stream sediment (ppm)

+ <2 o 2-5 O 5-10'

10-20 • >20.

2 4 6

miles

FIG. 8 REGIONAL DISTRIBUTION OF Mo IN STREAM SEDIMENT OF TRIBUTARY DRAINAGE

(Data refer to —SO mesh fraction)

54

Comparison of the patterns of Mo distribution

(Fig. 8) with the geological map of the area (Fig. 3) revealed

that the zones with the highest Mo values (blocks E and F

greater than 5 ppm) are roughly centred on the line of outcrop

of Clare Shale in the northern and central parts of the area.

Towards the south the Mo pattern becomes less well defined and

is finally indistinguishable from the background areas. This

is attributed to the structural thinning of the molybdeniferous

Clare Shale horizon as described in the section concerned with

general geology and in Chapter VI, and to topographic features

which also decrease the width of the sub-outcrop.

The extension of the anomalous zone to the west of

the line of outcrop of the Clare Shales roughly coincides with

the "fan" of glacially dispersed Clare Shale material in Fig. 12

and was investigated further in the studies of metal distribution

in soil and drift. The apparent extension of the Mo pattern

to the east is attributed to alluvial action by present-day

streams flowing east from the Clare Shale areas.

The molybdeniferous stream sediment zones (E and F)

centred on the Clare Shale outcrop are markedly anomalous (mean

Mo contents of 14.5 and 5.7 ppm respectively) compared with

the background areas underlain by O.R.S., limestone and

Namurian rocks (A, B and C - less than 2 ppm Mo). The area

of Namurian rocks in the north-west (D, Fig. 12) which is

partly covered by the Weichsel drift, is not appreciably

anomalous but has a mean stream sediment Mo content of 2.6 ppm.

Se in stream sediment (ppM)

+ <1.5 0 1.5-3.0 0 3.0-6.0 • >6.0

9 miles

FIG. 9 REGIONAL DISTRIBUTION OF Se IN STREAM SEDIMENT OF TRIBUTARY DRAINAGE

(Data refer to -80 mesh fraction)

foZ 0 =11

1111•11•MIIP

SELENIUM

A. O.R.S., L.1. 4St.Sh. etc.

TOTAL AREA. n = 19

10Z G 0.54.

so%

MOLYBDENUM

TOTAL AREA

fl a 720

10 20 SO 100 100 PPM

E. Mo "HIGH"ZONE.

n = 67 rl 0 = 14.5

0' 0 4 6' to so to too Ate

TA F. Mo "MODERATE" ZONE.

3p- n= SO

= 5.7 a

O 0

C. NAMURIAN. S.W. (no drift.)

n= 62.

Ga <2

11 a 312.

At%

0 • 01 1.1 2 7 is 50 7.

PPM

E. Mo "HIGH" ZONE.

n = 54

0 = 2.76.

F. Mo "MODERATE ZONE.

0 •7 PI;

B. LIMESTONE. n = 40

0 = 0.64.

0 o 14'.▪ ▪ 3

a C. NAMURIAN. S.W. IL.

n a 40

0= 0.29 ro%

n a 46 0 moirrome

0 O a r

D. NAMURIAN.N.W.

n = 29.

G 2.6 or o .7 7

PPM.

D. NAMURIAN. N.W.

(37, n = 31

G= 0.55

(drift.)

o 0 07 ,94.

0 • to

0

REGIONAL DISTRIBUTION OF METAL IN STREAM SEDIMENTS.

LOGARITHMIC FREQUENCY PLOTS FOR Mo AND Se. FIG. No.10.

55

This is sufficiently greater than background to suggest that

some molybdeniferous material has been added by the drift

cover.

(ii) Selenium

The pattern of Se distribution in stream sediments

(Fig. 9) is substantially the same as the Mo pattern, indicating

a common bedrock source. Mean Se values and ranges (Table 7) and

the frequency plots (Fig. 10) illustrate that, within the back-

ground range, stream sediments from the O.R.S. and limestone

areas (A and B, Fig. 12) contain more Se (0.54 and 0.64 ppm

mean values) than streams draining Namurian rocks (area C -

0.3 ppm Se).

The areas that were anomalous for Mo (E and F) also

carry appreciable concentrations of Se in the drainage sediment,

i.e. mean concentrations of 2.75 and 1.2 ppm Se respectively.

The area of drift-covered Namurian in the north-

west (area D) is anomalous with a mean Se level of 0.55 ppm

compared to the Namurian rocks in the south but the values are

comparable to those detected over the limestone in the east.

(iii) Copper and Vanadium

The mean Cu and V values on the different rock

types (Table 7) and the sample frequency histograms (Fig. 11)

indicate that these metals have a generally similar pattern

of distribution in the drainage to Mo and Se, the highest

PPM 0 10 26 56 limin

A. O.R.S..L.L'st.Sh. etc.

••••••••••

n=27

G=34.7

r

TOTAL AREA

11011•11•1111.1.

r-

D. NAMURIAN. N.W. n 29

—11: 53.3

1•111•11.1•1,

0 187.4.

1111••••4

F.Mo "MODERATE " ZONE.

n 36

0 = 121.0

41110•0010

O. NAMURIAN.

n 29

a 104.

COPPER

n = 296 B. L IMESTONE.

B. LIMESTONE.

C. NAMURIAN. S.W

E. Mo "HIGH" ZONE. n = 39. z n = 22 G=65.8

w a.

In , I

PPM 0 10 20 50 100200500

TOTAL AREA

411••••••,

n a 295

N CH

:-. 5

0 PE

RC E

NT.

FREQ

UENC

Y

E. Mo "HIGH" ZONE.

n a 22 .110111.1•11

G =92.5

F. Mo Mo "MODERATE" ZONE.

n a 36

mmomerm•

G 61.5

VANADIUM PPM PPM

a 20 50 1-2-5_ 0 10 20 iO 103200590

A. O.R.S. etc. Gm 55.4

n = 2 7 r—

•••••••••

r

M11•1111

n = 39

G = 29.2

••••••=1,

n a 62

0 = 44.3 FREQ

UEN CY

••••••••10,

C. NAMURIAN. S.W.

n a 62

0:102.4

•

REGIONAL DISTRIBUTION OF METAL IN STREAM SEDIMENTS. LOGARITHMIC FREQUENCY PLOTS FOR Cu AND V.

FIG. No.11.

Mo in soil 18-24 ins. A-F (ppm)

< 2 0 2 — 5 0 5-10 ® 10-20 • > 20

Bedrock and anomalous areas used for calculation of mean soil and sediment metal contents.

N Projected "Fan-shaped" zone of glacially dispersed Clare Shale matenal.

oii 2 4 6

M'rrosii l miles

FIG.12. REGIONAL DISTRIBUTION OF Mo IN SOIL AND DRIFT

Outline of anomalous stream sediment Mo patterns.

/Limit of glacial drift.

Glacial striae.

56

values occurring in the areas of Clare Shale and Clare Shale

drift. However, the contrast between background and anomalous

areas is much lower than for Mo or Se.

(iv) Other Elements

Mean values for Pb, Ga, Ti, Ni, Co, Mn and Cr

(Table 7) indicate some apparently significant variations

in stream sediments draining the different rock types:-

(a) The Pb content of sediment from the O.R.S.

and Lower Limestone Shales area is significantly high compared

with those derived from other rock types. This corresponds

with results obtained by Donovan (1965) and is in line with

the apparent stratigraphic control of some lead-zinc ore-bodies

in Ireland where the lower horizons of the Carboniferous lime-

stone are a favourable zone for mineralisation and contain an

overall higher background Pb content.

(b) Ga, Ti and Mn are enriched in the Namurian

areas. The higher Ga and Ti values possibly correspond to the

greater clay content of the argillaceous rocks compared with the

limestones.

(c) Ni apparently follows Mo, Se, Cu and V in

being enriched in the Clare Shale areas (zones E and F) but

the contrast is small and the apparent correlation may be due

to inadequate data or local dispersion features involving

secondary concentration in the stream sediments.

57

2. BEDROCK

Following the detection of anomalous geochemical

patterns in the drainage it is necessary to define them with

regard to metal distribution in the parent bedrock from which

the stream sediments are ultimately derived.

The stratigraphy and lithological characteristics

of the principal bedrock units has been reviewed in Chapter II.

The relative stratigraphic positions of these formations is

shown diagrammatically in Fig. 13, which also gives the mean

metal content of each unit and the range of values present.

All the major formations were sampled along the

regional traverse lines except the poorly exposed Lower Limestone

Shale horizon. This is unfortunate as it was therefore not

possible to confirm the presence in this horizon of the higher

concentrations of Pb indicated by the stream sediment samples.

Data are included for tuff and spongolite rocks although the

actual areal extent of these formations is limited. Values

for Clare Shales are based on serial samples collected along

semi-continuous sections as well as random outcrops. Data for

the non-marine Namurian rocks are divided into sandy and argil-

laceous types and composite values for the whole sequence are

also given.

(i) Molybdenum

Only the Clare Shales carry Mo values greater than

2 ppm which is the limit of detection by the spectrographic

Se Mo Pb Ni Co Mn P As SO4 PPM Zn

0/4, Cr Fe ,O

METAL CONTENT PPM Ga V Cu Ti

DEV

ON

IAN

Old

Red

Sandstone

—= Not Determined. M = Geometric Mean. n= No. of Samples. R = Range of Values.

n

R

M

8

<2

<2

6

01-05

0.18

7

4 - 35

11

7

1 - 16

12

8

40 -70

53

8

6 - 30

12

7

3000 - 6000

4720

8

30- 60

41

8

10 - 30

18

7

100-600

177

7

60-100

82

_ ..

5-6

5.7

7

— — — —

n

R

21

<2

6

01-01

19

5- 40

19

16 -30

21

70 -150

21

30 - 45

19

5000 - 8500

21

40-80

21

5 -40

19

130-900

19

100 - 200 6-20

20

-,-. — •

—

M <2 0.14 19 26 95 36 6420 58 24 406 124 79

n 29 12 26 26 29 29 26 29 29 26 26 27 4 4 4 4

R ..2 01-0 .5 4-40 7-30 40-150 6 -45 3000-8500 30-80 5 -40 100-900 60-200 5-20 <5 - 7 75-90 200 .<100-3000

M <2 0.16 17 21 81 27 5910 53 22 325 111 7.6 <5 80 200 48-2300

n 79 75 79 79 79 79 79 79 79 79 79 65 16 16 15 16

R 2 - 300 0.2 - 30 7 - 80 4 - 50 30 -4000 20 - 200 400- 8500 7 - 200 <5-85 3 - 6000 50 -300 0.5 -45 <5 -55 25 -125 <20-1000 150-34,000

M 27 2.90 22 15 365 79 2420 54 13.-20 335 130 4.5 4.3-11 50 100-135 3300

n 5 5 5 5 5 5 5 5 5 5 5 5

R 4-50 0.7- F6 6 -40 5-8 30-800 30-70 400-600 7-20 <5-7 40-400 50-85 0.5-1 .6 — — — M 16 1.3 10 5.6 365 45 550 12 <5 110 72 1.0

n 1 1 1 1 1 1 1 1 1 1 1 1 _ _ — ____ M <2 1.0 2 8 85 <2 6000 60 40 400 160

n 28 6 13 13 14 14 13 14 14 13 13 14 4 4 4 4

R <2 015-0-5 2 - 8 <2 - 10 40-100 2 - 15 10-600 <5 -60 <5 -8 40 -500 <2 - 30 <0 2-1.6 <5 30 - 65 100-200 <100 .

M <2 0.27 3.5 <2 61 4.3 88 8-10 <5 115 4.3-6- 8 012-11 <5 39 151 <100

Not exposed in area . , Not sampled.

n 2 2 2 2 2 2 2 2 2 2 2 2

R <2 01-01 7 30 70 -80 10 - 35 7000-8000 35 -40 8 - 15 700 80-1 50 6.0 — — —

M <2 . 014 7 30 75 19 7480 37 11.0 700 110 6.0

TRACE ELEMENT CONTENT OF MAJOR ROCK UNITS.

EMEMiniMPP EM Pi" Eir Nor-- 11111.11111111M.-

11111111111111-11111 1111•1111111111111-

111111-110111-1 111-1•11_11111- 111111111—M1111111

ommito rimaram Mal MEM INIZIMI 011•111111111MIENOM CICIMMICIIIIIM 1 --a--.

Sandstones

Siltstones

and

Mudstones.

Namurian (non-marine) Composite.

CLARE

SHALES

(marine)

Spongolite

Tuff

Limestones.

Lower Limestone Shales.

FIG. No.13.

4—T

ou

rna

isi

tr)

0 re

u_

0

ce

U

Na

mu

ria

n

1

a

58

method (Fig. 13 and Table 8). Since the contrast in Mo content

between the shales and the other rock types was so great, the

very considerable effort required to determine the actual lower

limit of concentration in these rocks was not considered to be

justified. However, the results are consistent with the average

values for the appropriate sedimentary rocks given by Krauskopf

(1955, p. 416), namely, shale, 1 ppm; sandstone, 0.1-1.0 ppm;

and limestone 0.1-0.5 ppm. The average value of 27 ppm obtained

from Clare Shales is also within the range expected for black

shales. Assuming the average values given by Krauskopf apply

in the study area, then the contrast in Mo content between the

Clare Shales and the neighbouring shales, sandstone and limestone

ranges from 25 - 250 : 1.

The regional distribution of Mo in rocks is given

in Fig. 14.

(ii) Selenium

As for Mo, Se is also concentrated in the black

shales (Figs. 13 and 15), the enrichment factor being in the

order of 15, which is somewhat less than that of Mo. Considering

the very low levels encountered and the precision of the analyti-

cal method employed, it is unlikely that differences in Se

content between the sandstones, Namurian shales and the lime-

stone are significant.

Mo in rock (ppm)

<2 0 2-5 • 5-10 O 10-20 • > 20

0 2 4 6

mites

FIG.14 . REGIONAL DISTRIBUTION OF Mo IN ROCK.

Sat in rock (PPrn)

<1 0 1 — 2 02-5

5 —10 • > 10

0

0

0 2 4 6

milts

FIG.15. REGIONAL DISTRIBUTION OF Se IN ROCK.

59

(iii) Other Metals

Data for the other elements analysed (Fig. 13)

is compared with the average concentrations in common sedi-

mentary rocks in Table 8. In the main they are of the same

order or fall within the range indicated.

With regard to the study area, it is apparent that

Cu and V follow Mo and Se in being concentrated in the Clare

Shales but as was the case in stream sediment, the anomaly

contrast is less pronounced.

The limestone, as would be expected from its compo-

sition is generally impoverished in most metals compared with

other rocks, the main exception being V. The two sandstone

members, the Old Red Sandstone and the Namurian, appear to

contain slightly higher proportions of some elements when

compared with the average sandstone (in particular Ga, Ti, Ni,

Co, Fe) but they are not pure sandstones and this discrepancy

is attributed to the relatively high proportion of argillaceous

matter in them.

The differences in metal content between the con-

formable marine Clare Shales and the non-marine Namurian

argillaceous rocks are attributed to the contrasting deposi-

tional environments. A more detailed study of the Clare Shales,

involving distribution of the elements, their mode of occur-

rence and possible means of concentration is given in Chapter VI.

Fig. 16 illustrates, in the form of a line diagram,

differences in metal content between the major rock types.

Namurian .iii L;tone Old Rod Sandstone

Average Black Shale 75-225 100-1000

AveraTe Sandstone 5-20 Carboniferous Lime- stone <5 39

Silts.:ones and Nulstones

Avera7e Limestone 4-20

Average Shale . 4 50-300 Crustal Abundance 5 130

Clare Shales 4.3-11.2

50

Table 8: Metal Content of the Major Rock Types Compared with Average Values

for Common Sedimentary Rocks

Average values from Krauskopf (1955) except where marked (*) and ("). (') Goldschmidt, (1954) (4") Green, (1959)

Mo Se Pb Ga V

PPm

Cu Ti Ni Co Mn Cr Fe203 %

Namurian Sandstone <2 0.18 10.7 11.6 53 12.0 4720 41 18 177 82 5.7 Old Red Sandstone <2 0.14 7 30 75 19.0 7480 37 11 700 110 6.0 Average Sandstone 0.1-1.0 1.0 10-40 5 10-60 10-40 3000" 2-10 1-10 385** 10-100 4.4**

Namuriar, siltstones and Nudotones <2 0.14 19.5 26 95 36 6420 58 24 406 124 7.9

Average Shale 1 0.5-1.0 20 15 50-300 30-150 4400** 20-100 10-50' - 100-400 6.2"

Clare Shales 27 2.90 22 15 365 79 2420 54 13-20 340 87 4.5 Average Black Shale 10-300 - 20-400 70 50-2000 20-300 - 20-300 5-50 - 10-500 -

Carboniferous L'stone <2 0.27 3.5 <2 61 4.3 88 8-10.4 <5 115 4.3-6.8 0.12-11 Avera4e Limestne 0.1-0.5 0.1-1.0 5-13 3 2-20 5-20 400** 3-10 0.2-2 1300" 5 1.85

Crustal Abundance 1 0.01 16 15 150 70 4400" 80 23 100* 200 7.1.

m PP As In As rpm Zn

rn

Other rock typos .2 ppm •

Other rock typos -40 5 ppm

------

O

•

0- • •

0-

METAL CONTENT (ppm)

2

5 10 20 50 100 200 500 t000

2000 5000 n:1003

O

•

-+-

7 0

-• 0 -4-

10

Mo

Se

Pb

Go

V

Cu

-0 ----- - Ti -4-

Ni

Co

-=-b--- ---- Mn

Cr

Mo

Pb

Go

V

Cu

Ti

Ni

Co

Mn

Cr

Fe203

F1G.16.DIAGRAM ILLUSTRATING THE MEAN METAL VALUES AND RANGE OF METAL IN THE FOUR MAJOR ROCK TYPES. O NAMURIAN. • CLARE SHALES 0 LIMESTONE • OLD RED SANDSTONE.

6].

Readily apparent contrasts in metal content that may form geo-

chemically mappable units or assemblages, characteristic of the

different lithologies, can be summarised as follows:-

Clare Shales - enriched in Mo and Se, Cu and V.

The contrasts for Cu and V are less pronounced than for Mo and

Se.

Limestone - appreciably lower than the other rock

types in Pb, Ga, Cu, Ti, Ni, Co, Cr, and Fe203.

Non-marine Namurian rocks - containing more than

twice as much Ti as the marine Clare Shales.

Because of the possible agricultural association

= of P and inorganic SO4 in the Mo cycle, a limited number of

samples were analysed for these constituents. The results

show little variation in the mean P content of the Clare Shales,

the limestones and the Namurian rocks., although phosphatic hori.'

zons are known to exist in some parts of the Clare Shales and

this may explain the high values of up to 1000 ppm P (O'Brien,

1953). With regard to SO4 there is an apparent enrichment in

the Clare Shales, compared with the limestone and Namurian

rocks.

3. OVERBURDEN

Regional sampling to determine the distribution

of metal in the overburden in relation to the stream sediment

and bedrock patterns was carried out at the sites shown in

Fig. 12; the sampling depth in both residual soil and drift

62

was 18-24 ins. The Mo content and other elements that could

be readily determined by the spectrograph were recorded for each

sample but because of time restrictions on the number of chemical

analyses the data for Se is limited to about one-third of the

samples.

The data summarized in Table 9 have been sub-

divided into zones, based on the bedrock and drift constitution

similar to those used for the presentation of the regional

stream sediment data (see Table 7).

(i) Molybdenum

Mo levels in overburden overlying background Namurian,

limestone and Old Red Sandstone rocks (Fig. 12, zones A-D)

averages less than 2 ppm (Table 9). The highest values, up to

30 ppm, occur over the line of outcrop of the Clare Shales.

The pattern of anomalous Mo values in the overburden

(Fig. 12) is in general closely related to the anomalous stream

sediment zones (E and F) which are also shown in outline in

Fig. 12. The range of Mo levels in the overburden is generally

greater and the distribution of anomalous samples more erratic

than the corresponding stream sediment patterns but this

apparently reflects the more sporadic nature of metal values in

the soils compared with stream sediments. However, the average

soil values 10-11 ppm and 3.6-4.7 ppm in the anomalous zones E

and F respectively, are roughly of the same order as in stream

sediments, namely 14.5 and 5.7 ppm Mo.

AREA No Se Cu V Pb Ga Ti Ni Co Ma Cr

24 20-300 60

24 20-400 74

24 10-160

34

24 24 5-40 850-1% 10 1860

24 24 <5-85 100-1% 14-15 470

B. Limestone 24 24 8-130 30-300 27 75

• 25 10 R <2-5 <0.2-1.3 M <2 <0.5

25 8-40 24

25 8-40 19

25 20-85 45

25 60-200

114

25 25 8-40 4000-1% 25 7760

C. 4.W. Namurian Weichsel drift absent

• 25 4 R <2-3 0.3-2.3 M <2 0.8

25 25 25 10-30 85-600 85-400 15 162 150

21 60-300

120

21 21 5-40 100-600 18 280

21 8-30 22

21 16-40 22

21 20-85 46

21 5000-1% 6670

D. N.W. Namurian and drift

21 6-50 27

21 30-200

105

n 22 1 R <2-6 0.6 M <2 0.6

E. "Mo" High Zone Cl. Sh. and mixed drift

II 27 14 R <2-30 0.5-8.0 • 10-11 2.7

19 14 <2-15 0.5-4 3.6-4.7 1.1

P. "Mo" Moderate II Zone. Cl. Sh• and R mixed drift

26 26 5-30 3000-1% 16 5310

26 13-85 27

A. O.R.S. L.L'st.Sh. n and basal limestone

8 2 <2-2 <0.2-0.5

<2 <0.5

8 8 8 30-100 50-200 40-130 52 82 77

8 8 6-30 2000-85000 16 5390

8 40-100 62

8 8 10-40 300-3000 25 690

8 60-130 98

20 20 30-160 60-600 87 250

14 14 30-70 50-400 50 130

26 26 26 26 20-300 <5-60 20-6000 60-500 63 16-20 350 130

Table 9: Metal Content of Soils and Drift from Different Bedrock Areas (Minus 80-mesh fraction, values in ppm; Horizon sampled 18-24 inches)

n • no. of samples. H • Range of values. M • Geometric mean. rn

km

64

The extension of the anomalous stream sediment zones

to the west is reflected in the overburden patterns. This has been

attributed to the 'carry-over' of molybdeniferous Clare Shale

material by the Weichsel ice-sheet (ref. glacial geology, Chapter

II) which advanced in a south-westerly direction across the area.

The Mo pattern in the drift in general corresponds to the expected

'fan-shaped' zone of glacially dispersed material from the Clare

Shale escarpment and is markedly limited to the south by the

terminal moraine. The influence of glacially transported Clare

Shale material on metal dispersion in the area is further

discussed in Chapter VII.

(ii) Selenium

Because of the limited number of Se analyses a map

of Se distribution in the overburden is not presented. However,

mean metal values for the various bedrock zones (Table 9) indi-

cate that Se is enriched in the areas that are anomalous for Mo

and in view of the similar stream sediment patterns of the two

elements it is probable that the regional overburden patterns

are also more or less identical.

Background levels of less than 0.5 ppm Se in the

O.R.S. and limestone areas to the east (areas A and B) and 0.8

and 0.6 ppm on the Namurian rocks (areas C and D) contrast with

average anomalous levels of 2.7 and 1.1 ppm in soils centred on

the Clare Shale sub.outcrop and drift in the Mo anomalous areas

E and IP .(Fig. 12).

65

(iii) Other Elements

Cu and V, which have been shown to be concentrated

in the Clare Shales along with Mo and Se, are similarly con-

centrated in the overburden of the molybdeniferous zones E and

F (Table 9).

There is also an apparent association of Cu with

the O.R.S. and the basal horizons of the limestone (area A).

Values for Cu in the overburden of this area are about twice

the concentration in the adjacent limestone (area B) and

Namurian soils (areas C and D). These data are not confirmed

by the stream sediment patterns however, and its validity may

be doubted in view of the limited number of samples (8) involved.

Data for the other elements examined are also given

in Table 9. Of particular interest are the high Pb values

associated with the basal limestone and O.R.S. soils (area A).

This trend is similar to that of Cu and confirms the Pb patterns

indicated by the stream sediment survey. The incidence of both

high Pb and Cu values in the vicinity of the O.R.S.-limestone

contact is interesting in view of the occurrence of Irish base

metal deposits in this horizon. It is of course more probable

that metal values detected in the study area reflect strati-

graphic variations in the bedrock rather than actual mineralisation.

66

4.. HERBAGE

Data on the regional metal patterns in herbage are

restricted to Mo, Se and Cu in samples collected along the

northern most east-west regional traverse (Fig. 17).

(i) Molybdenum

There is a very close correspondence between the

highest Mo values in the herbage (Fig. 17) and the anomalous

zones delimited by the stream sediment and soil surveys (Figs. 8

and 12).

Background levels in herbage range from 0.8 to 1.2 ppm

over the limestone and rise to 3.2 ppm approaching the anomalous

stream sediment zones. Anomalous values range up to 16 ppm Mo

near the line of outcrop of the Clare Shales. Over the Namurian

rocks and drift in the N.W. of the area (area D) background

levels range from 0,4 to 3.2 ppm Mo. Samples of herbage from

the background area of mainly limestone drift with some O.R.S.

and L. Limestone Shale material in the south-east also ranged

from 1.4 to 3.6 ppm Mo.

The established background levels of less than 3.6

ppm Mo for the area lie below the provisional threshold limit

of toxic herbage given by Walsh et al (1952) of 5 ppm Mo. The

potentially toxic levels of 8 to 16 ppm Mo in herbage coincide

with the anomalous stream sediment zones (greater than 5 ppm),

indicating a considerable area of potentially toxic herbage. The

more detailed relationship between the Mo patterns of the herbage

and the soil is examined in later chapters.

West.

t a- High. Anomalous Mo Stream Sediment

-*Moderate.. Zones.

Namurian4-- A—I,Limestone East

1 inch .= 2 miles. +-----I- Cu Dry Weight.

•-----• Mo .•

o----o Se

Projected outcrop Clare Shales.

0 s

I •

0 \

e

FIG.No.17. REGIONAL METAL CONTENT OF HERBAGE

Co.Limerick. North-end of Area, East-West Traverse.

VI A •1 Cob VI

N. OD 04 N NI NI Ira

to? ••▪ •• - CD ._

•st

30 30

10

3

2 a. 0.

1

0.5

0.3

0.2

01

10

5

3

0,5

0.3

0.2

01

0

• . o----o.. o. . ,,

b." 'oo

0

-d Other Se values .c0•2 ppm.

67

(ii) Selenium

Analysis of herbage from the northern regional

traverse (Fig. 17) and background studies in the south-east

indicate that on the generally well-drained soils the Se

content of the herbage does not exceed 0.5 ppm, which is well

below the accepted toxic threshold of 5 ppm (Fleming and Walsh,

1957), or even the lower level of 2 ppm suggested by Smith and

Lillie (1940). The absence of any excess of Se in the herbage

samples collected within the stream sediment anomaly is believed

to be due to local environmental factors. The sample sites were

mainly positioned on well-drained soils which, it will be demon-

strated in the following chapter, do not produce toxic concentra-

tions in the herbage.

(iii) Copper

Analysis of a limited number of samples from the

regional herbage traverse (Fig. 17) indicated that a fairly

broad anomalous.Cu zone, with levels in herbage ranging from

7.3 to 10.1 ppm Cu, was centred on the Mo anomaly. Background

Cu levels were in the range 3.9 to 6.1 ppm. Compared with Mo,

the contrast between background and anomalous Cu levels is low

and this corresponds with the pattern of Cu distribution in

soils, rocks and stream sediments.

68

5. DISCUSSION

The distribution of No and Se in the bedrock, soil

and stream sediment environments (summarized in Table 10)

indicates that they have generally similar regional dispersion

characteristics. This is confirmed by the similarity of the

regional bedrock and stream sediment plans (Figs. 14 and 15 and

Figs. 8 and 9, respectively).

Cu and V, the elements which along with Mo and Se

are most obviously concentrated in the black shale bedrock,

bear a similar relationship in soils and stream sediments.

The reflection of the bedrock relationship of Cu and Mo in the

soils of the area is of particular significance when the inter-

action of these elements in nutrition is considered later.

Anomalous concentrations of Mo in herbage are also accompanied

by a rise in the Cu content.

Comparison of the average data presented for the

bedrock, soil and drainage environments (Table 10) demonstrates

that for most elements the bedrock patterns are repeated in the

insoluble products of secondary dispersion represented by the

soils and stream sediments.

