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Postsubduction porphyry Cu-Au and epithermal Au deposits: Products of remelting of subduction-modified lithosphere

¹ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

View larger version (30K): [in this window] [in a new window]   Figure 1. A: Porphyry Cu generation as a product of normal arc magmatism; continental arc is shown, but similar processes can occur in mature island arcs. MASH—melting, assimilation, storage, and homogenization. SCLM—subcontinental lithospheric mantle. B–D: Remelting of subduction-metasomatized SCLM or lower crustal hydrous cumulate zones (black layer) leading to potential porphyry Cu-Au and epithermal Au deposit formation. B: Collisional lithospheric thickening. C: Postcollisional lithospheric mantle delamination. D: Postsubduction lithospheric extension. High Sr/Y and La/Yb magmas may be generated in all cases by residual or fractionating hornblende (±garnet, titanite) in the lower crust.

View larger version (29K): [in this window] [in a new window]   Figure 2. Concentrations of Cu and Au in silicate magma as function of R = (mass of silicate melt)/(mass of sulfide melt) (Campbell and Naldrett, 1979). Cu-rich magmas can form at relatively low R factors (R = 102–105), but leave a relatively Au-rich sulfide residue. Remelting of this sulfide residue (R 105) during second-stage melting events can generate relatively Au-rich magmas.