Controls on the porphyry Cu-Au mineralizing potential of magmas in post-collisional settings

Porphyry copper deposits are mostly related to calc-alkaline andesitic to dacitic magmatism above subduction zones. In the past two decades, many porphyry copper deposits were also confirmed to have formed in post-subduction tectonic settings, but ore-forming magmas in such settings are potassium-rich and the porphyry ores are frequently gold-rich. Prevailing models speculate that the post-subduction, potassium-rich magmas could have been sourced from either lower-crustal, sulfide-rich cumulates or from metasomatized lithospheric mantle related to previous subduction-related magmatism, and that these magmas are probably enriched in gold and thus could explain the gold-rich nature of the porphyry ores. Our project aims to test these hypotheses via a combined approach of piston-cylinder experiments (both partial melting and crystallization experiments) as well as studies on natural samples with particular focus on magmatic sulfides and melt inclusions.

Fig. 1 Distribution of porphyry Cu ± Au deposits and related epithermal deposits in the Alpine–Himalayan Tethyan orogenic belt. Tectonic reconstruction and ore-deposit age dating suggest that some of these ore deposits formed during subduction process, and some also formed during and/or after continental collision (Richards, 2014, Ore Geology Reviews, v. 70, pp. 323-345).
Fig. 2 Subduction versus post-subduction tectonic settings related to the formation of porphyry Cu deposits (Richards, 2011, Ore Geology Reviews, v. 40, pp. 1-26).