In the case of the more chemically-resistant rocks,

i.e. the Clare Shales and the Namurian argillaceous and arena-

ceous sediments, the metal content of the secondary products,

with the exception of Mn, is roughly the same order as the

bedrock content; However, the limestone, in which chemical

weathering factors involving the removal of CaCO3 in solution

Table 10: Comparison of the Man metal Contents of Bedrock. Soil and Drift and Stream Sediments

AREA SAMPLE TYPE Se Cu V Pb Ga Ti Ni Co Mn Cr

Old Red Sandstone Rock <2 0.14 19 75 7 30 7480 37 11 700 110

A. Mixed O.R.S., Lower Soil <2 <0.5 52 82 77 16 5390 62 25 690 98 L'st Shiles and basal

limestone Str. Sed. <2 0.54 35 55 66 9.4 2600 45 13.5 950 89

B. Limestone Rock <2 0.27 4.3 61 3.5 <2 88 8-10 4:5 115 4.3.6.8 Soil <2 <0.5 27 75 34 10 1860 60 14-15 470 74 Sed. <2 0.64 29 66 29 5 1180 49 8.2 429 44

C. S.W. Namurian. Rock <2 0.16 27 81 16.5 21 5910 53 22 325 111 Drift absent Soil <2 0.8 24 114 19 25 7760 45 15 162 150

Sed. <2 0.3 44 102 21 25 4940 66 30 1240 93

D. N.W. Namurian. Soil <2 0.6 27 105 22 22 6670 46 18 280 120 Some drift cover Sed. 2.6 0.55 53 104 36 24 5300 75 32 2020 100

Clare Shale Rock 27 2.9 79 365 22 15 2420 54 13-20 340 87

E. "Mo High" Anomalous Soil 10-11 2.7 87 248 Soil Zone Sed. 14.5 2.75 92 187 'Pr- 16 5310 63 16-20 350 130

F. "Mo Moderate" Anomalous Zone

Soil Sed.

3.6-4.7 5.7

1.1 1.2

50 61

132 121

Sed.177 13 2970 97 31 960 103 .'"'

ot

70

are pre-dominant, shows a postive enrichment of Cu, Pb, Ga, Ti,

Ni, Co and Cr in the soils and sediments compared with the

primary material.

From this it is apparent that while the primary geo-

chemical patterns may be retained in the secondary environment,

the mode of weathering of a particular bedrock can appreciably

affect the actual metal levels. Because of this, the contrast

with adjoining bedrock types having a different mode of weathering

may also be affected. Thus, although the limestone (Table 10)

contains appreciably less Cu, Pb, Ni and Co than the Namurian

rocks, the metal levels in the soil and sediment derived from

both sources are not significantly different.

However, the amount of V is not appreciably enriched

in the transition from limestone rock to soil to sediment, and

this demonstrates that the mode of dispersion of an individual

element may also influence the resultant secondary patterns.

Furthermore, Mn, which is appreciably enriched in the stream

sediments of the Namurian areas compared with the soil content,

shows that variations in the metal level can be quite large

between different environments.

The effect of secondary dispersion mechanisms on

the resultant geochemical pattern is discussed in greater

detail in Part C of this thesis, mainly with reference to

Mo and Se.

71

The relationships established between the stream

sediment patterns and the distribution of metal in the soils

and bedrock confirm the validity of stream sediment reconnais-

sance as a means of defining regional geochemical patterns.

With regard to biogeochemical studies, an area of

about 30 sq. miles was indicated in which anomalous, potentially

toxic concentrations of Mo and Se are present in the soils and,

in the case of Mo, probably also in the herbage. The relation-

ship of Se in the soil to the amount accumulated by pasture

herbage is obscure at this stage but is obviously affected by

environmental features other than the total content in the

soils.

72

CHAPTER V. DISTRIBUTION OF METAL IN THE FLYNN'S

FARM AREA

In order to examine more closely the relationship

between the stream sediment patterns and the metal content of the

local soils and vegetation more detailed sampling was undertaken

in the area where Se toxicity had already been recorded (Figs. 3

and 20). In addition to close-spaced stream sediment samples

(250 to 500 ft. apart) the soils and pasture herbage were

collected systematically on an 880 ft. square grid giving a

total of about 220 sample points over 5 sq. miles.

For convenience this area is referred to as Flynn's

Faro after the property at toxic soil site A (Fig. 20) where

much of the detailed work has taken place.

1. GENERAL DESCRIPTION OF THE AREA

The bedrock geology in relation to the region as a

whole is shown in Fig. 3 and in greater detail in Fig. 20.

The South Creek Clare Shale section referred to in

'Chapter VI is located roughly along strike from toxic site A

(Fig. 18) and comprises the basal horizons of the Clare Shales.

This section contains mean values of 71 and 15 ppm Mo and Se

respectively (other constituents are given in Table 12). The

extensive drift cover obscures the overlying horizons and their

metal content is not known. However, evidence from other rock

sections suggests that the overlying strata may contain some-

what lower values.

1 4. \ C'''..,.. ‘

II %'4%. , -, "4,0 • I e

I .rct on-rd.Frits.$6,37

I \ KILCOLMAN SCHOOL \

• AREA. .... •-• • 1,-..... r •"•, ''''..-1 , • trert-rot.Fig.3, • I ri/1 • ..,, t ..• - • 00-• I e . %

1 • • • .I...

..• I

i ' ► I I I • I . rr

I f .0 i

I I

I

r I

r • • I t

o i

. • . ,, i

I i r r , VA I r : .1 I , SP i ♦ / i il En • :..... .....

, ,... ...... , , ..., ... " 1 I

/

• 16/ / e / I /

.._ -

/. / frtsen-reLF*2.014-. , ....

r / I 4:- ) , --,

........, I .- J 1 I J I) I 0. 4. • I i .., • .. 11

/ `ea..

e i (LISOOR0011 HO. tar /

/ / t....-- t / II, . ,

.... ... .., ... I

I

It I I I ••"" "".. I Crook.C11. • • Vs .. i •

•,....,- • i , .- •

1/4'• r .../ 4•11.0.''.. O ( •

• I SOUTH CS. ROCK • • i i • SECg.,TION. iht?

....'' '40W...1 / I / •..„, , t 1 6,11 i

11. a , \

Cdr • , e" I

I /

1

CONTOUR INTERVAL 100 FEET. A, B KNOWN S. TOXIC sitsTuns NILE.

FIG. NO.18. TOPOGRAPHY AND PLACE NAMES-FLYNN'S FARM AREA.

73

The topography (Fig. 18) is controlled to a large

extent by the bedrock geology. Limestone occupies the flat to

gently undulating plain to the east and the more resistant Clare

Shales form the hilly area in the west which rises to more than

300 ft. above the plain.

The overburden is predominantly glacial drift with

the exception of minor occurrences of residual and alluvial

soils (Fig. 19). The drift is mainly boulder clay with some

gravel and sand deposits of fluvio-glacial origin. The material

composing the drift is largely determined by the rocks traversed

by the ice in a general westerly and south-westerly direction.

Thus over the limestone the drift is almost entirely composed

of limestone fragments and rock flour, whereas in the area

underlain by Clare Shales, the drift is made up of various

mixtures of the two rock types.

Alluvial deposits occupy flats flanking some of the

streams and are most extensive in the limestone area.

Peat deposits are rare and are confined to small

post-glacial depressions in which the major streams generally

rise. Underlying the peat, thin clay and marl horizons are

often present indicating that the initial stages of formation

took the form of shallow post-glacial lakes which developed

into swamps with severely impeded drainage.

The drainage conditions of the soils vary with

topography and the composition of the parent material. Residual

Clare Shale soils and much of the drift on the hill slopes is

71+

moderately well drained. However, soils of poor drainage may

be found on some of the slopes where the lower horizons are of

poor permeability. This particularly applies to some of the

limestone-rich boulder-clay deposits containing a large propor-

tion of fine rock flour which retards water movement. In

topographic depressions and along some of the stream flats,

drainage is usually poor to severely impeded. This is

especially so in the case of the peaty-swamp and alluvial

deposits. Recent land improvement programmes of ploughing and

channelling have slightly improved some of the poorly drained

areas by lowering the water table.

The streams follow artificial drainage channels

where they drain the old swamps but in the upper reaches they

are incised with colluvial banks and follow their natural course.

Agriculture is mainly devoted to grazing of dairy

cattle on small holdings of 10 to 30 acres. There is some

grazing of beef cattle and stud horses but very little tillage.

The known occurrences of toxic seleniferous soils,

originally investigated by the Agricultural Institute are

located on poorly drained peaty-swamp and alluvial soils

respectively (Fig. 20, sites A and B).

2. STREAM SEDIMENT METAL PATTERNS

(i) Molybdenum

The distribution of Mo in the drainage sediments

around Flynn's Farm (Fig. 19a) shows that the highest values

(a) 21 140' • 5=0111644450

450 Mo In stream sediment (ppm)

R A 0 1 : R NOW001 soil

Glacial drift ma. NA 4.01

Alluvium

(b) Mo In soil at 18-24 111.5 (ppm) <5 5-15 :-Me***.V 15-45 >45

(c) Mo In herbage (ppm dry matter) r"---1<5 :.::••:::. 5-to 1020 >2Q

FIG. 19. DISTRIBUTION OF Mo IN STREAM SEDIMENT, SOIL AND MIXED HERBAGE AND SIMPLIFIED OVERBURDEN MAP (after Irish Geological Survey, shown in (a) )

75

occur in the headwaters of streams draining the Clare Shales.

Peak values up to 800 ppm in organic-rich sediments are

associated with peaty and alluvial seepage areas overlying or

adjacent to the Clare Shales. Anomalous values in the range

50 to 100 ppm occur in South-West Creek where the stream drains

drift and residual soils of largely Clare Shale origin.

Downstream from the metal-rich headwaters there is

a general decrease in values as the streams pass onto the

limestone. Tributary streams draining the limestone, Namurian

sandstones and siltstones in the south-west, contain only

background values of less than 2 ppm Mo.

Relatively strongly anomalous samples of greater

than 10 ppm extend about 2000 and 2300 ft. downstream from the

peak values in Flynn's and South Creek respectively. Samples

of 5 ppm or greater extend 2500 and 7000 ft. downstream

respectively in the two streams. Below the confluence of

Flynn's and South Creeks slightly anomalous values in the range

2 to 5 ppm do occur but the distribution is somewhat erratic

and the contrast with background values low.

(ii) Selenium

The distribution of Se in stream sediments is

closely related to the Mo pattern (Fig. 20a). Peak values up

to 175 ppm at toxic soil site A, occur in the headwaters of the

streams draining peaty seepage areas on or near to the Clare

Shales. Values from 5 to 20 ppm are present in the sediments

(a) Z 10 50Z$O I . .1 t I mlimlSlOllt • CIGre Shales

S. in strum Mdiment (ppm)

(II) Sf in soli It 18-Zo1m. (ppm) rvstta 1'5-5 .>15

(C) S. In ~trbaq. (ppm dry matlcr) [--""ld5 [«::':'11'5-5 W1tJ 5"15 • >;s

FIG. :W. DISTRIBUTION OF Se IX ~1'RF:A?-1 SEDL'IENT, SOIL .~~D NIXED HERBAGE 'AND GEOL\)GY (aftel' Hodson Cr Le \~arne, 1961 shO\m in (a) )

76

of South-West Creek which drains residual Clare Shale soils and

glacial drift. Downstream from the headwaters the metal content

decreases as the stream passes onto the limestone. The drainage

train is maintained at anomalous levels where the stream is

flanked by alluvial but quickly drops to local background levels

(less than 2 ppm) where alluvium is absent as in the lower

reaches of South Creek. Tributary streams draining alluvium

deposited along the main stream also tend to carry anomalous

concentrations of Se.

The mean regional background is 0.7 ppm Se but may

fluctuate as high as 2 ppm. Values in excess of 2 ppm extend

about 3 miles downstream from the peak levels at the head of

the stream but clearly anomalous values of 5 ppm or greater are

limited to about 9000 ft. from the headwaters.

It is obvious that the length of the drainage train

is determined to a large extent by the presence or absence of

flanking alluvium.

(iii) Copper

Like Mo and Se, Cu also tends to be concentrated in

the stream sediments at the headwaters of the streams draining

the Clare Shales (Fig. 21).

Values range from 50 to 100 and 80 to 200 ppm Cu in

the headwaters of Flynn's and South Creeks, respectively, and

from 40 to 150 ppm in the drainage of the alluvium near the base

of the Clare Shales on South Creek. These compare with local

cOPPER'cotT.:gNT :k ponlY-s.bt:TREANt4.E.1) • • „ • 1.-0,0101.74

FIG. 21. DISTRIBUTION OF Cu IN STREAM SEDIMENTS

AND TOPSOIL-FLYNN'S FARM AREA

77

background values in the range 15 to 60 ppm in streams draining

the limestone. Anomalous levels greater than 60 ppm do not

extend more than 2000 ft. downstream from the base of the Clare

Shales.

The influence of the Clare Shales on the metal content

of the stream sediment is readily detectable but the contrast

between background and anomalous values' is relatively low com-

pared with Se and Mo.,

(iv) Vanadium

Vanadium is also concentrated in the headwaters of

the streams rising on the Clare Shales though the contrast with

local background values is even less marked than Cu (Fig. 22).

Background levels range from about 50 to 100 ppm V whereas

anomalous samples from the headwaters of Flynn's and South Creeks

range from 100 to 300 and 100 to 500 ppm, respectively.

3. METAL PATTERNS IN THE SOILS

(i) Molybdenum

The distribution of Mo in the soil at 18-24 ins. is

shown in Fig. 19b. Topsoil samples from 0-4 ins. showed a simi-

lar pattern but with slight variations in overall metal content.

The profile distribution of Mo in different soil types is des-

cribed in Chapter VII.

It is apparent that there is a close relationship

between the Mo content of the soil and the bedrock. Most of

VANADIUM CONTENT (ppm) of STREAM SEDIMENT (a) (- 80 mesh fraction)

VANADIUM CONTENT (ppm) of TOPSOIL (0"-4") (b) so 100 200 >200

FIG.22. DISTRIBUTION OF V IN STREAM SEDIMENTS AND TOPSOIL-FLYNN'S FARM AREA

78

the extensive anomalous soil areas in the west are related to

the metal-rich glacial drift or residuum derived from the Clare

Shales. The soil patterns reflect such features as the faulted

embayment in the eastern boundary of the Clare Shales and the

area of barren Namurian rocks in the south-west corner.

The influence of the bedrock on the metal content of

the soil is modified by secondary factors, in particular the

type of overburden and the drainage. Thus, peak Mo values up

to 3000 ppm occur in the poorly drained peaty-swamp deposits over-

lying or adjacent to the Clare Shales. On the better drained

Clare Shale residuum and drift the highest values are in the

order of 70 ppm Mo. The drift soils of limestone origin in the

east mostly contain less than 2 ppm Mo.

The extension of Mo values greater than 5 ppm east

of the Clare Shales in alluvium is apparently related to the

erosion and transport of metal-rich material from the headwaters

of the main streams. Peak values of 800 ppm occur in alluvium

directly downslope from the Clare Shale boundary on South Creek

where the deposits are subject to seepage from the shales.

However, alluvium on the limestone further downstream rarely

contains more than 15 ppm Mo. Alluvium derived from tributary

streams draining barren limestone drift contain background

concentrations usually less than 2 ppm.

Molybdeniferous soils in the range 15-45 ppm Mo east

of the Clare Shale boundary mid-way between Flynn's and South

Creeks is believed to be due to the occurrence of fluvio-glacial

79

gravels containing Clare Shale fragments. This material is

not associated with the more recent alluvial deposits but was

probably formed as the result of damming during the retreat of

the ice.

(ii) Selenium

The pattern of distribution of Se in the soils

is essentially the same as that for Mo (Fig. 20b). The Clare

Shale bedrock ic major feature controlling metal distribu-

tion in the soil and drift but as with Mo, peak Se values up

to 500 ppm are found in the peaty-swamps. Most drift and resi-

dual soils on the Clare Shales contain from 1.5 to 15 ppm Se.

The occurrence of seleniferous soils on the limestone

east of the Clare Shales is closely related to the alluvial depo-

sits. Concentrations up to 90 ppm are present in the alluvial

soils flanking Flynn's Creek at toxic site B. The dispersion

of Se downstream from the metal-rich headwaters has been much

more extensive than Mo as is also shown by the length of the

present day drainage trains.

(iii) Copper

Only topsoil samples were analysed for Cu but

the distribution is basically similar to that of Mo and Se

at 18-24 inches (Fig. 21b).

The greater part of the anomalous soil patterns

(more than 50 ppm Cu) is related to the metal-rich drift and

swamp deposits overlying the Clare Shales and to alluvial

8o

deposits flanking South Creek near the base of the Clare Shales

but elsewhere anomalous values seldom exceed 150 ppm. Most of

the limestone drift soils contain local background levels of

less than 50 ppm Cu.

One noticeable deviation of Cu from the Mo and Se

patterns is the area of background values (20-50 ppm) roughly

coincident with the residual Clare Shale soils (Fig. 19a) in

the north-west. Also, slightly anomalous concentrations of

Cu (50-80 ppm) on the limestone drift broadly correspond to

areas of alkaline soils (Fig. 23). It is believed that these

variations probably represent basic differences in the secondary

dispersion mechanisms of Cu compared with Se and Mo that modify

the original bedrock patterns.

(iv) Vanadium

The distribution of V in the topsoil is also closely

related to the bedrock patterns (Fig. 22h). Levels range from

100 to 500 ppm in soils over the Clare Shales, compared with

local background values of 60 to 100 ppm over the limestone.

The peak value of 700 ppm occurs in the alluvium on South Creek

and there are some slightly anomalous concentrations of V (100-

150 ppm) vaguely related to alluvium in the east.

Unlike Mo and Se there is no marked concentration of

V in the peaty-swamp soils.

81

4, METAL PATTERNS IN THE PASTURE HERBAGE

The areal distribution of Mo, Se and Cu was determined

by analysis of oven-dried herbage. The samples were mainly grasses

with some clover. Herbs were rarely collected unless they formed

a dominant part of the pasture.

(i) Molybdenum

Broadly speaking, the patterns of Mo in herbage

show a fair degree of correlation with the Mo content of the soil

irrespective of the local variations in soil type (Fig. 19c).

Anomalous herbage patterns are related to the Clare Shale residuum

and to Mo-rich drift and alluvium.

Local background levels for herbage growing on barren

limestone drift range from 0.6 to 7.2 ppm Mo, most values lying

between 1 and 3 ppm. This is comparable with the levels indi-

cated by the regional herbage traverse (Fig. 17).

Within the anomalous zone, peak herbage values occur

on the peaty-swamps and alluvial soils flanking South Creek. On

the better drained residual Clare Shale soils and molybdeniferous

drift, the peak values range up to 74 ppm.

The extent of higher than background concentrations

of Mo in herbage growing on alluvial soils overlying limestone

is in general greater in area than the readily detectable anomalous

patterns in the soil at 18-24 inches. Profile studies (Chapter VII)

have shown that slightly higher Mo values may accumulate in the

topsoil horizons. Also these areas of anomalous herbage can often

pH of TOPSOIL (0"-4") 5.3-6.5 Slight to

moderately acid.

6.6-7-5 Neutral to slightly alkaline.

<5.2 Strongly acid.

FIG. 23. pH of TOPSOIL-FLYNN'S FARM AREA

82

be related to alkaline soils (Fig. 23). The significance of this

in the light of relative metal availability is discussed in

Chapter VIII.

(ii) Selenium

Anomalous Se concentrations are found only on the

more alkaline seepage and alluvial soils within the seleniferous

area (Fig. 20c).

The peak values of 100 ppm Se occur in herbage growing

at toxic soilhcality A at the head of Flynn's Creek. Values up

to 10 ppm are recorded from toxic area B on alluvial soils. Local

loackground levels for herbage growing on barren limestone drift

are generally 0.3 ppm or less, with a few higher values reaching

0.9 ppm on alkaline soils.

On the moderately well-drained acid seleniferous,

residual and drift soils in the west, Se levels lie within the

background range, most herbage contents recorded being less than

0.5 ppm Se. The seleniferous vegetation growing on drift

between Flynn's and South Creeks adjacent to the base of the

Clare Shales is in an area subject to seepage and the soils are

alkaline in reaction.

The seleniferous alluvial soils flanking the North-

blast greek are strongly acid (pH 4.62-4.83) and the Se content

of herbage is small (less than 0.3 ppm). Thib is in contrast

to the high levels encountered in alkaline seleniferous alluvium.

Thus, in addition to the Se content of the soil it is apparent

that other environmental factors, in particular drainage and

83

soil reaction play a part in the uptake of Se by plants.

(iii) Copper

The Cu content of herbage ranged between 5 and 14 ppm

with no obvious pattern that could be correlated with the soil

metal contents or soil type. This contrasts with the regional

herbage traverse (Fig. 17) which featured background values in

the order of 0.4-3.6 ppm with a very broad anomaly about 3 miles

in width centred on the narrower molybdeniferous zone. Peak

values in this zone ranged from 7.3 to 10.7 ppm Cu. The lack

of correlation between soil and herbage patterns in the Flynn's

Farm area, is mainly attributed to the relatively low range of

soil Cu values compared with Mo and also the influence of other

factors involved in Cu uptake by plants.

5. DISCUSSION

The distribution of Mo, Se and Cu in the Flynn's

Farm grid confirmed the broad relationship between the metal

contents of drainage sediments and the bedrock, soil and pasture

herbage of the catchment area that had been indicated by the

regional stildieS. The study of V was restricted to rock, soil

and drainage sediment relationships. However, detailed examina-

tion of the overburden patterns showed that a number of features

reflected the influence of secondary geochemical factors on the

bedrock metal contents. Most notable were the effects of over-

burden type and drainage on the accumulation of very high con-

centrations of Mo and Se in peaty-swamp soils and of Se in

84

alluvium.

The foremost feature of the herbage-soil relation-

ship is the contrast between the Mo and Se patterns in herbage.

There is some degree of correlation between the total Mo content

of the soil and of the herbage irrespective of local variations

in soil type. In contrast, Se-rich herbage is only present on

more or less alkaline, poorly-drained seleniferous soils of swamp

or alluvial origin. It would thus appear that the effects of

local environmental features (e.g. soil type, drainage, pH) are

less restrictive on the uptake of Mo by plants than Se. As a

result, correlation of stream sediment patterns with the Se

content of herbage is dependent upon the interpretation of the

influence of other environmental factors in addition to the

metal content of the soil. Further attention is given to the

factors involved in the rock-soil relationship and the uptake

of Mo and Se in Chapters VII and VIII, respectively.

With regard to the interpretation of the geochemical

patterns in the light of animal health problems it is apparent

that there are considerable areas of herbage in which the metal

levels are far above normal. In the case of Se, the occurrence

of toxic pastures at sites A and B has already been reported

(Walsh and Fleming, 1952). On the basis of a toxic threshold

level of 5 ppm in oven-dried herbage (Fleming and Walsh, 1957)

there are at least four additional seleniferous localities

that may be considered toxic. There is also evidence that

85

sub-clinical toxicity may be induced by a much lower Se intake

in the order of 1 ppm (Smith and Lillie, 1940). Contouring the

herbage content at 1.5 ppm Se indicates there may be much more

extensive toxic pastures at a sub-clinical level.

Turning to Mo, Fleming and Walsh (1957) consider

10 ppm in dry matter to be definitely toxic and 5 ppm can be

taken provisionally as a threshold level in toxic herbage

(Walsh et al, 1952). There are therefore widespread potentially

toxic pastures associated with the anomalous soils. Some

symptoms of Mo toxicity, probably in the form of Mo-induced

Cu deficiency, have been reported from Co. Limerick (Fleming

and Walsh, 1957). Assuming similar plant-soil-sediment rela-

tionships for the region as a whole, the patterns revealed by

the regional stream sediment study outline a considerable area

in which clinical or sub-clinical Mo toxicity could exist

(Fig. 8).

86

PART C

CHAPTER VI. DISTRIBUTION OF METAL IN THE CLARE SHALES

Regional studies indicated that the Clare Shale

formation, deposited in a marine black shale environment, con-

tained concentrations of Mo and Se and to a lesser extent V

and Cu, far in excess of the amounts present in the adjacent

rock types. This confirmed data by the Agricultural Institute

(Fleming and Walsh) that the Clare Shale were the primary

source of Se in the soils of Co. Limerick. This chapter

describes the distribution of metals in the parent bedrock and

their possible mode of occurrence with particular reference to

Mo, Se, Cu and V. Proposals are also advanced as to possible

reasons for the concentration of Mo, Se and some other elements

in this horizon.

Study of metal distribution in the Clare Shales is

principally based on the sampling and analysis of four strati-

graphic sections (Figs. 2 and 25). The completeness of these

sections was governed by the exposures available, the major

shortcoming being lack of coverage across the limestone-shale

contact, which is totally obscured by drift.

Work by Hodson (1954 A and B) and Hodson and Le

Warne (1961) resulted in more detailed stratigraphic defini-

tion and mapping of the Clare Shales than hitherto. Hodson

and Le Warne's sub-division of the Clare Shales into zones

87

by means of the goniatite faunas has been adopted in this thesis

as the basis for stratigraphic contrD1 of the sections sampled.

Three principal zones are recognised, namely the E (Enmorphoceras),

H (Homoceras) and R (Reticuloceras) zones, respectively.

For convenience and partly because of incomplete

exposures, the R and H zones, which are relatively narrow, have

been combined and the E2

zone has been divided into upper and

lower sections of approximately equal thickness for the calcu-

lation of composite metal contents. The basal part of the E

zone (E1) is not represented in the study area.

1. VARIATION OF METAL CONTENT WITH LITHOLOGY IN THE

CLARE SHALFS

Within the Clare Shale formation, although they are

basically described as a typical black shale sequence, variations

in lithology do occur. Sample intervals were based on readily

definable features, such as colour, pyrite content, bedding, etc.,

indicating changing conditions of sedimentation that may be

reflected in variations in the metal content.

The shales are generally very well bedded and in

thin section are seen to consist of slightly rounded quartz

grains interspersed with a varying amount of argillaceous and

carbonaceous material (Fig. 24). The amount of carbonaceous

matter is greatest in the darker coloured shales and obscures

much of the other material in the thin sections. Very fine

bedding is seen as light and dark bands representing varia-

• or 111fr -16 •

"?•• "pp • 10. • •• s; 40p ..;

• E. ; , - 4, • alp*:.• -4 git . • 0...„1. • •:, 01110 *Or-

• °P-1/01111 .. • I. • .4. 0 ih6e.

• oleo. .1644 .•`° • g. • stet*:• : '4644- " •

..ar •••• ..t4r0 • . • • .4Ir. 04. ;41 0. • r` 4gie..11P.pir

fOr .;;;;;;;• • . . .1.14

..••;" r • . • Mk ? • • ,

lmm.

Well-bedded black shale, cut perpendicular to bedding. Angular quartz fragments in a matrix of opaque carbonaceous matter,microcrystalline quartz and argillaceous material. ( Sample 2215,basal E2 Zone,

South Creek Section.)

Spongolite. Siliceous spicules of recrystallited,microgranular quartz and radiating fibrous chalcedony, in a matrix of mainly opaque carbonaceous material, microcrystalline quartz and argillaceous matter. ( Sample 2217,basal E2 Zone,

South Creek Section.)

Highly pyritic black shale. Large,opaque,granular pyrite aggregates bordered by quartz in amatrix of quartz, carbonaceous material and smaller irregular pyrite grains. ( Sample 2246 ,upper E2 Zone,

Kilco1man Section.)

FIG.24. THIN SECTIONS OF CLARE SHALES.

88

tions in the carbon content. Pyrite occurs in several forms:

(a) usually as fine cubic grains forming aggregates aligned

roughly parallel to the bedding, (b) occasionally in concre-

tionary forms up to 1 inch in diameter, and (c) as large cubes

up to -i-1,-inch in size which are generally concentrated in thin

beds. All these forms would appear to represent re-crystalli-

zation of iron sulphide during diagenesis.

The presence of carbonaceous matter and iron sul-

phides is characteristic of the reducing, anaerobic depositional

environment of black shales. The siliceous shales described are

most probably all spongolites as described in detail by Le Warne

(1961).

The metal content of the different lithological

types characteristic of the Clare Shales varies as shown in

Table 11. The different shale species have been sub-divided

into the types most readily recognised in the field. The

criteria on which the descriptions are based are the amounts

of carbonaceous matter and pyrite visable in the field speci-

mens. Samples were restricted to the Kilcolman Creek section,

in which all types are represented, in order to avoid variations

due to differing depositional environments related to location

in the sedimentary basin.

The marked concentration of Mo and Se as well as

Pb, Cu, Ni and Co in the carbonaceous and highly pyritic black

shales is in accordance with the results recorded by other

workers, in particular Kuroda and Sandell (1954), Krauskopf

Table 11: Mean Metal Content of Different Shale Types.

