Investigation of the Overburden Signature of the ...€¦ · Engagement zone, a diamond-bearing, lamprophyric, heterolithic breccia, Wawa, Ontario; Ontario Geological Survey, Open

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Ontario Geological SurveyOpen File Report 6197

Investigation of theOverburden Signatureof the Engagement Zone,a Diamond--Bearing,Lamprophyric, HeterolithicBreccia, Wawa, Ontario

2007

ONTARIO GEOLOGICAL SURVEY

Open File Report 6197

Investigation of the Overburden Signature of the Engagement Zone, aDiamond--Bearing, Lamprophyric, Heterolithic Breccia, Wawa, Ontario

by

P.J. Barnett, D.C. Crabtree and S.A. Clarke

2007

Parts of this publication may be quoted if credit is given. It is recommended thatreference to this publication be made in the following form:

Barnett, P.J., Crabtree, D.C. and Clarke, S.A. 2007. Investigation of the overburdensignature of the Engagement zone, a diamond--bearing, lamprophyric, heterolithicbreccia, Wawa, Ontario; Ontario Geological Survey, Open File Report 6197, 21p.

e Queen’s Printer for Ontario, 2007

iii

e Queen’s Printer for Ontario, 2007.

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Barnett, P.J., Crabtree, D.C. andClarke, S.A. 2007. Investigation of the overburden signature of the Engagementzone, a diamond--bearing, lamprophyric, heterolithic breccia, Wawa, Ontario; Ontario Geological Survey,Open File Report 6197, 21p.

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Contents

Abstract ............................................................................................................................................................... ix Introduction ......................................................................................................................................................... 1 Bedrock Geology................................................................................................................................................. 1 Surficial Geology................................................................................................................................................. 4 Drift Exploration ................................................................................................................................................. 6 Methods ............................................................................................................................................................... 7 Results ................................................................................................................................................................. 9

Observations on Surficial Geology ............................................................................................................. 9 Till Matrix Particle Size Analysis ............................................................................................................... 9 Heavy Mineral Concentrates....................................................................................................................... 11 Mid-density Mineral Concentrates.............................................................................................................. 15 Till Matrix Geochemistry............................................................................................................................ 15

Discussions and Conclusions............................................................................................................................... 17 Acknowledgements ............................................................................................................................................. 19 References ........................................................................................................................................................... 19 Metric Conversion Table ..................................................................................................................................... 21

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FIGURES 1. Location of study area................................................................................................................................. 1 2. Bedrock geology of the area around the Engagement zone ........................................................................ 2 3. Map of surficial sediment distribution and the location of the Engagement zone and till samples

collected for the current study..................................................................................................................... 5 4. Location of samples collected for the Wawa study in relation to the bedrock geology .............................. 8 5. Patrticle-size distribution of till matrix samples.......................................................................................... 10 6. Distribution of normalized total kimberlite indicator mineral values in till HMC samples ........................ 12 7. Distribution of normalized gold grain values and their shapes in till HMC samples.................................. 13 8. Distribution of normalized heterolithic breccia indicator mineral values in till HMC samples .................. 14 9. Distribution of normalized epidote grain values in the 0.125 to 0.25 mm fraction of the mid-density

mineral fraction of till samples ................................................................................................................... 16 10. Trace element content of the -63 µ fraction of the till matrix ..................................................................... 17

PHOTOS 1. Exploration trench cut into till at the Engagement zone ............................................................................. 3 2. Lamprophyric heterolithic breccia exposed at the Engagement zone ......................................................... 4 3. Soil horizons developed in subglacial till exposed by trenching at the Engagement zone.......................... 6 4. Electron microscope backscatter image of the mid-density, 125 to 250 µ fraction of the till matrix

(sample 06-pjb-010, plug 1, field 1) illustrating the variation in crystal sizes making up grains of the till matrix............................................................................................................................................... 11

TABLES

1. Geochemical summary of selected elements (in ppm) from till samples.................................................... 16 Miscellaneous Release—Data 215 Till Compositional Database – Investigation of the Overburden Signature of the Engagement Zone, a Diamond-Bearing, Lamprophyric, Heterolithic Breccia, Wawa, Ontario, Canada; by P.J. Barnett, D.C. Crabtree and S.A. Clarke. This release presents the results of a study undertaken to determine if till sampling and analysis could be used for the exploration of diamond-bearing Archean rocks in the Wawa area. The area selected for study was the West Timmins Mining Inc. (BandOre Resources Ltd.) Engagement zone occurrence. Analytical results of heavy mineral concentrate, mid-density concentrates and till matrix geochemistry (ICP-MS and ICP-OES) of the till samples are provided as spreadsheet files (.xls or .csv formats) and as GIS files (.shp format). This digital data release complements Open File Report 6197. Available on 1 CD–ROM. This CD–ROM is available separately from the report.

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Abstract

A study was undertaken to determine if till sampling and analysis could be used for the exploration of diamonds hosted by Archean rocks in the Wawa area, some of the oldest diamond deposits in the world. The harder, relatively more erosion-resistant Archean diamond-bearing rocks do not produce the same indicator mineral signatures as the kimberlitic rocks that are the common target of diamond exploration in Canada. The area of the West Timmins Mining Inc. Engagement zone was selected for study because the lamprophyric heterolithic breccia exposed there is diamond bearing, its mineralogy has been studied, it is easily accessible and there is a thick cover of till in and around the occurrence to sample. The direction of ice flow associated with the deposition of the till in the area was toward the south (170 to 180º). Till samples for heavy mineral concentrate (HMC) analysis (methylene iodide, sg 3.2), mid-density mineral analysis (sg 2.96 to 3.2), till matrix geochemistry and pebble lithology studies were collected at 11 sites up-ice, over and down-ice flow of the Engagement zone.

