Visible gold content and lithology of till from overburden drillholes, Beardmore-Geraldton area, District of Thunder Bay, northern Ontario

A Canada-Ontario Mineral Development Agreement program of glacial geological research is presently underway in the Beardmore-Geraldton area of northern Ontario. This study is meant to test the usefulness of and provide guidelines for till sampling as a mineral exploration method. Elsewhere, it has been shown that analysis of the geochemistry, mineralogy and visible gold content of till samples can lead to the recognition of mineralized bedrock which acted as the source of glacially dispersed debris. In the vicinity of and northeast of Beardmore, samples from the uppermost metre of thin, discontinuous till contain numerous fine gold grains. This is a preliminary indication that surface till sampling is likely to be an effective exploration tool in this area. In the Wildgoose Lake-Geraldton area, however, thick till contains abundant Paleozoic limestone and Proterozoic metasediments, derived from the Hudson Bay Lowland 150 km to the northeast, which dilute and/or bury locally derived debris. In order to determine the stratigraphy and composition of this thick till fourteen rotasonic overburden boreholes were drilled by the Geological Survey of Canada, in cooperation with the Ontario Geological Survey, during September, 1987. The first analytical results of this drilling program, visible gold grain counts, are presented here. More detailed geochemical, lithological and mineralogical data will be presented in future publications. Included will be analysis for gold which may reside in a fraction which would be overlooked in visible gold analysis, such as gold in sulphides or extremely fine grained gold. Other elements, which may serve as indicators of gold mineralization, are also being studied. The Paleozoic carbonate (limestone) rich upper till which is present throughout the area and which is responsible for the great till thicknesses encountered in the study contains isolated single gold grains which are probably unrelated to local mineralization. Low gold grain counts, accompanied by very abundant sulphides, were obtained from the lower till in two holes located in Colter Township, between Turkey and Scroll Lakes. A high gold grain count and numerous sulphides were obtained in a lower till unit at a site located in central Lindsley Township. This hole was located on Highway 11 at a pipeline access road 0.3 km east of the Wildgoose Beach road. Neither the distance nor the direction of glacial dispersal for this till unit is known. Ice flow indicators such as striations and drumlins imply southwestward or south-southwestward dispersal. The possibility that this till is associated with an older west-southwestward ice flow should not, however, be discounted.