The Optimization of Geochemical Exploration for Gold using Glacial Till

Exploration & Mining Geology, Vol. 1, No. 4, 1992

IAN NICHOL Department of Geological Sciences, Queen's University, Kingston, Ontario, Canada, , O.P. LAVIN Newmont Exploration Ltd., Colorado, U.S.A. M.B. McCLENAGHAN Geological Survey of Canada, Ottawa, Ontario, Canada, and C.R. STANLEY, Department of Geological Sciences, The University of British Columbia, Vancouver, British Columbia, Canada

Exploration in most areas of Canada has to contend with problems posed by glacial overburden. In many areas exploration for gold has been based on the sampling of tills, frequently by deep overburden drilling, and analyses of heavy mineral concentrates. Notwithstanding the significant role that till geochemistry has played in the discovery of some important gold deposits over the last few years, increased appreciation of the nature of the glacial history and stratisgraphy and the character of gold within till has led to the recognition of a number of ways whereby the effectiveness of exploration can be improved upon. In order for till geochemistry to be useful in exploration, a number of conditions must be fulfilled, including: 1. mineralization, or alteration halo related to mineralization, subcropping at the bedrock/over-: burden interface; 2. glacial erosion and dispersal of a recognizable signature of mineralization into the glacial sediments; 3. preservation of glacial sediments containing this geochemical component (trace metal or mineral) , at positions subsequently selected for sampling (normally drill sites); 4. correct identification of specific till units and associated ice movement history; 5. collection of adequately large and representative samples; 6. appropriate sample preparation and processing; 7. appropriate geochemical analysis; and 8. correct data processing and interpretation. While we have no control over the first two geological conditions, and only limited control over till availability, we can control the quality and thoroughness of sampling, sample identification, sample preparation, analysis and interpretation. In particular attention needs to be focused on obtaining a large enough sample to be adequately representative, an unbiased sample must be collected, together with appropriate sample processing, analysis, data processing and interpretation. It is considered that by modifying or extending existing approaches to gold exploration, the chances of exploration success can be increased. In particular, analysis of both the heavy mineral and minus 63 /mi fractions of till is recommended because gold in till may occur in different size fractions.