HMC samples collected from till contained few kimberlite indicator minerals (<18 grains per 10 kg of sample). However, samples closest to the diamond-bearing heterolithic breccia contained the greater amounts. Heavy minerals that appear to indicate the presence of the diamond-bearing breccia include pyrope garnet, chromite, low-chrome diopside, forsterite, chalcopyrite, pyrite, gold (total and pristine grains) and goethite. For all heavy minerals studied the glacial dispersal trains appear to be short. The best defined train is of gold grains. It extends for more than 400 m down ice from the Engagement zone. Minerals such as actinolite and epidote that occur in the mid-density fraction of till samples are abundant in the breccia and in till samples collected in close proximity to the breccia. Geochemical analysis of the fine fraction (<63 μ) of till matrix samples returned elevated levels of Cr, Ni, Co and Zn in the immediate vicinity of the Engagement zone. Dispersal trains for most of the heavy and mid-density minerals and trace elements are short (<400 m) and result in exploration targets only slightly larger than the breccia itself.

Investigation of the Overburden Signature of the Engagement Zone, a Diamond-Bearing, Lamprophyric, Heterolithic Breccia, Wawa, Ontario.

P.J. Barnett1, D.C. Crabtree2 and S.A. Clarke 2 Ontario Geological Survey Open File Report 6197 2007

1Geoscientist, Sedimentary Geoscience Section, Ontario Geological Survey, Sudbury, Ontario. 2Geoscience Laboratories, Ontario Geological Survey, Sudbury, Ontario.

1

Introduction

The current study was undertaken to determine if till sampling and analysis could be used for the exploration of diamond-bearing Archean rocks. The area of the West Timmins Mining Inc. (BandOre Resources Ltd.) Engagement zone occurrence at Wawa was selected for study (Figure 1). This particular occurrence was selected, in part, because the dike is diamond-bearing (Cavey 2004; De Stefano, Lefebrve and Kopylova 2006), its mineralogy studied (Stone and Semenyna 2004; Lefebvre, Kopylova and Kivi 2005), it is easily accessible and there is a thick cover of till in and around the occurrence to sample (Morris 2001a). The direction of ice flow associated with the till in the area was toward the south (170 to 180º). Till samples were taken for heavy mineral concentrate analysis, mid-density mineral analysis, till matrix geochemistry and pebble lithology studies at 11 sites. Analytical results for this study are published separately from this report as Miscellaneous Release—Data 215 (MRD 215).

Figure 1. Location of study area.

Bedrock Geology

The study area is underlain by Precambrian rocks of the Central Michipicoten greenstone belt that was mapped by Sage (1994). The rocks consist of massive and pillowed, mafic metavolcanic rocks, intercalated with minor intermediate and felsic metavolcanic and metasedimentary rocks that are all cut by Proterozoic diabase dikes and sporadic felsic intrusions (Figure 2; Sage 1994; Cavey 2004; Wilson 2006).

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Following the discovery of diamonds in stream sediments south of Wawa (Morris, Murray and Crabtree 1994a), mineral exploration lead to the discovery of diamonds in Archean lamprophyric dikes and heterolithic breccias (Stone and Semenyna 2004). Although diamonds occur within lamprophyric dikes and heterolithic breccias, the heterolithic breccia facies is the primary diamond exploration target. Wyman et al. (2006) have investigated the timing and petrogenesis of the diamondiferous lamprophyres.

Figure 2. Bedrock geology of the area around the Engagement zone (after Cavey 2004; Lefebvre, Kopylova and Kivi 2005). The abbreviation, PVB, stands for polymict volcaniclastic breccia (Lefebvre, Kopylova and Kivi 2005); however, this rock type is referred to as heterolithic breccia in this paper.

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On the company’s property a series of exploration trenches (Photo 1) have been dug over a 60 to 110 m wide lamprophyric heterolithic breccia (Photo 2) in the area known as the “Engagement zone”. The breccia matrix at the Engagement zone is a medium to light green, fine-grained, well-foliated actinolite schist with up to 20% macrocrysts of dark hornblende and light actinolite (Stone and Semenyna 2004, p.7). The inequigranular matrix consists of macrocrysts that range in size between 0.2 and 1.5 mm (2.3 to -0.58 phi) and a groundmass that is commonly less than 0.1 mm (3.3 phi) in size (Lefebvre, Kopylova and Kivi 2005). Clasts in the breccia vary in size and are up to 9 m (-13.3 phi) in diameter and consist of mafic to felsic volcanic rock fragments and rare felsic plutonic and ultramafic clasts. The matrix of the heterolithic breccia that occurs at the Engagement zone consists of actinolite+albite+calcite with rare hornblende (Stone and Semenyna 2004, p.12). The breccia matrix is a possible source for abundant actinolite, fairly abundant titanite (up to 8%), and magnesiohornblende or magnesiohastingite, epidote, apatite and sulphide mineral grains in overburden samples in the area (Stone and Semenyna 2004). Trace element geochemistry of the breccia indicates elevated amounts of Ni, Cr and Co. “Some of the xenoliths show extremely high contents of Cr (2300 ppm) and Ni (1500 ppm) indicative of an ultramafic affinity” (Lefebvre, Kopylova and Kivi 2005, p.77).

Olivine, orthopyroxene, clinopyroxene, albite, anorthite, apatite and iron-nickel sulphide have been found to be primary inclusions in Wawa area diamonds (A. De Stefano, N. Lefebvre and M. Kopylova in Cavey 2004; De Stefano, Lefebrve and Kopylova 2006). The occurrence of both iron-rich and iron-poor olivine inclusions in these diamonds suggest 2 sources for the diamonds: a peridotitic and mafic parent rock source, respectively (A. De Stefano, N. Lefebvre and M. Kopylova in Cavey 2004; De Stefano, Lefebrve and Kopylova 2006).

Photo 1. Exploration trench cut into till at the Engagement zone.

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Photo 2. Lamprophyric heterolithic breccia exposed at the Engagement zone. The breccia here, appears to be more resistant to erosion than the surrounding pillowed, metavolcanic rocks and forms a low, broad, high in the bedrock surface. Joint and fracture spacing is wide making the breccia conducive to large block erosion and entrainment by overriding glacier ice.