Kilcolman Creek Section

Type of Shale

Black Dark-grey Light-grey Black Grey Siliceous carbonaceous semi-carbonaceous carbonaceous pyritic (Spongolite)

and pyritic

No. of samples 13 7 4 4 3 .5

Mo 15 10.8 5.0 69 22 16 Se 3.2 0.8 1.4 4.2 2.3 1.3 Pb 26 24 24 36 27 10 Ga 16 34 29 24 32 5.6 V 360 245 183 217 254 365 Cu 54 76 52 288 166 45 Ti 3150 5470 7520 5160 6950 548 Ni 38 81 68 116 121 11.5 Co 10 28 39 79 6o <5 Mn 194 510 418 200 722 109 Cr 164 150 164 121 147 72 Fe203 2.9 9.1 9.1 >35 9.5 1.0

(Mean metal values are weighted for sample width and are in ppm, except Fe203 which is given as a percentage)

00 ss0

90

(1956), Goldschmidt (1957) and Tourtelot (1962). The Mo and Se

content is lowest in the grey poorly carbonaceous, non-pyritic

shales and the spongolites. Pb, Cu and Ni also follow this

trend. The spongolites are deficient in most metals particularly

Pb, Ga, Ti, Ni, Co, Mn, Cr and Fe203 but are not markedly low in

Mo, Se and Cu and, in fact, contain the highest concentrations

of V.

The results show a distinct tendency for the highest

Mo values to be associated with the iron-rich, pyritic shale.

However, the Se content would appear to be more closely related

to the amount of carbonaceous matter present since the second

highest concentration of Se (3.2 ppm Se) occurs in the black

carbonaceous shales which are relatively deficient in iron

(2.% Fe203).

The possible mechanisms by which these patterns of

metal concentration have developed are discussed later in this

chapter.

24 VERTICAL AND LATERAL DISTRIBUTION OF METAL IN THE

CLARE SHALRS

The variation in metal content between the various

stratigraphic divisions of the Clare Shale sections is given in

Table 12 and Figures 25 and 26. It is apparent that there is

no obvious stratigraphic correlation of overall metal content

between sections and insufficient complete sections are available

to establish if there are consistent vertical patterns. However,

91

certain trends, the significance of which must be doubted in view

of the limited number of sections sampled, do exist and may throw

some light on the metal assemblages to be expected both laterally

and vertically within the sedimentary basin. The dispersion

patterns of the elements relative to one another may also be

some indication of environmental conditions existing at the

time of deposition. The variation in metal content due to

lithological differences in the shales as described in the

previous section must also be taken into account.

(i) Molybdenum and Selenium

Mo and Se demonstrate a degree of co-variance

(Figs. 25, 26a and 27) when restricted stratigraphic sections

are examined, i.e. over a period of sedimentation when relatively

uniform physio-chemical conditions of deposition existed.

However, where conditions favouring concentration of Mo differ

from those for Se, corresponding variations in the ratio of

abundance between the two elements should be apparent. For

example, the abrupt change in the Mo:Se ratio that occurs near

the top of the Kilcolman basal E2 section (Fig. 25), must indi-

cate changes in the factors controlling concentration of the

elements whether they be environment (pH, Eh) or compositional

(e.g. changes in major components such as iron sulphide or

carbon, or in the supply of Se and Mo into the basin).

Although no characteristic metal contents for either

Mo or Se can be defined for any particular horizon, the following

tentative conclusions may be drawn from the data:-

SECTION ZONE METAL CONTENT PPM Mo Se Pb Ga V Cu Ti Ni Co Mn

7. Cr Fe 203

71: ft F 7 - Sr 7 sr , 7 : sr 7 : 51' 1 7 : sr i 7 : Sr 7 • Sr 1 7 51* 7 51' 7 • 51' 7 51' 7 Si' BALLAGH R * H P S- 70 1.2-14 40-60 30 -SO 150-500 : 40 -10 0 5000 -8500 IS -150 ' < 5 -40 85 -200 100- 200 8-30

M 24 3-6 43 i38 280 60 6430 43.5 .7.3-9.8 110 1 130 89 i t It

SOUTH BASAL n: ft n : 115' 11 . 115' ; II 115. j 11 e 315- n e 1.15. : n . ns. n - ns• 11 Hs. . II : ns• II e 115 - II 11 s• n 11 5- ft -to-Iso s - 25 : 7 -40 1 S -IS 700 -4000' 40-ISO 400-SOD 10-ISO 1 5 -30 65-700 0 - 500 I 3 -90 CREEK E2 M 71 15 : 20 5.9 1220 92 710 79 13 220 130 3.0

n:ft 12 12 :127' 12 127'. 12 127' 12 . 127' 12 : 127' ; 12 • 127' 12 127' 12 . 127'. 12 127' 12 127' 12 127' 12 .27'

R + H R 2-70 0-2-9-0 . 7 - SO 14 -45 40 -500 30-200 3000- 8000 50 -150 20-80 300-3000 150- 2 50 8-70 M '4 1.1 , 27 34 180 110 6190 86 ; 43 510 120 i 7.5

KILCOLMAN UPPER n:ft 11 • 71I• 11 . 71 • 11 • 71I• 11 - 78' 11 • 711' 1 11 78' t If . 71' II : 71' j 11 ! 71 • 11 76' 11 , 70' . 11 . 711'

R s - las 0-2 -30 : 12- 40 ' 1- 30 160-1500 , 35-400 700-1000 30-100 <5 -70 100- 700 70-150 1.3- 45 CREEK E2 N4 20 1.2 20 , 23 440 59 4530 68 15-16 330 120 6.2

BASAL n: ft 9 113' ' 3 113.1 9 113' 9 113' 9 . 113' 9 , 113' 5 113' 9 • 113' 9 113' 9 • 113' 9 113' : 9 113'

R 3-50 . 0.7-5.0 ! 0 - so 5 -13 150 -1000 20 -150 400-4000 7- 70 <5 -10 40-600 40-300 0.5-1•6 E2 M 12 I 3.0 20 7.3 480 42 1460 19 41-6.5 300 150 1.2

..._ n:ft 10 • 122' , 10 122' tO : 122' 10: 122' 10 . 122' 10 . 122' 10.122' 10 - 12 2' 1 10 . 122' 10 122' 10 . 122' 10 122'

R +H R 2 -120 1.5-30 /3 - 40 0-30 30 - ISO 4 0 -200 800-4000 2 0 - 200 <5-$5 1 100-9000 50-200 , 4-35

.FOY NES A1 42 5.7 26 20 255 120 3180 62 ; 24 540 100 ! 9.3

ISLAND UPPER n:ft S : 139' S • I39' 5 , 119' 5 : 136' S - 1311' 5 - 139' 5 135' 5 139' 5 139' , i 5 130' 5 139' 5 731'

; R 3-70 0.5 - 5.11 1-30 4-20 100-500 30-100 400-4000 30 - 65 <5 - 30 20-600 60 -200 1 1.3-4.0

E2 /A 17 1.5 17 13 260 64 22 75 53 12-16 ' 270 , 130 Ii 3.8

COMPOSITE n 71 75 70 79 75 71 76 71 711 ; 79 I 76 1 •, 15

(incl. 0/c R 2 - 900 0-2- 3 0 7-10 4 -SO 90 -4 000 20 -200 400-8500 7 - 2 90 <5 - 65 I 3 - 6000 5 0- 300 I 0.S- 45

samples.) M 27 2.9 22 15 365 79 24 20 54 13-20 ! 335 130 1 4.5 _

n : ft = No. of Samples : Sect ion Feet. R = Range of Values. M = Geometric Mean

TABLE 12. MINOR ELEMENT CONTENT OF THE CLARE SHALES

I 1 3 I. NIMMIENSAFiNiint

ok Ms

6790134) 3I90.(70) 4530.(73) 2275(13)

1460,(33)

(d) TITANIUM ppm

(GALLIUM) (ppm)

64

COPPER ppm (VANADIUM) (ppm)

smog 11.03001

LEAD ppm (CHROMIUM)topm)

30) 27.020) 30.020) 20,050)

(f)

■ Nomorion sediments

' 4(36) R • H Zane f .114.(1.1) 42.(S7)

Clare Shales 12011-2) UPPof E2 Zone 17,(1411.._ Ltmtstons 71 5) 12,(3) Sasat E2 Zone

(a) MOLYBDENUM ppm

(SELENIUM) (PPlo)

I

ei

14

(Metal values shown are the geometric mean content of the section Sompled.rof a mote tlettatittl definition of the sections refer to fie. 2S.)

10 01 1 Selenium (ppm)

01 1 10 Selenium (ppm)

FIG. No.27 VARIATION OF MOLYBDENUM AND SELENIUM IN CLARE SHALES

+ H Zone

100 + Ballagh.

• Kilcoiman. 0. 0.

0 Foynes. C 0 .0 >. 10 0

1

•

II •

• o •

•

•

• •

0 00

Upper E2 Zone

• Kilcolman.

• Foynes

a.

C vs• .0

Basal E2 Zone 15 10

+ South Ck.

o Kilcolman.

1

100

or%

•

++ +

• • • • • • + + o • •

• •

• 40

0

• • • 0

0 0

+ 0 0 •

+ + 0 0 0

93

(a) The basal 150 ft. or so contain a relatively

high proportion of Se to Mo compared with the upper horizons,

when the basal E2

horizon from the South Creek and Kilcolman

sections are considered. However, these sections are very close

to one another with respect to the whole basin and may only

represent a restricted area.

(b) Again referring to the basal portion of the

South Creek and Kilcolman sections, large variations in metal

content can occur laterally over a short distance, in this case

about 1 mile, within the one general horizon. This would seem

to indicate abrupt lateral changes of sedimentary environment.

(c) There is a general similarity of pattern

between the uppermost R and H horizons of the three sections

sampled. Both Mo and Se show an overall decrease as the transi-

tion to non-marine conditions is approached. Within the R and

H horizon there is also an apparent increase in the thickness

of the zone of higher metal values in each section towards the

centre of the basin, i.e. from Ballagh to Foynes. This most

probably represents a thickening of the lithological succession,

characterised by a particular metal pattern towards the deeper

central part of the basin of deposition..

(d) Plotting of Mo/Se ratios against stratigraphy

for the R and H horizons shows some correlation between sections

(Fig. 28). The increase of the ratio down the section would

indicate a decrease in the proportion of Mo precipitated as

non-marine conditions are approached. Mo/Se ratios in the lower

Namur la n. I Ratio '4/Content

541 5 10 15 20 25 30 35 40

A

• _ 4-

It

• South Ck

-- Kik& man

Foynes

UPPER Ea Zone

Vertical Stale.

120

20 30 40 10

40 feet

BASAL E2.7.03, 80

L EOENQ Etallagh Section. •

R.H Zons

Clam Shales.

STRATIGRAPHIC RELATIONSHIPS OF Mo:Se RATIOS IN THE CLARE SHALES

JIG. 2S Limestone.

(For location of sections refer Fig. 25.)

94

parts of the sections do not show any common patterns, but this

may possibly be due to inaccurate stratigraphic positioning in

the absence of a well-defined marker horizon, in contrast to

the relatively well-defined transition to non-marine sediments

which marks the top of the Clare Shales.

(e) The concentration of Mo and Se in the uppermost

R and H horizon of the Foynes Inland section is not repeated in

the Kilcolman section and is probably the result of a strictly

local change in the environment.

(ii) Other Metals

The broad distribution of the other elements determined

is given in Fig. 26 and Table 12. Some brief comments on the more

prominent features of these patterns are as follows:-

Lead (Fig. 26f): The highest concentration is pre-

sent near the basin margin at Ballagh and there is a slight

tendency to concentrate in the uppermost horizons of the Kilcolman

and Foynes sections.

Copper (Fig. 26b): Co-variance of Cut. and Mo is

shown in Fig. 29. The concentrations of Cu increases towards

the centre of the basin and there is also a trend towards con-

centration in the upper horizons of the Fo7nes and Kilcolman

sections.

Nickel and Cobalt (Fig. 26c): These elements show

identical patterns of distribution with a slight increase in

values in the Kilcolman area, intermediate between the margin

0

0 + 00

+ O 0

• •

• •

•

• •

•

•

R + H Zone

100 + BaHugh.

S Kite°Irnah. a.

o Foynes. C •

a,0

10 O

1000 10 100

Copper (ppm)

100

Upper E2 Zone

• KlIcolman.

• Foynes

10 Basal E2 Zone

+ South Ck.

O Kilcolman.

•

• o•

o • • 0

• 0 • 0

• •

0 0 0

1 10

100

1000 Copper ( ppm )

FIG.No.29. VARIATION OF MOLYBDENUM AND COPPER IN CLARE SHALES

Mol

ybde

num

(p

pm

)

05

and centre of the basin, and a well-defined increase in the upper

horizons of this section.

Vanadium (Fig. 26b): V shows some similarity to

the Mo and Se patterns, being highest in the South Creek basal

horizon and with a similar distribution in the R and H horizons.

Gallium and Titanium (Fig. 26d): These two elements

have similar patterns of distribution with a well-defined tendency

to concentrate in the upper horizons. The Foynes section near the

centre of the basin carries the lowest values. It would seem

probable that the distribution of these metals reflects the

amount of argillaceous matter in the sediments with an increase

in detrital, terrigenous material towards the margins of the

basin and in the upper horizons as the basin filled up. The

overlying non-marine rocks carry greater concentrations of Ga

and Ti than the Clare Shales or the limestone.

Manganese (Fig. 26e): The Mn pattern is poorly

defined. In the upper zone the lowest value is at the basin

margin and there is a slight trend towards enrichment in the

upper horizons compared to the lower areas. In this respect,

the distribution of Mn is generally similar to that of Cu, Ni

and Co.

Chromium (Fig. 26f): This element appears to be

more or less uniformly distributed throughout the basin.

Fe 203 (Fig. 26e): Iron tends to increase in the

upper horizons. The pattern of lateral distribution is poorly

defined. It is noticeable that Mn, Cu, Ni and Co have a similar

96

vertical trend and that the Ti and Ga patterns are also somewhat

similar. The enrichment of Mo and Se in the basal South Creek

section is accompanied by a marked decrease in the overall iron

content. This is probably due to strongly reducing conditions

which favoured the precipitation of Mo and Se, whereas Fe largely

remained in the soluble Fe++ state.

3. MODE OF OCCURRENCE OF METAL IN THE SHALES

Observations on the lithological associations of Mo

and Se as well as Cu, Ni and Co, indicate that they reach their

greatest concentrations in the more carbonaceous or pyritic shale

types. This is in line with field observations by other workers

on the distribution of metals in black shales.

In the present study, attention was also given to the

mineralogical associations involving the quantitative examination

of the relationship of Mo and Se to S, C and Fe and the analysis

of mineral fractions.

(i) Relationship Between Sulphur and Selenium

Under the reducing conditions of deposition of black

shales it is considered that the proportion of primary sulphate

minerals present would be negligible. Sulphur analyses of shale

samples should therefore reflect, in the absence of epigenetic

sulphide material, the original sulphide content, most probably

as syngenetic iron sulphide, of the sediments.

0•

• •

•• •• •

0 Os 0

•

• •

•

. 0

0

0 0 O 0

„ Upper E2 0 Kilcolman

01 1 10 100 Selenium (ppm)

FIG. No.30 VARIATION OF SULPHUR-SELENIUM IN CLARE SHALES.

•

10

1

a.

0.01

Lower limit of o0 — detection.

+ South Ck.-Basal E2 • Kilcolman- R + H.

97

Sulphur analyses indicated a sympathetic relation-

ship between S and Se in stratigraphic horizons of limited

thickness within a given section (Fig. 30). No such relation-

ship is apparent, however, in samples that are widely separated

laterally. This is believed to be due to (a) variation in the

environmental conditions of deposition leading to corresponding

variations in the proportion of the two elements precipitated,

and perhaps (b) to differences in the composition of the material

entering the basin at different points.

(ii) Relationship Between Sulphur and Molybdenum

Mo also demonstrates a considerable degree of co-

variance with S in samples from restricted thicknesses within

individual sections. For example, the relationship is well

marked in the R and H zone of the Kilcolman section but the

amounts of Mo and S in this part of the section are not related

to those in the E2 zone of the same section (Fig. 31). Samples

from the upper E2 zone of the Kilcolman section fall into two

well-defined groups in which the Mo9 S relationship is also

apparent. In each group the samples represent consecutive-

horizons. The smaller group represents the lower horixons of

the upper E2 zone and from this it would appear that moving

upwards through the Clare Shales to the R and H zone the

amount of S deposited in general, increased relative to the

amount of Mo. A similar pattern can be detected for Se.

0 0

0 0 0 — Lower limit of detection.

10

• •

• •

•

0

1 o 0

•

0

• 0 4. 00

+ 0

0-01

+South Ck. Basal E2 Zone. • Kilcolman R +H Zon e.

OKilcolman OI 0. o " " Upper E2

10 100

1000 Molybdenum (ppm)

FIG. 31. VARIATION OF SULPHUR-MOLYBDENUM

IN CLARE SHALES

98

From this it would appear that in addition to the

amount of S accumulated in the shales another factor, possibly

the amount of Mo and Se available for precipitation from the

sea water, also controls the concentration of Mo and Se in the

sediments.

(iii) Selenium and Molybdenum in Relation to Organic

Carbon

Only four analyses of organic carbon were obtained

due to difficulties of analysis*. The amount of carbon present

was determined by combustion of the sample followed by absorb-

tion of CO2 in an alkaline base after removal of interferring

compounds. The results were adjusted for C present in car-

bonates, the amounts present being negligible at 0.4-0.8 per

cent.

The results showed only a low range of organic

carbon values from 4.27 to 5.76 per cent (Table 13). The

extreme range of Mo and Se contents was not reflected in any

marked variation in C content.

This result is in line with the work of La Riche

(1959) who, working on somewhat similar types of shale from

the L. Lias of England, did not find a linear relationship

between the amounts of Mo and organic carbon in the rock. He

did show that high Mo was always associated with high C but

that a high proportion of C did not necessarily involve a

*By Messrs. Herdsman, Chemical and Analytical Laboratories, Glasgow.

99

similar concentration of Mo.

Table 13: Organic Carbon Content of Clare Shale

Samples in Relation to the Mo and Se.

Content

Sample Mo Se Organic No. (ppm) (ppm) Caron

2210 Black, carbonaceous shale, South 150 20 5.31 Creek basal E2 zone.

2215 Black, carbonaceous, pyritic shale, South Creek, basal E

2 zone. 80 13 5.44

2217 Spongolite. South Creek basal E2 zone. 10 5 4.27

2246 Highly pyritic, black carbonaceous shale. Kilcolman Upper E

2 zone. 80 3.8 ,5.76

(iv) Selenium and Molybdenum in Relation to Iron

The total iron content of the Clare Shales was

determined spectrographically and is expressed as the equivalent

Fe203. The iron contents quoted will, therefore, include detrital

iron minerals deposited in the Clare Shale basin in addition to

iron precipitated with the sediments. It is probable that the

increased iron content of the upper horizons of the Clare Shales

(Fig. 26e) reflects, either the addition of a greater proportion

of detritial iron minerals into the basin as it filled up prior

to the transition to non-marine conditions, or, increased

O • 0

4 + •

0

10 • • • 0 • 0 • • • • • • • p• + to

+ * 0 54. ++o o •

A • It • 0 • o •

0 0

Legend

O Bottogh.R•H Zone.

• South Ck. Basal E2 . 01

• Kileolman. R•H

0 Upper Er 100

0

Oa ••

Basal E2.

Foynes. R • H.

• o • •

,tt o

0• t %.

0 0

0

10 100 MOLYBDENUM (ppm)

• • 00. • • (a t .0 • • « O® sk• +

.0 5 • « + 40 O e . + • • •

0 .0 • • 0 • • 0 O 0 . 0 o •

0 CO

0

01 01 1 10 30

SELENIUM (ppm)

FIG.32. RELATIONSHIP OF MOLYBDENUM AND

SELENIUM TO IRON IN CLARE SHALES.

.. • " Upper E2.

10

zt co 0 eNi co u.

1

100

precipitation of insoluble ferric compounds under more oxidizing

conditions of deposition in the upper part of the basin.

In either event, it is apparent from the overall

distribution of iron in the stratigraphic zones of the Clare

Shales that there is no overall correlation with the Mo and Se

patterns (Fig. 26a and e). For example, the basal E2 zone in

the South Creek section, which contains the highest concentra-

tions of Mo and Se, is characterised by a low iron content.

In the Kilcolman section which represents almost the total

thickness of the Clare Shales there is also no correlation of

Fe with Mo or Se.

The poor relationship between Fe and Mo or Se

indicated by the distribution of these elements in the Clare

Shald-:Basin as a whole is confirmed in individual samples

(Fig. 32). There is a vague correlation, however, when limited

number of closely related samples from the basal zone of the

Kilcolman section are considered.

(v) Distribution of Metal in Mineral Fractions

The variations of metal content in the different

lithological groupings of the Clare Shales described earlier,

as well as the relationship established between SI Mo and Se

suggested that the metal content of shale samples would vary

between the different mineral fractions present. Bearing in

mind the generally very fine nature of most of the shale

minerals, it was apparent that the most readily separable

101

constituent that might be closely associated with the distribution

of metal in the shale was the pyrite. Accordingly, selected samples

in which pyrite grains were visible, were separated into pyritic

and carbonaceous fractions using heavy liquids as described in

Chapter II.

It was hoped that the distribution of metals between

these fractions would indicate the probable modes of occurrence

and hence the probable behaviour of the elements during weathering.

It is possible, wf course,that there will be some migration of

metal during diagenesis, as pointed out by Korolev (1958) in

studies of Mo in sediments. The recrystallized nature of the

pyrite in the shales, as coarse cubes and granular aggregates,

points to considerable diagenetic changes of this type.

The optimum size for separation was from 80 mesh

(approx. 200 microns) down to silt size (20 microns). Conse-

quently, no account can be taken of the amount of metal held in

any microscopic sulphide grains that may be present in the finer

carbonaceous fraction. However, it is believed that for the

purpose of the experiment an adequate separation was achieved.

Of the three samples examined, sample 2246 contained

the greater proportion of pyrite and gave the most satisfactory

separation. The other two samples, nos. 2215 and 2261, contained

much smaller amounts of pyrite and the pyrite fractions had,

therefore, to be bulked. Nevertheless, the results served to

confirm the distribution pattern observed in sample 2246. Details

of the separation and the results of analysis of the different

fractions are given in Tables 14 and 15, respectively.

Table 14: Separation of the Pyrite Fraction from Some Clare Shale Samples

*Amount Carbonaceous Recovered Pyrite Fraction -argillaceous

Fraction

Weight Weight Weight qo (g) (g) of sample (g) of sample

Sample Size Weight`.

Fraction after Sample

(mjer)ns) sieving (g)

!Highly pyritic, black, 100-200 carbonaceous shale. 50-100 Kilcolman Lower E2 zone 20-50

(2246) Total sample

Pyritic, black carbona- 100-200 ceous shale. South Ck. 50-100

Basal E2 zone 20-50 Total

(2215) Sample

Pyritic, grey shale 100-200 Kilcolman R and H zone 50-100

(2261) 20-50 Total sample

18.4

17.8 96.7 4.8 26.97 13.0 73.03 28.0

27.1 96.9 6.7 24.7 20.43 75.3 27'.0

25.6 94.8 4.15 16.21 21.45 83.79 73.4

70.5 95.8 15.65 22.2 54.88 77.8

18 20 30 68 63.075 92.76 0.425 0.67 62.65 99.33

58 57.1 98.4 0.675 1.18 56.4 98,82 25 24.55 98.2 0.275 1.12 24.275 98.88 17 15.47 91.0 0.32 2.06 15.15 97.93 100.0 97.1 97.1 1.2? 1.30 95.825 98.9

63.075 92.76 0.425 0.67 62.65 99.33 (Insufficient pyrite for separation into size fractions)

*To ensure complete separation a small proportion of material was lost after sieving during separation of the sample into heavy and light fractions with tetra-bromo ethane.

Table 15: The Distribution of Minor Elements in Mineral Fractions of Clare Shale

Sample 2246

Element

Analysis of

Total Sample (ppm)

PYRITE FRACTION CARBONACEOUS-ARGILLACEOUS FRACTION

Metal Content of Size Fractions Percent Held of Total Metal in Shale

Metal Content of Size Fractions Percent Held of Total Metal in Shale

100-200 Microns

50-100 Microns

20-50 Microns

Mean 100-200 Microns

50-100 Microns

20-50 Microns

Mean

Mo 35 28 28 22 26 18.8 25 36 35 32 81.2 Se 2.5 25 20 20 22 75.6 2.0 2.0 2.0 2.0 24.4 Pb 30 20 13 10 14 10.8 30 30 40 33 89.2 Sn <5 200160 160 173 >91 <5 <5 <5 <5 <9 Ga 13 <2 <2 <2 <2 <4.9 10 10 13 11 >95.1 V 130 <5 <5 <5 <5 <1.5 60 100 130 97 >98.5 Cu 160 200 160 130 163 26.4 130 130 130 130 73.7 Zn 130 130 130 100 120 28.2 100 60 100 87 71.7 Ti 1600 300 300 300 300 5.0 1300 1600 2000 1630 95 Ni 85 200 200 160 187 62 30 30 40 33 38.2 Zr <200 500 500 500 500 >42 <200 <200 <200 <200 <58 Co 30 160 130 100 130 84 <5 10 10 6-8 16 Mn 400 130 100 85 105 8.3 300 300 400 330 91.7 Cr 60 5 5 3 4.3 1.6 50 100 85 78 98.4

Fe203 15% >30% >30% >30% >30% 75.6 3.7 4.2 5.0 4.3 24.4

0

Table 15 (continued)

Semple 2215'

Element

Analysis of Total Sample (ppm)

PYRITE FRACTION CARBONACEOUS-ARGILLACECUS FRACTION

Metal Content of Size Fractions Percent Held of Total Metal in Shale

Metal Content of Size Fractions Percent

20-200 Microns

Mean 100-200 Microns

50-100 Microns

20-50 Microns

Mean Held of Total Metal in Shale

No 5 31 31 2.6 5 ' 5 13 7.7 97.4 Se 9.5 175 175 11.8 8.0 9.5 9.0 8.8 88.2

Snmrle 2261

Mo 7.4 20 20 3.5 7 10 5 7.3 96.5 Se 2.3 26 26 16.0 2.0 2.0 1.5 1.8 84.0 Pb 30 30 30 1.2 40 30 30 33.3 98.8 Sn 5 <5 <5 <1.3 5 5 5 5 >1.3 Co 16 x 3 0.2 20 20 16 18.7 99.8 V 200 10 10 0.1 160 200 160 173 99.9 Cu 85 85 85 2.5 40 50 40 43.3 97.5 Zn 100 600 600 9.2 100 85 50 78.3 90.8 Ti 3000 1300 1300 0.5 3000 3000 4000 3330 99.5 Ni 85 500 500 9.9 60 60 60 60 90.1 Zr <200 <200 <200 < 200 4: 200 <200 <200 - Co 30 300 300 19.5 13 16 20 16.3 80.5 Mn 850 600 600 1.5 600 500 500 530 98.5 Cr 160 20 20 0.2 160 130 160 150 99.8 Fe203 5.6% >30% >30% 11.5 4.7 4.4 5.0 4.7 88.4

1 'Sample 2215 - insufficient samrle for complete spectrographic analysis of the pyrite fraction. The Mo content quoted for both fractions was determined chemically and may therefore be slightly lower than the equivalent spectrographic value.

105

It is apparent from the distribution of constituent

elements in sample no. 2246 that firstly, different metals have

varying affinities for concentration in the pyrite and carbona-

ceous fractions and secondly, there are trends for the degree

of concentration to vary with grain-size, particularly with

regard to the carbonaceous fraction. The significance of this

second feature is problematical because of the possible analy-

tical error involved.

Briefly, Mo in sample 2246 is not appreciably

concentrated in either the pyritic or carbonaceous-argillaceous

fraction. On the other hand, in samples 2215 and 2261, which have

a much smaller pyrite content (0.67 and 1.3 per cent, respectively

compared with 22.2 per cent), Mo is enriched in the pyrite by a

factor of 2.7 and 4 respectively. This feature can be specu-

latively attributed to variations in the amount of pyrite

available for including Mo. Nevertheless, in view of the wide

spatial separation of the samples in the sedimentary basin the

observed enrichment is just as likely to be due to variations

in the mode of deposition in a different environment. In all

samples the bulk of the total Mo present in the shale is held

in the carbonaceous fraction. In samples 2215 and 2261, the

proportion held in the pyrite is negligible, amounting to only

a few per cent and in sample 2246 only 18.8 per cent of the

total is included in the pyritic fraction.

