Weathering of the zinc-lead lode, Dugald River, northwest Queensland: II. surface mineralogy and geochemistry

Abstract

Gossans associated with the Dugald River zinc-lead lode contain anomalous concentrations of Zn, Pb, Ag, As, Cd, Cu, Sb, Se, Tl and Ba and differ from those on the more pyritic Western Lode (Zn, Pb, Cu, As, Tl) and those associated with copper mineralization in the hanging wall (As, Bi, Co, Cu, Mo, Ni, Sb). Mineralogical and geochemical variations in gossans along strike reflect changes in primary ore and gangue mineralogy, particularly towards the north, where the Dugald River lode and hanging wall copper mineralization merge. Leaching of more soluble elements from the surface and re-precipitation below have resulted in large geochemical variations in the top metre of the profile. Dispersion into wall rocks has occurred over two distinct periods: hydromorphic dispersion, before erosion removed much of the gossan and surrounding Corella Formation, has resulted in very high Zn contents (up to 9%) in the footwall, whereas a more even dispersion of target and pathfinder elements into hanging and footwall rocks is from recent weathering of the slightly elevated gossan.