Surficial Geology

The Quaternary geology of the Wawa area was mapped by Morris (2001a) at a scale of 1:50 000 (Figure 3). Morris (2001a) wrote a report describing the surficial material encountered and its origin of deposition. He also published several reports that include analytical results for numerous overburden samples (Morris 1999a, 1999b; 2001a, 2001b; Morris, Murray and Crabtree 1994a, 1994b; Morris et al. 1998).

A thin, discontinuous cover of till overlies bedrock in the southern half of the case study area (Morris 2001a). In the northern half, cover of till is thicker with thicknesses commonly ranging from 0.5 to 3 m. The till is stony and has a slightly silty to silty sand matrix (Photo 3). Analysis of C-horizon till samples (n=16) averaged approximately 71% sand, 28% silt and 1% clay within the Wawa area (Morris 2001a, p.16). Morris (2001a, p.19) suggests that areas of thicker till are commonly composed of flow tills.

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In the Wawa area, Morris (2001a) reports the existence of 2 sets of striae, an older set, ranging from 159 to 240º, that is present throughout the Wawa area, and a younger set, oriented between 220 and 290º, occurring east of the Magpie River.

Podzolic soils have developed in the till locally (see Photo 3). The soil commonly consists of a humus layer up to 5 cm thick, and a zone of eluviation (Ae horizon) that can exceed 5 cm in thickness and a Bf horizon greater than 15 cm thick. Depth of soil development ranges between 40 and 60 cm, below which essentially, unweathered C-horizon till occurs.

Figure 3. Map of surficial sediment distribution (after Morris 2001a) and the location of the Engagement zone and till samples collected for the current study.

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Photo 3. Soil horizons developed in subglacial till exposed by trenching at the Engagement zone.

Drift Exploration

Morris (1999a, 1999b, 2001a, 2001b), Morris, Murray and Crabtree (1994a, 1999b) and Morris et al. (1998) previously sampled surficial sediment (modern alluvium or stream sediment and till) to evaluate the regional mineral potential of the Wawa area. Morris et al. (1998) recommended sampling modern alluvium to obtain regional-scale patterns and anomalies and then use till for follow-up programs. They (Morris et al. 1998) found till was not a good sampling medium for regional sampling programs in the region because it was difficult and time consuming to find lodgement till to sample. Morris et al. (1998) also suggested that the distance of dispersal of indicator minerals is usually less that 5 km and commonly less than 200 m.

Results from these sampling programs suggested that the study of heavy mineral concentrates (HMC) for known kimberlite indicator minerals did not detect the area of diamond–bearing Archean rocks, particularly in the area of the present study, west of the Magpie River. Similar conclusions were also reached by Thomas and Gleeson (2000) and Stone and Semenyna (2004). Stone and Semenyna (2004, p.12) suggest that “in general, the dominant indicator minerals of kimberlitic rocks, including pyrope, olivine, diopside, chromite and ilmenite, are rare or absent in lamprophyres and breccias of the Wawa area”.

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Glacial dispersion from several of the lamprophyre dikes, including the Sandor property located to the northwest of the Engagement zone, have been studied by Thomas and Gleeson (2000). Their findings indicate that the dikes do not contain 2 of the commonly used kimberlite indicator minerals: pyrope garnet and chrome diopside. However, the till HMC contains low Mg, high Cr, and Zn-rich chromite and ilmenites of variable composition that could be used, along with the mineral actinolite that occurs in the methylene iodide (sg 3.2) lights, to find additional lamprophyre dikes. Till samples collected by Thomas and Gleeson (2000) down-ice flow of lamprophyre dikes contained elevated concentrations of Ni and Cr in the <0.177 mm fraction of the till matrix.

Methods

The current project’s goal was to determine the glacial dispersion of rock and mineral particles derived from the lamprophyric heterolithic breccia of the Engagement zone. In order to accomplish this, it was imperative to sample subglacial till, the direct product of glacier erosion and deposition preferably at sites that occur along the paleoflowline of the last glacier to cross the breccia. Because sampling was to take place over a 1 day period, another criterion for sample collection sites was easy access to the sample site with, preferably, a pre-existing exposure. Till from 11 sites that closely met these criteria were selected for sampling (Figure 4). At each site 3 samples were collected: a sample for heavy mineral and mid-density analysis, one for pebble lithology identification and one for particle size analysis and geochemistry.

A 10 to 15 kg sample of the <7 mm fraction of the till was collected for heavy mineral concentration and subsequent kimberlite indicator mineral (KIM), metamorphic/magmatic massive sulphide indicator mineral (MMSIM®) and gold grain determinations by Overburden Drilling Management Limited (ODM), Nepean, Ontario. The following description of the heavy mineral concentration process used at ODM was provided by S. Averill, President, Overburden Drilling Management Limited. Heavy mineral grains were separated from the <2 mm fraction of these samples by gravity tabling followed by heavy liquid refining using methylene iodide (sg = 3.2) and a magnetic separation to remove magnetite from the concentrate. This was followed by sieving of the nonferromagnetic heavies into 0.25 to 0.5 mm (medium sand), 0.5 to 1.0 mm (coarse sand) and 1.0 to 2.0 mm (very coarse sand) sizes and further electromagnetic sorting of the 0.25 to 0.5 mm minerals. The major (>15%) paramagnetic and nonparamagnetic minerals (i.e., the background mineral assemblage) in the 0.25 to 0.5 mm fraction of each sample were systematically observed and recorded in order of decreasing abundance using a binocular microscope, and the indicator minerals occurring in each size fraction were identified and put into vials. Energy dispersive x-ray spectrometry (EDS) analysis with a scanning electron microscope (SEM) was used to confirm visual mineral identification when required. During the tabling phase, a preliminary count of gold and/or platinum group mineral (PGM) grains was done and if any were observed, the finer (<0.25 mm) PGM and gold grains were micropanned from the table concentrates, measured and classified as to degree of wear during glacial transport. The processing methodology developed at ODM is described in greater detail in several other publications (Morris and Kaszycki 1997; Averill 2001; McMartin and McClenaghan 2001).

