Kimberlite Indicator Mineral Sampling in the Meadow Lake Area 1

M.J. Millard 2

Millard, M.J. (1994): Kimberlite indicator mineral sampling in the Meadow Lake area; in Summary of Investigations 1994, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 94-4.

The Saskatchewan Research Council (SAC) and Cameco Corporation entered into a jointly funded kim-berlite indicator mineral sampling program conducted during the summer of 1991 in the Meadow Lake area of west-central Saskatchewan. This program was similar in design and scope to that described by Simpson (1991) in southwest Saskatchewan, which sampled Ter-tiary and glaciofluvial gravels. The Meadow Lake pro-ject was initiated to expand the database of indicator mineral occurrences in Saskatchewan and to test addi-tional sample media such as till and third-order-stream alluvium. Sample site locations and descriptions, as well as the analytical data obtained during this program, are presented in a comprehensive report (Millard, 1994), which is available through the Resources Divi-sion, Saskatchewan Research Council.

1 . Study Area

The study area covers approximately 9450 km2 in west-central Saskatchewan (NTS 73K-1 to 73K-10). The Meadow Lake area was chosen for a number of rea-sons: 1) rocks belonging to the Lower Colorado Group, which are equivalent in age (Late Albian-Cenomanian, Late Cretaceous) to the wall rocks in the Fort a la Corne kimberlite field, form the bedrock surface in the eastern part of the study area; 2) the drift is relatively thin (50 m) over much of the area; and 3) the presence of ice-thrust features. In areas of thick drift, ice-thrusting potentially brings to surface older till units that are de-rived from local bedrock lithologies. Figure 1 shows the location of the project area in relation to Saskatchewan in general.

2. Geology

The geology of the Meadow Lake area is discussed by Christiansen and Whitaker (1974), Christiansen et al. (1975), and Maathuis and Schreiner (1982).

The oldest lithostratigraphic unit that forms the bedrock surface in the Meadow Lake area is known as the Lower Colorado Group. This unit, which subcrops in the eastern part of the area, is equivalent in age to the wall rocks in the Fort a la Corne kimberlite field. The Upper Colorado Group overlies the Lower Colorado Group. The base of the Second White Speckled Shale is a re-gional stratigraphic marker in drill hole logs, and marks the base of the Upper Colorado Group. The overlying

Montana Group is represented by the Lea Park Forma-tion.

Continental, fluvial, and Jacustrine (?) sediments form the bedrock surface in the vicinity of Loon Lake. This material, which has been assigned a Tertiary-Quaternary age (Christiansen and Whitaker, 1974), con-sists of about 6 m of fine- to medium-grained sand overlain by about 24 m of non-calcareous silt which is clayey at the base and sandy at the top. None of the

Meadow Lake Indicator Minerals Project Area

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SASKATCHEWAN

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Cenomarnan-T uroman Boundary

Soutl1ern Saskatchewan Indicator Minerals Project

U.S.A.

Figure 1 - Location map of the study area in relation to the Province of Saskatchewan.

(1) Project funded by Cameco Corporation (66 percent) and Saskatchewan Research Council (33 percent). (2) Resources Division, Saskatchewan Research Council, 15 Innovation Blvd., Saskatoon, Saskatchewan, S7N 2X8.

Saskatchewan Geological Survey 181

bedrock units are known to be exposed in the Meadow Lake area.

The Empress Group (Whitaker and Christiansen, 1972) consists of stratified gravels, sands, silts, and clays that lie between the bedrock surface and the lowest till. The Empress Group sediments that occur in the Meadow Lake area are primarily found in the buried Hatfield Val-ley where they were deposited during the time of the first advancing ice-sheet (Christiansen et al., 1981). These sediments are also not known to occur at the pre-sent surface in the study area.

