AECL-6439 ATOMIC ENERGY A A L'ÉNERGIE ATOMIQUE OF CANADA LIMITED fSjP DUCANADA LIMITÉE A GEOLOGICAL RECONNAISSANCE STUDY OF M LAC DU BONNET BATHOLITH LEVE DERECONNAISSANCE GEOLOGIQUE DU BATHOLITE DU LAC DU BONNET H. Y. Tammemagi, P. S. Kerford, J. C. Requeima and C. A. Temple Whiteshell Nuclear Research Etablissement de Recherches Establishment Nucléaire? de Whiteshefl Pinawa, Manitoba ROE 1LO February 1980 février
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AECL-6439
ATOMIC ENERGY A A L'ÉNERGIE ATOMIQUEOF CANADA LIMITED f S j P DU CANADA LIMITÉE
A GEOLOGICAL RECONNAISSANCE STUDY OF M LAC DU BONNET BATHOLITH
LEVE DE RECONNAISSANCE GEOLOGIQUE DU BATHOLITE DU LAC DU BONNET
H. Y. Tammemagi, P. S. Kerford, J. C. Requeima and C. A. Temple
Whiteshell Nuclear Research Etablissement de RecherchesEstablishment Nucléaire? de Whiteshefl
Pinawa, Manitoba ROE 1LOFebruary 1980 février
ATOMIC ENERGY OF CANADA LIMITED
A GEOLOGICAL RECONNAISSANCE STUDY OF THE LAC DU BONNET BATHOLITH
As the contact of the batholitli is approached, the <?rey gneiss
becomes more heavily Intruded by pegmatitles and grades into
a more felsic rock, showing bands of orangy-red feldspar and
black biotltes, which giva it a migmatitic appearance. It is
our belief that this gradation from grey gneiss to migmatite
along the contact of the batholith was due to metasoznatic
fluids derived from the batholith.
3. Great Falls Quarts Diorite
The Great Falls quartz diorite Is a large, medium-grained,
black and white speckled pluton found to the north of the Lac
du Bonnet batholith. From field relations, the Great Falls
intrusive Is considered earlier than the batholith since the
LUC du Bonnet batholith contains inclusions of the quarcz-rich
diorite rock.
Plagioclase is the major feldspar forming up to 60% of the
rock while quartz (25%) and biotite (15%) are the lesser com-
ponents. In outcrop only a slight foliation exists.
4.3 MICROSCOPIC DEFORMATIONAL FEATURES
A study of the microscopic deformational features of the Lac
du Bonnet batholith and some of the country rocks showed that the batho-
lith has undergone the least amount of deformation of the units in the
area. The metasediments and the gneissic units have been subjected to
metamorphism, as recrystallization and crushing were evident in all thin
sections.
Fifteen thin sections of LDB granite were inspected and their
cataclastic features recorded- They were divided into three groups,
based upon the amount of deformation, on the following basis:
- 12 -
1. Deformed
a. Quartz grains exhibiting undulose extinction and deforma-
tion bands
b. Finer crushed grains or microbieccia
c. Quartz grains showing a mosaic textu/e with interfacial
angles of about 120°
d. Kinking in the biotlte crystals
e. Small biotlte crystals, and finely crushed material
occasionally wrapped around larger crystals - giving an
augen-type texture
f. Plagioclase crystals fractured across their lamellae and
often bent.
2. Moderately Deformed
a. Quartz exhibiting undulose extinction
b. Quartz forming defcrmational bands
c. Quartz grains showing a mosaic texture with interfacial
angles of about 120° and some crushing.
3. Minor Deformation
a. Quartz exhibiting undulose extinction
b. Quartz forming deformational bands.
The locations of the three groups of deformation are shown in
Figure 7. The parts of the batholith that are deformed most are local-
ized at the borders. This type of localization, according to Moor-(22)house , is often indicative of a protoclastic origin whereby the
intrusive is still in movement after the granite has partially or wholly
solidified causing a crushing of the finer crystals. In the central
part of the batholith a slight decrease in the amount of deformation is
- 13 -
observed from south to north, with samples at the north showing virtu-
ally no deformation. The significance of this trend is not known.
5. STRUCTURE
5.1 FOLIATION
Rocks generally display a foliated character of two main
types: primary foliation caused by flow in the liquid or partially
liquid state and secondary foliation caused by shearing of the solidi-
fied rock.
From field and pétrographie studies of the Lac du Bonnet
batholith and surrounding regions, the following conclusions have been
derived:
1. The foliation in the batholith is of prir .— origin. This
conclusion is based on the following observations: the folia-
tion is generally parallel to the wall rock; the phenocrysts
generally show no signs of deformation or of rotation into
their preferred direction after magma solidification; and the
granite displays a normal interlocking texture of the minerals.
2. The foliation in the couuLry rock is of secondary origin.
This is displayed by an abundant amount of cataclastic deform-
ation in crushing, by the reorientation of crystals and by the
recrystallization of minerals.
The orientation o£ foliations measured in at;d around the bath-
olith is displayed in Figure 8. The near vertical and steeply dipping
foliation in the granite indicate that the batholith probably has near
vertical or slightly outward dipping boundaries and is not a shallow
dipping sheet to the north as postulated by McRltchie .
- 14 -
5.2 JOINT FRACTURE SETS
5.2.1 General
Measurements and observations of the fracture or joint systems
were made at 73 slues, as described in section 3, by laying two perpen-
dicular measuring tapes across the outcrop. All fractures which inter-
sected the measuring line were recorded.