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Figure 4. Location of samples collected for the Wawa study in relation to the bedrock geology (Cavey 2004, Lefebvre, Kopylova and Kivi 2005).

The methylene iodide light mineral fraction (sg <3.2) of each sample obtained by ODM was further processed at the Ontario Geoscience Laboratories (OGL). The light fraction was dry sieved and the 0.125 to 0.25 fraction was processed with tetrabromoethane (sg = 2.96) to isolate the mid-density mineral grains including actinolite. A split of these grains was mounted and the chemistry analysed using a Zeiss EVO-SO SEM equipped with an Oxford Instruments energy dispersive (ED) spectrometer. From the resultant chemical information, mineral identification of each probed grain was determined and the content of the various mid-density minerals, including actinolite, estimated. Microprobe analysis using a Cameca SX-50 EPMA of picked mineral grains from ODM, primarily potential KIMs and MMSIM®s, was also undertaken by the OGL.

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Samples of between 50 and 100 clasts from the >7 mm to 2.54 cm fraction of the till were collected for lithology identification. The pebble lithology data, however, is not included in this report because identification of the various types of mafic rocks proved difficult in the size range of pebbles collected.

Samples of the till matrix were collected for particle size analysis and the -63 μ fraction isolated for geochemical determinations. The sample split for geochemical determinations was air dried, gently disaggregated, if necessary, and then sieved through a 250-mesh nylon sieve (63 μ). A 0.5 g sample of the -250-mesh fraction under went an aqua-regia digestion and was analyzed using Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) and ICP – Optical Emission Spectrometry (OES). MRD 215 contains information on data quality as determined by the insertion of duplicates and certified and noncertified reference materials.

Results

OBSERVATIONS ON SURFICIAL GEOLOGY

The dominant surficial sediment in the vicinity of the Engagement zone is till. It ranges in thickness from less than 0.5 to greater than 3 m. The spatial distribution of the till has been previously mapped by Morris (2001a). The till is stony and has a silty sand to sandy silt matrix. Morris (2001a, p.19) suggested that areas of thicker till are commonly composed of flow tills. In the study area, only thick till associated with minor ridges appear to be composed of flow tills. The flow tills, however, appear to be of subglacial debris and therefore appropriate to sample for mineral exploration. Elsewhere, the thicker till in the area of this study appears to be predominantly subglacial in origin, predominantly lodgement till, and commonly reflects variations in local bedrock composition.

Striation orientations measured in the study area vary between 170 and 180º except at one site where 2 sets were observed, an older 190º set cut by a younger 170º set of striations. This site occurred along the flank of a deep, north-trending valley which may have influenced the local ice flow direction.

TILL MATRIX PARTICLE SIZE ANALYSIS

Particle size analysis of the <2 mm fraction, or till matrix, of the till samples collected at each site averaged approximately 69% sand, and 31% silt. The sand content, however, ranged from 39.5 to 84.4%, the silt content from 15.5 to 59% and clay-sized particles from 0 to 1.3%. From a closer examination of the particle size distribution, the samples tend to have either a bimodal or trimodal matrix distribution (Figure 5). Particles in the till matrix fall into 3 main size ranges: coarse- to very coarse-grained sand (1 to -1 phi), fine- to medium-grained sand (1 to 3 phi) and fine- to coarse-grained silt (4.5 to 6.5 phi). Sites proximal to the breccia tend to have particle size distributions with particles concentrated in the coarse- to very coarse-grained sand and fine- to medium-grained sand fractions, whereas samples collect farther down-ice from the breccia have particles concentrated in the fine- to medium-grained sand and fine- to coarse-grained silt ranges (see Figure 5). This trend illustrates the effectiveness of the abrasion and crushing processes that occurs at the base of a warm-based glacier. The coarser particles are abraded and crushed and are broken down into smaller particles with the increase in distance travelled at the base of the glacier.

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Figure 5. Patrticle-size distribution of till matrix samples (in phi units on lower x-axis, in microns, μ, on upper x-axis and per cent on y-axis).

Samples with a high particle concentration in the coarse- to very coarse-grained sand size range tend to be from sample sites proximal to the breccia and may reflect the incorporation of the megacrysts of the breccia or breccia fragments into the till. When compared to till particle size distribution curves that have been generated from till samples from the Caribou Lake greenstone belt, which also show 3 peaks, differences are greatest at the fine end of the particle size curve. The high concentration of particles in the silt fraction of some of the samples at a distance down-ice of the breccia are finer-grained than in the tills of the Caribou Lake greenstone belt area (see Figure 5). The very fine grain size of the breccia matrix (<0.1 mm (3.3 phi) Lefebvre, Kopylova and Kivi 2005) at the Engagement zone may be responsible for this, as particles tend to be abraded to their terminal grade, the size of crystals in the source rocks (Dreimanis and Vagners 1969). In the mid-density 0.125 to 0.25 mm fraction of the till about 58% of the grains are mineral aggregates. Of these mineral aggregate grains, about 82% are made of crystals that range between 5 and 30 μ in size (Photo 4). The presence of the peak in the fine- to coarse-grained silt-sized particle range (4.5 to 6.5 phi) is likely due to the abrasion and crushing of these aggregates and may indicate that heterolithic breccia occurs up-glacier flow of samples that contain this peak in their particle size distribution. A peak in this grain size may also occur as a result of the incorporation of previously deposited glaciolacustrine clay and silt or the breakdown of carbonate clasts (Dreimanis and Vagners 1969).

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Photo 4. Electron microscope backscatter image of the mid-density, 125 to 250 µ fraction of the till matrix (sample 06-pjb-010, plug 1, field 1) illustrating the variation in crystal sizes making up grains of the till matrix. Many grains within this size range are mineral aggregates commonly composed of crystals 5 to 30 µ in size.

