A metasomatised mantle origin for post-collisional porphyry ore-forming magmas in the Sanjiang metallogenic belt, Southwest China

We constrain the magma sources of representative post-collisional ore-associated and barren suites in the Sanjiang metallogenic belt, Southwest China. The ore-associated suites generally have higher Mg# and Cr and Ni contents than the crustal melts. Also, they show wide ranges of whole-rock Nd and zircon Hf isotopes that are similar to the subduction-modified mantle-derived alkaline volcanic rocks in the region. Combing with the geochemical model, we suggest that the ore-associated suites dominantly originated from partial melts of subduction-metasomatised mantle by fractional crystallisation. In contrast, the barren suites are mainly characterised by low Mg# and Cr and Ni contents that are comparable to the crustal melts and they have enriched whole-rock Nd and zircon Hf isotopes, indicating a metasomatised lower crustal origin. The different magma sources play an important role in controlling the fertility of contemporary ore-associated and barren magmatic suites during post-collisional porphyry ore formation.