Metalliferous economic geology of the Mt Isa Eastern Succession, Queensland

Abstract

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°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 <1680 Ma metamorphosed siliciclastic sequence. They exhibit affinities with the giant deposit at Broken Hill including high‐metamorphic‐grade host rocks, skam‐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 it is unclear whether they are products of a pre‐metamorphic mineralising event or are coeval with the Cu‐Au systems.