Till sampling in the Casa-Berardi gold area, Quebec: A case history in orientation and discovery

Abstract

Sauerbrei, J.A., Pattison, E.F. and Averill, S.A.,, 1987. Till sampling in the Casa-Berardi gold area, Quebec: A case history in orientation and discovery. In: R.G. Garett (Editor), Geochemical Exploration 1985. J. Geochem. Explor., 28: 297-314. Inco Limited discovered gold in northwestern Casa-Berardi township, Quebec, in April 1981. The discovery, named the Golden Pond Zone, is located under approximately 45 m of overburden.Diamond drilling at Golden Pond up to August 1983 indicated two main zones of Au mineralization on either side of a major east-west-trending graphitic fault zone. The mineralization consists of pyrite-arsenopyrite-native Au-bearing quartz-carbonate veins in carbonatized Archaen sediments and volcanics. A reverse-circulation overburden drilling program was undertaken in the vicinity of the Golden Pond zone in December 1983. The program, under the management of Overburden Drilling Management of Ottawa, was designed to test for glacial dispersal of the known mineralization and thereby to evaluate the effectiveness of till sampling as an Au exploration method in the Casa-Berardi area. Gold and As anomalies related to the Golden Pond zone are found mainly in heavy-mineral concentrates of the lower till that lines the bedrock depression which is spatially associated with bedrock mineralization. These anomalies occur south of the known mineralization and constitute an example of a glacial dispersal train. Most of the till gold grains are very fine (50-150 microns). The gold grains in the till 100 m south of the Golden Pond zone are delicate while the majority of those encountered 400 m to the south are either irregular or abraded, indicating transport over greater distances. Following the success of orientation survey, till sampling was used as a screening tool to evaluate geophysical and/or stratigraphic targets east and west of the Golden Pond zone prior to diamond drilling. During the initial sampling program in early 1984, targets were commonly tested at intervals of either 300 m or 400 m along strike and 25-100 m down ice. Closer-spaced sampling was undertaken to further define anomalous dispersal trains prior to diamond drilling. Two reversecirculation holes drilled 300 m apart in April 1984 to test the continuation of the Golden Pond geophysics encountered an anomalous gold-arsenopyrite dispersal train 2.5 km to the east. Followup till sampling in June 1984 further defined the anomalous train. The heavy-mineral concentrate from the bottom till sample of a hole 100 m east of the earlier anomalous hole contained approximately 700 very delicate gold grains, mostly in the 50-100 micron size range, and was concluded to be at source. Diamond drilling in July 1984 confirmed the existence of the Golden Pond East zone. 0375-6742/87/$03.50 © 1987 Elsevier Science Publishers B.V.