Overlying the Empress Group is the Sutherland Group comprising three till units (Christiansen, 1992) and their associated inter- and intraglacial sediments. The Suther-land Group (Christiansen, 1992) includes: a) the Floral Formation, which contains two tills and associated non-glaci al units; 2) the Battleford Formation (Christiansen, 1968), the upper-most till in west-central Saskatchewan; and 3) post-glacial sediments that are collectively, though informally, known as Surficial Stratified Drift. In addition to weathering horizons and oxidation zones that are sometimes preserved at the top of an individual unit, the tills can be differentiated by geochemical, geo-physical, and material properties (Christiansen, 1992; Schreiner, 1990). No attempt was made during the course of this study to classify the till samples beyond Sutherland Group or Battleford and Floral formations.

Surficial stratified deltaic and lacustrine sediments are extensive in the east where they were deposited in Gla-cial Meadow Lake during the fast deglaciation in the area (Christiansen et al., 1975). Elsewhere, glaciofluviat deposits are found in meltwater channels such as the Beaver River Valley.

3. Sample Collection A total of 108 surficial samples in the Meadow Lake area were collected during the summer of 1991. These included: nine samples of alluvium primarily from third-order streams; 15 samples of coarse-grained glacioflu-vial material, primarily from eskers, terraces, and outwash plains; 15 samples of till from glacial-thrust fea-tures; and 69 samples of till primarily from morainal plains. Samples were taken from natural and man-made exposures; such as road cuts, gravel pits, farm dugouts, and silage pits; as well as from hand-dug pits. Detailed field notes and photographs were taken at each sample site.

4. Sample Processing All samples collected in the field were sent to the SRC Geochemical Laboratory and were processed according to standardized SRC procedures. A 2 kg split of the original sample was retained for archival purposes. A small split (approximately 200 g) of the archival split from the till samples was submitted for fine fraction geo-chemical analyses (ICP/AA).

Kimberlite indicator minerals were selected from the ma-terial with a magstream specific gravity unit between

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3.0 and 4.2 (mid fraction). The mid fraction was wet screened to 0.25 mm and the coarse fraction was exam-ined under a binocular microscope. The primary mineral grains sought were pyropic garnets and potential orthopyroxene and clinopyroxene kimberlite indicators. The >0.81 mm fraction (non-magstreamed) of the heavy-mineral concentrates was also examined.

Potential indicator mineral grains were selected based primarily on colour and grain morphology. A total of 6042 grains were selected from the 108 samples. These grains were further colour classified and grouped prior to being submitted tor microprobe analysis.

All microprobe analyses were completed by the Depart-ment of Geological Sciences at the University of Saskatchewan using a JEOL Model JXA-8600 probe. The probe conditions and settings were 15 kV=10 nA, 10 µm defocused beam using PRZ correction and SPI standards.

A total of 1148 mineral grains underwent microprobe analysis, of which 363 were determined to be kimberlite indicators. All grains were mounted and individually probed. The probe mounting blocks and diagrams are stored at SRC.

Classification of the indicator minerals was based upon discriminate indices developed by Dawson and Stephens (1975, 1976) and Stephens and Dawson (1977). Ninety-four samples contained indicator mineral grains excluding G5 garnets, which although abundant in lamproites (Fipke, 1991) can also be of metamorphic origin. Table 1 lists the indicator minerals identified dur-ing this project, excluding G5 garnets.

Table 1 - Indicator-mineral grains identified (modified after Dre-ver, 1992). Gamet groups and names from Dawson and Stephens (1975, 1976). Pyroxene groups and names from Stephens and Dawson (1977). GS gamets are not included as they could be of a metamorphic/metasomatic origin.

