Till and vegetation geochemistry at the Talbot VMS Cu-Zn prospect, Manitoba, Canada: implications for mineral exploration

Abstract

The Proterozoic Talbot VMS occurrence in the Flin Flon-Snow Lake terrane is buried under more than 100 m of Palaeozoic dolomites and Quaternary glacial till. Structurally controlled anomalies of Zn, Cu, Ag, Pb, Au, Mn, Hg, Cd, Co, Bi and Se in the clay fraction of till depth-profiles indicate upward element migration from the buried volcanogenic massive sulphide mineralisation and near-surface chemostratigraphic deposition. Principal component analysis and molar element ratios indicate that separation of the <2 µm clay fraction reduces chemical heterogeneity and increases trace-element yield relative to the <250 µm fraction of the till. The greatest anomalies occur at or below 30 cm depth and over faults, suggesting that elements were deposited in the till after upward migration through structures. The ratio Zn/Al in the <250 µm fraction can be used as a proxy for Zn in the clay fraction, producing high-contrast anomalies. Carbon isotopic compositions indicate that these anomalies are related to organic carbon in the clay fraction. Humus, moss and black spruce bark are of limited use for exploration in this environment, because they accumulate atmospheric Pb and Cd, most likely from the Flin Flon smelter at 160 km NW. Black spruce tree rings that formed before smelter operations commenced indicate Zn and Mn anomalies in an uncontaminated sampling material. Much of the initial vertical migration of elements to the surface at the Talbot prospect was driven by upward advection of groundwater through fractures in the dolomite, resulting from a combination of subsurface karst collapse and remnant hydrostatic pressure during glacial retreat.