Characterising VMS mineralisation at the Palaeoproterozoic Home of Bullion copper deposit, Aileron Province, central Australia

Abstract

The Home of Bullion deposit is a copper-lead-zinc ( silver-gold) deposit located 28 km east of Barrow Creek in BARROW CREEK, central Australia. Approximately 1000 t of copper was produced from Home of Bullion between 1923 and 1951 making it one of the largest copper mines in the Aileron Province. Despite its history, the style of mineralisation is still under discussion. This Record presents new results from field observations, petrography and whole rock geochemistry, together with published geochronology data, to constrain the timing and style of mineralisation at Home of Bullion.

The deposit consists of four stratiform lodes hosted by the Palaeoproterozoic metasedimentary and metaigneous rocks of the Bullion Schist. Massive sulfide mineralisation is characterised by tabular bodies of pyrrhotite, sphalerite, chalcopyrite and minor galena oriented parallel to bedding of the surrounding Bullion Schist. Local stratigraphy is characterised by mica schists, minor metasandstone, and mafic amphibolite, all of which are metamorphosed to lower greenschist facies and multiply deformed. Sulfides and silicates in the massive sulfide mineralisation are foliated and in metamorphic equilibrium, indicating mineralisation predates metamorphism and deformation.

Geochronology indicates metamorphism occurred within ~20 my of deposition of the Bullion Schist, implying mineralisation is likely near-syngenetic. Mafic amphibolites are spatially associated with mineralisation and have basalt to basaltic andesite protoliths derived from a source with significant crustal input. In the Bullion Schist, variable SiO2, Al2O3, MgO, and Fe2O3 concentrations are indicative of chlorite, pyrite, and sericite hydrothermal alteration in the hanging wall and footwall. Values of pathfinder elements bismuth, cadmium, and antimony correlate well with values of resource elements copper, zinc, lead, gold, and silver. Anomalous values of resource and pathfinder elements are identified in a ~20 m wide zone surrounding the mineralisation. These characteristics are consistent with a siliciclastic-mafic type volcanogenic massive sulfide deposit that forms in extensional environments with clastic sedimentation such as back-arc basins.