Timing relationships between felsic magmatism and mineralisation in the central Victorian gold province, southeast Australia

Abstract

New SHRIMP U–Pb data from major felsic intrusives and dykes confirm that initial gold emplacement in the central Victorian gold province was metamorphic‐related, pre‐dating the emplacement of Devonian intrusions in the western Lachlan Fold Belt by as much as 80 million years. Importantly, together with previously published geochronological constraints, these data strongly suggest that no genetic link exists between the main phase of ‘metamorphism‐related’ orogenic gold mineralisation and magmatism in the central Victorian gold province. A subsequent ‘intrusive‐related’ phase of gold mineralisation, often accompanied by elevated copper, tungsten, molybdenum or antimony, formed synchronously with, or post‐dated, the emplacement of Devonian plutons and dykes, and thus is spatially (if not genetically) related to melt generation at depth. These timing relationships differ from those found in many other orogenic gold districts in which ore emplacement is closely associated, spatially, with felsic magmatism. The introduction of metamorphically derived fluids well before magmatism is seen to reflect variations in the timing of peak metamorphic conditions at different crustal levels. The extensive development of melt in this environment is thought to occur in response to the transfer of thermal energy from the mantle into the overlying, thickened crust in a Cordilleran‐type setting, which is dominated by episodic subduction‐accretion processes. The new SHRIMP U–Pb data also demonstrate that many of the major granites throughout the central Victorian gold province have a composite intrusive history and are the product of multiple tectonomagmatic events.