Discriminating magmatic and hydrothermal processes in borehole data: implications for orogenic gold in Yilgarn Craton, Western Australia

In this paper we give an example from the Fortitude North prospect in the Kurnalpi Terrane of the eastern Yilgarn Craton, where the integration of geochemistry with borehole petrophysics can be used to identify lithological units, infer geological processes (e.g., magmatic differentiation, alteration and weathering) and constrain geological and geophysical models of the prospect. We use major and immobile trace element concentrations to discriminate between primary lithologies and identify differentiation trends in the mafic magmatic units. Density and seismic velocity measurements show broad correlation with primary rock types, with unaltered dolerite tending to have higher density and velocity compared to basalts and altered rocks. Magnetic susceptibility measurements are used to corroborate geochemical differentiation trends, specifically magnetite fractionation in dolerite units. A range of gold pathfinder and chalcophile elements are used to identify hydrothermal alteration related to gold mineralisation. Integrating geochemistry and petrophysics at drillhole- and prospect-scales helps to constrain important geological processes and demonstrates how those processes can be interpreted from geophysical data sets.Open-Access Online Publication: May 29, 202