Iron oxide copper-gold (IOCG) systems form in a range of lithologies, including variably metamorphosed felsic and mafic volcanics, carbonates and siliciclastic sedimentary rocks. The chemistry, porosity and permeability of the host rocks control the reactive potential of mineralising fluids. They form across a range of crustal rheologies, from mid-crustal (ductile) to upper-crustal (brittle) conditions. IOCGs are focussed via a range of structural controls, including permeable strata, shear zones, fault jogs, splays and intersections and breccia pipes. The mechanism of fluid localisation controls geophysical zonation (e.g., planar vs concentric zonation). IOCGs also comprise a spectrum of mineralisation assemblages from reduced, pyrrhotite-dominant examples to magnetite-, and more oxidised, hematite dominant deposits. Such Fe-bearing minerals have contrasting magnetic, density and conductivity properties, and therefore redox/pH and geophysical properties are linked. The interaction of major controls, including host rock chemistry, rheology, structural controls, and redox/pH conditions, define the style of geophysical anomaly associated with an IOCG system. The Cloncurry mineral system comprises a spectrum of deposit styles, not observed across the other major IOCG provinces, and provides an excellent window into the array of possible geophysical signatures. This study synthesises findings of Cloncurry METAL, a three-year study which collected integrated petrophysics, mineralogy and structural data from almost every major deposit/prospect in the Cloncurry district. It provides petrophysical properties of the host rocks and mineralised lithologies across the mineral system and explore some of the ways variations in host rock chemistry and rheology, structural controls and redox/pH zonation interact to form contrasting geophysical targets.

Open-Access Online Publication: May 29, 2023