In sample 2246, Se is concentrated in the pyrite

by a factor of 10.8 and in the other two samples the enrichment

factor is even higher at 20 and 14,.4. In view of the low

io6

pyrite content of the latter two samples (Table 14), the amount

of Se held in the pyritic fraction relative to the total amount

of Se in the shale is low, being only 11.8 and 16 per cent,

respectively. In sample 2246 however, 75.6 per cent of the

total Se in the sample is included in the pyrite fraction. In

view of the much lower average pyrite content of the Clare Shales

as a whole (approximately less than 1.7 per cent pyrite by

calculation from sulphur analyses of the Kilcolman section),

the pattern observed in the other two samples can be taken as

being more representative of the Clare Shales. Briefly, the

bulk of the Se, similar to Mo, is apparently included in the

carbonaceous fraction.

In sample 2246, Cu is distributed in a generally

similar manner to Mo, having a slight affinity for the pyrite

fraction. This is more marked in sample 2261 which contains less

pyrite. Of the other elements, Co and Sn seem to be almost

entirely concentrated in the pyrite fraction. Zn, Ni and Zr show

a marked preference for the pyrite fraction but presumably also

have some association with the organic or argillaceous minerals.

Pb and Mn have a tendency to concentrate in the carbonaceous-

argillaceous fraction but also occur in the pyrite phase. Gal

V, Ti and Cr are strongly associated with the carbonaceous-

argillaceous fraction, presumably due to the organic affinities

of V and the association of Ga and Ti with Al in clay minerals.

Cr may be present as a detrital mineral but could also be

intimately associated with the clay minerals as it can be

reduced and precipitated in sediment as a hydroxide.

107

In sample 2261, the only marked exceptions to the

metal distribution observed in sample 2246, are Pb and Mn which

are more or less equally divided between the two fractions. The

partition of Sn in sample 2261 is somewhat anomalous and may

represent an analytical error, the values present being close

to the limit of detection of 5 ppm Sn.

With regard to the influence of grain-size, the

apparent variations in metal content are mostly within the

probable range of analytical and sampling errors, and no reliable

conclusions can be drawn from these data.

4. SUMMARY OF RESULTS

Prior to discussing the preceding data with regard

to the possible origin of abnormal concentrations of some metals

in the Clare Shales, a brief summary of the salient features of

metal distribution is given:-

(i) There is a marked concentration of Mo and Se

in the Clare Shales, a typical black carbonaceous, often pyritic,

marine shale facies. Cu and V are also concentrated in this

horizon but the contrast in metal content with the other adjacent

rock types is less marked.

(ii) The content of Pb, Ni, Co, Mn and Cr in the

Clare Shales and the overlying non-marine Namurian sediments, are

roughly similar. There is an apparent enrichment of Ga, Ti and

Fe in the Namurian rocks when they are compared with the Clare

Shales as a whole, but the contents of these metals in the upper-

108

most R and H zone of the Clare Shales is of the same order as in

the non-marine sediments. This is taken to indicate that the

depositional environment in the deeper, earlier deposited hori-

zons of the Clare Shales was not favourable to the accumulation

of Ga, Ti and Fe but, as the basin filled up, conditions favoured

their deposition prior to the transition to non-marine conditions.

This pattern is in many respects the reverse of that cf Mo and Se

which tend to reach their highest concentrations, particularly

in the central part of the shelf in the basal horizons of the

Clare Shales (ref. Fig. 26). The conditions that have given

rise to the enrichment of Fe and its associated metals in the

upper horizons of the Clare Shales and the non-marine Namurian

rocks may involve either an increased proportion of detrital

iron and clay minerals being introduced into the basin as the

transition to non-marine conditions approached, or to changes

in the physio-chemical depositional environment which encouraged

increased precipitation of these metals. In view of the fact

that the Mo and Se content also increases upwards in the Foynes

section the second alternative is preferred at this stage.

(iii) The patterns of Mo and Se distribution in

relation to the morphology of the Clare Shale basin of sedimenta-

tion are generally similar, indicating similar modes of concent-

ration in the sediments. Thf.s is also reflected in a certain

degree of co-variance between Mo and Se in individual samples.

Stratigraphically though, the relative abundance of each metal

to the other may vary.

109

Certain other metals with similar patterns of

distribution in relation to the basin may also be grouped

together. Notable examples are Ni and Co, and Ti and Ga. These

groups can also be expected to reflect similar modes of concent-

ration.

V and Cu follow Mo and Se in reaching their highest

concentrations in the basal horizon of the Clare Shales in the

South Creek section but otherwise the general patterns tend to

differ.

(iv) The highest concentrations of Mo and Se are

associated with the more carbonaceous and pyritic shales. Pb,

Cu, Ni and Co show a similar trend. V, however, does not show

a marked preference for any particular shale type and this may

be due to the association of this element with the more evenly

distributed carbonaceous'matter than with sulphide minerals.

(v) There is a rough degree of correlation between

the sulphur content of shale samples and the Mo and Se content.

The relationship is restricted to groups of samples that are

spatially located close together, usually within specific strati-

graphic horizons. It is most probable that, in the event of a

close relationship between the precipitation of sulphides and

Mo and Se in black shale the relative sulphur and metal contents

will be related to both environmental conditions of deposition

and the supply of the constituent elements into the basin.

These features will vary with the morphology of the basin

and also stratigraphically with time.

110

(vi) There is no definite correlation between the

total organic carbon content and Mo and Se in the shales but, in

view of the limited number of samples examined and the tendency

for high Mo and Se values to occur in the more carbonaceous rocks,

this factor cannot be discarded entirely as having no influence

on metal accumulation.

(vii) Any association between Mo, Se and Fe is

confused by the analytical method employed which included Fe

present in detrital minerals as well as precipitated material.

(viii) The distribution of metals in the mineral

fractions determined by the separation of pyrite from the carbon-

aceous and argillaceous rock matrix reveals groupings of various

elements depending on their affinity for concentration in either

fraction. In certain cases, these groupings consist of metals

with similar patterns of distribution in the Clare Shale basin

as a whole. For example, Ga and Ti which show a roughly similar

degree of concentration in the carbonaceous-argillaceous fraction

have similar patterns of distribution in the stratigraphic zones

of the Clare Shales. Co and Ni which are preferentially concent-

rated in the pyrite fraction to much the same degree are also

similarly distributed stratigraphically. This can be attri-

buted to similar modes of concentration for these elemente in

the sediments as well as similar behaviour during diagenesis.

With regard to Mo and Se, separation of the pyrite

fraction revealed that the bulk of the total metal content of the

shales is included in the carbonaceous-argillaceous fraction,

although Se in particular, is strongly concentrated in the

111

pyrite. Mo, on the other hand, tends to be more Equally distri-

buted between the two fractions implying an affinity for both

mineral phases.

(ix) Primary dispersion studies have shown that

the Clare Shales can be readily defined on the regional scale

as a bedrock unit in which abnormal concentrations of Mo and Se

are present compared with the adjacent rock types. However, in

the Clare Shales themselves, the distribution patterns of both metals

indicate that (a) the concentrations present are most likely to be

dependent on the local depositional environment, and (b) it is

not possible to define any characteristic horizon or area of the

Clare Shales in which peak metal levels can be expected to occur.

The occurrence of the highest Mo and Se values recorded in the

basal E2 zone of the South Creek section must be due to a favour-

able local lithology and physio-chemical conditions during

deposition because the equivalent horizon of the Kilcolman

section, situated a little over a mile away, does not contain

exceptionally high levels of Mo and Se. Similarly, the rise

in Mo and Se content in the uppermost horizon of the Foynes

section is not repeated in the Kilcolman section.

5. ORIGIN OF MOLYBDENUM AND SELENIUM IN THE CLARE SHALES

The basic geochemistry and geological occurrence

of Mo. and-Se in sedimentary rocks haVe been the subject of many

papers, in particular, good accounts for both elements are given

in Rankama and Sahama (1950), Goldschmidt (1954), Krauskopf (1955)

112

and Cannon (1964). Mo occurrences are well described by Kuroda

and Sandell (1964), La Riche (1958) and Korolev (1958); while

for Se the reader is referred to Goldschmidt (1933, 1935), Byers

et al (1938 - series of reports), Edwards and Carlos (1954),

Rosenfeld and Beath (1964) and Lakin (1961). A good general

review of the black shale environment in which the Clare Shales

have accumulated is given by Dunham (1961). Also Manheim (1961)

has described in detail a geochemical profile across the Baltic

Sea which may have many features in common with the basin in

which the Clare Shales were deposited. La Riche's work on Mo

in the L. Lias of Southern England is particularly pertinent

to the study because of its geographical proximity to the present

study area and the similar lithology.

The most detailed information on the stratigraphic

distribution of Se relates to the Western United States where

seleniferous rocks are not confined to black shales but include

normal shales, both marine and non-marine, sandstones, some which

are carbonaceous, and tuffs. It has been suggested that the

abundance of seleniferous rocks in this area is associated with

volcanic activity (Goldschmidt, 1954). Except for the tuff

occurrences in the limestone in the Co. Limerick area, there is

no evidence of a similar relationship in Ireland. Many of the

higher Se values recorded in the U.S. are in carbonaceous rocks,

generally shales but some carbonaceous sandstones in which high

Se also occurs. Very high Se values, as well as Mo, have been

recorded associated with vanadium-uranium ores in the sandstones

and siltstones.

113

Many writers have pointed out the association of Se

with sulphides, the ionic radii of S-2(1.74A°) and Se 2(1.94A°)

being so close that Se can readily enter the sulphide lattice.

The actual S:Se ratio appears to vary depending on the origin

of the sulphides but no hard and fast rule can be laid down for

this. Edwards and Carlos (1954) worked on the possibility of

using these ratios to differentiate between the origins of sul-

phide deposits. A high Se content is associated with some

sulphides of hydrothermal origin but a low Se content is not

positive evidence of sedimentary origin. In addition to the

records of high selenium concentrations in carbonaceous rocks,

vanadium-uranium ores and sulphides, excessive concentrations

have been noted in sedimentary iron and manganese ores, tuffs,

native sulphur, limonitic concretions, ferruginous sandstones,

meteorites, phosphate rock, coal deposits and very rarely, in

limestone. Of principal interest to this thesis though is the

relationship of Se concentrations to carbonaceous shales and

sedimentary pyrites.

Most data on Mo in sedimentary rocks are confined

to shales and it is generally agreed that the maximum concentra-

tions are found in thoSe with an appreciable amount of carbonaceous

material. As for Se, Mo is also associated with vanadium and

uranium-bearing sandstones and shales and is also found enriched

in some coals and phosphate deposits. It has also been found

concentrated in pyritic shales, e.g. in Wisconsin where the

ilk

pyritic shales contain 5 to 20 times as much Mo as adjacent

pyrite-free shales (Kuroda and Sandell, 1954). Normal shales,

sandstones, and limestones generally carry only minor concentra-

tions of Mo.

The recorded concentration of both Mo and Se in

carbonaceous and pyritic shales is in accordance with the patterns

observed in the Clare Shales in Co. Limerick. Various mechanisms

have been suggested for the concentration of these elements in

sedimentary rocks rich in organic matter and pyrite. Most of the

information however, concerns Mo. Because of the general associa-

tion of Mo and Se in the Clare Shales it is probable, however,

that similar mechanisms are involved and the possible modes of

concentration can be expanded to include both elements. However,

varying SeTMo ratios would suggest slight differences in mechan-

isms if it is assumed that the supply of both elements to the

basin was relatively even. The concentrating mechanisms suggested

by different writers are based on the facts that far greater

quantities of both metals have been supplied to the sea than are

at present in solution and that sea-water is apparently under-

saturated with respect to these elements (as well as many other

common metallic ions). The possible mechanisms for concentrating

Mo and Se can be summarized as follows:-

(i) Detrital accumulation.

(ii) Direct precipitation by changes in

temperature, pressure and pH.

(iii) Precipitation as sulphides.

115

(iv) Adsorption on hydrous Fe (or Mn) oxides, iron

sulphides or on organic matter.

(v) Organic processes.

Krauskopf (1956) and Korolev (1958), in particular, have fairly

recently done much work on the relative importance of these

processes. Little of the work has concerned Se, but Mo has

been extensively studied and possibly some of the conclusions

can be extended to Se as mentioned previously.

Detrital accumulation is not a viable mechanism

because of the generally low concentration of the elements in

the parent sources of the 4roded material and because of the

observed distribution of the elements with regard to lithology.

Krauskopf has proved experimentally that direct precipitation

due to physio-chemical changes would not be possible in a

natural environment with the concentrations present in sea

water.

Because of the common association of these elements

with carbonaceous and pyritic sediments, the other mechanisms seem

more feasible. Krauskopf (1956) considers that direct precipi-

tation as sulphides is questionable, "because observed concentra-

tions bear no apparent relation to the solubilities of the

sulphides". Organic deposition of metals after concentration in

living organisms is a possibility, as it is known that certain

metals can be concentrated in particular organisms. However,

Krauskopf does not consider this to be an adequate mechanism for

Mo, although it is a possibility for some other elements.

116

Most workers consider adsorption the most feasible

means of concentration in organic and sulphide-rich sediments.

In brief, because of their association with organic-rich and

pyritic sediments, adsorption on organic matter and iron hydro-

xides or sulphides is the most widely accepted mechanism.

Because of the varied association of Mo and Se with both carbon-

aceous and pyritic fractions in the shale specimens examined in

Co. Limerick, it is possible that adsorption on both organic

and iron material must be considered possible. Nevertheless,

the very different hypothesis put forward by Korolev (1958) with

regard to Mo, is considered particularly reasonable and could

well explain the occurrence of metal in the Clare Shales. Very

briefly, Korolev considers that the preponderance of Mo asso-

ciations with organic substances does not indicate that the organic

material itself adsorbed the metal. Instead, he has shown

experimentally that Mo is co-precipitated with iron sulphides

from solutions approximating to natural waters. Most of the Mo

is concentrated in melnikovite in the form of a sorbed sulphide

compound. During aging of the sulphide to pyrite, migration may

take place so that all the Mo does not occur in the more coarsely

crystalline forms. The sequence of mineralisation is hydro-

troilite (FeS.n H20)

melnikovite (FeS2) > pyrite.

With regard to Se, in view of its close relationship with Mo

in the Clare Shales, the writer proposes that Se may follow a

similar sequence of concentration. However, because of their

117

similar ionic radii, Se may substitute for S ions in the lattice

of the sulphide species precipitated, in addition to adsorption.

This is in line with the slightly greater affinity shown by Se

compared with Mo for the pyrite fraction in the shales (Table 15).

The reducing environment that existed in the basin during the

deposition of the black shales will of course, facilitate the

accumulation of organic matter in addition to the precipitation

of iron sulphide minerals. Larskaya (1961), working on bitumi-

nous Mezozoic sediments, demonstrated a connection between

organic matter content and authigenic Fe and S minerals. He

believed that the reducing conditions that gave rise to the

accumulation of organic matter also favoured the precipitation

of iron in the argillaceous sediments. This would explain the

characteristically carbonaceous nature of black shales

associated with the concentration of Mo and Se in Co. Limerick.

Any study of the present day distribution of metal

in the Clare Shales must of course take aconnnt of possible

diagenetic changes. Assuming that the sulphide content of the

shales was originally in the form of fine precipitates containing

Mo and Se e.g. hydro-troilite as described by Korolev, it is

apparent that considerable migration of iron sulphide has taken

place to produce the coarse cubic and aggregated forms of pyrite

present in the shales today. Metals, such as Mo and Se included

in the original sulphides, may, of course, have different mobilities

relative to the iron sulphides and to one another during recrystal-

lization. For example, the retention of most of the ready

n8

substitute Se for S in the pyrite lattice but only partial

retention of the Mo would explain the greater proportion of

Se in the pyrite fraction of the present-day shales. When the

iron sulphides recrystallized to form coarse pyrite, Mo on the

other hand, may have found a substitute host mineral in the

carbonaceous and ar,illaceous material of the shale matrix.

In view of the negligible concentrations of Mo and

Se in the overlying Namurian sediments deposited in the same

basin, there is no evidence to suggest that abnormal concentra-

tions of either metal were present in the sea water at the time

of deposition of the Clare Shales. This was suggested by La

Riche (1959) for the concentration of Mo in the generally similar

L. Lias shales of England. Concentration of Mo and Se was

therefore affected by abnormal physio-chemical conditions of

black shale deposition rather than excessive concentrations in

the sea water.

Briefly, with regard to the accumulation of other

minerals, it has been shown that only V and Cu in addition to

Mo and Se, are preferentially concentrated in the Clare Shales

compared with the argillaceous non-marine Namurian sediment

(Fig. 13). Thus the abnormal depositional environment of the

Clare Shale basin favoured the concentration of these elements

only, all the others studied being just as readily deposited

under relatively normal sedimentary conditions.

119

CHAPTER VII. DISTRIBUTION OF METAL IN OVERBURDEN

Previous chapters (IV and V) have given a broad

description of the areal extent of Mo and Se in the secondary

soil and drift environments. This chapter is concerned with the

more detailed description of the geochemical patterns in the

various soil and overburden types and the factors involved in

metal dispersion.

Under the influence of weathering agencies the

bedrock metal patterns are modified in the overburden by the

redistribution of Mo and Se as soluble or insoluble weathering

products. Soluble material may be removed in ground or surface

drainage and in certain cases be selectively re-deposited because

of environmental changes. Physical factors may involve the

transport of solid rock material or insoluble weathering pro-

ducts and again the material may be subsequently re-deposited

or removed from the area altogether in suspension or as stream

sediment. Biological factors, in particular the uptake of

metal by herbage, may halt or modify dispersion.

1. RESIDUAL SOILS

Residual soils are relatively restricted in the

area compared to the widespread occurrence of glacial drift.

The exception is the ground underlain by Namurian rocks in the

south-west beyond the terminal moraine of the Weichsel glacia-

tion (Fig. 12). Elsewhere, residual soils are generally confined

120

to those hillsides on which drift was never deposited or has

since been removed by erosion.

(i) Distribution of Metal in the Soil Profiles

(a) Molybdenum and Selenium

The distribution of Mo and Se in residual soils was

examined by analysis of selected profiles of soils developed on

each of the major rock types (Table 16). The profile formed

from metal-rich Clare Shales was taken from the extreme west

of the Flynn's Farm area (Fig. 18-BP27). Profiles on other

rock types were sited well away from any possible influence

of metal-rich drift. Only freely-drained soils could be rep-

resented because of the widespread nature of drift and peat

deposits.

Clare Shale Residuum

Under free-drainage conditions the soil developed

on Clare Shales (BF 27) shows a well marked increase in Mo

content with depth. Se follows a similar pattern but with

less contrast between the highest and lowest values.

There is a well-marked association between the

acid-soluble iron content of the profile and the Mo and Se

contents but organic carbon, which is enriched in the surface

horizons only, cannot be correlated with the Mo and Se patterns.

The pH of the soil increases down the profile. In view of the

Table 16: Distribution of Molybdenum and Selenium in Residual

Soil Profiles

Sample Depth No. (ins) Soil Description

Metal Content of -80 mesh fraction Mo Se C Fe pH Mo (ppm) (ppm) (0 (2,) Se

1. Well-drained soil developed on Clare Shales (Hole No. BP 27)

(2479) 0-4 Dark grey, organic, sandy loam (2480) 4-7 Dark grey, organic, sandy loam (2481) 7-14 Dark grey sandy loam with black shale

fragments (2482) 14-20 Grey sandy and clayey loam with semi-

decomposed shales (2483) 20-27 Grey sandy clays with black shale

fragments (2484) 27 Clare Shale bedrock (nearby shale

outcrop analysis)

5 2.3 6.27 0.4 4.68 2.2 7 3.2 8.o 1.8 4.86 2.2

18 5.0 3.8 3.2 5.35 3.6

15 3.2 2.9 3.0 5.68 4.7

25 5.5 2.9 3.6 5.54 4.5

3 0.8 - - - 3.75

2. Well-drained soil developed on limestone Hole No. BP 1)

(2002) 0-4 Medium brown, humic silty-clay loam <2 0.8 3.34 2.0 (2003) 4-8 Medium brown, silty-clay loam <2 0.8 1.8 2.2 (2004) 8-12 Brown clayey loam <2 0.8 1.03 2.3 - (2005) 12-15 Loamy clay <2 0.5 0.53 2.4 - (2001) 15 Limestone bedrock (nearby limestone

outcrop) <2 0.5 -

Table 16 (continued)

Metal Content of -80 mesh fraction

Sample Depth Soil Description ho Se C Fe pH Mo

No. (ins) (ppm) (ppm) (%) (%) Se

3. Moderately-drained soil developed on Namurian rocks (Hole No. BP 17)

(2401) 0-4 Dark brown, highly organic loam <2 4.5 6.6 2.7 (2402) 4-10 Mixed organic loam and yellow-brown

sandy clay <2 2.0 3.24 3.6 - (2403) 10-18 Yellow-brown clayey sand with decomposed

siltstone fragments <2 2.3 1.56 5.6 (2404) 18-30 Yellow-brown sandy clay with sandstone

and siltstone fragments <2 2.3 1.27 4.8 - 30 Namurian bedrock - no outcrop

(Average Namurian rocks) <2 0.16 - - - -

4. Well-drained soil developed on Namurian siltstones (Hole No. BP 108)

(4171) 0-7 Grey-brown silty loam <2 1.3 - - - (4172) 7-14 Mottled yellow-brown clays and

decomposed siltstone fragments <2 1.3 - - - - (4173) 14-24 Red-brown sandy clay with siltstone

fragments <2 1.1 - _ - - 24 Siltstone bedrock (nearby siltstone

outcrop) <2 0.5 - _ _ -

-ou• u Jam venue. a au-, - AL— •

Metal Content of -80 mesh fraction

pH Mo

Se Soil Description Sample Depth

No. (ins) 1

No Se C Fe (ppm) (ppm) (%) (c-:)

i ii, 5. Well-drained soil developed on Old Red

Sandstone (Hole No. BP 16)

0-2 Dark brown, peaty loam <2 0.2 2-7 Light grey silty leached sand <2 <0.2 7-13 Pink silty sand and siltstone pebbles <2 <0.2 13-19 Deep pink " SI SI II <2 <0.2 19-24 Red siltstone and sandstone fragments,

fine sand matrix <2 <0.2 24-36 Weathered red sandstone and siltstone <2 <0.2 36 Red siltstone bedrock <2 0.1

I

I (2394) 1 (2395) (2396)

1 (2397)

I

(2398)

2399)

Table 16 (continued)

124

low metal content of the nearby Clare Shale outcrop (3 ppm Mo,

0.8 ppm Se) and of undecomposed shale fragments from the basal,

horizon of the profile (2 ppm Mo, 0.3 ppm Se, 1.1% Fe203), the

trend for metal to be enriched in depth in the profile is

probably due to leaching of Mo and Se from the upper horizons

or from metal-rich soils upslope followed by accumulation with

iron oxides that precipitate in the less acid lower horizons.

Groundwaters from a nearby, less well-drained Clare Shale profile

contain 7.5 and 1.0 ppb Mo and Se, respectively.

The Mo:Se ratio also increases down the profile

indicating that Mo is preferentially retained in the lower

horizons. Se, which is only enriched in the lower horizons by

a factor of about 2 compared with topsoil (enrichment factor

for Mo is 5), varies less through the profile as a whole. It

may be that the enrichment of organic carbon in the upper

horizons plays a part in modifying the Se pattern and, in view

of evidence proving the affinity of Se for organic matter given

later in this thesis, it is most probable that this is the case.

Mo on the other hand, is not affected by the higher concentrations

of organic carbon in the upper horizons.

The mechanisms by which concentration of Mo has

taken place along with iron in the lower horizons of the profile,

can be explained by co-precipitation of the soluble molybdate

(M004 ) ion with ferric oxides as described by Jones (1956) or

by adsorption of molybdate on previously precipitated iron

125

oxides (Jones, 1957). Se derived from weathering of the Clare

Shales is probably present in groundwaters as the readily soluble

selenate (Se04=) ion or the slightly soluble selenite (Se03 ).

Reference to the stability field diagram of the common ionic

forms of Se (Figs. 41 and 42) shows that the pH-Eh environment

of groundwater taken from borehole BP 106 nearby to BP 27 falls

close to the equilibrium boundary between the selenite and

selenate forms; the actual values for BP 106 were pH 5.4, Eh

+0.535V, 1.0 ppb Se. It has been shown by Williams and Byers

(1936) that in the presence of ferric ions, dilute solutions

of selenites form a very insoluble precipitate that approximates

to the composition of basic ferric selenite (Fe2(OH)4 Se03),

and Byers et al (1935, 1936, 1938) give numerous examples of

the association of Se with ferruginous precipitates. The

accumulation of Se in the lower horizons of the residual soil

profile could, therefore, be due to a generally similar process

to that which has given rise to the concentration of Mo. The

formation of secondary iron oxides that have played such a

large part in the accumulation of both metals can be attributed

to the precipitation of insoluble ferric oxides, derived from

the oxidation of pyrite in the Clare Shales. With regard to

the possible modifying influence of organic carbon in the top-

soil horizons on the Se pattern, this is most likely due to

adsorption on organic material. Accumulation of Se in the

topsoil cannot be attributed to the decay of seleniferous

vegetation in situ as pasture herbage growing on the site does

126

not contain detectable amounts of Se (i.e. less than 0.2 ppm).

Molybdenum in Residual Profiles Over Other Rock Types

Profiles developed over the other rock types contain

very much lower amounts of metal, which for Mo are below the

limit of detection. Consequently, nothing can be said about

the behaviour of Mo in these environments but it is apparent

that background Mo levels of less than 2 ppm in the bedrock are

not modified to any appreciable extent by enrichment processes

during soil formation. Se patterns are however, detectable.

Selenium in Limestone Residuum

In the limestone soil profile (Table 16, BP 1)

the Se content decreases slightly in the basal clayey horizon

but this may be due to analytical error at the low levels of

concentration involved. It is just possible however, that the

higher Se level in the overlying horizons is associated with the

greater organic carbon content. The range of iron values is low

but points to a general increase downwards in the same manner as

the profile developed on the Clare Shales. The low Se content

of the limestone bedrock (0.5 ppm) indicates that no enrichment

takes place in the soils.

Selenium in Namurian Sandstone and Siltstone Residuum

The profiles developed on Namurian rocks (BP 17 and

BP 108) both show slight enrichment of Se in the upper horizons.

127

The increase is most marked in the least well-drained profile

(BP 17) and the high value of 4.5 ppm Se in the topsoil can best

be related to adsorption on organic matter accumulated in this

horizon. There is no relationship between Se content and the

distribution of iron. As in the case of the residual Clare

Shale profile, the metal content of pasture herbage at this

site is negligible and adsorption would therefore appear to be

from Se in soil water. The Namurian bedrock was not exposed

at this site but as regional rock sampling revealed that the

Se content of the Namurian sediments ranged from 0.1 to 0.5 ppm

it is apparent that a considerable degree of enrichment takes

place in the organic topsoil horizon but not in depth.

The other soil profile developed on the Namurian

rocks (BP 108) has formed under much better drainage conditions

without excessive organic matter in the topsoil. In line with

the less organic nature of this soil the amount of enrichment

of Se in the profile is small (1.2 ppm Se compared with 0.5 ppm

in shales collected from a nearby quarry).

Selenium in Old Red Sandstone Residuum

Except for the organic-rich, almost peaty topsoil

horizon of the residual soil developed on the Old Red Sandstone,

the Se content of the profile falls below the limit of detection.

Comparison of the Se content of the topsoil (0.2 ppm) with that of

bedrock adjacent to the profile site (o.1 ppm) indicates negligible

enrichment.

128

(b) Other Metals

Profile data for a number of the other elements is

given in Table 17. In addition, information on the SO4 and P

content is presented because of the possible association of

these factors with Mo in nutrition. The As content of these

soils has also been determined.

Considering the Clare Shale profile (BP 27), the

overall contents of Pb, Ga, V, Cu, Ti, Cr and Ag tend to be

higher in the soil compared to the amounts present in the bed-

rock. To this extent they follow the patterns of Mo, Se and Fe

already described. On the other hand, there is no significant

concentration of Zn, Ni, Co and Mn and it can be assumed that

these metals are more mobile under the acid conditions of soil

formation from Clare Shales. With the exception of Ag, the

vertical vayiation of metals in the profile is not so well

marked as for Mo and Se. There is some evidence that Pb, Ga,

V, Cu, Ni, P and As are slightly enriched in the lower horizons.

Enrichment of Ag in the lower horizons is well marked and the

concentration of 1.3 ppm is notable compared to the content of

<0.2 ppm in most soil, rock and sediment samples from the area.

