Humus and till geochemistry over the Doyon, Bousquet and Williams gold deposits

CIM Bulletin, Vol. 80, No. 898, 1987

C.F. GLEESON, C.F. Gleeson and Associates Ltd. Iroquois, Ontario, and D.G. SHEEHAN Lac Minerals Ltd. Toronto, Ontario

The results of humus and overburden geochemical surveys over the Doyon, Bousquet and Page- Williams gold ore deposits are presented. These studies show that humus sampling for gold gives negative results over the Doyon deposit. The lack of response is probably caused by the presence of 1 m of relatively impermeable glaciolacustrine clay and silt that overlies 1 m to 2 m of till over the surface expression of the ore zone. By contrast, positive responses for gold occur in humus samples over the Page-Williams A and C gold deposits. The "A " ore zone is covered by several metres of exotic calcareous till over 0.5 m to 1 m of older, locally derived till. Anomalous values for gold in humus range from 10 to 35 ppb over the orebody. Overburden over the "C" ore zones is much thinner, generally it consists of less than 2 m of sandy till. Trenching humus anomalies that range from 10 to 1360 ppb Au uncovered the gold mineralization. The geochemical dispersal trains in till from the Doyon ore-body and the Page- Williams "A "zone are relatively short (i.e. less than 200 m) because both deposits occur in the lee of bedrock highs that shielded them from extensive glacial quarrying. Dispersal trains from all three pyritic gold deposits can be defined using either the fine fraction or heavy mineral fraction of the till. The intensity of the gold in till anomalies over the ore zones is variable. Therefore, it would be misleading to attach rigid significant threshold gold values to overburden drilling results. Each case must be evaluated based on bedrock topography, sample density, overburden type, thickness of till, as well as size, type and orientation of the target exposed to glacial erosion.

Mots Clés: Mineral exploration, Geochemical surveys, Gold ore deposits, Humus geochemistry, Till geochemistry, Overburden drilling.