The object of these observations was to record quantitative
descriptive data on fractures which could assist in developing an under-
standing of groundwater flow in fractured crystalline rock. Some of the
parameters which need to be determined are: orientation, length, frac-
fre termination, connectivity (i.e., how is one fracture connected to
another and how continuous is the fracture itself), spacing and sheeting.
The major difficulty in obtaining the required data is that,
aside fiom orientation measurements, very little work has been done pre-
viously in this area. Thus, there is no commonly accepted terminology
nor standard field technique. In addition exposures of bedrock are gen-
erally not sufficient in areal extent to obtain data on fracture lengths.
It is difficult to classify joints because of their great variability in
shape and character, which is further complicated by near-surface weath-
ering effects such as exfoliation.
Large areas of outcrop are very scarce and thus it was diffi-
cult to assess quantitatively the length of the fractures. In general
they are a metre to several tens of metres in length and are vertical to
subvertical in dip.
Fractures in the batholith terminate in a variety of ways.
Many of them end in other fractures while others die out in bare rock.
Some fractures bifurcate into two separate fractures which usually end
in bare rock while others splay off into several small cracks.
- 15 -
Sheeting is evident throughout the batholith as irregular wavy
fractures. Many large, flat outcrops appear to be sheet fracture sur-
faces.
When analyzing the ler.gths of fractures, two groups were used:
1. Fractures with known lengths
2. Fractures with unknown lengths, where one or both ends of a ,•
fracture are covered by overburden, yielding only a minimum /
length.
Average length of fractures with known lengths is 6.2 metres
while the average length for fractures with unknown length- is greater
than 15.2 metres. A histogram (Figure 9) of the length of fractures
versus the number of fractures clearly shows that as the length of frac-
tures increases the number of fractures recorded decreases. Since out-
crops %rere seldom larger than a few tens of metres in dimension, a large
proportion of the fractures had unknown lengths due to their termination
under overburden.
The strikes of fractures were recorded and displayed on indi-
vidual Rose diagrams for each site. The orientations of the fracture
sets do not show any major trends related to the shape of the pluton.
The strikes of all fractures in the batholith were then combined on a
single Rose diagram (Figure 10). Two main sets of fractures exist in
the batholith: a NE.-SW. striking set and another which strikes NW.-SE.
These main fracture sets were compared with a Rose diagram for the frac-
tures of the country rocks (Figure 10) and regional fracture maps by
McRitchie^ ' and Grisak et al.' K The orientations of the fractures
in the country rock, although exhibiting more variation and an additional
N.-S. set, are similar to those recorded in the batholith. The main
fracture set orientations were compared to the foliation orientations
recorded at several sites throughout the batholith. The data clearly
- 16 -
Indicated that the major fracture sets do not parallel the foliation
directions at any ot the sites. Therefore it is concluded that the
fracture patterns in the pluton probably reflect the action of regional
stresses and are not related to the foliation formed by the emplacement
of magma.
The SW.-NE. trending fracture set has an average spacing of
3.2 metres/fracture while the NW.-SE. striking fracture set has an
average spacing of 2.8 metres/fracture. Average spacing at specific
sites ranges from 1 to 10 metres/fracture.
The orientation of pegmatite dikes in the pluton is shown su-
perimposed on the Rose diagram of Figure 10. A definite NE.-SW. trend
is apparent. This coincides with the orientation of one of the fracture
sets. It is concluded that the NE.-SU. striking fractures were the ear-
liest fractures to have formed In the batholith.
The results of this section (and the next one) are preliminary
in nature and more work needs to be done in this area. In addition to
standardizing field techniques and terminology, the observations need to
be described in a more rigorous quantitative fashion. Because of the
inherent variability in fracture data, a statistical approach to frac-
ture description seems warranted.
5.2.2 Old Pinawa Dam Site
At Old Pinawa, an abandoned dam site (site 15 on Figure 4),
the exposure of outcrop is far superior to that found elsewhere in the
batholith. For this reason a more detailed fracture study was carried
out at this site. Figure 8 shows the position of Old Pinawa with re-
spect to the batholith. Two study sites were chosen: study site A
which exhibited a greater fracture density than average and site B which
showed only very light fracturing. A and B are located about 150 m from
each other.
- 17 -
For this phase of the study, a more detailed fracture mapping
method was devised which allowed large fractures to be described in
terms of their component fractures (Figure 11). It was felt that the
new mapping procedure would record the maximum joint information. The
component fractures, which show offsets of a few centimetres up ci> a
quarter of a metre, often are not connected to each other at the sur-
face. To what degree the fracture components are connected to each
other at depth is unknown. Long joints that are composed of a number of
offBet components are ubiquitous throughout the batholith. This obser-
vation is important fcr hydrogeological studies since potential ground-
water flow along such fractures could be seriously restricted by the
offsets.
The strikes of all fractures recorded at Old Pinawa are dis-
played on a Rot.o diagram in Figure 10c. The diagram shows three main
sets: a NE.-SW. set (Set 1), a NW.-SE. set (Set 2), and a NNW.-SSE.
set (Set 3). The first two sets are typical of the batholith, but the
third set is not.
Table 2 represents the fracture data collected from study
sites A and B. It is evident that the fracture density varies consid-
erably over very short distances within the pluton.
Figure 12 again illustrates a decrease in the number of frac-
tures as the fracture length Increases. A Rose diagram of the pegmatite
dikes at the Old Finawa dan site shows a definite NE.-SW. trend, which
is similar to the trend of the Set 1 fractures, as seen In Figure 10c.
