Magmatic Controls on Au/Cu Ratios in Porphyry Ore Fluids: Constraints From Crystal-Melt Experimentation

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9909576CandelaSome Cu and Au-bearing ores, such as many porphyry, skarn and sheeted vein-type deposits, are related spatially and temporally to intermediate to felsic intrusive igneous rocks. However, the controls on the Cu to Au ratio in these deposits are not clear. We propose to study one aspect of the magmatic behavior of Cu and Au that can shed light on how Cu/Au of ore can be affected by magmatic parameters. In the proposed research, we will investigate the partitioning of Cu and Au among the phases magnetite, biotite and melt. Experiments on magnetite and biotite will be conducted over a range of temperatures and pressures. The oxygen fugacity will also be varied in the experiments. We will combine the results of the proposed research with our published results on the partitioning of Cu and Au between sulfide minerals and melt to evaluate the effect of the sequestering of ore metals on the Au/Cu ratios of intrusion-related ore fluids.