Evaluation of the contributions of gold derived from hypogene, supergene and surficial processes in the formation of placer gold deposits

Abstract Placer gold particles have traditionally been considered as either detrital products of weathering or authigenic minerals growing within placers. Recent advances in understanding chemistry/bio-geochemistry demonstrate that growth specific environments is plausible, but opinions differ on the importance ‘new’ overall placer inventory. Here we draw upon visual inspection over 40 000 polished particle sections from locations worldwide to evaluate implications alloy composition and heterogeneity determining contributions fluvial We conclude that: (1) model formation widespread demonstrable; (2) supergene may be a locally important constituent placers; (3) gold-rich rims comprise two distinct components – surface micron-scale addition pure Au tens-of-microns-scale inner rim formed by Ag depletion; (4) inventories modification biogenic processes considerably overstated.