OTHER NORTHERN STUDIES

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Quaternary Geology of the Waddy Lake Area Applied to Prospecting for Gold

by Janet E. Campbell1

Campbell, J.E. (1985): Quaternary geology of the Waddy Lake area applied to prospecting for gold; in Summary of Investigations 1985. Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 85-4.

The Saskatchewan Research Council (SRC) has initiated a project in the Waddy Lake area (Fig. 1) to document such Quaternary geology conditions as the type, distribution and stratigraphy of deposits; the source of materials; and the direction and distance of transport. This information will be used to determine the most useful sampling media and the most effective techniques for drift prospecting.

The 400 km2 study area, centred around Waddy Lake. coincides with the area of bedrock mapping being carried out by the Saskatchewan Geological Survey. This region of the La Ronge Belt was chosen because of the presence of known gold deposits and showings, and its complex Quaternary geology, which includes the presence of Lake Agassiz lacustrine sediments.

A summary of this summer's field investigations and some preliminary observations are included in this report, together with a preliminary map (Sheets 1 and 2, map

m Phanerozoic

D Ath1;1bo1<:a Group (Hellkion)

D Pre · A1habo1ca baHrnent

~ Major shtor zone

Figure 1 - Location of the study area.

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'Resources Sector. Saskatchewan Research Council. Saskatoon.

pocket) showing the distribution of surficial deposits. The final Saskatchewan Research Council report, to be published at a later date, wilt include the results and interpretation of all work and analyses.

Procedure

The first stage of the study involved the mapping at 1 :20,000 scale of the deposit types and their areal distribution. Airphoto interpretation of the surficial geology was completed prior to the fieldwork. Ground­checking was carried out at 285 sites. Hand-augered holes or small pits were dug to an average depth of 80 cm at most of these sites. At six locations (WL-277 to 285), large backhoe pits expose sediments to a depth of 3.5 m.

Subsurface stratigraphic information was obtained by drilling 18 power-augerholes along the Waddy Lake access road approximately 1000 m apart at depths of 2 to 20 m, the average depth being 8.3 m. It is assumed that most holes reached bedrock, although this is not certain since the augerdrill cannot penetrate bedrock or very large boulders. Basal till was encountered in all but one hole. The information obtained from these holes will aid in characterizing the drift units and their mode of formation and will, in turn, be used to develop a model of the Quaternary geology for the area.

Representative samples of the various deposits were collected, but the main emphasis has been on sampling the till wherever it was encountered. Surface samples were taken from the C-horizon when possible. One hundred and eight bulk till samples weighing between 5 and 8 kg were collected throughout the study area, including 16 from augerholes. Surface bulk till samples were preferentially taken from the up-ice side of highlands, ridges and outcrops wherever possible.

General Geology The areal distribution of surface material is shown on the accompanying surficial geology map (Sheets 1 and 2, map pocket). The approximate percentages by area of materials are: bedrock (30), glacial till (35 to 40). glaciolacustrine (15 to 20), organic (10), and glaciofluvial (less than 5). Based on information provided from the augerholes and exposures examined, the complete stratigraphy is:

6) Organic material 5) Brown silty till 4) Lacustrine sediments

3) Fluvial sediments 2) Grey sandy till (greenish to brownish) 1) Bedrock

Some or all of the units above bedrock are locally absent.

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Bedrock Outcrop is relatively abundant but is commonly masked by moss and lichen. The predominant rock types are metavolcanics. metasediments and felsic to intermediate intrusives (Harper, 1984). Weathered bedrock, in the form of fe/senmeer, has been found around Round Lake. The undulating terrain of the exposed bedrock and the limited overburden drilling in the Waddy Lake area suggest a highly variable bedrock surface topography.

Glacial Till Two tills previously detected in exposures and augerholes in the region (Schreiner. 1984) were confirmed during the present investigation.

The lower grey sandy till is commonly greenish-grey, dense. has a silty sand matrix and contains abundant granules and angular to subangular gravelly clasts. the last-mentioned forming 30 to 50 percent of the deposit. This till reflects the local bedrock l ithology. A greenish­grey variety of this till is rich in volcanic rocks (mainly andesite), in contrast to a till originating from the pluton which tends to be brownish-grey and more sandy.

