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Abstract

Fluids rich in H2O and CO2 transport energy and mass in Earth’s crust and play a significant role during the deposition of mineral deposits. For a range of pressures, temperatures, and fluid compositions in the Earth’s crust, a buoyant immiscible phase of CO2coexists with a higher-density aqueous liquid. The density difference between these phases can generate carbonic flow systems because buoyant CO2 is driven to shallower levels in Earth’s crust at higher rates than pressure gradients are able to drive aqueous liquids. Here we consider this effect to extend existing hypotheses of processes that formed the Mesoproterozoic Mount Isa Copper ore bodies in Queensland, Australia. We investigate the potential role of a buoyancy driven carbonic fluid in the formation of the Mount Isa deposit. Our numerical simulations show that a giant copper sulphide deposit is able to form by such a process within thousands of years. Comparable hydrodynamic scenarios may be relevant for other hydrothermal deposit types, where processes such as upward flow of an aqueous liquid driven by vertical pressure gradients or free thermal convection are unlikely to achieve realistic rates of flow and metal transport.