5.2.3 Discussion
Although there is some inherent variability in the fractures
observed in outcrop on the bathclith, it appears th: - Fractures occur in
sets which can be characterized by orientation and spacing. Individual
joints appear often to be composed of components which are slightly off-
- 18 -
set from each other. Long fractures are less frequent than short ones.
There can be great variability in fracture density even over distances
as small as a few hundred metres. It is concluded that far more re-
search is required In this area of structural geology.
5.3 LINEAMENT STUDIES
Field study of major fracture zones or faults is intrinsically
difficult since such features are generally more eroded than the sur-
roundings, yielding vegetated valleys or forming depressions for rivers
and lakes. However, two large lineaments, visible on an aerial photo-
graph, were visited and inspected. In the field the lineaments are de-
pressions or valleys between two elongated hills. The edges of the
hills are straight and usually sub-vertical and their orientations are
the same as the major joint sets of the hill. No shearing or major
fracture zones are observed on either Hide of the depression. Therefore
the lineaments probably formed as the result of weathering on joint
sets, which may have been locally more closely spaced than average.
An area about 6.5 km by 6.5 km, termed LDB-1, (see Figure 8)
was chosen for analysis of lineament orientations. Figure 13 shews the
lineaments of the study area as well as some north-south and east-west
sampling lines. Wherever a sampling line crossed a lineament, its ori-
entation was recorded. A total of 119 lineament orientations were re-
corded and plotted on a Rose Diagram in Figure lOd where three sets are
seen: NE., N.-S. and SE. When this diagram is compared to Rose dia-
grams of fractures (Figures 10a and c) a definite correlation can be
seen. The NE.-SW. and the NW.-SE. liniment sets are similar in orien-
tation to the major joint sets in the batholith. Although the north-
south set of lineaments does not correlate with any major fracture set
in the batholith (Figure 10a), it does correlate with the third set
found at Old Pinawa as well as with fracture sets recorded at various
individual sites around the batholith. Therefore it is possible that
these lineaments are large-scale erosion features of joint sets which
- 19 -
may locally be quite closely spaced. An interesting feature is thai the
NE.-SW. lineament set is parallel to the trend of the Winnipeg River and
Pinawa Channel.
Two areas, LDB-1 and LDB-2, o-ich about 6.5 x 6.5 km f.soe Fig-
ure 8 ) , were chosen for lineament analysis similar to that performed by
Brown and Thivietge , so that the LDB batholith could be compared to
plutons in Ontario being categorized by the Geological Survey of Canada.
They tabulated data for 317 plutons on the basis of size, outcrop, major
lineament density and total lineament density, and selected the 22 which
had the most optimal structural conditions of the last three parameters,
as well as being greater than three kilometres in diameter. Measure-
ments on the LDB batholith yielded the following data:
Site % Outcrop Major lineament density Total lineament density
(mile/mile2)* (mile/mile2)*
LDB-1 35 0.53 4.43
LDB-2 12 0.60 2.73
Figure 14 shows a summary from reference 15, with the LDB-1
and LDB-2 data superimposed. LDB-1 and LDB-2 rank in the part of the
group which has better structural integrity, that is, fewer fractures.
Therefore the LCB batholith belongs to the less fractured, granitic
group of rocks as defined in the matrix of rock types to be assessed
during the concept verification phase (see section 1 ) .
British units are used so that comparison can be made to reference 15.1 mile = 1.61 km; 1 mile2 = 2.59 km 2
- 20 -
6. GEOCHEMISTRY
6.1 CHEMICAL ANALYSES
Forty-five samples were selected for chemical analyses. 1:ie
sample locations, which occur predominantly In the central portion of
the batholith, are shown in Figure 4. Although most of the samples were
of typical LDB granite, a few sampIts of pegmatites, hypabyssal phases
and country rock were included for comparative purposes.
The samples were analyzed for: SiO-, A1.0-, Fe.O , FeO, MgO,
CaO, Ua-O, K_0, TiO_, MnO, Be, Ga, Y, Pb, Sn, C, P, Ba, Rb, Sr, Cs, Li,
Tl, Th, U, Zr and Hf. The selection of those elements was based on
studies by Taylor' ' and Ewers and Scott .
The Department of Earth Sciences, University of Manitoba, the
Analytical Science Branch, WNRE, and a commercial laboratory performed
the analyses, as listed in Table 3. In most instances elemental analyses
were performed both at the University of Manitoba and at WNRE and cross-
checks were carried out by other laboratories. For the sake of consis-
tency, University of Manitoba resu'.ts have been used as far as possible
in this study. WNRE results and interlaboratory cross-checks are des-
cribed in references 26 and 27.
Abundances of the 10 major and 17 trace elements are tabulated
in Appendix A for the 45 rock samples which were analyzed. In addition,
mesonorms were determined, based on the Niggli norm calculation with
alterations by Barth for granite rocks. A computer program was
written to perform the mesonorm calculations, based on procedures out-
lined in reference 29. Average values for LDB granite were determined
from those samples considered representative of the main phase of the
batholith; see Table 4 and Appendix A.
- 21 -
6.2 COMPARISON TO OTHER GRAMITES
The average elemental abundances in LDB granite are compared
to the compositions of the standard granite and granodiorite of Taylor
in Table 4. The elemental abundances were plotted versus the differen-
tiation index of Thorton and Tuttle in Figures 15a and b. These
plots consistently show that the Lac du Bonnet camples follow the gen-
eral trend expected of a rock more differentiated than a standard grano-
diorite or granite.
