Metalliferous economic geology of the Mt Isa Eastern Succession, Queensland

Recent discoveries east of Mt Isa such as Cannington (Ag-Pb-Zn) and Ernest Henry (Cu-Au-Co) have significantly increased the known metal endowment of the major Proterozoic metals province formed by the McArthur Basin and Mt Isa Inlier in northern Australia. The `Eastern Succession' or 'Cloncurry' ore systems include Cu-Au, Au-only, Pb-Zn-Ag and U-REE types that are quite distinct from deposits further west despite the broadly similar age and tectonic evolution of the host sequences. The abundant Cu-Au deposits exhibit no fundamental stratigraphic control and are localised by faults that channelled high temperature (300-500 degrees C) and very high salinity ore fluids at about the end of the ca 1620-1500 Ma Isan Orogeny. Circumstantial evidence points to a link with granitoids of the late to post-orogenic Williams-Naraku Batholiths. Sulfides were deposited through combinations of fluid cooling, wall-rock reactions and phase separation. In one case (Osborne deposit) it has been shown that mineralisation occurred at depths of more than 4.5 km. The Fe-oxide-Cu-Au association and styles of mineralisation in the largest deposits forge links with other Proterozoic provinces (e.g. Gawler Craton and Tennant Creek inlier). Pb-Zn-Ag occurrences are much rarer but include two major deposits (Cannington and Dugald River). The examples in the southeast of the area including Cannington are restricted to a <1680Ma metamorphosed siliciclastic sequence. They exhibit affinities with the giant deposit at Broken Hill including high-metamorphic-grade host rocks, skarn-like gangue and spatial association with various quartz-garnet, magnetite-rich, and gahnite-bearing lithologies, These deposits display evidence of a protracted evolution including substantial effects of late to post-orogenic alteration and ii is unclear whether they are products of a premetamorphic mineralising event or are coeval with the Cu-Au systems.