HEAVY MINERAL CONCENTRATES

The heavy mineral concentrate (HMC) was examined for gold and platinum group minerals (PGM). The 0.25 to 0.5 mm fraction was examined for kimberlite indicator minerals (KIMs) and metamorphic/magmatic massive sulphide indicator minerals (MMSIM®) and the 0.5 to 2 mm fraction of the HMC was examined for KIMs as well. KIMs include Cr-pyrope, eclogitic pyrope-almandine and Cr-poor pyrope garnets, Cr-diopside, chromite and Mg-ilmenite (Averill 2001). Common MMSIM®s include gahnite, Cr-rutile, spessartine, Mn-epidote, staurolite and anthophyllite (Averill 2001). The results of the HMC analysis performed at ODM are presented in MRD 215 (available separately from this report). The results have been normalized with respect to a 10 kg sample of till matrix (<2 mm fraction).

No diamonds (sg 3.5) were observed in the till heavy mineral concentrate samples collected for this study, even though the Engagement zone breccia is diamond bearing (Cavey 2004; Stone and Semenyna 2004). The majority of diamonds from the Engagement zone are in the 0.15 to 0.212 mm size range (Cavey 2004) and therefore very few, if any, would have been in the HMC that were examined and picked in this study. The total number of normalized KIMs range from 1.2 to 17.5 grains per 10 kg sample and their distribution in relation to the Engagement zone is displayed in Figure 6. The dominant KIMs were chromite and forsterite with only one pyrope garnet identified. The garnet came from sample 06-pjb-002, which was taken from till resting directly on the diamond-bearing heterolithic breccia. Electron microprobe analysis of the grain’s chemistry indicates that it has a G-9 lherzolitic composition (Gurney and Moore 1993). Normalized chromite grain counts ranged from 0 to 8.8 grains per 10 kg sample. Their chemistry falls short of the diamond inclusion field (Fipke, Gurney and Moore 1995) with

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respect to their Cr2O3 content. Forsterite grains range from 0 to 8.8 grains per 10 kg sample. Microprobe analysis of the forsteritic olivines confirm that most of these grains have forsterite numbers that exceed Fo90. Samples with abundant forsterite grains are centred on the heterolithic breccia; however, forsterite grains are as abundant in the sample collected approximately 1.5 km up-ice flow direction of the Engagement zone. Fayolite grains in till HMC are in greatest abundance near the Engagement zone as well (up to 8 grains per 10 kg). The coexistence of both iron-rich and iron-poor olivines, apparently derived from the same source, is uncommon; however, both minerals occur as inclusions in diamonds from the Engagement zone breccia (Cavey 2004; De Stefano, Lefebrve and Kopylova 2006).

The best defined glacial dispersal train in the Engagement zone area is the dispersion of gold grains (Figure 7). Although the normalized total gold grain values in till samples are low (<13.4 grains per 10 kg), the dispersal train can be observed to extend greater than 400 m from the heterolithic breccia. This

Figure 6. Distribution of normalized total kimberlite indicator mineral values in till HMC samples (geology after Cavey 2004; Lefebvre, Kopylova and Kivi 2005).

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may only be the tail end of a much larger train because no samples were collected immediately up-ice flow to properly define the head of the train. The distribution of pristine gold grains roughly coincides with the distribution of total gold grains indicating that the source of gold is probably local. The sample taken 1.5 km up ice of the Engagement zone contains a normalized value of 9.3 grains per 10 kg sample; however, these grains have reshaped or modified shapes which suggest greater transport distances and are likely from a different source than the gold grains in till samples at the Engagement zone.

Sulphide grains that were initially dispersed into the till can be subsequently affected by postglacial weathering and not survive in the heavy mineral concentrate (Averill 2001). They are commonly low in number in near-surface till samples (Averill 2001). Grains of pyrite and chalcopyrite were only found in till samples collected over or immediately down-ice flow from the heterolithic breccia.

Figure 7. Distribution of normalized gold grain values and their shapes in till HMC samples. Dot labels are the total normalized gold grain values per 10 kg sample, and dot size is proportional to this total normalized grain value (geology after Cavey 2004; Lefebvre, Kopylova and Kivi 2005).

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Several other heavy minerals in the till samples appear to be spatially associated with the heterolithic breccia of the Engagement zone. Low chrome diopside grains (up to 12.5 grains per 10 kg) are present in till samples overlying the Engagement zone. Goethite occurs in all the till samples collected over the Engagement zone and its dispersal train exceeds 400 m in length. However, goethite also occurs in the sample of till collected 1.5 km north of the Engagement zone. The distribution of low magnesium ilmenite (crustal ilmentite) grains, chromite grains that do not have the chemical composition of a KIM, and low Cr-diopside grains, all indicate the presence of the heterolithic breccia. If the normalized values of the grains of these minerals are added together with the number of pyrope garnet and forsteritic olivine grains, then a sample of till taken over the Engagement zone contains 31.2 grains per 10 kg compared to 16.6 grains per 10 kg in the sample collected up-ice flow of the zone (Figure 8). Again glacial dispersion appears to have resulted in very short (<200 m) dispersal trains.

Figure 8. Distribution of normalized heterolithic breccia indicator mineral values (total HBIM is the sum of the KIMs, low Mg ilmenites and low Cr diopside grains) in till HMC samples (geology after Cavey 2004; Lefebvre, Kopylova and Kivi 2005).

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MID-DENSITY MINERAL CONCENTRATES

Minerals associated with the diamond-bearing heterolithic breccia of the Engagement zone that can occur in the mid-density (sg 2.96 to 3.2) fraction of till samples include actinolite, titanite, magnesiohornblende, magnesiohastingite, epidote and apatite (Stone and Semenyna 2004). Titanite and epidote can also be found in the heavy mineral fraction of till samples. Epidote forms part of the major constituents of the HMC samples from the study area along with augite, hornblende, diopside and almandine garnet.