The concentrations of thorium and uranium in the LDB samples
are high (Table 4 ) . This enrichment was observed by Farquharson to
be characteristic of the English River gneiss belt of which the Lac du
Bonnet btthollth is a member. The Th/ll ratio of 2.8 is lower than that
(33)of standard granite or granodiorite, or than the average value of 4.2
for the Canadian Shield -
The major elemental abundances in the LDB granite are quite
similar to those of a single phase leucogranite of Kolbe and Taylor
In summary, the major and trace element analyses indicate that
the central portion of the LDB batholith is relatively homogeneous and
forms a single phase granite which suffered more differentiation than
the standard granite of Taylor^ .
6.3 DISCUSSION
6.3.1 Ternary Plots
A ternary plot, Figure 16, of QTZ:OR:PLAG (quartz:orthoclase:
plagioclase) calculated from mesonormative mineral abundances shows that
the Lac du Bonnet samples cluster within the granite field of the IUGS
igneous classification system. The average value for QTZ:OR:PLAG is
32:29s39 and comparison to the modal analyses obtained in section 3
- 22 -
shows this same general distribution (Figure 6). Thus the Lac du
Bonnet batholith can be classified as a granite, but with a composition
lying close to the granodiorite boundary.
A Lernary plot, Figure 17, of QTZ:OR:AB (quartz:orthoclase:al-
bite) shows a close cluster of points near the centre of the ternary
triangle. Figure 17 shows that the average LDP, sample falls on the
3000-bar contour of confining pressure. This isobaric minimum is based
upon a water-saturated composition , which is compatible with the
presence of late-stage pegmatites. The uniform chemical composition,
the 3000-bar confining pressure and the presence of pegmatites suggest
that the pluton formed from a magma which solidified at a relatively
shallow depth of 10 km or less.
6.3.2 Alkalinity and Differentiation Indices
The Alkalinity Ratio of Wright(
A1.0 + CaO + Total Alkali
A12O3 + CaO - Total Alkali
is commonly used to distinguish rocks from a common source and to sepa-
rate those phases which are present.
The Lac du Bonnet rocks plot within the alkaline field as seen
in Figure 18. The various fields of the alkalinity ratio versus SiO_
diagram are representative of observed rock associations, but no trends
are observed in the LDB samples suggesting there is only one phase pre-
sent.
Another index of magmatic evolution is the Differentiation(31)
Index of Thorton and Tuttle , which is based upon the sum of the
salic mineral constituents. For the Lac du Bonnet rocks this is the sum
of normative quartz, orthoclase and albite. The index is a guide in de-
- 23 -
termining how far a magma has evolved toward its ultimate composition
and is also a useful means by which to observe variations in chemistry.
The plot of the differentiation index versus SiO, composition,
shown in Figure 19, indicates that the Lac du Bonnet rocks are over-
saturated in SiO, and that they are located within the contour interval
of the most commonly found igneous rocks.
Teng and Strong found a variation of + 8% SiO, for the
single phase Swift Current granite in Newfoundland over a change in dif-
ferentiation index of 25%. The Lac du Bonnet samples have a variation
of + 6% SiO, over 12% change in differentiation index. A similar com-
parison for barium gave a range of + 1000 ug/g for the LDB samples while(25)
the Cullen granite in a study by Ewers and Scott gave ranges from
+ 5000 to + 1000 pg/g for a single phase. This chemical evidence sup-
ports the field evidence which suggests the central portion of the
batholith is essentially single phase.
6.3.3 Areal Distribution
Areal distribution of the elements shows no distinct trends
and often wide variations are observed within a small area. Because of
pegmatitic mineralization in the Bernic Lake area just outside the
northeast boundary of the batholith, particular attention was given to
lithium, beryllium, cesium, rubidium and thallium. However, the concen-
trations of these elements are no higher than would be expected and no
trends in areal distribution can be detected. This lack of persistent
trends for even trace elements reflects the homogeneous nature of the
batholith. It must be stressed that far more sampling is required,
particularly in the eastern portion of the batholith, before definite
conclusions can be drawn.
- 24 -
6.3.4 Magma Source
The volume of magma necessary to produce a body the size jf
the Lac du Bonnet batholith suggests that genesis by differentiation
from a basic magma 1B improbable. Even if the magma had been contami-
nated by silica-containing material, the volume of basic magma would
have had to be enormous to form a batholith of this size. If it had
formed from a basic magma it would seem likely that closely associated
rock bodies or various phases would be present, which is not the case.
Therefore the granite probably originated by partial melting of pre-
existing crustal material.
(38)The peraluminous index of Chappell and White
(Na.O + K-0 + CaO)
was one of the factors they presented to distinguish between igneous or
sedimentary origin of granites. A high value of the index indicates
sedimentary origin. The average value for the LDB standard samples is
1.5, with all samples except one pegmatite having values well above 1.1,
the limit which delineates igneous and sedimentary origins. The two
pegmatite samples both show lower values because of late-stage chemical
changes, which rapidly increase K,0 while reducing Al 0 . The Lac du
Bonnet rocks are therefore considered, by this index, to have probably
formed from a magma derived from a sedimentary rock type.
The presence of more than 1% mesonomative corundum is also
considered to reflect a sedimentary origin . The average corundum
content for the LDB rocks is 2.1%, although it should be noted that* (14)
Chappell and White used a CIFW norm not a mesonorm. Other studiesindicate that the CIPW norm for LDB granite will be significantly lower
(38)than 2.1%. Chappell and White ' felt that granites of sedimentary
origin normally have x Na_O content of less than 3.2%; however the
Cross, Iddings, Firrson and Washington.