Sulphate was only determined in the topsoil because of analytical

interference by excessive concentrations of iron in the lower

horims.

With regard to residual soils developed over lime-

stone, Old Red Sandstone and Namurian rocks, it is apparent that

few elements vary greatly through the profile.

Table 17: Metal Content of Residual Soil Profiles

(-80 mesh fraction)

Depth (ins) Pb Ga V Cu Zn Ti Ni Co Mn Cr

SO4 ppm

P ppm

Fe203

H W %JD

Limestone (BP 1) (Samples 2002-2005)

4000 4000 5000 4000

600

6o 6o 6o 85

5

16 16 20 20

<5

600 600 400 400

10o

6o 60 85 85

5

3000 3500 2500 2000

<100

200 200 120 120

200

6 6 5 6

0.3

0-4 4o 4-8 40 8-12 30 12-15 3o Bedrock (2001) 5

lo 85 4o 8 6o 3o 6 6o 4o 8 85 5o

<2 4o 3

loo 130 85 85

<50

Clare Shale (BP 27) (Sam les 2479-2483)

4000 4000 3000 3000 3000 2000

lo 13 3o 20 30 30

<5 I; 19

;r li

<5

85 loo 100

100 100 130

300 600 1000

850 500 300

1250 - - - - -

2500 4000 3000 6000 5000 -

6.o 6.o 6.6 6.o 13.0 1.1

0-4 4o 4-7 4o 7-14 6o 14-20 50 20-27 6o Bedrock 20

16 Soo 20 3o 85o 3o 3o 1300 4o 3o 85o 4o 3o 1000 3o 13 400 16

5o <50 5o <50 5o 50

Namurian (BP 17) (Samples 2401-2404)

35 35 38 38

6000 6000 10000 85oo

5910

13 16 3o 3o

52.7

10 10 13 13

21.9

400 300 400 300

325

loo 35 loo 85

111

- 1000 1000 500

48-1300

160 300 200 1000

200

8 6 20 10

7.5

0-4 20 4-10 8 10-18 10 18-30 8 Bedrock

16.6 (averse)

16 loo 6o 16 85 6o 20 100 6o 16 85 5o

20.7 81.3 26.7

Table 17 (contined)

Depth (ins)

Pb Ga V Cu Zn Ti Ni Co Mn Cr SO4 ;ppm ok

-Ppm P Fe 0

c.2 3 ppm /0

Old Red Sandstone (BP 16) (Samples 2394-2400)

0-2 13 6 3o 8 <5o 6000 20 5 130 40 1.3 2,7 8 6 3o 6 <5o 8500 lo <5 20 6o 1.0 7-13 8 8 5o 3o <5o 850o 16 <5 3o loo 2.0 13-19 8 8 5o 16 <5o 6000 16 <5 85 6o 3.0 19-24 4o lo 85 4o loo 6000 4o 10 300 100 8.o 24-36 20 8 5o 4o 5o 5000 3o 16 300 6o 6.o Bedrock 7 3o 7o lo <50 7000 4o 15 700 So 6.o

Carbonate Arsenic

Silver

- not detectable in all samples, CO.,` = <0.1% - only detectable (i.e. >5 ppm) in basal-7horizons of limestone and Clare Shale soils, i.e. B BP 1 12-15 ins 7 ppm As, BP 27 20-27 ins 7 ppm As.

- only detected (i.e. >0.2 ppm) in Clare Shale soil profile (BP 27)

0-4 ins 0.2 ppm 14-20 ins 0.8 ppm

4-7 ins 0.5 ppm 20-27 ins 1.3 ppm

7-14 ins 0.8 ppm Bedrock

<0.2 ppm

131

The pattern of distribution in the limestone profile

would seem to result simply from the removal of CaCO3 by chemical

weathering resulting in the more or less uniform concentration of

the other elements which are immobile under alkaline conditions

of soil formation. Most elements appear to have been concentrated

in the order of 5-10 times during the transition from limestone

to soil. The obvious exceptions to this are V and to a lesser

extent Zn which are presumably at least partly mobile under these

conditions. In a similar fashion Mo and Se which can form

soluble basic salts under alkaline weathering conditions would

also migrate. Organic matter in the topsoil does not appear

to h-ve influenced the patterns.

The soil profile on Namurian rocks is not distin-

guished by any well-marked variation in the amount of metal

between horizons. Pb is concentrated by a factor of two in

the peaty topsoil and the basal horizon is enriched in P. Ni

is impoverished in the upper horizons by a significant factor

of two. The bedrock from which the profile developed was not

exposed but comparison of the overall metal content of the

profile with the average composition of the Namurian sediments

indicates that the metal contents of the soil closely reflect

those of the bedrock. Compared with the marked enrichment

of most metals in the limestone soils, it. is probable that

the more uniform distribution of metals between rocks and soils

of Namurian origin reflects the dominantly mechanical weathering

132

of arenaceous and argillaceous sediments in contrast to the

more chemical nature of limestone weathering.

The profile developed from a sandy-siltstone facies

of the Old Red Sandstone shows a slight enrichment of Pb, Cu

and Zn in the basal horizons of the soil compared with the bed—

rock. Ga and Mn on the other hand are significantly lower in

the basal soil horizons than in the parent bedrock. Vertical

patterns in the profile show a general increase of most metals,

with the exception of Ti and possibly Cr, towards the base of

the profile. It is most probable that the concentration of

metal is associated with the conspicuous accumulation of iron

oxides in the lower soil horizons. The peaty topsoil is marked

by an increase in the concentration of Pb, Ni, Mn and possibly

Co.

(ii) Size Analysis of Residual Soil Samples

Size analysis was carried out on four selected

samples, two from the anomalous profile developed on Clare

Shale bedrock (BP 27) and one each from background limestone

(BP 1) and Namurian soil (BP 17) profiles. The mechanical

composition and the Mo and Se contents of the different size

fractions are shown in Fig. 33. Details of some other elements

are given in Table 18. Organic matter and secondary iron oxides

were not destroyed prior to separating the finer fractions as

this would have led to leaching of Mo, Se and other metals.

Size Fractions. A 2mm - 20mesh. B 20mesh-38 rr C 38 ^ - 80 D 80 -125 E 125 -200 if F 200 - 0.02 mm G Silt and Clay

E F G C D

0-

0

Limit of 4 Total Fe —detectionloW:

Mo

Fe r-

4-

-5.0

4.5

E a. a.

•

C ti

O

as

/1-, ofi •

40

PSe

—3

Se ..-* • AcidSolFe. •

40

4 2 •\ a. t a. / . e is. I ;,co

11...., ..

_ . cs / I •---•-- -5.. --

.c. _a' m

1:.i'- o

0._._.- f..........+.........+.........4.

.............+1- al

4 - D .. 0 o (I) A B C D E F G (ii) A B C D E F G

Topsoil.(0 -4 ins.Sample24799E3P27.) C horizon( 20-27ins. 2483• BR27 )

Well-drained, Residual Clare Shale Soil.

4 -8 ins. Sample 2003,BR1. 10-18 ins. Sample 2403,BR17.

Residual Limestone Soil. Residual Namurian Soil.

FIG.No• 33. SIZE ANALYSIS OF RESIDUAL SOILS.

133

Mineral aggregates cemented by these constituents will,

therefore, be included in the coarser fractions. Consequently

the size analysis obtained is not an accurate representation

of the true mechanical composition of the sample.,

(a) Molybdenum and Selenium

Size analysis of the two samples from the topsoil

and C horizon of the metal-rich profile developed on the Clare

Shales (samples 2479 and 2483, Fig. 33) indicated a high propor-

tion of coarse sand (particles greater than 0.2 mm in diameter,

i.e. plus 80 mesh) in these samples. This is believed to be

due to the gravelly nature of the soils formed from the

siliceous, platy shale bedrock but also includes undispersed

organic aggregates as shown by the relatively high organic

carbon content of the coarser fractions in the C horizon.

There are marked differences in the metal patterns

developed in the two samples. In the C horizon both Se and

Mo are concentrated in the fine fractions, whereas in the

topsoil the concentration of Se in the fine fractions is much

less marked and the distribution of Mo is more or less even.

In the C horizon it is apparent that there is a very close

correlation between the Se, Mo and acid-soluble iron; total

Fe203 and organic carbon also follow the same general trend.

The relationship between Se, Mo and acid-soluble iron was

expected because of the similar patterns of these elements

134

in the profile as a whole. The correlation of organic carbon

contents with Mot Se and Fe is probably due to the mode of

occurrence of this material. Organic carbon has presumably

been introduced into the C horizon by the washing down of

fine particles of organic matter from the topsoil which have

accumulated in the finer fractions. It is not possible to

determine how much the organic carbon content influences the

distribution pattern of Se although it has already been suggested

that organic carbon may accumulate Se in the topsoil of the

profile. The total Fe203

content, determined spectrographically,

reflects the pattern of distribution of acid soluble Fe but the

concentrations det•rmined are greater by a factor of about two

to three. It would appear that the pattern of Mo and Se in the

C horizon is principally controlled by the concentration of iron

oxides in the finer fractions.

In the topsoil the relatively even spread of both

Mo and Se is reflected in the distribution of total Fe203.

Acid-soluble iron and organic carbon were unfortunately not

determined. However, in view of the correlation between total

Fe203 and the other elements in the C horizon the even distri-

bution of metal between fractions is probably related to the

relatively consistent levels of iron and organic carbon. The

latter results are probably due to the formation of undis-

persed mineral aggregates bound together by organic matter

and secondary iron oxides.

135

In the limestone soil (2003) Mo was only detectable

in some of the fractions but showed a definite tendency to

concentrate with Fe203

in the -80 mesh fraction, i.e. fine

sand, silt and clay. Se was also concentrated in the finer

fractions.

Mo was not detectable in the Namurian soil sample

(2403). The distribution of Se in this sample shows the metal

concentrated in both the coarsest and finest size ranges.

This is difficult to explain but, in view of the lack of

correlation with the Fe203 pattern, it is provisionally

attributed to the association of Se with organic matter as

shown by the profile studies.

(b) Other Metals

The degree of variation in the distribution of

other metals in the different size fractions is not as well

marked as in the case of Mo and Se (Table 18). In the lime-

stone soil, most elements with the exception of Mn and Co

are slightly concentrated in the fine fractions, but

essentially no consistent trends are evident in the data for

soils derived from other rocks.

2. TRANSPORTED OVERBURDEN

Glacial drift covers by far the greater part of

the area but some other types of transported overburden, in

particular colluvial and lacustrine accumulations in swampy

Table 18: Distribution of Other Metals in Size Fractions of

Residual Soils (Metal content in ppm)

Profile BP 27 Well-drained

A

SIZE FRACTIONS*

Pb Ga v Cu Ti Ni co Mn Cr

15 10 300 8 3000 10 <5 70 300

4o 15 300 10 3000 10 <5 70 400

3o 12 300 10 3000 10 <5 70 250

4o 15 400 10 4000 20 <5 80 300

20 12 400 10 4000 20 <5 70 250

15 8 300 lo 4000 10 <5 70 250

15 8 200 15 3000 10 <5 70 200

topsoil (0-4 ins) developed on Clare Shales (Sample 2479)

Profile BP 27 C Horizon

Pb Ga V cu Ti Ni co Mn Cr

30 20 700 3o 4000 30 <5 8o 400

20 18 700 3o 4000 30 <5 80 400

4o 20 700 20 4000 30 <5 150 500

5o 20 800 30 3000 30 <5 150 500

6o 25 500 40 2000 30 <5 150 600

7o 20 600 4o 3000 20 <5 150 500

6o 12 500 30 3000 20 <5 100 500

(20-27 ins) of Clare Shale

soil (Sample 2483)

Table 18 (continued)

Profile BP 1 Limestone Soil

SIZE FRACTIONS*

Pb Ga V Cu Ti Ni

15 5 20 3o 2000 50

10 5 30 20 1000 50

10 4 30 30 1500 4o

40 4 10 20 Soo 30

3o 5 15 15 1000 4o

3o 5 30 20 4000 30

4o 18 So 4o 6000 7o

(4-8 ins) (Sample 2003)

Co 10 15 15 10 30 15 20 Mn 600 600 600 1000 Soo 700 700 Cr 50 50 50 30 40 70 100 Zn <50 <50 <50 50 <50 50 200

Pb 10 7 lo 3 8 15 15 Ga 20 15 15 15 15 15 30

Profile BP 17 Namurian Soil V 70 50 60 50 6o 6o 7o Cu 30 20 20 20 30 30 30

(10-18 ins) (Sample 2403) Ti 7000 5000 6000 4000 7000 Soo° 8000 Ni 4o 20 30 30 30 30 30 Co 15 5 15 lo lo 10 15 Mn 300 200 300 150 400 250 400 Cr 70 63 70 60 8o 100 120 Zn 1 70 70 70 50 50 50 70

* A = 2 mm (=10 mesh) -20 mesh C = 33 mesh -80 mesh B = 20 mesh -38 mesh D = 30 mesh -125 mesh

E = 125 mesh -200 mesh F = -200 mesh -0.02 mm G = Silt and Clay

(-0.02 mm)

138

depressions and valley alluvium, although of limited extent, are

of special importance because of their association with toxic Se

occurrences.

(i) Colluvium

Colluvial deposits are rare in the area. A limited

occurrence of material of this origin is present on the slope

flanking the southern edge of the swamp deposits of Flynn's

Farm (Figs. 18 and 34) and consists of mixed limestone and

Clare Shale detritus derived from the combined action of hill-

wash and gravity creep from adjacent drift and sub-outcropping

Clare Shales. The areal extent of the colluvial material is

poorly defined and these deposits combine features of both

residual and drift profiles.

Briefly, the Mo and Se patterns in the colluvial

profiles BP 8 and BP 50 (Fig. 34) are similar to the residual

Clare Shale profiles in showing a general increase in metal

content down the profile accompanied by some enrichment in the

topsoil. In BP 8 however, the Se content does not increase

down the profile along with Mo and also the iron content of

the profile is the reverse of that in Clare Shale residuum

(decreasing from 6% Fe203 in the upper horizons to a mean

value of 2.5% Fe203

in the Mo-rich basal horizons). For this

reason it is believed that the metal patterns reflect the high

metal content of unweathered Clare Shale rather than accumula-

7.5

Eh and pH of Ground Water. **.

- ---• +0•4

03- 1 pH 70 + + „• ..... -.6'.. • -----

6,5 • -------- -

PA. y 250

2 250

c, 360

•••••

70 0 airy N 0

a.00/ •rasefr mart

125 70 \ bS. ••••

•".*' . \ 4 56 40 ,i)",747.a47 4./0/ pave/ /

6 VERTICAL SCALE 20 inches to 1 inch.

TOPO.and HORIZONTAL SCALE 40 feet to 1 inch.

1430 Soil metal content-ppm.

NORTH-SOUTH VERTICAL SECTION ACROSS SOUTH MARGIN OF PEATY SWAMP AREA. -FLYNN'S FARM-

Showing Metal Content of Soils Developed under Varying Drainage Conditions from Severe Impedence at Left to Free Drainage on Right of Section.

(Mo content of peaty samples has been adjusted for loss of material on ignition prior to analysis.)

175

490

• 1# 74 Ab0Y. a

BP 3 Se Z Mo 5. 50'

I 317; ------- et. 800 5 5

1 1100 ,•-• 5 /3441.

2000

./ 7250

200

-1;; a

\ 0

B Se100.

P

O

e'r*1Y 5/5 8007

800 - 200 _5_

Y

•

0

&NOBPV°

38

_ \

spa so 150 k.

1500 .7 125

r ""7 37.6%

18

0

0 /

\ o\ 100 / ,

of,z354 rave/ q d.o

•

s • • ep tai

1 1.9.5

160 --1 /I , 05 S r--lib/ •

• 1.5

30

6

Se102. 30 it, 047, .12

•--__

13 0 5.5

k. •

0 / 30

16 s'•

3 0

??' • 63

•

Se 50.

z ----- b At eAfg. e

28 Q.7?"1",.. 0Va:yeS -lo'/X•170.0??5.5 4;1. 0...06-74;-6.i.

0 \

Metal Content of Ground Water.

Mo(ppb) Se(ppb) Eh BP 50 8.1 7.0 volts. Drain 45.0 14

P- 0

B S Se 8

/e4- 40

&ow"' ' . ..., --

260 • Semi.ofe4;...c. .c/JZ. • 5' .5

Yer...rrool/s 4,/114 -r./ • rey- a

• ‘4,4,5. e. -.A0 V4,11 . • .67.

. 70

•-•"" i I • '":>

I }Tarr Aale 86.InevA,

100 k / 0

°P •

56. /

=•••••• .0•••••

FIG.No. 34.

100

120

40

30

12

30—

139

tion with Fe oxides, the upper soil horizons having been leached

of Mo and Se. The Clare Shale rock section exposed in South

Creek nearby and along strike averages 71 ppm Mo and 15 ppm Se.

In BP 50, downslope from BP 8, the increase of Mo

and Se down the profile is reflected in an increase in 1 the iron

content from 1.1 - 2.0 Fe203 in the upper horizons to 3.8,;L

Fe203 in the basal horizon. In addition to the possible leaching

of Mo and Se from the upper soil horizons, the increase downwards

of Mo and Se values is most probably associated with the precipi-

tation of iron minerals leached from up profile and upslope as for

Clare Shale residuum.

These soils occur on the margin of the peaty-swamp

that constitutes the seleniferous toxic soil area of Flynn's Farm.

Erosion of the soil has contributed largely to the basal

"lacustrine" horizons on which the toxic peaty soils have

developed. Leaching of the metal-rich soils has also contributed

metal-rich groundwater to the swampy depressions.

(ii) Glacial Drift

Soils derived from glacial drift are the most

widespread in the area. Thus, the Ballincurra, Elton, Howard-

stown and Kilrush Series are all derived to a large extent from

drift material (Figs. 5 and 7). The distribution of trace

elements in the drift is therefore, of major agricultural

importance. Post-glacial erosion of the unconsolidated glacial

i4o

deposits has also been a major source of the detrital constituents

of alluvial and swamp deposits.

(a) Areal Distribution of Metal in Drift

Analysis of drift soils at 18-24 ins depth showed

that the metal content of glacial drift reflects the metal content

of the underlying bedrock, modified by transport of rock material

in the direction of ice movement (Fig. 12, Tables 9 and 10). The

most striking example of this is the "fan" of molybdeniferous

drift southwest of Foynes (Figs. 2 and 12) related to the Weichsel

ice advance. Within this area, the"carry-over" of Clare Shale

also noted by Synge (1966) is shown by the presence of black shale

fragments mixed with limestone and Namurian detritus up to 5 miles

"down-ice" from the line of outcrop. In the west, where the line

of advance of the ice did not cross the Clare Shale boundary,

black shale material is absent from the drift. This observation

is consistent with the regional geochemical pattern of the area

and is confirmed by analyses for Mo of drift observed to contain

Clare Shale fragments.

On a more detailed scale in the Flynn's Farm area

the areal distribution of metal in drift is closely related to

the bedrock pattern, and the highest concentrations of Mo, Se,

Cu and V occur in drift overlying the metal-rich Clare Shale

sub-outcrop (Figs. 12, 19-22). To the west the spread of metal-

rich drift onto the Namurian sandstones and siltstones corresponds

iLa

with the presence of Clare Shale fragments in the till. However,

the presence of Mo-rich drift up to 1-mile east of the base of the

Clare Shales (Fig. 19) is contrary to the movement of metal-rich

material "down-ice", the ice having advanced in a west and south-

west direction. In this case, where black shale fragments are

visible in the predominantly limestone drift (e.g. in a gravel

quarry about 800 ft east of the base of the Clare Shales between

Flynn's and South Creeks) their presence is attributed to fluvio-

glacial wash downslope from the Clare Shale escarpment.

Particularly in the topsoil horizons, anomalous concentrations

of Mo and Se are sometimes detectable in drift soils up to

several thousand feet east of the Clare Shale horizon. Where

there is no visible evidence of Clare Shale fragments in the

parent drift it is believed that damming of waters between the

escarpment and the ice front during retreat allowed flooding

by waters containing metal in solution and suspension. Part of

this metal has been retained in the drift and concentrated in the

topsoil on weathering.

In general, because of the complexity and persis-

tence of the drift, it is not possible to make any close comparison

between the actual metal content of drift and underlying bedrock.

The metal patterns in fresh Jrift are dependent both on the amount

of dilution of metal-rich black shales by barren material and the

direction of ice movement. This is modified locally by fluvio-

glacial factors and the effects of weathering during soil forma-

tion.

11+2

(b) Distribution of Metal in Drift Profiles

The Elton Series soils are derived from limestone

drift sometimes with a small admixture of other rocks including

shale. The underlying bedrock is generally limestone except

where there has been a "carry-over" of limestone drift onto

other rock types. Soils of this series are well to moderately

drained loams and generally occupy gently undulating ground.

Leaching has played a prominent part in the soil-forming

process and much or all of the parent calcareous rock has been

leached. The organic content of the topsoil is medium to high,

depending on drainage.

Gley soils comprising the Howardstown and Kilrush

Series have developed under conditions of impeded drainage and

are characterized by bluish-grey and grey colours in the mineral

horizons, commonly with ochreous mottling.

The Howardstown Series occurs on flat, poorly

drained predominantly limestone drift but may also form on

alluvium derived mainly from limestone. These soils are of

clay-loam to clay texture and the profile is characterized by

a dark-brown organic surface horizon overlying strongly gleyed,

grey and mottled lower horizons. The division between horizons

is not well marked. Leaching has not played a large part in the

soil development and much or all of the original CaCO3 remains

in the profile, except in the topsoil.

Table 19: Drift Soil Profiles Selected for Study

Bac

kgro

und

Met

al

Valu

es

Parent Drift Well Drained

-----.._

Moderately Drained Poorly Drained

Predominantly Limestone

BP 29 (Elton)*

Predominantly Namurian

BP 4? (Kilrush)

Ano

mal

ous

Met

al

Valu

es

Predominantly Clare Shale

BP 106 (Kilrush)

Predominantly Limestone

BP 3 (Elton)

B1 11 (Howardstown)

Predominantly Limestone Minor Clare Shale

BP 22 (Elton)

BP 33 (Elton-Howardstown)

BP 23 (Howardstown)

Mixed Clare Shale, Namurian and Lime- atone.

BP 36 (Elton?)

BP 37 (Kilrush)

*The classification of the profiles studied for metal distribution into soil series is based on the Irish Soil Survey classification. Actual identification is by the writer and must therefore be considered as provisional only.

144

The Kilrush Series had developed under similar

conditions of poor drainage to the Howardstown Series but occupies

the higher ground overlying the Namurian rocks and also Clare

Shales (area D, Fig. 12). The parent drift material is mostly

of Namurian and Clare Shale origin, often with some admixed lime-

stone. The poor drainage conditions under which these soils have

developed is attributed by Finch and Ryan to a high silt content

and poor structure and are considered as surface water gleys.

They have a clay-loam and silt-loam texture with an organic top-

soil horizon overlying greyish-brown gleyed horizons.

Table 20: Some Physical Characteristics of Elton, Howardstown and Kilrush Series Soils of Drift Origin (After Soil Survey of Ireland)

Elton Series

Depth (ins.) 0-8 8-15 15-23 25-40 pH 5.5 5.7 6.6 7.3 Organic Carbon (0 3.1 1.3 0.9 0.2

Howardstown Series

Depth (ins.) 0-6 6-10 10-18 18-24 24-45 pH 5.8 6.o 6.8 7.9 8.3 Organic Carbon 8.6 3.7 0.9 0.3 0.3

Kilrush Series

Depth (ins.) 0-5 5i-15 15-23 23-26 26-36 PH 6.3 6.2 5.9 5.5 5.7 Organic Carbon (%) 3.5 1.4 0.4 0.4 0.3

145

Molybdenum and Selenium in Background Soils

The glacial drift profiles selected for study include

two profiles of limestone drift and Namurian sandstone and silt-

stone composition respectively, containing only background metal

values (Table 19)

The background limestone drift profile (BP 29 -

Table 21) contains insufficient Mo for any pattern to be detected

and it is apparent that soil formation has not involved any

significant enrichment of the Mo content of the parent drift.

This corresponds with the data obtained by regional drift

sampling (Fig. 12). The profile was not analysed for Se but

it is not expected that soil development will have involved

significant changes in the Se status of the drift. This con-

clusion is based on (a) the low Mo, levels present in the profile,

(b) the low Se levels in limestone drift established by regional

sampling (mean 0.5 ppm Se), and (c) the similarity of the profile

developed on the liMestone drift to the residual profile developed

on limestone of similar composition (BP 1 - Table 16).

The soil profile developed on drift of Namurian

sandstone and siltstone origin shows a well marked increase, by

a factor of about two, of Se in the organic-rich topsoil horizon.

Mo is also slightly enriched in the topsoil compared with the

parent drift.

Table 21: Glacial Drift Profiles in Background Areas

BP 29 Moderately well-drained, predominantly limestone boulder elm. (Soil type, Elton Series)

Sample No.

Depth (ins)

2497 0-3 2498 3-9 2499 9-14 2500 14-18 2701 18-24

Medium brown, friable sandy loam

<2 Light to medium brown sandy loam with some limestone pebbles <2 Light brown gritty clay loam with some limestone -.,72ebbles <2 Light brown clay loam with some limestone pebbles

<2

Light brown loamy drift gravelly boulder clay

<2

Profile Description No Se

(ppm) (ppm)

BP 47 Moderately drained, predominantly Namurian sandstone and shale boulder clay. (Soil type, Kilrush Series)

Sample No.

Depth (ins)

3704 0-6 3705 6-11 3706 11-20 3707 20-32

3708 32-40

Dark brown, humic, sandy ca.ay loam Light grey brown, slightly mottled, sandy clay loam Grey, slightly mottled clay loam with sandstone fragments Grey-brown black clay. .Sandstone and siltstone fragments in sandy clay Grey-brown black clay. Sandstone and siltstone fragments in sandy clay

Mo (ppm)

Se (1)pm)

2 1.2 <2 0.8 <2 0.6

<2 0.5

<2 0.6

Profile Description

147

Molybdenum and Selenium in Anomalous Areas

The occurrence of anomalous concentrations of Mo

and Se in drift soils can generally be related to the presence

of Clare Shale fragments in the parent drift or, where the drift

is deposited close to the Clare Shale escarpment, to the addition

of metal-rich material from lakes dammed against the scarp during

retreat of the ice-sheet.

In describing the geochemical characteristics of

anomalous drift soil profiles it is apparent that the Mo and Se

content of the unweathered drift will be dependent on the compo-

sition and proportion of Clare Shale material mixed with barren

rock types. However, features of soil formation, in particular

groundwater movement and drainage, accumulation of organic matter

and iron oxides, leaning etc., will result in re-distribution of

metal in the weathered section of the profile. The profiles can

therefore be classified as shown in Table 19 according to (a)

the composition of the parent drift and (b) the soil series

which incorporates variations in drainage, horizon development,

etc.

Well-Drained to Moderately Well-Drained Drift Soils of

Dominantly Limestone Origin (Mainly Elton Series)

Anomalous profiles BP 3 and 22 (Table 22) and also

BP 29 containing background metal levels fall within this

category. In BP 3 and 22 which are located on moderately

sloping hillsides, the groundwater level is below the profile

Table 22: Glacial Drift Profiles with Anomalous Molybdenum and Selenium Contents

Sample Depth No. (ins) Profile Description

Mo Se Mo/Se pH Acid Total (PPM) Soluble Fe203 Fe

(%)

vrgq C ; (0 I

BP 3 Moderately well-drained, predominantly limestone, gravelly boulder clay. Moderate metal values. Soil classified as grey-brown podzolic of the aton Series.

Medium brown friable silty loam 7 3.2 Medium brown clayey loam with minor mottlin3 5 1.5 Light brown gritty clayey loam. A few limestone

pebbles 5 0.8 Light brown lsightly weathered gravelly limestone

boulder clay 5 1 Light brown less weathered gravelly limestone

clay 4 1.0 Light brown less weathered gravelly limestone

clay 2

2_ 6.65 0.75 6 3.5 3.3 7.35 0.6 6 1.8

1

6.25 8.13 0.4 4 0.8

8.41 2 0.3

3.6 8.43 1.6 '.0.2

8.40 2

2126 0-6 2127 6-10 2128 10-18

2130 18-26

2131 26-34

2133 34-38

BP 11 Moderately poorly-drained, predominantly limestone gravelly boulder clay. Moderate-high metal values. Soil is intermediate between A grey-brown podzolic of the Elton Series and a gley of the Howardstown Series.