SEM analysis of the mid-density mineral grains within the 0.125 and 0.25 mm fraction of the till samples of the present study indicate that there are high amounts (>10%) of epidote, actinolite and hornblende grains. Titanite grains commonly make up less than 4% and apatite less than 1% of the total grains investigated (between 1653 and 3019 grains per sample were analysed). Titanite is likely occurring in the mid-density fraction as inclusions or segments of grains and may show up in greater concentrations in the HMC fraction. Titanite is not normally considered a KIM or a MMSIM® and therefore was ignored during the picking process of the HMC.

Epidote appears to be the most useful mineral to help pinpoint the heterolithic breccia of the Engagement zone (Figure 9) where till samples contain 21% or more epidote grains in the 0.125 to 0.25 mm mid-density fraction of till samples. Till samples taken proximal to the Engagement zone also contain actinolite that exceeds 15% in concentration; however, several samples collected away from the zone also exceed 15% actinolite grains. The other mid-density minerals, hornblende, titanite and apatite, do not seem to be as useful as epidote and actinolite to locate the Engagement zone breccia.

TILL MATRIX GEOCHEMISTRY

Table 1 contains a geochemical summary of selected elements analyzed using both ICP-MS and ICP-OES. A complete geochemical data set is contained in MRD 215, released in conjunction with this report. Results from the geochemical analysis (ICP-MS) of the -63 μ fraction of the till matrix samples indicate that chromium, nickel and zinc can be used to pinpoint the heterolithic breccia. Figure 10 shows the distribution of Cr (Figure 10a) and Ni (Figure 10b) in the study area. Co, Cr, Ni and Zn concentrations determined by ICP-OES also achieve this goal. Figure 10c and 10d display the distribution of Co and Zn in till samples, respectively. Dispersal trains of these elements are a few hundred meters to greater than 400 m in length. All of these elements have been reported to be enriched in the heterolithic breccia of the Engagement zone (Stone and Semenyna 2004; Lefebvre, Kopylova and Kivi 2005).

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Figure 9. Distribution of normalized epidote grain values in the 0.125 to 0.25 mm fraction of the mid-density mineral fraction of till samples (geology after Cavey 2004; Lefebvre, Kopylova and Kivi 2005).

Table 1. Geochemical summary of selected elements (in ppm) from till samples.

Number of Samples 11

Detection limit Average

Standard Deviation Minimum Maximum

Cr (ICP-MS) 1 212.0 23.6 164.5 246.0 Ni (ICP-MS) 1 94.4 10.2 80.0 111.0 Zn (ICP-MS) 1 54.4 5.4 46.0 63.0 Co (ICP-OES) 0.04 23.4 2.4 18.6 27.1 Ni (ICP-OES) 0.2 90.7 10.2 75.2 106.9 Zn (ICP-OES) 2 49.5 4.9 42.1 58.4

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Figure 10. Trace element content of the -63 µ fraction of the till matrix; A. Cr (ICP-MS), B. Ni (ICP-MS), C. Co (ICP-OES) and D. Zn (ICP-OES). See Figure 9 for bedrock geology legend (geology after Cavey 2004; Lefebvre, Kopylova and Kivi 2005).

Discussions and Conclusions

The sample density in this study is not sufficient to properly delineate glacial dispersal trains, but is adequate to determine the response of till to the overriding of the diamond-bearing heterolithic breccia of the Engagement zone. In general, the till does respond to this overriding in several ways. The sample (06-pjb-007) collected 1.5 km up-ice flow direction from the Engagement zone was intended to be a background sample site because no heterolithic breccia has been mapped or reported in this area. However, results from several of the analysis of this till sample may indicate otherwise.

In regard to the particle size distribution in the till, there appear to be changes in the till matrix with an initial peak occurring in the coarse- to very coarse-grained sand component of the matrix which then tends to decrease with greater distance down ice flow from the breccia. A corresponding increase in the fine- to coarse-grained silt size range occurs as the initial debris collected from the breccia is crushed and abraded to its terminal grade, that of the initial crystal size of the breccia matrix.

The normal suite of KIMs are not abundant in the till sample HMCs collected at the Engagement zone. This is in part due to the initial mineral composition of the breccia and the relative hardness of the diamond-bearing Archean rocks compared to younger kimberlitic rocks present in other parts of the province. The Archean rocks do not appear to be as erodible as younger (Tertiary) kimberlite pipes and are therefore not likely to release indicator minerals to the same degree. At the Engagement zone, the

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heterolithic breccia forms a positive landscape element, whereas kimberlite pipes commonly occur as a negative landform or depression. Subsequent metamorphic alteration of the breccia has also resulted in key compositional differences as well as affecting its erodibility.

Morris et al. (1998), Thomas and Gleeson (2000) and Stone and Semenyna (2004) all reported that the normal KIM signature is not associated with the diamond-bearing Archean rocks of the Wawa area. The dominant indicator minerals of kimberlitic rocks, such as pyrope, olivine, diopside, chromite and ilmenite, are rare or absent in the diamond-bearing rocks of the Wawa area (Stone and Semenyna 2004). Glacial dispersion of indicator minerals from several of the lamprophyre dikes, including the Sandor property located to the northwest of the Engagement zone, has been studied by Thomas and Gleeson (2000). Their findings indicate that the dikes do not contain 2 of the commonly used kimberlite indicator minerals: pyrope garnet and chrome diopside. However, they suggest that the till HMC contains low Mg, high Cr, Zn-rich chromite and ilmenites of variable composition that could be used, along with the mineral actinolite that occurs in the methylene iodide (sg = 3.2) lights, to find additional lamprophyre dikes.

Increases in the content of low-Cr diopside, low-Mg ilmenite (crustal ilmentite), nonkimberlitic chromite, goethite, forsteritic and fayalitic olivine grains occur in close proximity to the heterolithic breccia at the Engagement zone. The coexistence of both iron-rich and iron-poor olivine grains, apparently derived from the same source, is uncommon; however, both minerals occur as inclusions in diamonds from the Engagement zone breccia (Cavey 2004). Any one of these minerals alone is not enough to pinpoint the heterolithic breccia source; however, when combined a much more promising result occurs.