The upper till is thin and discontinuous and has been recorded at six sites. At two of these sites (backhoe pits WL-281 and 285), the till is less than 100 cm thick. At augerhole site WL-318. the till is over 3 m thick. The upper till is brown with a clayey to sandy silt matrix containing a lower percentage of smaller and more rounded clasts. The composition of this till reflects the incorporation of stratified sediments which have been overridden. This overriding is thought to be related to a minor readvance of ice into the Lake Agassiz basin (Schreiner, 1984).

Glaciofluvial Deposits Less than 5 percent of the Waddy Lake area 1s covered by glaciofluvial sand and gravel. These deposits occur mainly in small channel-like depressions or as isolated kames. Just north of Rogers Lake. a kame complex includes several small eskers which form part of the lake's shoreline. Another large deposit is located around the gold deposit at Wedge Lake. Several sandy areas appear to be transitional between fluvial and lacustrine environments.

Glaciolacustrine Deposits Clayey to sandy silt is the predominant glaciolacustrine material present although fine sand and clay are also

found. The structure of these sediments is most commonly massive but laminated and/ or varved varieties also occur at depth, as encountered typically in many of the backhoe pits and augerholes.

Glacial lake sediments are extensive but discontinuous. These sediments vary greatly in thickness, partly due to the rugged underlying topography. Permafrost is discontinuous but abundant in these sediments. Glaciolacustrine sediments were found at a maximum elevation of approximately 439 m (1440 ft.) in three locations. A cobble beach at approximately 457 m (1500 ft.) elevation is evidence of the highest lake level found to date. Several other beaches found in the Waddy Lake area occur at elevations ranging from 392 m (1285 ft.) to 450 m (1475 ft.). Washed and reworked till, and boulder lags also provide some indications of the extent of the glacial lake.

Organic Deposits Most of the small lakes and major creeks and rivers in the area are bordered by wetlands. Muskeg occurs sporadically throughout the area. Three of the drier muskegs tested are relatively shallow (less than 100 cm thick) and are overlain by silts and clays or boulder lags. Pa/sen are present in some of the larger and wetter deposits, indicating the presence of permafrost.

Ice Direction Indicators Numerous stnae were noted on outcrops throughout the study area. ranging in direction from 1880 to 2050, although 19()0 to 1920 are the most common. These directions may represent more than one ice movement. Several roches moutonees with similar orientation have been found in this area.

Sample Analaysis Characterization of the drift units by geochemistry, heavy minerals and pebble counts is included in the study. In addition, all samples are being subjected to textural analysis. At present, 158 till samples (including bulk till samples) have been analyzed at the SRC for copper, silver. arsenic, and gold. These samples were sieved to 0.1 mm (-150 mesh) and analyzed by atomic absorption. Heavy mineral separation of the bulk till samples is presently in progress at the SRC using a Wilfley Table and Superpanner. Samples are also being panned manually to separate the gold grains, which are then described and counted before the concentrates are assayed . The results from the gold grain counts and the geochemical and heavy mineral analyses will be compared to determine the most representative analyses. These analyses will provide background information for interpretation of mineral distribution (especially gold) in the tills, and will aid in the identification of the drift units most effective for exploration sampling.

Summary and Conclusions Although few analytical results are yet available, several important preliminary observations can be made:

1) Two distinct tills are present in the area. The upper brown silty till is thin and very discontinuous. The basal or lower. grey sandy till is more prevalent. Variations in the lithology of the lower till reflect the variations in the local bedrock source, making it the preferred sampling medium.

2) Glaciolacustrine sediments are found at elevations as high as approximately 439 m (1440 ft.). The maximum lake level has been established by the presence of a cobble beach at 457 m (1500 ft.) .

3) The rugged nature of the bedrock and till surface causes great variability in the thickness of the lake sediments.

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Acknowledgements The cooperation of the Saskatchewan Mining Development Corporation, Golden Rule Resources Ltd. and Goldsil Resources Ltd. in allowing access to their properties is gratefully acknowledged. Special thanks are given to Placer Development Ltd. for their assistance, cooperation and support during this summer's fieldwork. especially to Bill Pentland and Michael Gareau for their help and numerous fruitful discussions.

References Harper, C.T. (1984): Geological mapping, Waddy Lake

area (part of NTS 64D-4 and -5); in Summary of Investigations 1984, Sask. Geol. Surv., Misc. Rep. 84-4, p6-20.

Schreiner, B.T. (1984): Quaternary geology of the Precambrian Shield, Saskatchewan; Sask. Energy Mines. Rep. 221, 106p.