Magmatic to hydrothermal transition: a structural and tectonic influence on formation of porphyry Cu and epithermal ore deposits

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A delicate balance between events is required to generate a magmatic-hydrothermal system such as a porphyry Cu or epithermal deposit, assuming that the geochemical character of the parent magma is appropriate. Time is required to exsolve a fluid from a crystallizing magma chamber that escapes to rise buoyantly into the overlying hydrothermal system.  Moreover, the magmatic system must be contained and the hydrothermal fluid focused up a permeability structure (faults, dikes), and not be allowed to disperse widely into the hydrosphere.  In essence, there can be no catastrophic event that drains a chamber of magma or hydrothermal fluids, induces rapid cooling such that exsolution of hydrothermal fluids is suppressed or limited, or that the pressure seal around the magma chamber is continually disrupted such that hydrothermal fluids escape unfocussed.  Of the many potential factors that play a role, the influence of tectonics on magma chamber growth and delivery of a metalliferous hydrothermal fluid has largely escaped the attention of the economic geology research community.  However, physical volcanologists have worried about the question, arguing that the size and morphology of volcanoes and by inference the subvolcanic magma body is influenced by the tectonics during magmatism.  Essentially. tectonics as a important fundamental control on the subvolcanic intrusion and any derivative hydrothermal system as the overall geochemistry of the system.      As magma chambers beneath porphyry and epithermal deposits are in only rare cases of extreme post-mineral deformation accessible for study, an understanding of the tectonic environment conducive to the formation of these chambers must be inferred from the structural evolution of the associated hydrothermal deposits. This proposal continues a systematic investigation of structural controls and tectonic setting of porphyry and epithermal ore deposits in convergent margin magmatic arcs. This grant period will initiate work 2 porphyry Cu environments, the Cadia Cu-Au systems in Australia and the giant porphyry Cu-Mo deposit at Quellaveco (Peru).  These sites that different opportunities to examine indirectly the question.