Thomas and Gleeson (2000) suggested that by combining the total number of chromite and Mg-ilmenite grains in a sample, several of the diamond-bearing mafic dikes could be located in the area around Highway 17 west of the Engagement zone. Other nondiamondiferous mafic dikes, however, were also indicated. The distribution of the total chromite and Mg-ilmenite grains in till samples provided exploration targets that exceeded 3 km in diameter at a count of greater than 5 total grains. Thomas and Gleeson (2000) suggested that when comparing the distribution of the mid-density mineral actinolite and the chromite and Mg-ilmenite distribution, areas of coincident highs would indicate high priority targets for diamond exploration.

For the current study, the mid-density mineral epidote was found in greater abundance in till samples collected close to the heterolithic breccia. Actinolite was also abundant in these samples; however, some of the till samples distal to the Engagement zone also contained abundant actinolite grains. As suggested by Thomas and Gleenson (2000), actinolite can be used to help delineate the lamprophyric dikes and heterolithic breccias in the Wawa area; however, epidote may prove to be more useful. Epidote, however, can also occur in the methylene iodide heavy mineral fraction, where its abundance is not commonly reported and was not investigated in the current study. Both actinolite and epidote can occur widely in metavolcanic rocks and their usefulness as indicators of heterolithic breccias may be diminished in other areas.

Till samples collected by Thomas and Gleeson (2000) down-ice flow of lamprophyre dikes west of the Engagement zone contained elevated concentrations of Ni and Cr in the <0.177 mm fraction of the till matrix. In the current study these elements, as well as Co and Zn, were also elevated in the -63 µ fraction of most till samples collected in close proximity to the heterolithic breccia.

In conclusion, the diamond-bearing Archean rocks of the Wawa area do not appear to shed the same types or amount of indicator minerals as younger kimberlite pipes in other parts of Ontario. This is in part due to different initial mineral composition, postdepositional alteration and the relative erodibility of

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the 2 different types of diamond-bearing rocks. Indicator minerals for the breccia may include pyrope garnet, low-Cr diopside, low-Mg ilmenite (crustal ilmentite), nonkimberlitic chromite, goethite, forsteritic and fayolitic olivine grains. Mid-density indicator minerals may include epidote and actinolite, and Ni, Cr, Co and Zn content of the -63 µ fraction of the till matrix may be used to locate the heterolithic breccia of the Engagement zone.

Many of these minerals, however, are common in a wide range of altered Archean plutonic and supracrustal rocks. On their own they make unreliable indicator minerals of diamondiferous source rocks as suggested by Stone and Semenyna (2004); however, by using assemblages of these minerals, a greater chance of delineating potential diamond-bearing heterolithic breccias may be possible. The relatively low amounts of indicator minerals being shed from the diamond-bearing Archean rocks also poses problems. It produces very short dispersal trains, commonly less than 400 m. This results in the production of only slightly larger targets for mineral exploration than the breccias themselves.

Acknowledgements

The authors would like to acknowledge the co-operation of D. Wagner and W. O’Connor, West Timmins Mining Inc. for allowing access to the Engagement zone for study and sampling. We would like to thank A. Wilson, Ontario Geological Survey, for bringing this interesting project to our attention. Excellent field assistance was provided by A. Ryan during till sampling. The heavy mineral concentrate processing and analysis of the collected till samples was done at Overburden Drilling Management, Nepean, Ontario. Till chemistry, particle size analysis, electron microprobe analysis of picked heavy mineral grains and mid-density mineral concentrates were conducted at the Ontario Geoscience Laboratories. The work of all the staff involved at both laboratories is gratefully appreciated. Review of the manuscript by Dr. J.A. Ayer, D. Stone, R.I. Kelly and C.L. Baker, Ontario Geological Survey, lead to improvements.

References Averill, S.A. 2001. The application of heavy indicator mineralogy in mineral exploration, with emphasis on base

metal indicators in glaciated metamorphic and plutonic terrain; in McClenaghan, M.B., Bobrowsky, P.T., Hall, G.E.M. and Cook, S.J. (eds.), Drift Exploration in Glaciated Terrain, The Geological Society of London, Special Publication no.185, p.69-81.

Cavey, G. 2004. Summary geological report on the GQ property for Band-Ore Resources Ltd., Sault Ste. Marie Mining Division, Ontario: Technical Report under NI-43-101F1; filed December 17, 2004, with SEDAR®, see Sedar Home Page, 39p.

De Stefano, A., Lefebvre, N. and Kopylova, M. 2006. Enigmatic diamonds in Archean calc-alkaline lamprophyres of Wawa, southern Ontario, Canada; Contributions to Mineralogy Petrology, v.146.

Dreimanis, A. and Vagners, U.J., 1969. Lithologic relation of till to bedrock; in Wright , H.E. Jr. (ed.), Quaternary Geology and Climate, Proceedings VII, INQUA Congress, v.16, p.93-98.

Fipke, C.E., Gurney, J.J. and Moore. R.O. 1995. Diamond exploration techniques emphasizing indicator mineral geochemistry and Canadian examples; Geological Survey of Canada, Bulletin 423, 86p.

Gurney, J.J. and Moore, R.O. 1993. Geochemical correlations between kimberlitic indicator minerals and diamonds; in Diamonds: Exploration, Sampling and Evaluation, Prospectors and Developers Association of Canada, Toronto, Short Course, p.147-172.

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Lefebvre, N., Kopylova, M. and Kivi, K. 2005. Archean calc-alkaline lamprophryes of Wawa, Ontario, Canada: unconventional diamondiferous volcaniclastic rocks; Precambrian Research, v.138, p.57-87.

McMartin, I. and McClenaghan, M.B. 2001. Till geochemistry and sampling techniques in glaciated shield terrain: a review; in McClenaghan, M.B., Bobrowsky, P.T., Hall, G.E.M. and Cook, S.J. (eds.), Drift Exploration in Glaciated Terrain, The Geological Society of London, Geological Society Special Publication no.185, p.19-43.