- 25 -
average Ha 0 content for the Lac du Bonnet rocks is 3.6Z. These fac-
tors, taken as a whole, are inconclusive, but suggest that a sedimentary
origin is more probable than an Igneous origin.
H 7 Sift ( f\\
The initial Sr/ Sr ratios determined by Penner and Clark
yielded a value of 0.7086 which they interpreted as indicating that the
LDB bathollth originated from pre-existing crustal material or that the
ieotopic composition was altered by assimilation of rubidium-rich rocks
during emplacement. This figure was later revised to 0.6998 by Farquhar-
son which may indicate an upper mantle source. It is considered
that there is insufficient data at the moment to reach a definite con-
clusion.
A ternary plot of Na.CkJCChCaO in Figure 20 shows the Lac du
Bonnet rocks clustering In the same region as the leucogranite of Kolbe( 34)and Taylor . These Snowy Mountains leucogranltej are hypothesized to
have formed from sedimentary rocks. Comparison of elemental abundances
of the Snowy Mountains leucogranites to the Lac du Bonnet samples shows
that major elemental abundances are similar although the trace elements
show a wide variation.
The ternary diagram, Sr:Ba:Rb (strontium:barium:rubidium),
shown in Figure 21, classifies the Lac du Bonnet rock as an anomolous(39)granite according to El Bouselly and El Sokkary . The anomolous gr a-
nite field is considered to include those granites which have either
formed by or been subjected to metasomatism, have undergone chemical
changes or were not formed by a simple mechanism. An impoverishment of
rubidium is considered to be related to metamorphic or metasomatic pro-(39)cesses , however the LDB batholith rocks do not show low rubidium
content.
Comparison of the LDB granite with the standard values of El(39)Bouseily and El Sokkary , as shown in Table 5, indicates rubidium,
strontium and barium concentrations between those of normal granites and
granodiorite.
- 26 -
6.3.5 Other Rock Types
Schlieren
Samples 0816IB and 38155C consistently plot separately from
the other main phase samples. On the QTZ:OR:PLAG ternary plot (Figure
16), according to IUGS nomenclature they are termed as tonalité. Their
differentiation index indicates a less differentiated rock. Comparison
of these two samples with average Lac du Bonnet granite (Table 6) indi-
cates that the elemental abundance of most major elements is similar;
however the CaO content is greater and K_O content is definitely less in
the two samples compared to the LDB granite.
From field notes, 08164B is described as schlieren and 38155C
has the appearance of typical granite. These rocks can represent either
an earlier phase not totally reassimilated into the melt or an inclusion
from earlier rocks Into which magma Intruded. Comparison of the
Na-O.-ICOrCaO ternary plot, seen in Figure 20, with those by Nockolds and
Allen indicates that none of the differentiation trends which they
present are comparable to that joining the pegmatites, main phase and
schlieren samples of the Lac du Bonnet rocks. Samples 08164B and 38155C
probably represent country rock which was intruded by Lac du Bonnet
magma. Sample 38155C has probably been more assimilated and for that
reason was not recognized as schlieren. The original composition of the
samples cannot be determined because of the wide variation in abundances
between the samples, as seen in Table 6, and their probable contamina-
tion by the intruded magma.
Pegmatites
Two samples of pegmatites were collected from the southern
edge of the batholith. The observed field relationships between the
pegmatites and granite suggest that they formed from the same magma.
- 27 -
Extreme potassium and rubidium enrichment and a drop in barium
concentration, all indicators of progressive fractionation, are observed
in the pegmatite samples {Table 6). The pegmatites, therefore, represent
an end-product of crystal fractionation and were not formed by remelting
of rock material. The lack of metamorphism in the batholith and the
fact that some of the pegmatites appear to fill an early fracture set
(see section 5.2) support this conclusion.
Hypabyssal Phase
Sample 35157C was from an outcrop referred to by McRitchie as
a hypabyssal phase (see Figure 5) because of its similar rock properties
and close association to the Lac du Bonnet batholith . The chemical
composition of sample 35157C compared with average plutonic values indi-
cates the hypabyssal phase is a more differentiated rock, although sev-
eral samples of the LDB granite, listed in Appendix A, are chemically
quite similar to sample 35157C. No definite conclusions can be drawn on
the basis of a single sample.
7. CONCLUSIONS
The following conclusions concerning the geology and geochem-
istry of the Lac du Sonnet batholith have been reached:
1. The pluton is a pink, medium- to coarse-grained, equigranular-
to-slightly-porphyritic granite to granodiorite rock showing
a mild concentration of microcline phenocrysts In the centre
of the batholith.
2. The edges of the batholith show a distinct foliation and
banding with numerous inclusions.
- 28 -
3. Field mapping led to significant redrawing of the southern
contact.
i. The central portion of the batholith appears to be predomi-
nantly a single phase; two minor phases were observed.
5. Microscopic deformatlonal ieatures of the batholith show it to
have undergone the least amount of deformation in the region,
confirming earlier hypotheses of its late emplacement.
6. The slight foliation in the batholith is of primary origin
while the foliation in the country rocks is of secondary
origin.
7. Foliations near the batholith boundaries indicate that the
pluton probably has vertical to slightly outward dipping con-
tacts.
8. Two main sets of fractures, a NF.-SW. set and a NW.-SE. set,
were found to exist in the batholith.
