Surficial exploration methods for detecting low sulfide high precious metal and Ni-Cu-PGE mineralization in glaciated terrain

Abstract

The increasing difficulty of finding near-surface mineral deposits in glaciated terrain requires modification of conventional exploration techniques (drift prospecting) that can assist in exploring for deposits buried under glacial sediment cover of variable thickness. To address this challenge, a humus and soil (developed in till; “C-horizon till”) sampling study was conducted in the Drury and Denison townships in the South Range of the Sudbury Igneous Complex (SIC) to develop surficial mineral exploration techniques that are suitable for low sulfide, high precious metal (LSHPM) and massive sulfide Ni-Cu-PGE mineralization. The objectives of this project were to assess the suitability of humus and till for delineating geochemical anomalies in an established mining camp (the Sudbury Mining Camp) and characterize the chemistry of chalcopyrite, pentlandite and sperrylite grains in till derived from LSHPM (the Vermilion Cu-Ni-PGE-Au deposit) and Ni-Cu-PGE (the Crean Hill deposit) mineralization. Results of this study suggest that the natural geochemical signature of humus in the Sudbury Mining Camp is strongly overprinted by anthropogenic contamination such that the geogenic signal is only apparent in humus samples collected in the vicinity of known Ni-Cu-PGE mineralization. Glacial dispersal from Ni-Cu-PGE mineralization is apparent in C-horizon till and compared to the background (up-ice) concentrations, the C-horizon till samples collected immediately down-ice of the Vermilion deposit are enriched over 20 times in Pt, Au, and Cu, and over 30 times in Ni. Pathfinder elements that show a strong, positive correlation with Ni, Cu, Au, and PGEs (Pt, Pd, Ru, Rh, and Ir), that are also derived from LSHPM and Ni-Cu-PGE mineralization are As, Bi, Co, Cr, Pb, Sb, and Te. Ore minerals that survive glacial transport and post-glacial weathering and are the best indicators of Ni-Cu-PGE-Au mineralization are chalcopyrite, sperrylite, and gold grains. Glacial modification of ore minerals is limited to physical comminution and does not affect their chemical composition. Precious metals are detected in ore minerals derived from LSHPM mineralization. These consist of Ag, Au, Ir, and Pt in chalcopyrite, Ag, Au, Pt, Pd, Rh, and Ru in pentlandite and Ag, Au, Ir, Pd, Rh, and Ru in sperrylite.