Copper- and gold-rich deposits in deformed turbidites at Cobar, Australia: their structural control and hydrothermal origin

The Cobar mining field, New South Wales, consists of three types of deposits: copper plus gold-rich ones, 0 to 18 km south of Cobar (Central, The Peak, and Coronation-Queen Bee areas); copper plus lead plus zinc-rich ones, 10 km north of Cobar (C. S. A. mine); and silver plus lead plus zinc-rich ones, 40 km north of Cobar (Elura mine). All deposits are hosted by folded and cleaved Early Devonian thin-bedded turbidites and lie oblique to bedding. Previous ideas of ore genesis have varied from epigenetic (by early workers) to remobilized syngenetic by more recent ones. The copper plus gold deposits discussed here are structurally controlled and lie in zones of silicification on or adjacent to major faults. With the exception of minor, massive lead-zinc mineralization, mineralization occurs in veins (generally in quartz veins) and as disseminations in silicified rock. Surface veins around deposits of the Central area have been grouped into six geometric sets, with formation taking place over a prolonged history during the D//1 deformation of the surrounding sediments. This implies that the vein-style mineralization is epigenetic in origin and that it resulted from precipitation from hydrothermal fluids circulating through major faults and adjacent fractures connected to those faults.