9. The orientations of the fracture sets in the batholith appear
to be caused by regional forces and not related to the intru-
sion or cooling of the batholith.
10. The NE.-SW. set of fractures, containing pegmatite veins, was
considered to be the earliest set of joints to develop in the
pluton.
11. Long linear joints were observed to be the combination of sev-
eral smaller component fractures.
12. Lineaments, observed on aerial photographs of the batholith,
may be the result of weathering of closely spaced joint sets.
- 29 -
13. The main phase exhibits a uniform composition and no elemental
nor mineralogical trends were observed.
14. The pluton shows characteristics of having been emplaced rela-
tively near the surface flO km).
15. The geochemical data is Inconclusive, but favors the hypothe-
sis that the probable source ct the parental magma is from a
partial melt of earlier crustal material.
8. ACKNOWLEDGEMENTS
We are indebted to many people who, during the course of this
study, provided valuable assistance and discussion concerning geological
methods, regional geology and interpretation of our observations. Spe-
cial thanks are extended to W.C. Brisbin, P. Cerny, M.E. Durocher and
C.W. Bird. D. Beauchamp and G. Thorne assisted in computing and D.R.
Greig assiôted with calculations and drafting of figures. He thank K.
Ramlal and P. Cerny of the Department of Earth Sciences, University of
Manitoba and A. Wikjord, N. Pearson and the Analytical Science Branch of
WNRE for providing the geochemical analyses. C. Kamineni of the Earth
Physics Branch, Energy, Mines and Resources, Ottawa kindly performed a
number of pétrographie analyses.
- 30 -
REFERENCES
1. J. Boulton (éd.), "Management of Radioactive Fuel Wastes: TheCanadian Disposal Program", Atomic Energy of Canada LimitedReport, AECL-6314 (1978).
2. H.Y. Tammemagi, "Geological Disposai of Radioactive Wastes -The Canadian Development Program", Atomic Energy of CanadaLimited Report, AECL-5392 (1976).
3. S.R. Hatcher, S.A. Mayman and M. Tomlinson, "Development ofDeep Underground Disposal for Canadian Nuclear Fuel Wastes",in proceedings: International Symposium on the UndergroundDisposal of Radioactive Wastes, Otanieml, July 2-6, 1979.
4. H.Y. Tammemagi, "Developing the Data for Nuclear Waste Dispo-sal - Investigations of the Lac du Bonnet Batholith", Geosci-ence Canada, in press.
5. W.D. McRitchie, "Petrology and Environment of the Acidic PlutonicRocks of the Wanipigow-Winnipeg Rivers Region, South-EasternManitoba", in Manitoba Mines Branch Publication 71-1. 57 (1971).
6. A.P. Penner and G.S. Clark, "Rb-Si Age Determinations from theBird River Area, Southeastern Manitoba", Geolog. Assoc. Canada,Special Paper £, 105 (1971).
7. P. Cerny and D.L. Trueman, "Distribution and Petrogenesis ofLithium Pegmatites in the Western Superior Province of theCanadian Shield", Energy, in press.
8. H.D.B. Wilson, "The Superior Province in the Precambrian ofManitoba", Geolog. Assoc. of Canada, Special Paper ±, 41 (1971).
9. B.W. Harris, "Significance of Garnet and Cordierite from theSioux Lookout Region of the English River Gneiss Belt, North-ern Ontario", Contrib. Mineral. Petrol. 5tf, 91 (1976).
10. R.B. Farquharson, "Revised Rb-Sr Age of the Lac du Bonnet QuartzMonzonite, Southeastern Manitoba", Can. J. Earth Sci. 1£, 115(1975).
11. P. Cerny and A.C. Turnock, "Pegmitites of Southeastern Mani-toba", Geolog. Assoc. Canada, Special Paper 9_, 119 (1971).
12. G.P. Beakhouse, "A Subdivision of the Western English RiverSubprovince", Can. J. Earth Sci. 14, 1481 (1977).
13- P. Chagarlamundi, "Resistivity and Seismic Refraction Surveysover Pleistocene Deposits in Southern Manitoba", M.Sc. Thesis,University of Manitoba, 1971.
14. P. Cerny, D.L. Trueman, D.V. Ziehlke, B.E. Goad and B.J. Paul,"Pegmatite Mineral Evaluation Project, 1975-1979", in preparation.
15. P.A. Brown and R. Thivierge, "Pluton Categorization", AtomicEnergy of Canada Limited Technical Record, TR-36, in preparation.
16. P.W. Jeran and J.R. Mashey, "A Computer Program for the Ster-eographic Analysis of Coal Fractures and Cleats", U.S. Bureauof Mines, Inf. Circ. 8454 (1970).
17. R. Balk, "Structural Behaviour of Igneous Rocks", Geol. Soc.An>., Man. 5 (1937).
18. D.U. Ziehlke, "Aulneau Batholith Project", Progress Report,Centre for Precambrian Studies, Part 2, 6 (1975).
19. A.W. Kleeman, "The Origin of Granitic Magmas", Jour. Geol.Soc. Aust. 1£, 35 (1965).
20. Geological Survey of Canada, "High Resolution Aeromagnetic To-tal Field and Vertical Gradient Survey", Open File report, 1979.
21. U.C. Brisbin, "A Gravity Profile across the Lac du Bonnet Bath-olith in Southeastern Manitoba", Atonic Energy of Canada Lim-ited, Technical Record, TR-17, in preparation.