2322 0-4 Medium brown, slightly gleyed sandy clay loam 20 5 4 2323 4-8 Light brown sandy clay loam with limestone and

black shale pebbles 12 3.8 3.2 2324 8-12 Light brown, grey weathered boulder clay 7 1.2 6 2325 12-24 Light brown-grey boulder clay 5 0.3 17 2326 24-36 Light brown-grey boulder clay 5 0.3 17

Mo Se Mo/Se pH Acid Total Org. (ppm)

Sample Depth No. (ins) Soluble

Fe203 C Fe (%) (4) (%)

Profile Description

BP 106 Poorly drained Clare Shale ground moraine. Gley soil, Kilrush Series.

4105 0-12 Dark brown-black humic loam 6 7.5 0.8 4106 12-24 Dark grey loamy clays with black shale fragments 2 2.5 0.8 4107 24-36 Grey clays with many shale fragments 16 3.7 4.3 4108 36-54 Grey gravelly clays and semi-decomposed shale

fragments 85 9.0 9.4

Table 22 t;continued)

BP 22 Moderately well-drained, predominantly limestone with some admixed Clare Shale, boulder

2428 0-6

clay. Grey-brown podzolic, Elton Series.

Light brown friable silty clay loam with some pebbles 15 3.5 4.3 2.3 8 2.75

2429 6-11 Light brown friable silty clay loam with limestone and some black shale pebbles 10 2.0 5.0 2.4 6 1.19

2430 11-17 Orange brown gritty clay with limestone and some black shale pebbles 5 2.2 2.3 2.8 8 0c57

2431 17-24 Light brown gritty, slightly weathered, boulder <2 1.8 4 0.15 2432 24-36 clay with predominantly limestone fragments, <2

very minor Clare Shale

1.5 <1.3 1.6 3 0.28

Table 22 (continued)

1 Sample Depth Igo Se Mo/Se PH Acid Total Org.1 1 No. (ins) Profile Description (ppm) Soluble Fe

203

1 Fe

W (%) (%)J

BP 23 Poorly-drained, predominantly limestone with minor Clare Shale boulder clay. Gley soil, Howardstown Series. Drift comp. similar to BP 22.

0-4 Brown-grey, mottled, gleyed silty clay loam 15 6.5 2.3 8 4-9 Dark brown-humic, gleyed loam 12 7.5 1.6 6 9-16 Dark brown-humic,gley, almost peaty 12 3.0 1.5 4 16-23 Dark brown peaty gley 8 9.5 0.85 1.6 23-29 Grey clay and sand. Limestone black shale

pebbles <2 2 <1 0.8 29-36 Light grey, sandy boulder clay. Limestone

black shale pebbles <2 2 <1 0.6 36-45 Light grey, sandy boulder clay. Limestone

black shale pebbles <2 2 <1 0.8

BP 33 Moderately poorly-drained, predominantly limestone with some Clare Shale boulder clay. Slightly gleyed intermediate between Elton and Howardstown Series.

0-4 Medium brown mottled, gleyed, humic loam 7 7.3 0.95 4-9 Medium grey-brown, gritty gleyed loam 5 4.3 1.2 9-15 Light grey, mottled, weathered sandy boulder clay 10 0.7 14 15-24 Light grey, sandy limestone and black shale

boulder clay 15 1.0 15

2434 2435 2436 2437 2438

2439

2440

2781 2782 2783 2784

Table 22 (continued)

1 Sample Depth Mo Se 1 No. (ins) Profile Description (ppm)

iff

2785 24-36 Light grey, sandy limestone and black shale boulder clay

15 1.2 9.2 2786 36-48 Light grey, sandy limestone and black shale 7

boulder clay 2787 48-6o Fresh, grey, boulder clay, predominantly

limestone some shale 3 2789 60-72 Fresh, grey, boulder clay, predominantly

limestone, some shale <2 0.4 <5.75 72-80 Fresh, grey, boulder clay, predominantly

limestone, some shale <2

Mo/Se pH Acid Total Org.! Soluble Fe203 C

Fe (;.) (2.) (i,-)

2800

2801

2802 1

2803 ! 1 2807 1 2808

BP 36 Moderately well-drained, boulder clay, predominantly Clare Shale with limestone and Namurian sandstone and siltstone. High proportion of dense clay.

0-5

5-13

Medium brown slightly mottled silty loam with some drift pebbles

Brown, slightly weathered boulder clay with Clare 12 1.3 9 5

Shale sandstones and limestone pebbles 15 1.5 10 6

13-21 Brown, slightly weathered boulder clay with Clare Shale sandstones and limestone pebbles 12 1.3 9 6

21-38 Grey, fresh boulder clay. High proportion of fine clay in matrix 7? 1.5 4.7? 6

38-50 Boulder clay, predominantly Clare Shale with 15 1.5 10 8 50-57 some limestone and sandstone 10 1.5 6.6 6

Bp 37 Poorly-drained gravelly boulder clay of predominantly Clare Shale and Namurian sandstone and siltstone with some limestone. Gley soil of Kilrush Series.

2820 2821 2822

0-4 4-10 10-14

Dark brown humic gley Dark brown peaty gley. Some shale fragments Light ,friey humic clay. Some weathered rock

12 30

fragments 7 2823 14-26 Grey boulder clays with limestone, Clare Shale

and Namurian fragments 6 2824 26-35 Grey boulder clays with limestone, Clare Shale

and Namurian fragments 6 2825 35-45 Grey boulder clays with limestone, Clare Shale

and Namurian fragments 6

1.0 12 5 1.5 20 8

0.5 14 3

0.7 8.4 5

6 1.0

8

1 1

Table 22 (continued)

---;

Sample Depth Mo Se Mo/Se pH Acid Total Org. No. (ins) Profile Description (ppm) Soluble

Fe203 C

Fe (;,,) (s,) (%)

153

depth. Mo and Se are concentrated in the surface horizons and

this can be correlated with the distribution of both iron and

organic carbon. Soil development has involved leaching of CaCO3

from the upper horizons and it would appear that the accumulation

of iron in the upper horizons represents immobile iron oxides

retained in the soil under the neutral to alkaline conditions

of weathering. The accumulation of organic carbon in the upper

horizons is the result of normal biogenic activity with some

eluviation of organic matter into the lower horizons by downward

percolating waters.

The mechanism by which Mo and Se are retained in the

.upper part of these well-drained profiles can be attributed to

adsorption on either the organic carbon or the iron oxides. In

view of the fact that the iron oxides are considered to be relic

rater than freshly precipitated compounds it is thought that

adsorption on organic matter may be the predominant factor in

metal retention. However, because of the well-marked association

of Fe with Mo and Se in some other profiles (e.g. BP 27) and the

general co-variance of both iron and carbon with No and Se, the

possible influence of iron cannot be discounted.

Well-Drained Drift Soils of Mixed Origin

Profile BP 36 has been taken from boulder clay

overlying Namurian rocks and is made up of sandstone and silt-

stone, a large proportion of Clare Shale fragments and some

154

limestone. The high iron content of the fresh drift in the

profile (approx. 6.5% Fe203) is a measure of the high Namurian

rock content (averaging 7.5% Fe203),and Clare Shale (averaging

Fe203). Much of the rock matter making up the boulder

clay at this site has been transported a considerable distance,

as indicated by the presence of Clare Shale and limestone

fragments at least five miles from the nearest outcrop source.

Movement by the ice-sheet has also involved the transport of

this material several hundred feet in altitude to its present

site. It seems reasonable that after transport of several miles

by the ice, adequate mixing of the Clare Shales with barren rock

types should have occurred. Consequently, in view of the negli-

gible quantities of Mo and Se in the barren rock types, Mo and

Se values of 10 ppm Mo and 1.5 ppm Se in the unweathered drift

will be a measure of the proportion of the Clare Shale present.

Taking into account the average Mo and Se content of Clare Shales

(27 ppm Mo and 3.0 ppm Se) it appears that this soil is developed

from drift composed of about one-third to a half Clare Shale

detritus. These proportions are in line with the iron content

of the drift mentioned previously.

Soil development has not involved any significant

redistribution of Mo and Se in the profile. This is attributed

to the only slightly weathered nature of drift due to the high

proportion of dense, impervious rock-flour of argillaceous and

arenaceous rock types in the matrix.

155

Poorly Drained Drift Soils of Dominantly Limestone

2ELFin

Profiles BP 11 and 23 are typical of the gley soils

developed under conditions of impeded drainage. BP 23 is sited

close to BP 22 and the parent drift is of generally similar

composition. The parent drift at site BP 33 is also similar

and the drainage conditions under which soil formation has taken

place are moderate, being intermediate between those of BP 22 and

BP 23. As in the freely drained profile, Mo and Se are concent-

rated in the upper horizons along with iron as shown by the Fe203

contents of BP 23. Organic carbon analyses were not made but

visual examination of profile BP 23 (Table 22) has indicated

development of a humic, almost peaty B horizon. Se has been

substantially enriched in this horizon compared with Mo. The

uppermost organic horizons of the moderate to poorly-drained

profile BP 33 also contain high concentrations of Se compared

to the amount of Mo present.

From this it can be deduced that under conditions

of poor drainage Se tends to be more enriched in the upper more

organic horizons than in the corresponding horizons of better

drained drift. Mo on the other hand, although enriched in

the topsoil does not appear to be present in much greater con-

centrations than in equivalent well drained soils. It would

appear that adsorption of Se on the organic material is the

most likely mechanism for concentration as, in BP 23 for example,

there is no correlation between Se and Fe203

in the uppermost

156

organic-rich horizons. The mechanism by which Mo accumulates

in the poorly drained soil of BP 23 also appears to be linked with

the organic nature of the upper horizons.

Poorly Drained Drift Soils of Mixed Origin

Profile BP 37 has been derived from drift boulder clay

similar to that of BP 36. Poor drainage has encouraged the develop-

ment of organic-rich A and B horizons and both Mo and Se show a

tendency to accumulate, particularly in the almost peaty, gleyed

B horizon. Iron has also concentrated in this horizon but is

not substantially enriched in the topsoil.

Poorly Drained Clare Shale Drift Soil

Soils of solely Clare Shale drift origin are very

restricted in extent and no examples of soil development under

good drainage conditions were located. The profile developed

under conditions of impeded drainage (BP 106, Table 22) exhibits

many of the characteristics of the residual profile developed on

Clare Shales (BP 27, Table 16). Both Mo and Se are enriched in

the lower horizons and in view of the general similarity of the

profile structure to the residual Clare Shale profile it is most

probable that the accumulation of metal towards the base of the

profile can be similarly attributed to the influence of

accumulated iron oxides. However, the poor drainage conditions

have modified the soil profile by encouraging the development

157

of an organic-rich humic topsoil similar to other poorly drained

soils developed on drift of mixed bedrock origin. Both Mo and Se

are enriched in tlis horizon. Comparison of the relative concentra-

tions of Mo and Se in this profile indicates that comparatively

more Se is retained in the upper part of the profile as was

recorded for poorly drained anomalous soils of mainly limestone

origin. As suggested in the discussion of the residual Clare

Shale soil it is possible that although both metals may be sorbed

or co-precipitated with secondary iron oxides, the greater affinity

of Se for organic matter leads to excessive concentrations of Se

relative to Mo in the upper horizons of the soil. The Mo:Se

ratio of 9.4 in the basal horizon of this profile very closely

reflects the average Mo:Se ratio of 9.2 in the Clare Shale bedrock.

Compared with Mo/Se ratios of 0.8 in the topsoil this is an indi-

cation of the selective retention of Se in the upper more organic

part of the profile.

Other Metals

The distribution of several other elements was

investigated in four profiles (Table 23). Under moderately good

drainage conditions, the predominantly limestone boulder clay

profiles (BP 3 and BP 22) showed a slight increase in most metals

in the upper horizons in a generally similar but less well marked

pattern to Mo and Se. Most likely this represents residual

accumulation of material remaining after leaching of CaCO3. Ga

and Ti, commonly associated with clay minerals are enriched in

158

the upper horizons. Most cationic metals, e.g. Pb, Zn, Cu, Ni,

which would tend to be insoluble under the alkaline conditions

of weathering limestone also accumulate in the upper horizons.

Under the impeded drainage conditions of BP 23, the

pattern of enrichment in the upper horizons is generally similar

to that of well-drained profiles but the concentration of most

metals is more marked. This follows the greater concentration

of Fe in the upper horizons. Cu, in particular, is similar to

Se in being markedly concentrated in the organic-rich surface

horizons.

In BP 36, limestone is subordinate to the other rock

constituents of the drift tri.ereby inducing a more acid weathering

environment. The distribution of some metals in this profile

diverges from the Mo-Se pattern. Thus, there is a marked increase

of Mn in the upper horizons and a less well marked concentration

of Pb. There is also some evidence that Cu may be slightly

leached from the upper horizons.

(c) Mechanical Analysis of Drift and the Distribution of Metal Between Size Fractions

The mechanical composition of four drift samples

was determined and analyses made of Mo, Se and in certain cases

organic carbon and acid-soluble Fe (Fig. 35). Ten other metals

and the total iron content were also determined spectrographi-

cally (Table 24). The drift investigated consisted of a topsoil

Table 23: Metal Content of Selected Glacial Drift Profiles

Sample Depth Mo Se Pb Ga V Cu Zn Ti Ag Ni Co Mn No. (ins) (Parts per million)

BP 3 Moderately well-drained drift gravel and boulder clay. Predominantly limestone origin.

2126 0-6 7 3.2 40 10 100 50 150 4000 <0.2 85 3o 600 2127 6-10 5 1.5 5o 8 loo 5o 130 5000

loo 3o 600

2128 10-18 5 0.8 4o 6 85 6o loo 4000 tt 85 3o 400 213o 18-26 5 I 3o 5 85 4o <50 3000

2133 34-38 2 1 3o 4 4o 30 <5o moo 2131 26-34 4 ? 1.0 3o 4 85 3o <5o 200

It

85 20 200 tt

6o 20 200 !I

6o 16 16o

BP 36 Moderately well-drained mixed boulder clay of Namurian, Clare Shale and limestone origin.

12 1.3 4o 13 200 85 100 4000 <0.2 50 20 600 15 1.5 20 13 200 85 100 6000 85 3o 3000 12 1.3 20 13 300 85 85 6000 It 85 30 1300 7 1.5 13 8 130 4o 5o 4000 5o 20 400 15 1.5 16 13 300 130 loo 6000 It 85 3o 600 lo 1.7 16 lo 300 13o 5o 6000 it 85 3o 400

0-5 - 5-13 13-21 21-38 38-50 50-57

BP 22 Well-drained drift of mainly limestone with some Clare Shale material.

15 3.5 50 lo loo loo loo 5000 <0.2 loo 3o 10 2.0 50 13 100 100 130 6000 tt 130 3o 5 2.2 60 16 130 100 100 600o IT 130 4o

600 600 85o

0-6 6-11 11-17

Cr Fe203 (%)

85 85 85 85 6o 6o

6 6 4 2 1.6 2

85 5 85 6 85 6 6o 6 160 8 130 6

loo 8 85 6 loo 8

2800 2801 2802 2803 2807 2808

2428 2429. 2430

Table 23 (continued)

Sample No.

Depth (ins)

Mo Se Pb Ga V Cu Zn (Parts per million)

Ti Ag Ni Co Mn Cr Fe203 (50

2431 2432

BP 22

<21 <2 1

1 •

30 16

6 6

60 85

4o 4o

<50 <50

3000 4000

<0.2 It

60 6o

30 20

500 300

85 60

4 3

17-24 24-36

2434 2435 2436 2437 2438 2439 2440

BP 23 Poorly-drained drift of mainly limestone with some Clare Shale material_

15 6.5 4o 10 300 85 130 5000 <0.2 85 30 300 fi 12 7.5 5o 16 400 loo 130 600o 100 30 500

12 8.o 4o 13 400 1000 loo 5000 85 20 200 8 9.5 30 8 200 850 50 4000 60 13 200

tl 4o lo 100 <2 2 lo 4 6o 16 <50 2000 ft 5o lo loo <2 2 13 4 6o 20 <50 3000

<2 2 13 4 6o 3o <50 2000 50 16 100

85 130 130 85 4o 4o 4o

8 6 4 1.6 0.8 0.6 0.8

0-4 4-9 9-16 16-23 23-29 29-36 36-45

161

sample (2126), slightly weathered drift from the C horizon of

the same profile (2130), slightly organic boulder clay forming

the base of a swamp deposit (2156) and fresh boulder clay of

mixed Clare Shale and Namurian origin with some limestone (2808).

The mechanical composition of the -2 mm fraction of

the drift (material larger than "coarse sand" size was not

included in the study) shows that a high proportion consists of

silt and clay-sized particles. The amount of very fine "rock-

flour" is highest in the fresh boulder clay sample (2808) and

least in the weathered topsoil and in the boulder clay underlying

the peat swamp (samples 2126 and 2156). This is attributed both

to the aggregation of particles by organic matter in these

samples and to the greater susceptibility of the finer limestone

particles to the action of weathering agencies.

Dealing with the distribution of metal (Fig. 35 and

Table 24) in the fresh boulder clay of mixed origin (2808 -

BP 36, ref. Table 22 for profile description) it can be seen

that No, Se and most other metals including iron, are relatively

evenly distributed between the size fractions. Such an even

pattern could be expected in view of the dominantly mechanical

origin of glacial till, in which unsorted freshly comminuted rock

particles have been subjected to a minimum of chemical weathering.

Ti tends to be impoverished in the 80 to 200 mesh-size and this

may be related to the grain size of the host mineral which was

probably ilmenite in the Namurian rocks.

a U

C a a)

Sec;

4 Mo.,

4

io +Total Fe403

-o

5'

Froclion - 20 mesh.

mesh. B 20mesh-38 a p

A 2mm

C 38 - 80 " (1) a

D 80 „ - 125 a 21a

E 125 - 200 a

F 200 „ - 0.02mm. -3 G Silt and Clay.

Mo A -F<2ppm.

Total Fe+

0

..1

Mod. well-drained, sandy boulder-clay. Predom. limestone orign. Sample 2126, BP 3 , 0" - 6". A B C D E ABC D E F G

Sample 2130, BP 3 , 18" - 26"

Fe a

nd

Org

.0 (%

)

E a. a.

Mo

an

d Se

BC DEFG Sample 2156, BP 6., 31" - 42" Gravelly boulder-clay, under-tying peaty-swamp.Flynn'sFm.

Mo,

Se

(PM

)

A B C D E F G• Sample 2808 . BP 36 , 50"-57". Fresh b.-clay of mixed limest. Pare Sh. and Namurian orign.

FIG.No.35. SIZE ANALYSIS OF GLACIAL DRIFT SAMPLES

SHOWING DISTRIBUTION OF METAL BETWEEN FRACTIONS.

Table 24: Distribution of Metal in Size Fractions of Glacial Drift (Metal Contents in ppm except for Fe203 which is in %)

(Size Fraction AaG as for Fig. 35-and Table 18)

Profile BP 3 Topsoil 0-6 ins,

predominantly sandy lime-

stone boulder-clay

(Sample 2126)

Profile BP 3 18-26 ins,

sandy, predominantly lime-

stone boulder clay

(Sample 2130)

A

Mo 8 8 6 4 4 3 8 Se 5.2 3.5 2.2 1.8 1.3 1.0 2.7 Pb 100 30 50 4o 7o 5o 30 Ga 10 5 7 7 10 7 15 V 7o 7o 7o 5o 40 4o 200 Cu 4o 40 40 50 4o 50 50 Zn 300 150 120 120 150 100 150 Ti 4000 3000 3000 2000 3000 5000 4000 Ni 8o 70 8o 70 70 70 100 Co 30 20 30 5o 4o 30 20 Mn 1000 500 1000 2000 3000 800 400 Cr 90 70 70 50 70 70 200 Fe203 10.0 6.o 5.o 5.0 5.o 4.o 6.o

Mo <2 <2 <2 <2 <2 <2 4 Se 1.3 1.6 1.5 1.4 1.3 1.5 1.2 Pb 8 12 10 15 15 10 30 Ga 2 2 <2 2 2 2 8 v 6o 7o 60 5o 5o 4o 70 Cu 8 10 8 10 20 10 50 Zn <50 <50 <50 <50 <50 e50 <50 Ti 300 300 400 300 5000 2000 3000 Ni 30 30 40 40 50 50 100 Co <5 <50 5 5 5 lo 30 Mn 150 200 150 200 200 150 500 Cr 30 40 40 40 4o 60 100 Fe203 1.0 1.3 1.6 1.6 1.6 1.6 4.0

Table 24 (continued)

(Size Fraction A-G as for Fig. 35 and Table 18)

A

Mo <2 <2 4 4 3 3 40 Se o.8 2.3 5.5 3.o 2.1 1.2 23.0 Pb 5 7 7 4 5 4 30

Profile BP 6 (31-42 ins) Ga <2 <2 <2 <2 2 2 8 v 70 8o 8o 5o 7o 7o 8o

Gravelly boulder-clay underlying

peaty-swamp. Flynn's Farm Cu Zn

15 <50

4 <50

7 <50

4 <50

5 <50

5 <50

4o <50

Ti 300 500 500 300 400 1000 2000 (Sample 2156) Ni 10 10 10 10 20 20 70

Co <5 <5 <5 <5 5 5 20 Mn 250 250 250 300 400 400 400 Cr 15 20 20 20 20 30 150 Fe203 0.6 0.8 1.3 o.8 1.6 1.6 3.0

Mo 5 7 6 6 8 3,2 9 Se 2.8 2.0 2.1 1.8 1.8 2.0 2.1 Pb 15 30 10 15 20 15 30

Profile BP 36 (50-57 ins) Ga 10 15 8 10 10 12 15 V 70 80 70 70 100 80 120

Unweathered boulder clay of Cu 50 6o 60 8o 80 70 8o mixed Namurian, Clare Shale Zn <50 <50 <50 <50 <50 <50 50

Ti 7000 6000 6000 2000 1500 7000 7000 and limestone (Sample 2808) Ni 50 50 40 8o 70 80 8o

Co 20 15 15 30 30 30 30 Mn 400 600 700 600 700 400 500 Cr 100 8o 80 70 8o 8o 120 Fe203 6 8 8 8 6 8 8

161+

In the other samples, in which weathering agencies

have been active, the Mo and Se content in particular, varies

markedly between the size fractions. The least altered,

sample (2130, BP 3) was collected from 18 to 26 inches in slightly

weathered limestone drift. Mo is enriched in the silt and clay

fraction and this can be correlated with a marked rise in the

Fe203

content of this fraction. Se, on the other hand, is more

evenly distributed between the fractions, except for a slight

increase in the Se content of the 125 to 200 mesh fraction which,

considering the low levels being determined, is probably not

significant. The lack of corielation between Se and Fe203

contents in the silt and clay fraction would seem to indicate

that Se, unlike Mo, is not associated with secondary iron oxides

in the slightly weathered drift. The relatively even distribu-

tion of Se between fractions is most probably the result of

association with organic matter which is distributed fairly

evenly between the size fractions with a slight increase in the

finest fraction. Most other elements (Table 24) follow both Fe

and C in being concentrated in the silt and clay fractions.

In the topsoil sample (2126) and the drift underlying

swamp deposits (2156) the effects of weathering are much more

marked and are reflected in wide variations in the Fe and organic

carbon content of the different size-fractions. The patterns of

iron and organic carbon in these two samples are basically different

in that in the topsoil there is a marked accumulation of both

constituents in both the finest and coarsest fractions. In the

165

drift unc:',erlying the swamp iron and organic carbon are enriched

only in the silt and clay fractions. Mo and Se both closely

follow these patterns.

In the topsoil (2126), the well-drained and leached

nature of the soil would indicate that the Mo and Se contents

represent relic compounds remaining after leaching of CaCO3

during soil formation. The concentration of iron and organic

carbon in the coarse fraction is attributed to the formation of

iron-rich organic aggregates that are not broken down during

mechanical analysis. The anomalous concentrations of Mo and Se

in the drift underlying the swamp (sample 2156), are believed

to be due to the hydromorphic introduction of metals and sus-

pended organic matter from metal-bearing groundwaters and the

overlying metal-rich peat deposits. Unaltered drift of similar

origin situated nearby (ref. drift and swamp section, Fig. 39)

contains <2 ppm Mo and 0.8 ppm Se in the -80 mesh fraction

compared with 30 ppm Mo and 15 ppm Se in sample 2156. Organic

carbon and precipitated iron oxides have both accumulated with

Mo and Se in the finest fractions of the altered drift.

Briefly, with regard to the distribution of other

metals between size fractions of the altered drift, it can be

seen from Table 24 that many of them tend to follow the iron

oxide pattern and in general possess a similar pattern of

distribution to Mo and Se. More obvious exceptions to this

pattern in the topsoil drift (2126) 14-40'Cu, Ni and C. which do not

vary between size fractions. These metals on the other hand,

166

are concentrated along with iron in the fine silt and clay

fraction of sample 2130 collected from 18 to 24 ins in the

same profile.

In the more organic drift from beneath the swamp

deposits (sample 2156), V and possibley Zn and Mn are obvious

exceptions to the general pattern of concentration in the finest

fraction, along with iron and organic carbon. It would seem

that the conditions giving rise to the co-precipitation or

adsorption of the other elements on iron oxides or organic carbon

do not affect V and possibly not Zn and Mn.

(iii) Alluvium

Alluvial deposits flank many of the streams in the

area and it has been shown (Chapter V) that where the streams

rise on the Clare Shales, anomalous concentrations of No and Se

in soils and herbage are often associated with these deposits.

Investigation of the alluvial material has involved

(a) analysis of related profiles containing both anomalous and

background metal concentrations, (b) sampling of a traverse

across the alluvium comprising toxic soil Site B, and (c) size

analysis of selected samples. The mechanisms by which Mo and

Se are dispersed in alluvium are also discussed.

167

(a) Distribution of Metal in Profile

Molybdenum and Selenium

Background Areas

Extensive areas of alluvium overly the limestone

drift in the eastern half of the study area (Fig. 5). Regional

soil sampling indicated that at a depth of 18-24 ins this material

carried only background metal concentrations (Fig. 12). A more

detailed description of the vertical distribution of Mo and Se

in typical profiles through these deposits is given below

(Profiles BP 14 and BP 30).

The Mo and Se contents of the alluvial horizons in

profile BP 14 are appreciably higher than in the underlying

drift and there is a slight increase in the Se content of the

uppermost alluvial horizons. In BP 30 Se was not determined

but, in view of the fact that the Mo content is very low, Se

can be expected also to be present in only small concentrations.

Mo is slightly concentrated in the uppermost topsoil horizon of

this profile and is just detectable. Although the metal content

of the alluvial soils is slightly greater than in the drift

it is apparent that significant variations, that would bring

about anomalous concentrations, do not occur in background areas.

Briefly,with regard to other elements (Table 26),

it is apparent that most metals determined in profile BP 14

are slightly enriched in the alluvial horizons compared with

the underlying unweathered drift. However, metal concentrations

2378 0-4 2379 4-10 2380 10-15 2381 15-20 2382 20-30 2383 30-42 2384 42-48 2385 48-54

Table 25: Description and Molybdenum and Selenium Content of Alluvial Profiles from Background Areas

Sample Depth Mo Se No. (ins) Profile Description (ppm) (ppm)

BP 14 Moderately poorly-drained shallow alluvium of predominantly limestone origin overlying limestone boulder clay.

Light-brown mottled silt-clay loam ) 2 1.5 Light-brown mottled sandy-clay loam ) Alluvium 2 1.8 Light-brown yellow sandy, mottled clay ) 2 1.0 Weathered, organic drift soil, mottled with limestone pebbles <2 0.5

) Boulder clay, predominantly limestone <2 0.3 ) with a few O.R.S. fragments. Clay <2 ) ) matrix grey with some iron <2 ) 0.2 ) mottling <2 )

(For other elements refer Table 24. Data refers to -80 mesh fraction)

BP 30 Alluvium of predominantly limestone origin overlying limestone boulder clay. Severely impeded drainage. Background metal values.

2702 0-4 Dark brown, humic clay loam 2 2703 4-8 Light brown mottled silty clay <2 2704 8-13 Light grey-brown, slightly mottled clay <2 2705-7 13-42 Light grey, silty alluvial clay <2 2708-9 42-46 Light grey clay with limestone fragments <2 2710-12 46-60 Limestone drift, gravel and boulder clay <2

(Profile adjacent to B/G drift profile BP 29)

169

in the upper "sub-outcropping" slightly weathered drift horizons

(15-30 ins) are not significantly lower than in the alluvial

material and it is possible that concentration is due to the

effects of weathering of the alluvial soils.

Anomalous Areas

Alluvium carrying higher than background concentrations

of Mo and Se flank many of the streams draining the Clare Shales

or areas of drift containing Clare Shales. The geochemical

environment under which the alluvial deposits has been formed

varies (a) with the dominant rock types incorporated in the

detrital fraction of the alluvium, (b) with the physio-chemical

character of the stream waters and (c) with the drainage conditions

under which later soil-forming processes have taken place.

