Structural and Rheological Controls on Hydrothermal Fluid Flux within Orogenic Gold Systems — Insights from the Oberon Deposit, Granites-Tanami Orogen, Australia

Abstract The Oberon orogenic gold deposit within the Paleoproterozoic Granites-Tanami orogen provides insight into the evolution of mineralized hydrothermal systems and highlights critical controls on fluid flux. Here, we present the first detailed description of this economically significant deposit. We find that an interplay between rheological architecture, varying stress field, and hydrothermal fluid pressure significantly influenced the orientation, grade, and endowment of mineralization. Three discrete generations of mineralized veins are identified (V1/V1′OB, V2/V2′OB, and V3/V3′OB). Approximated stress field reconstructions based upon the vein arrays indicate that the Oberon deposit was subject to a low, yet variable, differential stress environment throughout its evolution. A regionally observable stress field reconfiguration between V1/V1′OB and V2/V2′OB vein development resulted in a transition from a transcurrent to a reverse shortening stress regime. This led to the generation of an incipient S2OB axial planar foliation, which was exploited by auriferous hydrothermal fluids. Critically, within the imposed reverse compressional stress regime, hydrothermal fluids were forced to attain supralithostatic pressures, and the resultant V2/V2′OB vein network forms the main stage of gold mineralization. The local abundance of all vein sets is controlled by rheological contrast, and most mineralized veins occur within rheologically competent siliciclastic sediments, especially where such units are juxtaposed against rheologically incompetent rocks such as altered mafic intrusions and carbonaceous mudstone.