22. W.H. Moorhouse, "The Study of Rocks in Thin Section", Harperand Row, New York, 1959.
23. G.E. Grisak, J.A. Cherry, J.A. Vanbof and J.P. Blumele, "Hy-drogeologic and Hydrochemical Properties of Fractured Till inthe Interior Plains Region", Royal. Soc. Canada Special Paper12 (1976).
24. S.R. Taylor, "Applications of Trace Element Data to Problemsin Petrology", Physics and Chemistry of the Earth 6_, 133 (1965).
25. G.R. Ewers and P.A. Scott, "Geochemistry of the Cullen Gran-ite, Northern Territory", BMR Journal of Australian Geologyand Geophysics 2_, 165 (1977).
26. "Analysis ?i Surface Outcrop Rocks in the Lac du Bonnet Batho-lith, Field Samples 1977", Atomic Energy of Canada LimitedTechnical Record, TR-23 (1979).
27. "Analysis of Surface Outcrop Rocks in the Lac du Bonnet Batho-lith, Field Samples 1978", Atomic Energy of Canada. Limited,Technical Record, TR-22 (1979).
- 32 -
28. T.F.W. Barth, Theoretical Petrology, 2nd ed. John Wiley andSons, New York, 1962.
29. C.S. Hutchinson, Laboratory Handbook of Pétrographie Techniques,John Wiley and Sons, New York, 1971.
30. S.R. Taylor, Geochemistry of Andésites, Origin and Distributionof Elements. Symposium held in 1967, published 1968, p. 559.
31. C.P. Thorton and O.F. Tuttle, "Chemistry of Igneous Rocks I.Differentiation Index", Am. J. Sci. Zb%, 664 (1960).
32. R.B. Farquharson, "Radioélément Content and Variation in someGranodiorites of Southeastern Manitoba and Adjacent Ontario",Can. J. Earth Sci. K3, 993 (1976).
33. D.M. Shaw, "Uranium, Thorium and Potassium in the CanadianPrecambrian Shield and Possible Mantle Compositions", Ceochim.Cosmochim. Acta 31» 1111 (1967).
34. P. Kolbe and S.R. Taylor, "Major and Trace Element Relation-ships in Granodiorites and Granites from Australia and SouthAfrica", Contrib. Mineral. Petrol. 12_, 2 0 2 (1966).
35. O.F. Tuttle and N.L. Bowen, "Origin of Granite in the Light ofExperimental Studies in the System NaAlSi,OH-KAlSi.Oa-SiO?-H,O",Ceol. Soc. Am. Mem. ]±, 1 (1958). J
36. J.B. Wright, "A Simple Alkalinity Ratio and Its Application toQuestions of Non-Orogenic Granite Gneiss", Geological Magazine106, 370 (1969).
37. H.C. Teng and D.F. Strong, "Geology and Geochemistry of the St.Lawrence Peralkaline Granite and Associated Fluorite Deposits,Southeast Newfoundland", Can. J. Earth Sci. 13_, 1374 (1976).
38. B.W. Chappell and A.J.R. White, "Two Contrasting Granite Types",Pacific Geology ji, 173 (1974).
39. A.M. El Bouseily and A.A. El Sokkary, "Relation Between Rubidium,Barium and Strontium in Granitic Rocks", Chem. Geol. 16, 207(1975). ~
40. S.R. Nockolds and R. Allen, "The Geochemistry of Some IgneousRock Series", Geochim. Cosmochim. Acta k_, 105 (1953).
41. J.A. Cherry, G.E. Grisak and W.E. Clister, "HydrogeologicStudies at a Subsurface Radioactive Waste Management Site inWest-Central Canada", Underground Waste Management and Arti-ficial Recharge, Vol. 1, 1973, pp. 436-467.
- 33 -
TABLE 1
DATA RECORDED AT EACH SITE (OUTCROP)
A. General Description
1. location of outcrop2. size of outcrop3. type of rock and its homogeneity4. grain size5. mineral components and their percentage6. dikes7. inclusions8. main fracture sets9. horizontal sheeting
B. Sample
A representative sample of approximately 1 kg taken and labelled.
C. Fracture Analysis
1. measuring tape placed and bearing recorded.
2. rock type, dikes, inclusions recorded.3. fractures recorded:
a. location on tapeb. stride and dip (where possible)c. attitude, i.e., linear, irregular or curvedd. compound or singlee. lengthf. open or tightg. vegetation
It. repeated with tape perpendicular to original bearing.
- 34 -
TABLE 2
OLD PINAWA - FRACTURE PARAMETERS AT 2 LOCATIONS
Site A
Joint
Set
Set
Set
Sets
1
2
3
Azimuth
031°
135°
166°
Spacing(Metres)
4.7
7.0
5.5
Frequency(Fracturesper Metre)
0.21
0.14
0.18
FractureLength*(Metres)
18.4
24.6
15.2
ComponentLength(Metres)
8.3
10.3
6.69
Site B
Set
Set
Set
1
2
3
033°
-
-
22.
-
-
9 0.
-
-
04 14.0
-
-
4.2 3.0
-
-
2.5
* includes all fractures.
- 35 -
TABLE 3
CHEMICAL ANALYSIS METHODS
Element Laboratory Method
FeO
TiO,
MgO
CaO
MnO
Trace
Ba
Sr
Zr
P
C
Sn
Cs
Rb
Y
Li
Th
Be
Ga
Hf
Pb
U
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
University of Manitoba
Bondar-Clegg & Co.
University of Manitoba
Bondar-Clegg & Co.
University of Manitoba
University of Manitoba
Bondar-Clegg & Co.