Morris, T.F. 1999a. Geochemical, heavy mineral and pebble lithology data, surficial sampling program, Wawa region, northeastern Ontario; Ontario Geological Survey, Open File Report 5981, 74p.

Morris, T.F. 1999b. Summary of geochemical, heavy mineral and pebble lithology data, surficial sampling program, Wawa region, northeastern Ontario; Ontario Geological Survey, Miscellaneous Release—Data 40.

Morris, T.F. 2001a. Quaternary geology of the Wawa area, northeastern Ontario; Ontario Geological Survey, Open File Report 6055, 67p.

Morris, T.F. 2001b. Miscellaneous data related to the Wawa Quaternary geology mapping project, northeastern Ontario; Ontario Geological Survey, Miscellaneous Release—Data 73.

Morris, T.F. and Kaszycki, C.A. 1997. Prospector’s guide to drift prospecting for diamonds northern Ontario; Ontario Geological Survey, Miscellaneous Paper 167, 63p.

Morris, T.F., Murray, C. and Crabtree, D.C. 1994a. Results of overburden sampling for kimberlite heavy mineral indicators and gold grains, Michipicoten River–Wawa area, northeastern Ontario; Ontario Geological Survey, Open File Report 5908, 69p.

Morris, T.F., Murray, C. and Crabtree, D.C. 1994b. Results of overburden sampling for kimberlite heavy mineral indicators and gold grains, Michipicoten River–Wawa area, northeastern Ontario; Ontario Geological Survey, Miscellaneous Release—Data 13.

Morris, T.F., Crabtree, D., Sage, R.P. and Averill, S.A. 1998. Types, abundances and distribution of kimberlite indicator minerals in alluvial sediments, Wawa–Kinniwabi Lake area, northeastern Ontario: implications for the presence of diamond-bearing kimberlite; Journal of Geochemical Exploration, v.63, p.217-235.

Ontario Geological Survey 2004. Mineral Deposit Inventory Version 2 (MDI2), October 2004 Release; Ontario Geological Survey.

Sage, R.P. 1994. Geology of the Michipicoten greenstone belt; Ontario Geological Survey, Open File Report 5888, 435p.

Stone, D. and Semenyna, L. 2004. Petrography, chemistry and diamond characteristics of heterolithic diamond-bearing breccias and lamprophyre dikes at Wawa, Ontario; Ontario Geological Survey, Open File Report 6134, 39p.

Thomas, R.D. and Gleeson, C.F. 2000. Use of till geochemistry and mineralogy to outline areas underlain by diamondiferous spessartite dikes near Wawa, Ontario; Exploration Mining Geology, v.9, p.215-231.

Wilson, A.C. 2006. Unusual Archean diamond-bearing rocks of the Wawa area; Institute on Lake Superior Geology, Field Trip Guidebook, v.52, pt.3, 30p.

Wyman, D.A., Ayer, J.A., Conceicao, R.V. and Sage, R.P. 2006. Mantle processes in an Archean orogen: evidence from 2.67 Ga diamond-bearing lamprophyres and xenoliths; Lithos, v.89, p.300-328.

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Metric Conversion Table

Conversion from SI to Imperial Conversion from Imperial to SI

SI Unit Multiplied by Gives Imperial Unit Multiplied by Gives

LENGTH1 mm 0.039 37 inches 1 inch 25.4 mm1 cm 0.393 70 inches 1 inch 2.54 cm1 m 3.280 84 feet 1 foot 0.304 8 m1 m 0.049 709 chains 1 chain 20.116 8 m1 km 0.621 371 miles (statute) 1 mile (statute) 1.609 344 km

AREA1 cm@ 0.155 0 square inches 1 square inch 6.451 6 cm@1 m@ 10.763 9 square feet 1 square foot 0.092 903 04 m@1 km@ 0.386 10 square miles 1 square mile 2.589 988 km@1 ha 2.471 054 acres 1 acre 0.404 685 6 ha

VOLUME1 cm# 0.061 023 cubic inches 1 cubic inch 16.387 064 cm#1 m# 35.314 7 cubic feet 1 cubic foot 0.028 316 85 m#1 m# 1.307 951 cubic yards 1 cubic yard 0.764 554 86 m#

CAPACITY1 L 1.759 755 pints 1 pint 0.568 261 L1 L 0.879 877 quarts 1 quart 1.136 522 L1 L 0.219 969 gallons 1 gallon 4.546 090 L

MASS1 g 0.035 273 962 ounces (avdp) 1 ounce (avdp) 28.349 523 g1 g 0.032 150 747 ounces (troy) 1 ounce (troy) 31.103 476 8 g1 kg 2.204 622 6 pounds (avdp) 1 pound (avdp) 0.453 592 37 kg1 kg 0.001 102 3 tons (short) 1 ton (short) 907.184 74 kg1 t 1.102 311 3 tons (short) 1 ton (short) 0.907 184 74 t1 kg 0.000 984 21 tons (long) 1 ton (long) 1016.046 908 8 kg1 t 0.984 206 5 tons (long) 1 ton (long) 1.016 046 90 t

CONCENTRATION1 g/t 0.029 166 6 ounce (troy)/ 1 ounce (troy)/ 34.285 714 2 g/t

ton (short) ton (short)1 g/t 0.583 333 33 pennyweights/ 1 pennyweight/ 1.714 285 7 g/t

ton (short) ton (short)

OTHER USEFUL CONVERSION FACTORS

Multiplied by1 ounce (troy) per ton (short) 31.103 477 grams per ton (short)1 gram per ton (short) 0.032 151 ounces (troy) per ton (short)1 ounce (troy) per ton (short) 20.0 pennyweights per ton (short)1 pennyweight per ton (short) 0.05 ounces (troy) per ton (short)

Note:Conversion factorswhich are in boldtype areexact. Theconversion factorshave been taken fromor havebeenderived from factors given in theMetric PracticeGuide for the CanadianMining andMetallurgical Industries, pub-lished by the Mining Association of Canada in co-operation with the Coal Association of Canada.

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