Abstract

The Cobar mining field, New South Wales, consists of three types of deposits: copper + gold-rich ones, 0 to 18 km south of Cobar (Central, The Peak, and Coronation-Queen Bee areas); copper + lead + zinc-rich ones, 10 km north of Cobar (C.S.A. mine); and silver + lead + 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 + 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. In the Central area deposits, mineralized veins are north-northwest-trending steeply east-dipping, northwest-trending steeply east-dipping, and subhorizontal. The steep north-plunging shape of the orebodies reflects maximum dilation at the intersection of the north-northwest-trending and northwest-trending sets of veins.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.

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