In the detailed study area around Flynn's Farm (Figs.

18-23), it is possible to define several different types of

alluvium. Most common and of greatest agricultural importance

because of their relatively widespread extent and high Se content

are calcareous alluvial deposits on the limestone flanking

streams flowing east from the Clare Shales. These extend as

far as 3 miles downstream from the Clare Shales and include the

toxic seleniferous soils at site B (Fig. 20). Typical profiles

are described in Table 28 and shown in Figs. 36 and 37.

Characteristically., these soils are neutral to alkaline in

reaction with only minor peat development. In contrast,

•-•-•—• METAL CONTENT OF SOIL te-24 ins

RED CLOVER.

-Peaty grey lapsed

L grey Sandy and onarly clayt

Slut -grey clay

DrtIt

OP 70

at tr

IMRE SPA BPS, 1P7I 11P4I BP! RES BPAL

SCALE OF S. VALUES (SO WWI fraction )

DISTRIBUTION OF SELENIUM IN ALLUVIUM -_, , ? _: _ _ _ _-? . ,

. , . .‘ .1 i NORTH-SOUTH SECTION ACROSS ALLUVIAL FLAT

: z z .. .. - . 3 Toxic Soil Site B. .. ..

o as

VERTICAL SCALE RICHES FIG. No. 36.

MO Sentient of Sod Clover (ppm)

—4

Si t

o. 31 3 cent•ni of ground rater (pm.)

I .

alts

'.7

DP3

• e , '' .. e .• • \ • s' -

SCALE OP Me VALUES

(-SO mesh(ruction

s to PPM

DISTRIBUTION OF MOLYBDENUM IN ALLUVIUM. • • • e' •-• 7 — / • • • .•• • / • • .• • to \ •

NORTH-SOUTH SECTION ACROSS ALLUVIAL FLAT

Toxic Soil Site B. SCALE AND LEGEND AS FOR PIONs

FIG.No. 37.

Table 26: Metal Content of Background Alluvial Profiles (BP 14, ref. Table 25)

Horizon Depth Pb Ga V Cu (ins)

Zn Ti Ag Ni Co Mn Cr Fe203 Parts per million

(6-4 160 16 85 30 160 5000 Alluvium 4-10 160 20 100 30 200 6000

L10-15 130 16 130 60 160 5000 Weathered it 15-20 100 13 130 60 100 4000 Drift

(20-30 160 16 loo 85 loo 6000 ( 30-42 85 8 60 30 <50 3000 Drift 1 42-48 loo 6 4o 3o <50 2000 48-54 85 6 6o 20 <50 3000

<0.2 60 20 200 loo 5 99 85 4o 200 loo 6 It 85 5o 600 130 8

100 40 850 160 8 it 85 3o 85o 130 6

50 20 400 85 4 FI 40 20 500 60 3

50 16 16o 85 4

171

alluvium derived predominantly from Clare Shales (Table 26,

BP 28) is strongly acid in reaction and peat horizons are well

developed.

Alluvium of Predominantly Clare Shale Origin

North-west of Flynn's Farm alluvium has been

deposited flanking North-west Creek (Figs. 18 and 19). Here

the adjacent overburden consists largely of Clare Shale residuum

and drift. Detrital material in the lower horizons of the

alluvium is formed mainly from Clare Shale fragments. Severely

impeded drainage conditions have led to substantial peat develop-

ment in the upper horizons of the profile which in this respect

is similar to some of the peaty-swamp deposits (Table 27).

The profile is divided into two major horizons.

Firstly, a basal layer (47-85 ins) of essentially detrital

material consisting of blue-grey clays and rock fragments,

mainly black shale, which contains on average 9.5 ppm Mo and

2.25 ppm Se. Overlying this is a characteristically organic-

rich series of horizons of fine clays, silts and peaty material

containing significantly higher concentrations ranging from

10-30 ppm Mo and 4.5-20 ppm Se.

The acid pH of this alluvium (4.88-5.95) is in

contrast to the neutral to alkaline reaction of alluvium

deposited in the limestone areas.

Table 27: Profile (BP 28) of Anomalous Alluvium of Predominantly Clare Shale Origin

Sample No.

Depth (ins)

Profile Description pH Mo Se

(ppm) (ppm)

2485 2486 2487 2488 2489 2490 2491 2492 2493 2494

0-5 5-11 11-20 20-32 32-39 39-47 47-54 1 54-66 66-77 7?-85 .1

Dark grey, humic, silty gley. Black shale fragments Dark grey-brown peaty gley Dark brown silty peat Dark brown silty peat Dark brown silty peat Light grey, fine organic-rich clay Blue grey clay with black shale fragments

I, and some limestone and chert material. Proportion of black shale increases near base of hole. Near .bedrock?

. 5.23 5.36 5.41 4.94 4.88 5.17 5.34 5.30 5.82 5.95

15 15 25 25 25 10 8 12

ir 8 10

4.5 5.0 7.0 11.0 20.0 4.5

2.25

Metal content of groundwater in hole: 1.2 ppb Se, 6.0 ppb Mo, 1300 ppb Fe.

Horizon Depth

(ins)

Gleyed I 0-5 topsoil 1 5-11

11-20 Silty c 20-32 peat 1. 32-39 Organic clay39-47

Alluvial 47-54 I

1 54-66 clays and

sand 1 66-77 t 77-85

Table 28: Metal Content of Alluvium of Predominantly Clare Shale Origin (BP 28)

(For complete profile description refer to Table 27. Data refer to -80 mesh fraction)

(Metal contents of the peaty horizons have been adjusted by estimation for the loss of organic matter on ignition prior to spectrographic analysis)

Mo Se Pb Ga V Cu Zn (Parts per million)

Ti Ag Ni Co Mn Cr Fe2o3

1

/0

15 4.5 40 20 500 130 100 5000 0.3 60 20 160 100 8 15 5.0 30 16 400 160 85 5000 0.2 85 20 200 130 10 25 7.0 25 13 320 600 70 4000 o.4 16o 5o 65o 8o 6 25 11.0 32 8 700 1600 80 4800 0.9 320 32 48o 110 5 25 20.0 32 16 700 800 130 4000 0.8 8o 25 480 110 8 10 4.5 30 30 850 160 160 5000 <0.2 130 30 100 160 10 8 ) 30 13 400 100 16o 6000 <0.2 100 40 100 16o 3 12 (

2.25 4o 16 400 130 loo 6000 <0.2 130 6o 400 16o 8

8 30 16 300 100 130 6000 <0.2 100 60 400 130 8 10 i 40 16 200 100 130 5000 <0.2 100 50 300 160 8

174

When considering the possible mechanisms that have

influenced the dispersion of Mo and Se it is apparent that the

broad sub-division of the profile into a detrital lower horizon

and an upper organic-rich layer, reflects two different phases

of deposition and geochemical environment. It is believed that

the lower horizons of blue-grey clays and rock fragments rep-

resents mechanical alluvial conditions in which detrital material

was deposited in a post-glacial depression by the old free-

flowing stream. Following the initial filling of the depression,

severely impeded more or less swampy conditions developed, in

which fine material only was deposited by a slew-moving stream,

coincident with the growth and deposition of peaty matter.

Geochemically therefore, the Mo and Se content of the basal

horizons represents the metal content of the mechanically

deposited old stream sediment. The Mo and Se contents of this

horizon are 9.5 ppm Mo and 2.25 ppm Se, which closely correspond

to the present-day active stream sediments from North-West Creek

which contain on average 11.7 ppm Mo and 2.4 ppm Se.

The onset of impeded drainage peaty conditions with

the accumulation of organic matter in the sediments, affected a

change in the geochemical environment. It is believed that the

enrichment of Mo and Se along with Cu, Ag, Ni and Mn in the

peaty horizons (ref. Table 28) is most probably associated with

adsorption of metals by organic matter from percolating etream

waters and also groundwaters leaching from the adjacent Clare

175

Shale residuum and drift-covered hillsides. There is no signi-

ficant enrichment of Fe 02.3 (Table 28) in the peaty horizons

compared with the basal alluvial horizons, and Pb, Ga, Zn, Ti,

Co and Cr have a similarly fairly uniform distribution of values

between the organic and basal clayey horizons. Presumably these

metals do not have an affinity for organic matter under these

conditions.

In the upper gleyed topsoil layers (0-11 ins), the

levels of Mo, Se, Cu, Ag, Ni, Co and Mn are significantly lower

than in the more organic-rich, peaty horizons and the levels

approach those present in the basal horizons.

Alluvium of Mixed Clare Shale and Limestone Origin

Profile BP 10 (Table 29) was taken from the alluvium

flanking South Creek adjacent to the base of the Clare Shales

(Fig. 19). This profile is similar to BP 28 in having a peaty

horizon at 22-46 ins which is enriched in both Mo and Se,

overlying a basal mineral alluvial horizon. However, in this case,

a second silty alluvial horizon (0-22 ins), which contains an

appreciable concentration of organic matter, overlies the peaty

layer and contains roughly similar Mo and Se concentrations.

Anomalous Alluvium of Predominantly Limestone Origin

Profiles BP 2 and BP 4 (Table 30 and Figs. 36 and 37)

were collected from the alluvial flat flanking Flynn's Creek at

toxic soil Site B (Fig. 19). The nearby catchment consists of

Table 29: Profile and Molybdenum and Selenium Contents of Alluvium of Mixed Clare Shale and Limestone Origin

Sample Depth No. (ins) Profile Description

Mo Se (ppm) (ppm)

2305 0-4 Dark grey-brown humic, sandy gleyed loam 50 2306 4-10 Dark grey-brown humic, sandy gleyed loam 70 2307 10-14 Grey, silty mottled organic clay 70 2308 14-22 Dark grey clays with black shale and limestone

.fragments 70 2309 22-30 Peaty horizon of dark brown peaty clay 60 2310 30-42 Peaty clay with some black shale fragments 70 2311 42-46 Mixed grey silty clay and peaty clay 40 2312 46-60 Grey silty clay, few root fragments 12 2313 60-72 Light grey sandy clay with root fragments 15 2314 72-84 Light grey clays with grit horizons and black shale 30

and limestone fragments

9.0

1 12.0

I

5.0

177

limestone drift containing only moderate to background concentra-

tions of Mo and Se (ref. BP 3, Table 22) but the headwaters of the

stream, about one mile distant, rise in the metal-rich peaty swamp

area adjacent to the base of the Clare Shales at toxic soil Site A.

Detrital rock fragments in the alluvium are predominantly lime-

stone with only very rare black shale fragments.

The alluvium can be sub-divided into two major horizons

(Fig. 36). A basal layer of clays and sandy gravels represents

mechanically deposited, stream sediments filling depressions in

the post-glacial stream valley. Overlying these deposits are

calcareous, manly horizons with some sandy intercalations. The

marl deposits of fine sediments and precipitated CaCO3 are believed

to be similar to those being deposited in parts of the present-

day streams (refer Chapter IX). The quiet, semi-lacustrine

conditions under which this took place followed,the infilling

of the lower parts of the stream valley by detrital sediments.

Soil development in the upper horizons of the profiles has given

rise to a gleyed, organic-rich topsoil.

The characteristic feature of metal distribution in

these deposits is the high concentration of Se compared with Mo.

It has been shown that in Clare Shale source rocks the Mo:Se

ratio is in the order of 9:1 and this ratio holds for most of

the residual overburden, drift and Clare Shale alluvium previously

described. It is evident therefore, that preferential accumulation

of Se has taken place during the formation of these deposits.

5.5 ( 2138- 18-24 Light grey coarse grit, some sandy clay 8.60 0.20 <2 .1

2134 0-4 Dark brown, peaty, silty gley 7.13 1.3 8 40 2135 4-8 Mixed peaty gley and sandy grey clay 8.21 0.6, <2 5 2136 8-18 Light grey sandy clays with some limestone

pebbles 8.62 0.33 <2

Table 30: Profile Description and Molybdenum and Selenium Content of Anomalous Alluvium of Predominantly Limestone Origin (Ref. Figs. 36 and 37)

Sample Depth No. (ins) Profile Description

pH HC1 Org. Mo Se Soluble C (ppm) Fe (%) (%)

BP 2

2117 0-6 Dark brown organic-rich, gleyed silt loam 7.28 1.10 9.39 20 20 2118 6-12 it ti It ft II II ti 7.60 0.5 4.93 15 17 2119 12-17 It it II tf If It It 7.65 0.37 5.76 8 22 2120 17-24 Light grey clayey sand. Limestone and

black shale fragments 8.54 0.15 1.0 2 t 18 2121 24-32 Light grey sandy clay. Some root fragments 8.33 0.17 2.69 5 3 2122 32-36 Light cream manly clay. Some root fragments 8.4o 0.27 4.59 15 55 2123 36-45 Light cream manly clay. Root fragments 8.48 0.18 2.56 8 40

2124 45-54 Blue-grey alluvihm silty clay. Limestone pebbles 8.40 0.30 0.78 5 11

2125 54-66 Grey drift boulder clay 8.72 0.48 0.19 2 1.5

BP

pH HO]. Org. Mo Se Soluble C (ppm)

Fe(%) (%)

Sample Depth No. (ins) Profile Description

<2 18 3 14

<2

<2

<2 1 3.5

8.28 1.10 8.501

(1.4 8.50J

8.33 1

(1.8 <2

BP 4

2139 24-28 Light cream manly clay with root fragments 2140 28-40 Light grey, manly clays with root fragments 2141 40-51 Grey mottled alluvial clay, minor sands and

limestone pebbles 2142 51-63 Grey mottled alluvial clay, minor sands and

limestone pebbles 2143 63-75 Grey mottled all•ivial clay, minor sands and

limestone pebbles

2144 75-85 Grey mottled alluvial clay, minor sands and limestone pebbles

Table 30 (continued)

Depth

Se (ins)

BP 2 20 28 Peaty gley I

0-66 15 17

t 12-17 8 22

f 17-24 2 18 Manly clays

I 24-32 51

1

32-36 15 55 36-45 8 4o

Alluvial clay { 45-54 5 11

Drift 54-66 2 15

BP 4

Featy gley { 0-4 8 40

f 4-8 <2 5 1 8-18 <2I Manly clay 1 18-24 <2 f 5°5

24-28 <2 18

28-40 3 14 40-51 <2 I 51-63 <2 y Alluvial cla

[ 63-75 <2 3.5

75-85 <2 1

Table 31: General Metal Content of Anomalous Alluvium of Predominantly Limestone Origin

Pb Ga V Cu Zn ppm

Ti Ni Co Mn Cr Fe203

Organic Carbon

Acid Sol. Fe

40 6 300 loo 85 4000 6o 20 600 160 6 9.39 1.10 30 5 100 85 <50 850 50 16 160 85 3 4.93 o.5o 16 4 6o 130 " 85o 6o 13 loo 4o 2 5.76 0.37

8 2 6o 13 I, 85o 40 lo loo 3o 0.8 1.o o.15 10 8

3 3

60 50

16 20

I, it

1300 1300

60 60

10 13

100 100

4o 4o

1.3 1.6

2.69 4.59

0.17 0.27

6 <2 6o 13 n 500 3o 8 130 20 1.3 2.56 0.18

13 3 60 8 ,t 1300 50 10 100 30 1.6 0,78 0.30

13 3 85 8 II 1300 40 10 160 30 1.3 0.19 0.48

5o 8 60 100 100 4000 85 20 300 100 4.o 1.3

13 4 6o 20 <50 4000 30 13 130 60 1.3 o.6 8 3 4o 8 " 2000 30 <5 16o 16 1.0 1 5 2 50 6 ,1 600 30 5 130 16 o.8 1

0.33

10 2 100 13 " 600 3o <5 130 13 0.6 0.2

30 4 60 20 it 1 3000 50 13 200 60 3.0 1.10 85 5 60 30 " 4000 60 20 400 85 4.0 16 6 60 30 ti 4000 60 20 400 85 4.0 I

1.4

30 5 85 40 If 3000 85 20 200 85 3.0 ) 20 5 85 4o ft 2000 60 20 200 85 3.0 i

1.8 L

181

From Fig. 36 and Table 30, it is clear that the

highest concentrations of Se occur in the marly clay horizons

and the topsoil. Except for the enrichment of both acid-soluble

and total Fe in the topsoil, it is apparent that there is no

correlation between the Se content and the amount of iron present.

On the other hand, the highest Se concentrations in the marly hori-

zons can be correlated with high organic carbon contents (Table 31).

It is believed that adsorption on this material has lead to the

accumulation of Se. It will be shown (Chapter IX) that similar

processes of organic matter accumulation in calcareous marly

deposits, accompanied by an enrichment in Se, are taking place

in the present-day streams. The basal mineral alluvial clays

contain only 0.78% compared with 2.5 to 4.59% organic carbon

in the marl deposits. The mechanism of CaCO3

precipitation to

form the marl deposits is believed to be from the stream waters

under conditions probably closely similar to those in Flynn's

Creek adjacent to these deposits. Under these conditions CaCO3

with up to several percent included organic matter is being

deposited from waters at a pH of 8.25 containing 396 to 4247pg

HCO3- per litre and 7.6 to 9.0 ppb Se and 16.3 ppb Mo in

solution.

Mo on the other hand, is not significantly

concentrated in the marly horizons compared with the basal mineral

sediments and it would appear from this that the mechanism giving

rise to the accumulation of Se in the organic-marls does not

influence the dispersion of Mo. These observations are confirmed

182

by data on present-day stream sediments (Chapter IX) in which

it is shown that most of the dispersed Mo is in the iron oxides

in the sediments whereas Se accumulates in organic matter. The

amount of Mo present in the marly and basal clay horizons can

therefore be attributed to mechanically deposited mineral

sediments.

In the topsoil horizon both Mo and Se appear to be

significantly concentrated compared with the immediate underlying

horizons. In the case of Se this can be correlated with the higher

organic matter content of this horizon and reflects similar patterns

of Se distribution in other overburden profiles examined. It is

believed that the higher iron content of the topsoil (1.1-1.3%

acid-soluble iron compared with less than 0.5% in the underlying

marl) is the principal means of retention of Mo in this horizon.

It has been observed that after heavy rainfall complete satura-

tion of the topsoil horizons occurs so that the groundwater level,

normally 12-24 ins from the surface, rises to mix with the surface

water. A precipitate of fine iron oxides accumulates in the surface

waters under these conditions, presumably by the oxidation of

ferrous iron in the groundwaters to the less soluble ferric form.

Under such conditions co-precipitation or adsorption of Mo from

groundwaters (which contain from 0.25 to 4.25 ppb Mo) could occur

as shown by Jones (1956 and 1957).

Briefly, with regard to other elements, it can be seen

from BP 4 (Table 31) that most metals, including Pb, Ga, Cu, Ti,

Ni, Co, Mn, Cr, Fe and possibly V are distributed in a reverse

183

trend to Se and the highest concentrations occur in the basal

clay horizon. Zn and Ag were not present in detectable

quantities. Most metals have concentrated with iron oxides

and Mo in the topsoil horizon compared with the underlying

marl.

(b) Size Analysis of Alluvium

Two samples, one (2120) from the organic marly clay

horizon and the other (2124) from the basal alluvial clay were

subjected to mechanical analysis (Fig. 38). The marl sample

included material from one of the sandy intercalations in this

horizon. The basal clay sample consisted almost entirely of

very fine sand, silt and clay.

In the marly sample Se is highly concentrated in the

silt and clay fraction (35 ppm) compared with about 5 ppm in the

fine sands. There is also a significant rise in the Se content

of the 20-80 mesh fraction of the coarse sands. Organic carbon

has a similar pattern of distribution to Se and this substantiates

observations on the influence of organic carbon on Se accumulation

in this material. Mo was only detectable in the silt and clay

fraction in which the highest Fe concentrations also occur.

It is believed that the concentration of Mo in this fraction can

be attributed to inclusion in detrital matter containing iron

oxides. The profile studies of alluvium did not show any

evidence of the precipitation of Fe in the alluvium, except in

the topsoil horizons and for this reason a detrital origin for

10 -

oco•

(0-

40 -

SN

O1

13

VS

4 3

21S

Oft

**I

lo -

Jo

/0 -

0

A to G Size fractions as for drift size analysis. FIG.35.

317

-PC A - F Mo =<2 ppm.

of

9Se 70

- ►

ro

►

; + Org.C. +0

10

/0

( 'A

)SN

O1

1.3V

EIA

32

IS

Org

.0 a

nd

Fe(

/.)

. de lotion.

-0 A

Sample 2120 BP 2 17" -24:' Marty clayey sand.

FIG.No.38. SIZE ANALYSIS OF ALLUVIUM SAMPLES.

AND DISTRIBUTION OF METAL BETWEEN FRACTIONS.

Jr

Jo

Alf

E a. C.

.a /( C

0 /0

0

is

J0

if

,20

lb.

Mo

an

d Se

(p

pm

)

/0

0

.14

io Org

.0 a

nd

Fe (

/. )

A Sample 2124 BP 2 45"-54" Alluvial clay.

184

Mo is favoured.

In the sample from the basal alluvial clay (2124)

the distribution of both Mo and Se follow Fe203 in being

f6elatively evenly distributed between sizes with some slight

enrichment in the coarse sand and the silt and clay. Organic

carbon was not determined but the profile studies (Table 30)

indicate that the organic carbon content of this horizon was

very low (0.78%) and presumably does not play a large part

in metal distribution. The even distribution of Mo and Se

in this sample, along with Fe203, is in line with the basically

mechanical origin attributed to this horizon.

With regard to the other metals determined (Table

32), most elements, with the exception of V in the marl sample,

follow the Mo and Se patterns.

(iv) Peaty-Swamp Deposits

Although of relatively small areal extent, the three

deposits of this type in the Flynn's Farm area (Figs. 18 and 19a)

are of particular significance in that they contain the highest

concentrations of Se and Mo recorded in the area (refer Chapter V,

3). Herbage growing on these soils may also contain extremely

high concentrations of Mo and Se.

The peaty-swamps have formed in post-glacial

depressions in the till adjacent to or overlying the Clare

Shales. The Irish Soil Survey (Finch and Ryan, 1966) classify

*A

BP 2 Marly clayey sands (Sample 2120, 17-24 ins)

Mo Se Pb Ga

<2 1.9 5 <2

<2 9.5 7 <2

<2 8.o 5 <2

<2 5.o 5 2

<2 4.5 5 <2

<2 4.5 7 <2

5 35 35 7

v 60 7o 4o 40 3o 3o 5o Cu 7 8 7 6 4 3 50

(ppm) Zn <50 <50 <50 <50 <50 <50 <50 Ti 100 100 100 200 400 700 2000 Ni 8 7 7 8 10 8 70 Co <5 <5 <5 <5 <5 <5 20 Mn 200 150 150 150 400 400 300 Cr 10 10 7 7 20 20 70

CO Fe203 0.3 0.5 0.6 0.6 o.6 0.5 1.6

BP 2 Alluvial clay (Sample 2124, 45-54 ins)

Mo 2 4 4 2 2 2 4 Se 2.0 5.8 7.0 2.0 2.5 2.8 9.5 Pb 20 7 7 6 6 7 20 Ga <2 <2 <2 2 2 2 5 v 7o 7o 6o 7o 8o loo 400 Cu 5 7 7 7 7 6 20

(ppm) Zn <50 <50 <50 <50 <50 <50 <50 Ti 100 200 300 200 500 700 3000 Ni 10 20 20 20 20 20 60 Co 5 5 5 5 5 5 15 Mn 500 400 200 400 400 400 500 Cr 10 15 15 15 20 15 60

(%) Fe203 1.0 0.8 1.0 0.6 1.0 1.0 1.3

185

Table 32: Distribution of Metal Between Size Fractions of Alluvium

*A 2 mm - 20 mesh B 20 mesh - 38 mesh C 38 mesh - 80 mesh

D 80 mesh - 125 mesh E 125 mesh - 200 mesh F 200 mesh - 0.02 mm

G Silt and clay

186

these deposits as being of alluvial lacustrine origin. The early

lacustrine stages are marked by fine clays and sands eroded from

the surrounding limestone drift and Clare Shale overburden. At

the margins of the deposits this material may merge with colluvium

derived by hillwash and gravity movement of drift and Clare Shale

detritus from upslope (refer Fig. 34).

Mixed with the detrital sediments are distinctive

calcareous marl horizons probably of similar origin to CaCO3

being precipitated in the present-day streams and in the alluvial

deposits described previously. This material also contains up to

several percent organic carbon (Table 34).

Swamp conditions developed as the lake filled with

sediments and marl and these horizons are overlain by peat. Severe

decomposition during soil formation of much of the peaty matter has

since occurred and resulted in a fine, black, sticky peaty-gley B

horizon. The topsoil horizon is a dark-grey to brown peaty or

humic gley-loam.

The Irish Soil Survey (Finch and Ryan, 1966) classify

these soils in the Flynn's Farm area mainly as peaty phases of the

Drombanny Series. They describe them as low-lying, poorly drained,

rich in organic matter and neutral to alkaline in reaction. With

regard to the high concentrations of Se and Mo, Finch and Ryan

point out that these soils only contain excessive amounts of Mo

and Se where they are associated with the Clare Shale beds or drift

containing Clare Shales.

187

Studies of metal dispersion in this environment were

mostly carried out by means of profiles taken along two sections

across the east margin (Fig. 39 - toxic soil site A) and the south

edge of the peaty swamp at the head of Flynn's Creek (Fig. 34).

In the former, drainage is dominantly from limestone drift with

moderate metal values. The latter traverse flanks colluvium and

drift of dominantly Clare Shale origin with generally higher metal

values. A background profile from a peaty swamp overlying Namurian

rocks was also collected. Confirmatory profiles were sampled from

the peaty areas immediately north and south of Flynn's Farm

(Fig. 19a).

Metal values from the more peaty horizons were deter-

mined spectrographically. Where the organic matter content is known

the metal values have been adjusted for loss on ignition. Where

the organic content is not known, the adjustment was by estimation

based on the appearance of the sample. In view of the very wide

range of Mo values in particular, and the fact that organic carbon

levels seldom exceed 25 per cent even in the more peaty horizons,

it is considered that the estimates of loss by ignition will not

appreciably affect the significance of the results.

(a) Distribution of Metals in Peaty-Swamp Profiles

Background Areas

A profile (BP 109, Table 33) overlying barren Namurian

rocks situated well away from any drainage from Clare Shale soils

or drift, showed that although there is some concentration of both

pH,Eh

Mo Se

•

75x.0 50 20

7 0 3 5 $. 2

6.5 2 0 • o

Se = 2.6 ppb Mo tr 30

BPS eH =.0.49 V Se Mo Ph = 72

(En readings 28-7-65 1115 hrs.) MoSe ppb

------- ----------- 100 --- pH Eh -- + 'Vol It 73 .44

E GROUND WATER SAMPLES

r 5

011 35 533 2 .) //

, • -I- .••

4. I ‘• .3 3 -"'

<2

0

04

et.

<2

c2

<2

o sj

TOPO.and HORILSCALE (FEET) I 5 10 20 30 40

VERTICAL SCALE( INS.)

IIIS 40 Soil metal contents-ppm.

FIG. No. 39.

- 10

70-.03 5

49e44'r.

3 1,

C, C>

4°51, °

—<5-6 -050 ✓ ,

' / e. 5 / 0

- e

15 30 r' tcl 7'. \ ‘4 \ ., '. 1 , \. 0/f

40.:,;_c:,_ —,..' •-&,. 'c,'' tc;.;: <75' ' c, <:, c::, C? <="-C3 CP C; 4:3.6:1 z'

.

30/0/ C ••- e.

"‘ 4950 a

229 150 , .. = !"1:1 ! I — 4' 3 C Ground Water _ _ 2. _ top 2 ''-208,050 .- - -- - - 1- I ' '.- - - Level. .. 4

i ... „, i in too =, - i

. , 1

140 .700

• Mo content of ground water. (ppb) -0 $e

pH of ground water. Eh

BP911 Se Mo

94 911 °Pm0

6

49 Se Mb BP. 95.

SP19 DP97 DP93

Se Mo Se Mo Sc Me Se 14°S.M°25 20 fie./714:;' 25 0 -.....,

, • -.*--;-:-• 40 • 2$ 30 1.fe : t:r o t 1 ..... 2110 30 • ••• 25 30 '''' _ _ 19 3° --1.-- 41

,

.612_12.1), 95 _ S... t" ••i 35 50 1.1, .;

39 40 ..--* ', - ., e ,

- -.1. 2 -., /

0 : O

1 0

- tin 2.4

2 0---- ------ -------

Organic-rich topsoil.

Organic manly clay, Marl. Some organic tl root remnants and gastropod shells. 1,, • alack,semi-dec ornp peat soil.

'•-•

•-1; t Weathered drift with

Drift gravel and boutder-clay. some organic matter Predom.lirriest. some CLSh. frogs.

