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.