Gold mineralization at the Golden Blocks gold field

Abstract

In the Golden Blocks area, vein-type gold and sparse sulphide mineralization occur in slightly metamorphosed, complexly deformed, Lower Ordovician sandstones and mudstones. Primary gold mineralization is associated with quartz veins in deformation zones occurring near the contacts of several carbonaceous mudstones. Eighty-five percent of the gold production from the area has come from five workings confined to the stratigraphically lowest, most widespread occurrence of mudstone. The distribution of primary mineralization is controlled by two factors: 1. The deposition of gold by solution- wall rock interactions between mudstone sediment constituents and mineralizing solutions 2. The confinement of lodes formed within mudstones to those portions of deformation zones which are close to or intersect sandstone units. Productive gold deposits are confined to those primary lodes, permeable to supergene solution movement, which intersected the Upper Cretaceous weathering surface. The Ordovician sediments hosting the ore-bodies are only weathered to depth along deformation zones, and primary ore values appear to be enriched to workable grades by supergene processes.