Minerals Identified Number of Grains

Garnets Group Name

G1 G3 G4 (?) G6 GS G9 G10 G11 G12

Pyroxenes Group

CPX1 CPX2 CPX4 CPX5 OPX5

Picroil menite

Titanian pyrope Calcic pyrope-almandine Titanian, calcic, magnesian almandine Pyrope-grossular-a1mandine Ferro-magnesian grossular Chrome-pyrope Low-calcium chrome-pyrope Titanian uvarovite-pyrope Knorringitic uvarovite-pyrope

Name

Sub-calcic diopside Diopside Low-Cr-diopside Chrome-diopside H ig h-Ti-enstatite

3 132

2 39

117 40

2 6 1

1 9 6 1 3

Summary of Investigations 1994

5. Ice Directions

Surficial geology maps of the Meadow Lake area (Chris-tiansen et al., 1975; Sedimentary Resources, 1988) indi-cate that the most recent (Late Wisconsinan) ice flowed generally from northeast to southwest over much of the area; although there is evidence of some southeasterly flow in the ice-thrust moraine southeast of Cold Lake. These ice directions are related to the ice sheet that de-posited the Battleford Formation and very little is known about the ice-flow directions prior to the Late Wisconsi-nan. Work is currently in progress to more precisely de-fine older (pre-Late Wisconsinan) ice directions, which should help determine potential source areas for the in-dicator minerals.

6. References Christiansen, E.A. (1968): A thin till in west-central Saskatche-

wan, Canada; Can. J. Earth Sci., vs, p329-336.

___ __ ( 1992): Pleistocene stratigraphy of the Saskatoon area, Saskatchewan, Canada: An update; Can. J. Earth Sci., v29, p1767-1778.

Christiansen, E.A., Acton, D.F., Long, R.J., Meneley, W.A., and Sauer, E.K. (1981 ): Fort Qu'Appelle Geology: The Val-leys - Past and Present; Saskatchewan Culture and Youth, Interpretive Report No. 2.

Christiansen, E.A., Padbury, G.A., and Long, R.J. (1975): Meadow Lake Geology: The Land - Past and Present; Museum's Branch, Sask. Dep. Tourism and Renewable Resources, Interpretive Report No. 1.

Christiansen, E.A. and Whitaker, S.H. (1974): Geology and Groundwater Resources of the Waterhen River Area (73K) Saskatchewan; Sask. Resear. Coun., Gaol. Div., Map No. 19.

Dawson, J.B. and Stephens, W.E. (1975): Statistical classifica-tion of garnets from kimberlites and associated xenoliths; J. Geol., v83, p589-607.

Saskatchewan Geological Survey

____ (1976): Statistical classification of garnets from kimberlite and associated xenoliths - addendum; J. Geol., V84, p495-496.

Drever, G.L. (1992): Meadow Lake Indicator Mineral Project 1991-92, Summary of Results, Cameco Corporation, unpubl. rep.

Fipke, C.F. (1991 ): Significance of chromite, GS Mg-almandine garnet, zircon and tourmaline in heavy mineral detection of diamond bearing lamproite (abstract); The Geological Society of CIM, First Annual Field Conference (Prog. abstr.), Saskatoon, Sept. 1991, p30-31.

Maathuis, H. and Schreiner, B.T. (1982): "Hatfield Valley" Aquifer System in the Waterhen River area (73K), Saskatchewan, Volume I (Text and Appendices A to D); Sask. Resear. Coun., Publ. No. G-744-7-C-82.

Millard, M.J. (1994): Kimberlite indicator minerals in the Meadow Lake area, Saskatchewan. Sask. Resear. Coun., Publ. No. R-1210-1-E-94.

Schreiner, B.T. (1990): Lithostratigraphic correlation of Sas-katchewan tills: A mirror image of Cretaceous bedrock; Sask. Resear. Coun., Publ. No. R-1210-3-E-90.

Sedimentary Resources (1988): Surficial geology of the Water-hen area (73K), Saskatchewan; Sask. Resear. Coun. (map).

Simpson, M.A. (1991 ): Kimberlite Indicator Minerals in South-western Saskatchewan; Sask. Research Council, Publ. No. R-1210-8-E-91.

Stephens, W.E. and Dawson, J.B. (1977): Statistical compari-son between pyroxenes from kimberlite and their associ-ated xenoliths; J. Geol., v85, p433-449.

Whitaker, S.H. and Christiansen, E.A. (1972): The Empress Group in southern Saskatchewan; Can. J. Earth Sci., v9, p353-360.

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