WEST - EAST VERTICAL SECTION ACROSS EAST MARGIN OF FLYNN'S TOXIC FIELD.

Showing Variation of Metal Content of Ground Water and Soil between Moderately Drained Drift and Peaty-Swamp Area with Impeded Drainage.

Boulder bed.

0

188

metals in the lower peaty horizons, values are not appreciably

greater than normal background levels.

Table 33: Distribution of Molybdenum and Selenium in Peaty-Swamp Profiles from a Background Area (BP 109)

Sample Depth No. (ins)

Horizon Description Mo Se

(ppm) (ppm)

4174 0-8 Dark grey-brown peaty, silty gley <2 1.5 4175 8-24 Dark brown to black peaty 6 1.3 4176 24-31 Dark brown to black peat 4 3.0 4177 31-54 Fine, grey-green clay <2 1.0

Peaty-Swamp Profiles from the Anomalous Flynn's Farm Area

A typical profile (BP 6) from toxic site A (refer

Fig. 39 for complete section) shows the following vertical distri-

bution of metal (Table 34).

This profile is similar to typical seleniferous soil

profiles described by the Agricultural Institute from the same

area. The neutral to alkaline nature of the soils is attributed

to alkaline waters draining the surrounding calcareous drift.

Both Mo and Se are enriched in the peaty horizons and

there is a marked increase in the proportion of Mo towards the

base of the peat and in the clay horizon. However, in the topsoil,

marl, upper peat horizons, Se and Mo contents are about equal.

The drift sampled from the bottom of the profile a6mpared with

Table 34: Profile (BP 6) and Distribution of Molybdenum and Selenium in Peaty-Swamp De-cc:telt, Flynn's Farm Area

Sample Depth No. (ins) Profile Description

pH Mo Se Organic HC1-(ppm) (ppm) Carbon Soluble

Fe (%)

2150 2151 2152 2153 2154 2155 2156

BP 6 (Ref. Fig. 39)

Dark brown, organic rich, silty clay loam Black, peaty silty gleyed loam Dark brown-black peaty loam Black, crumbly, peaty loam Dark grey-green silty organic-rich clay Light cream sandy marl Dark grey gravel drift. Predominantly limestone with some black shale. Some alteration by overlying deposits, some marl.

7.01 6.74 6.67 6.53 4.3 7.55 7.8

50 150 150 600 700 40 30

48 7.9 1.9 228 11.8 2.4 200 19.1 2.8 190 19.0 3.0 150 11.6 3.0 45 2.6 1.1 15 1.8 0.9

0-7 7-11 11-15 15-21 21-28 28-31 31-42

BP 7 (Ref. Fig. 34)

2272 0-6 Dark brown peaty gley 6.35 360 250 2273 6-12 Dark brown-black peaty gley 5.80 800 250 2274 12-18 Black, sticky, peaty material 3.25 1100 360 2275 18-25 Black, sticky, peaty material 4.82 2000 490 2276 25-36 Green-grey and cream sandy clays marly 6.69 7o 175 2277 36-49 Cream, sandy marl 7.15 7o 125 2278 49-54 Drift gravel and clay with black shale and 7.33 4o 56

limestone pebbles

Table 34 (continua-1)

Sample Depth No. (ins)

Profile Description pH No Se Organic HC1-(ppm) (ppm) Carbon Soluble

Fe (%)

BP 13

2332 0-4 Dark brown peaty gley loam 5.5 46 18 20.3 2333 4-10 Dark brown loamy peat 100 39 - 2334 10-18 Medium brown peat - 400 114 - 2335 18-24 Dark brown to black peat - 400 96 21.7 2336 24-36 Dark brown to black peat 460 84 2337 36-42 Dark brown to black peat - 460 175 - 2338 42-48 Grey, sandy, limestone gravel drift, some 20 90 -

peaty mud

191

adjacent fresh drift (Fig. 39) shows evidence of alteration, with

the introduction of organic matter, Mo and Se. Size analysis of

this sample (No. 2156, Fig. 35) showed a concentration of Mo and

Se in the silt-clay fraction and a close correlation of metal

contents with Fe and organic carbon. Throughout the profile there

is a general trend for both metals to follow acid-soluble iron and

organic carbon content. Se shows a greater affinity for the organic

marl horizons than Mo.

A profile from the south side of the peaty area (BP 7,

Fig. 34) shows a similar metal pattern to BP 6, but the peak values

are much higher, up to 2000 ppm Mo and 490 ppm Se.

Profiles adjoining BP 7 (Fig. 34) and BP 6 (Fig. 39) also

demonstrate an accumulation of metal in the peaty horizons and

confirmatory profiles from the northernmost peaty swamp area showed

a similar relationship (Fig. 19a). In this swamp there is no develop-

ment of marl or clay horizons underlying the peat which rests

directly on drift. A representative profile (BP 13) is shown in

Table 34.

With regard to other elements, Table 35 records their

distribution in the typical swamp profiles BP 6, BP 7 and BP 103

(Figs. 34 and 39).. Compared to the metal content of the underlying

drift, only Cu, Ni, Co and possibly V and Fe follow Mo and Se in

being consistently present in high concentrations in the peaty and

organic-rich clay horizons. Pb, Ga, Zn and Mn are enriched in

these horizons in only one or two of the profiles, and Ti, Ag

and Cr have no apparent affinity for the organic peaty material.

Table 35: General Metal Content of Peaty-Swamp Soils - Flynn's Farm Se Toxic Field

Horizon Depth (ins)

Mo Se Pb Ga V Cu Zn

(Parts per million)

Ti Ni Co Mn Cr Fe203

(%)

BP 6 Toxic Soil Site A (Ref. Fig. 39)

1 Topsoil gley 0-7 50 48 85 8 3O0 16o <5o 4000 6o 20 600 85 6 1 i, .1 7-11 150 228 60 8 400 300 u 4000 16o 3o 85o loo lo Peaty gley 11-15 150 200 30 4 1000 300 " 4000 300 20 600 130 30?

n n 15-21 600 190 30 3 1300 160 " 3000 300 20 400 85 >357. Organic clay 21-28 700 140 40 10 400 130 " 8500 200 50 160 130 16 Marl , 28-31 40 45 6 2 85 60 " 600 10 5 200 20 1.6 Drift 31-42 30 15 13 3 130 30 " 3000 60 13 100 60 1.6

BP 7 South side of Flynn's toxic field (Ref. Fig. 34)

Topsoil gley 0-6 360 250 35 3 360 150 90 2700 450 55 350 55 >35? II II 6-12 800 250 15 3 320 130 80 1600 48o 5o 16o 50 >35?

Peaty gley 12-18 1100 360 3 7 300 90 60 700 4000 600 100 30 >35? ,/ ft 18-25 2000 490 1 20 250 20 <50 180 5000 1500 loo 8o >35?

Organic clay 25-36 70 175 2 3 60 10 IT 50 600 60 85 5 3.0 Marl 36-49 70 125 4 3 60 6 " 300 500 60 130 8 2.0 Drift 49-54 4o 56 13 3 60 10 " 2000 130 30 400 6o 1.3

BP 103 (Ref. Fig. 34)

Topsoil gley 0-6 150 55 30 10 130 160 100 3000 300 85 300 60 2.0 Peaty gley 6-23 1500 200 10 4 4o 200 <50 850 N.D. 85 130 50 6.o Drift 23-50 100 38 10 2 30 50 <50 850 100 30 200 50 0.8

Ag not detectable, i.e. less than 0.2 ppm

193

V, although enriched in the peaty horizons, does not accumulate in

significant amounts in the clayey and organic marl material.

Topsoil development is marked by a general decrease in

the Mo and Se content compared with the lower peat horizons. The

decrease is much more marked in the case of Mo than Se. Under the

conditions of peat-swamp formation followed by soil-formation,

possibly involving freer drainage in the upper horizons, it is

evident that the conditions giving rise to retention of Mo have

favoured the lower peat horizons whereas Se is retained in much

more even amounts throughout the profiles.

The relationship between topsoil and the underlying

peaty horizons differs between the two major profiles, BP 6 and

BP 7, for many of the other elements (refer Table 35). Pb is

enriched in the topsoil of both profiles but other metals, in

particular Ga, V, Cu, Ti, Zn, Co, Mn show consistant variations

related to soil horizon.

(b) Lateral Metal Distribution Patterns in the Peaty-Swamps and Adjacent Overburden

At the margins of the swamp deposits, variations in the

soil composition largely reflect the drainage conditions under which

the soils have developed. Thus, the contents of Mo and Se (refer

Figs. 34 and 39) are lowest in the better drained soils near the

margins and reach their highest concentrations in the poorly drained

organic-rich horizons in the swamp area itself. The peaty-swamp

soils of BP 7 and adjacent profiles contain in general higher

194

concentrations of Mo and Se than profiles in the section containing

BP 6 (Fig. 39). This reflects the metal content of the overburden

flanking the swamp at these points. The slopes adjacent to BP 7

consist of dominantly Clare Shale colluvium and drift whereas the

drift near the section containing BP 6 is composed largely of

limestone material. From this it appears that local variations

in the Mo and Se content of the swamp soils will largely depend

not only on soil horizon but also on the composition of the flanking

soils and rock type.

In the north-east corner of Flynn's toxic field (Fig. 39)

the peaty-swamp soils are flanked by limestone drift containing less

than 2 ppm Mo and 0.5 to 0.8 ppm Se in the unweathered drift and

10 ppm Mo and 6 ppm Se in the topsoil. The increase in Mo and Se

values in the swamp soils is closely related to the extent of the

peaty horizons and drainage as reflected by the depth of the water

table. Near the edge of the deposit peaty material has developed

directly on top of the drift and moderately high metal values are

present in this horizon over a width of about 100 ft. Where the

swamp deposits proper commence with marly and organic-rich clays

intercalated between drift and peat, the metal levels rise rapidly

in the peaty horizons and the poorer drainage conditions are

reflected in the rise of the groundwater level to within about

one foot of the surface. It is apparent that the rise in metal

levels is most noticeable in the lower peat horizons but in the

upper peat horizons and topsoil above the water table level,

195

enrichment by a factor of about two times is involved. It can

be seen from Fig. 39 that the rise in metal level of the soils of

the marginal slopes to the swamp is marked by an abrupt drop in

the Eh and pH of groundwaters and general rise in the Mo and Se

content of groundwater.

Metal patterns on the south margin of the swamp deposit

(Fig. 54) are somewhat more complex because of the high concentra-

tions of Mo and Se present in the adjacent limestone and Clare

Shale overburden. In the topsoil horizon the Mo and Se levels

rise very rapidly over less than 40 ft. at the transition from

moderately drained gley mineral loams in profile BP 102 (30 ppm

Mo and 9.5 ppm Se) to the peaty gleys of profile BP 101 (160 ppm

Mo and 90 ppm Se).

In the sub-surface horizons upslope, the high concentra-

tions of Mo and Se in the basal horizons of profiles BP 8 and 50)

which were briefly described in the section on colluvium A has been

largely attributed to the high metal content of the adjacent Clare

Shale bedrock. Clare Shale detritus, along with limestone material

derived from drift, forms a high proportion of the soils developed.

The lower metal content of the upper horizons is believed to be

due to the leaching of Mo and Se, indicated by the relatively high

concentrations of Se (7.0 ppb) and to a lesser extent Mo (8.1 ppb)

in groundwater from BP 50. The high metal content of these waters

compared with the lower concentration in similarly drained drift

soils from the section shown in Fig. 39 is believed to be a

dominant factor controlling the higher concentrations of Mo and

196

Se in the adjacent peaty deposits downelope shown in Fig. 34.

In view of the fact that the lower soil horizon intersected by

profile BP 102 in drift boulder clay between the colluvial and

swamp deposits shown in the section, contains only low to moderate

concentrations of Mo and Se (16 and 1.5 ppm, respectively), it is

unlikely that large scale mechanical movement of metal from up-

slope is involved. The relatively high concentrations of Mo and

Se in altered drift immediately underlying the swamp deposits in

this section (in BP 7, 100, 103 and 101) is therefore attributed

to the precipitation of Mo and Se from solution following seepage

from upslope. Adsorption on organic matter in this horizon is

considered the most likely mechanism for metal retention because

of the very low Fe content of the drift underlying the peat (0.8%

Fe203 in BP 103 and 0.6% in BP 101).

With regard to other metals a comparison j.s made

between the metal contents of profile BP 102, situated just

upslope from the border of the peaty swamp shown in the section

in Fig. 34 and profile BP 101, in peaty material about 30 ft from

BP 102 (refer Table 36). Overall, the peaty profile contains)

besides high Mo and Se contents, slightly higher levels of V, Cu,

Zn, Ni, Co, Mn and Fe. Values for Pb, Ga, Ag and Cr are much

the same in both profiles and Ti is deficient in the peaty phase.

Analysis of profile BP 6 (Table 35) and profile BP 95 from the

same section gave generally similar results, although the degree

of enrichment in the more peaty profile (BP 6) was somewhat

greater. It is believed that this is at least in part related

Table 36: Comparison of the Metal Content of Peaty and Non-Peaty Soils on the Margin of Peat Swamp Deposits (Ref. section, Fig. 34)

BP 101 (Peaty) BP 102 (Non-peaty) Metal (PPm) Topsoil

0-6 ins Peat 6-20 ins

Altered Drift 20-30 ins

Topsoil 0-6 ins

Clay Loam ft-12 ins

Drift 12-37 ins

Mo 160 130 30 30 15 16 Se 1 90 125 18 9.5 5.5 1.5 Pb ' 50 32 16 30 40 16 Ga 10 5 4 6 8 10 V 130 85 50 85 85 4o cu loo 8o 3o 6o 60 10 Zn 160 8o <50 <50 50 <50

Ti 2000 180 850 3000 3000 100 Ag 0.2 0.2 <0.2 0.2 0.2 <0.2 Ni 100 18o 6o 85 loo 5o

co D 30 35 16 20 30 20

Mn 400 18o 160 200 85 200

Cr 85 85 30 60 85 60

Fe203 1.5 1.2 0.6 0.9 0.7 o.8

Organic Carbon

% 8 20 2 3 1.5 0.5 (Estimated only)

198

to the greater Fe203 content of 10-35 per cent compared to 2 per

cent in BP 95.

(c) Accumulation of Molybdenum and Selenium in Peaty-Swamp Soils

The accumulation of metals in peat deposits is a

relatively commonly recorded phenomena (Mitchell (1954 in Scotland,

Cannon (1955) in the United States and Salmi (1950) in Sweden).

The latter two authors report excessive concentrations in swamp

areas associated with nearby base metal deposits. Lakin and Byers

(1945) describe Se-enriched lacustrine deposits possibly similar

to the basal horizons in Flynn's Farm swamp. They attribute this

enrichment to mechanical erosion and leaching of Se from adjacent

seleniferous drift. The Irish Agricultural Institute (Fleming and

Walsh, 1957), recognise the association of seleniferous soils with

metal-rich Clare Shales and correlate the metal-rich horizons with

those of highest organic status. They also attributed the source

of the metal to leaching from the surrounding drift which contains

moderate amounts of both Se and Mo. The actual process of accumu-

lation is considered by them (and by Finch and Ryan (1966)) to be

a function of the organic cycle, by uptake of metal from solution

by plants with subsequent retention in peat residues. They

consider the form of Se in the soil to be mainly inorganic

selenite (Se03') because of the much greater solubility of selenate

and organic Se compounds and also because of the low levels of

water-soluble Se from toxic soils (in the order of 0.33 to 2.9%

of total Se present.

199

The recent studies confirmed that the seleniferous peat

bogs were confined to Clare Shale areas of severely impeded drainage.

The relationship between the highest Se values and the most organic-

rich horizons was also apparent. It is also clear though, that

because of the high concentrations of both metals in the relatively

organic-poor marl, clay and altered drift horizons, factors other

than the uptake of metal by plants contribute to metal accumulation.

Also the divergence of Mo patterns from those of Se in

certain horizons indicates that other mechanisms, possibly co-

precipitation or adsorption of Mo and Se, influence secondary

dispersion in these deposits.

Firstly with regard to the source of metal in the peaty

soils; the metal-rich nature of groundwaters entering the peaty

swamp area at Flynn's Farm from the adjacent drift and Clare Shale

colluvium was confirmed by the analysis of groundwaters draining

into the swamp (Figs. 40, 34 and 39). Values of 0.6-7.0 ppb Se

and 3-27 ppb Mo compare with background values of generally less

than 0.5 ppb Mo and Se for groundwaters well away from the Clare

Shale area. It is significant that the metal content of the water

in BP 8 (8.1 ppb Mo and 7.0 ppb Se) in dominantly Clare Shale

colluvium and drift is higher than that in BP 48 (3.1 and 1.0 ppb Mo

and Se) in predominantly limestone drift. This relationship is

reflected in the metal content of the adjacent peat deposits which

is generally higher at the southern edge of the deposit than in the

north-east section. It is also apparent from the above plans and

sections that the metal content of groundwaters from within the

•

o SPRINGS AND SEEPAGES.

• o 5

• • • •

"M. 1r.

•

1t,

—

100 200

20 11 • • •

•

FEET

2.5 NORTH CK.CATCHMENT AREA.(Ref.rtg.No. 52. )

3.-

4.1 69

1.6 01.25

7.5 is\ 8.75 3.1 \IV 1•5 e e 5.4

121 re

• SIO •, • • t6.25

• • ...225 •

•-•.‘ 1

1 e?

t''' e

\.„ ?•-• 2.5

•••

▪ ••• ▪ ow*

• 'L .4"

BP 50 ® 7 Section tine.

\ir-q•e..... Re f.Fig.No. 34. FIG.No. 40.

FLYNN'S FARM, PEATY-SWAMP AREA

Mo and Se CONTENT OF GROUND and STREAM WATERS.

2-1

100 4 •••

•

400 El" 7-1

1000 14 mat 38

N

• maw Or.

110 BP.6.

2.6 I

1

4.5 56

40 14

a. 66

em. •

2 5 Mo ppb Section-Ref.Fig.No. 39, 6 Se ppb

17 t

I A PEATY SWAMP 31 37.5 1

DRAINAGE 1 CHANNELS: 1 Well

CI AUGER HOLES.

200

swamp is considerably higher (up to1000 ppb Mo and Z4ppb Se)

than that of the waters draining into it. The groundwater Mo and

Se contents can be correlated with the metal content of the soil,

as described in greater detail in Chapter IX. From this it must

be assumed that changes in the swamp environment are taking place

and involve either concentration of the amount of Se and Mo in

solution by surface evaporation or re-solution of metal previously

accumulated in the swamp deposits.

In view of the climate, which does not favour evapora-

tion, and the substantial water flow in the streams and from

springs carrying high concentrations of Mo and Se (Fig. 4o), re-

solution is favoured. A third possibility is that deep ground-

waters beyond the range of sampling are introducing very high

concentrations of metal from underneath into the swamps. However,

this is discounted because of the close relationship between the

Mo and Se content of waters and the soils at the margins of the

swamps.

Having earlier discounted a mechanical origin for the

high Mo and Se concentrations in the swamp deposits because of the

generally low metal contents of much of the adjacent drift and

established that moderate concentrations of metal enter the swamp

by near-surface drainage from the surrounding catchment area, the

four main possibilities by which Mo and Se may accumulate in the

peat s and organic marly clay sediments of the swamp are:- (i)

direct precipitation of metal, (ii) co-precipitation with iron

oxides, (iii) adsorption on dead organic matter, and (iv) uptake

201

of Mo and Se by vegetation growing in the swamp followed by

retention of these metals in the peat. A fifth possibility

related to Mo accumulation, is that of sorption of molybdate ions

on clay minerals, which has been shown by Jones (1957) to take

place at pH 2 to 4, is discounted firstly, because of the high

pH of the waters tested (6.7-7.2) and secondly the calcareous and

organic, rather than clayey nature of the deposits.

Dealing firstly with the possibilities of direct

precipitation of Se and Mo compounds (i) due to changes in the

pH and redox environment, it can be seen from the data on the pH

of the groundwaters shown in the sections, Figs. 34 and 39 and in

Fig. 42 that there is little or no significant changes in pH.

This is attributed to the buffering action of the high HCO3

content of groundwaters from the ubiquious limestone drift

(347 to 521 mg/litre HCO3). With the exception of weathering

Clare Shale material, all natural waters in the area (refer

Chapter IX) contain similar concentrations.

With regard to Mo, reference to the stability fields

of the more common natural ionic forms (Fig. 41) indicates that

soluble Mo is most probably present as molybdate (Mo0147). At the

pH of groundwaters in the section shown in Figs. 39 and 42

(6.7 to 7.2) work by Jones (1957), on the precipitation of ferric

molybdate, the most likely precipitate to form under these condi-

tions, shows that the Mo content of the waters (3 to 110 ppb Mo)

is well below the saturation level of this compound at this pH

-04 Mo Fe

+ ye.

1.4 Normal range of surface

condit ions.

Temp. = 25°C

Press. 2 1 atmos.

Conc. 10 -7M.

1.2

1.0

0.8

Se 04'

0.6

4, 0.4

0 S. '

S 4 eo

0.2

Se

0*,

-0.2

Mo+"

Fe

-06

•—•••

se,

%.1

0 2 4 6 6 10 12 pH

FIG. No. 41. STABILITY FIELDS OF SOME IONIC

SPECIES OF Mo, Se and Fe.

(after Krauskopf 1955.)

—ye.

Se \ I •

•98 •

11006

6° /23' 7 9',

e

•

H2Mo04 •

0

4-- pH range normal surface conditions

+0.6

+0.5

•

+0.4

Weathering CI.Sh.

106 • Se 04=

-a 0 Sca

197•:93`‘'l •

\9496.95;\

• 4902

+0.1

0.0 2 4 6

8

10 pH

• Flynn's Farm Peaty Swamp. ° Alluvium-Toxic Site B

Numbers refer to profile sites -Ref. sections Fig.Nos.34,39.

F1G.No. 42. pH-Eh STATUS OF GROUND WATERS

With Reference to Stability Fields of Se,Mo&Fe. (For complete fields refer Fig•Na 41. )

202

(refer Fig. 43, about 500 µg/ml i.e. 500,000 ppb Mo). The direct

precipitation of Mo compounds is therefore, discarded as a possible

means of accumulation in the peat-swamps.

Reference to the stability fields of Se (Fig. 41) and

the pH conditions of the groundwaters (Figs. 34, 39 and 42), shows

that over the narrow range of pH prevailing, no change is likely

in the ionic state of the Se in solution. The commonly occurring

Fe, Se compound, basic ferric selenite as described by Williams

and Byers (1936), is extremely insoluble but as is also shown in

Fig. 42/any increase in the acidity of waters would encourage the

presence of iron in the relatively soluble ferrous (Fe++) state.

The Eh of groundwaters, which is shown to drop by

almost 0.2 V between the more freely drained overburden and the

peaty-swamps (Figs. 34, 39 and 42), may appreciably affect the

ionic state of Se but not of Mo, within the range of normal surface

conditions (Fig. 41). Selenates are accepted to be readily soluble

but only exist under relatively oxidising alkaline conditions.

Selenites formed under less oxidising acid conditions are only

slightly soluble and readily precipitate mainly by reaction with

ferric iron to form the basic ferric selenite. It can be seen

from Fig. 42 that the Eh of the groundwaters from drift soils

falls close to the equilibrium boundary between selenite and

soluble selenate. The drop in Eh of groundwaters on entering

the swamp brings the redox environment farther within the stability

field of the much less soluble selenite ion and may therefore result

in the reduction of selenate to selenite.

+1

. / C

/ /

1

500

400

E

300

C

200 C

0

100

2

4

6

8

10 pH

SOLUBILITY OF FERRIC MOLYBDATE AT VARYING pH.

(Adapted from Jones 1957)

F1G.No. 43.

203

It is considered that while direct precipitation of

some Se compounds may take place it is hardly likely that this

constitutes the principal mechanism by which metal accumulates

in the swamps. Also it has been pointed out on the previous

page that Mo,which follows a generally similar pattern of

dispersion to Se, would not be affected by the pH-Eh changes pre-

vailing.

With regard to the co4precipitation with iron oxides

(ii), iron has been shown to be closely associated with the

retention of Mo and Se in some of the residual soils of the area,

most probably by sorption or co-precipitation. The accumulation

of theSe elements by iron oxides has also been described by other

workers, amongst them Williams and Byers (1936) for Se and Jones

(1957) for Mo. There is a certain degree of correlation between

the Mo and Se contents of the swamp soils and the iron content of

the profile (Table 35) but this correlation is also paralleled by

the organic carbon distribution. The occurrence of very high

total Fe203 contents in profiles BP 6 and 7 is not consistent

for all peaty profiles from the Flynn's peaty-swamp. The peaty

horizons from profiles BP 101 and BP 103 (refer Fig. 34) do not

contain excessively high amounts of iron (1.2 and 6.0% respectively)

although they are of similar appearance to the equivalent horizons

in BP 7 and contain high Mo and Se values (130 ppm Mo, 125 ppm Se

and 1500 ppm Mo and 200 ppm Se respectively).

The overall correlation between Mo, Se and Fe is, if

anything, more marked between Mo than Se specifically, particularly

201+

if the lower marly-clay and altered drift horizons of BP 6 are

considered. This is, in general, in line with data from other

soil types and in stream sediments.

The reducing, more acid environment of a peaty-swamp

at the time of formation should tend to favour the mobilization

of iron in the more soluble ferrous form. For this reason, it is

considered that the concentration of iron in certain horizons may

largely be due to post-depositional processes that have taken

place subsequent to initial Mo and Se concentration in the swamp.

However, re-distribution of iron has quite possibly modified the

Mo and Se patterns. Efimov (1962), working on transitional peat

bogs in the Leningrad area, attributed the concentration of iron

in certain lower horizons to the reaction between an aerated upper

peaty zone and reducing basal zones. Iron present in groundwaters

in the basal horizons rises by capillary action in the profile

during the summer months until, on reaching the upper aerated zone,

oxidation to the insoluble ferric form takes place with subsequent

precipitation and concentration. It is believed that such a process

may in part at least explain the distribution of iron in the peaty

profile BP 6, for example. It may of course involve the co-

precipitation of Mo and Se from solution but would not affect metal

already present in the profile sorbed, for example, on organic

matter. The low iron values in profiles BP 101 and 103 (Fig. 34)

at the shallow margins of the peaty swamp may indicate that re-

distribution of iron by this means only takes place in the deeper

205

parts of the swamp as in BP 6 and 7. Evidence has already been

presented of a similar process influencing the Mo patterns in

alluvial deposits (p. 182).

A major feature of the peaty-swamps is their high

organic matter status (Table 35, BP 6) which can also be correlated

with distribution of Mo and Se in profile. Studies of the marly

alluvial deposits indicated that Se was concentrated by sorption

on organic matter and that, except in the topsoil horizons, iron

did not enter into the process of metal retention. Later drainage

studies (Chapter IX) have confirmed the sorption of Se by organic

matter. In view of the close correlation between Se and organic

matter in the peaty deposits it is considered most probable that

sorption of Se from groundwaters entering the swamps is a major

factor in the retention of this element. With regard to Mo it

is difficult to define the relative influence of sorption on

organic carbon in relation to the effect of co-precipitation or

sorption on the secondary iron oxides. However, it is believed

that the presence of high concentrations of Mo and Se in ground-

waters from the swamp may be an indication of the relationship

between metal and organic matter. This is because cultivation

of these areas, which has involved drainage and subsequent aeration

of the surface horizons, has contributed to the weathering of these

soils. Breakdown of organic matter in the upper horizons with

consequent release of metal would be a ready contributor of Mo

and Se in a soluble form to near-surface groundwaters. This would

explain the apparent contradiction of high metal concentrations in

206

the present-day groundwater in the swamps and the proposal that

the swamp soils originally obtained their metal content by sorbtion

from groundwaters entering it from solution. Metal held on iron

oxides would not seem to be so readily released.

An alternative method by which organic matter may have

contributed to the accumulation of Mo and Se in these deposits is

by the uptake of metal by growing plants followed by retention in

the peat formed from this vegetation. This is the method suggested

by Fleming and Walsh (1957) who had noted the generally similar

levels of Se in the herbage and the supporting soil (Chapter VIII).

However, the writer does not consider that such a process will

adequately explain the accumulation of metal for the following

reasons:-

(a) the high concentrations of both Mo and Se

associated with some of the non-peaty basal marl, clay and under-

lying drift horizons;

(b) the divergence of Mo and Se in certain adjacent

horizons (cf. the horizons at 11-15 and 15-21 ins, BP 6, Table 35)

because it is not considered likely that the relative uptake rates

of the two elements in plants would differ so greatly;

(c) studies of metal uptake by plants in the following

Chapter VIII show that the concentration of Mo and Se in plants is