University of Manitoba
University of Manitoba
W?T"S
Bondar-Clegg & Co.
University of Manitoba
Bondar-Clegg & Co.
University of Manitoba
Bondar-Clegg & Co.
WNRE
University of Manitoba
Bondar-Clegg & Co.
X-Ray Fluorescence Spectrometry (XRF)
XRF
Tota
Fe 0, by calculation
XRF
If high by XRF; if low by AA
XRF
Atomic Absorption Spectrophotometry (AA)
XRF
XRF
XRF
Flame Emission Spectrophotometry (FE)
XRF
Coloriraetry
Combustion/Gravimetry
XRF
Flameless hi*:=sion Spectrophotometry (FLE)
FE
Optical Emission Spectrography (OES)
XRF
FE
XRF
FE
XRF
OES
FLE
XRF
- 36 -
TABLE 4
AVERAGE ROCK ANALYSES
MajorElements
sio2
A12O3
Fe2°3FeO
TiO2
MgO
CaO
Na2O
K2O
MnO
TraceElements
Cs
Rb
Tl
Ba
Sr
Y
Th
U
Zr
Hf
Li
Bet>
C
Sn
Ga
Pb
Lac
%
72.83
14.53
0.92
0.66
0.20
0.42
1.17
3.59
4.83
0.03
PS/B
9.6
185
1.7
750
194
5.6
25
9
201
3.8
37
1.7
301
329
6.7
29
20
du Bonnet
Range
76.9-68.1
16.5-12.6
1.40-0.45
1.60-0.22
0.27-0.04
0.71-0.11
1.81-0.57
4.55-2.98
5.84-3.78
0.09-0.012
13.3-0.2
327-85
< 1.0-2.4
1718-391
782-28
14-1
36-5
26-1
300-118
7-1.5
110-17
2.9-0.8
742-2
710-115
13-2
34-23
27-11
Standard
Granite<30)
71.20
14.70
1.28
1.80
0.40
0.55
2.00
3.54
4.18
0.05
5
145
1.0
600
285
40
17
4.8
180
4
30
5
700
-
3
20
30
Standard
Granodiorite^30^
66.90
15.70
1.06
2.59
0.57
1.57
3.56
3.84
3.07
0.06
4
110
0.9
500
440
30
10
2.7
140
3
25
-
920
-
2
18
15
* Major elements based on 29 representative samples, trace elements often
on less than 29
- 37 -
TABLE 5
Rb:Ba:Sr RELATIONSHIPS
Granodiorite
Normal Granite
Strongly DifferentiatedGranites
AnomolouE Granites
Lac du Bonnet Granite
1
Kb
140
190
260
210
185
Ba(fg/g)
1170
550
140
1030
750
Sr
810
70
20
280
194
Rb/•
7
23
62
14
16
: BaX
55
69
33
66
66
: Sr
38
8
5
18
17
- 38 -
TABLE 6
CHEMICAL COMPOSITION OF OTHER ROCK TYPES
Element
Sample
(Z)sio2
A12O3
Fe2°3FeO
TiO2
MgO
CaO
Na2O
K2O
MnO2
(Wg/g)
BaSrZrCsRbTlyLiThUBeHfPCSnGaPb
D.I.
Pegmatites
04734B
72
14
0
0
0
0
0
2
9
0
4165692.
491
1475400.-
8738292424
97.
.8
.8
.25
.10
.06
.10
.20
.30
29
02
7
8
8
10106A
73.1
14.2
0.22
0.12
0.08
0.07
0.04
0.75
11.08
0.01
28939-8.3
6491.8-
22-50.51.5
1313927176
98.4
Schiieren
08164B
68.3
15.10
1.5
2.32
0.42
1.84
2.84
4.85
1.66
0.09
942081344.2
1792.121148625.04.0
87332810385
74.0
38155C
72.3
15.0
0.68
0.54
0.21
0.52
2.77
5.78
1.14
0.02
_286
-2.9441.7-
23--2.3-
480491
--6
84.3
Hypabyssal
35157C
75.3
13.2
0.76
0.42
0.14
0.20
0.87
3.55
4.88
0.02
3891151241.2
2242.22312232.13.0
131328123113
93.4
Average
Granite
72
14
0
0
0
0
1
3
4
0
7501942019.
1851.5.372591.3.
3013296.2920
89.
.8
.5
.92
.66
.20
.42
.17
.59
.83
03
6
76
78
7
7
FIGURE 1: The Location of the Lac du Bonnet Batholithin Southeastern Manitoba
FIGURE 2: The Lac du Bonnet Batholith and i t s Regional Geolcgy.After Beakhouse (12), McRitchie (5) and Wilson (8).
600 900 METRES EAST
tà5n
LACUSTRINE SILTY UNIT
LACUSTRINE CLAY UNIT
CLAY-LOAM TILL UNIT
BASAL SANDY DRIFT UNIT
LACUSTRINE SAND AND GRAVEL UNIT
PRECAMBRIAN BEDROCK
FIGURE 3: Stratigraphy of the Surficial Deposits along a Profile Nearthe Waste Management Site, WNRE (from Reference 41)
5 (0 Km
FIGURE 4: Sites Where Samples Were Obtained and Fracture Measurements Recorded. Chemical AnalysesWere Done on Samples from Sites Whose Numbers are Underlined.
f Contacts : de f i nod,—.,SN, undefined
* « • > . « noundary of strongfoliation
fOkm
FIGURE 5: Geological Map of the Lac du Bonnet Batholith