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.

中文翻译：

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三江成矿带碰撞后斑岩成矿岩浆的交代地幔成因

我们对西南三江成矿带代表性的碰撞后伴生矿套和贫瘠套的岩浆来源进行了限制。伴生矿套一般具有比地壳熔体更高的 Mg#、Cr 和 Ni 含量。此外，它们还显示出广泛的全岩 Nd 和锆石 Hf 同位素，与该地区俯冲改性的地幔衍生的碱性火山岩相似。结合地球化学模型，我们认为伴矿岩套主要来源于俯冲交代地幔的分异结晶作用的部分熔融。相比之下，贫瘠岩套的主要特征是 Mg# 含量较低，Cr 和 Ni 含量与地壳熔体相当，并且全岩 Nd 和锆石 Hf 同位素富集，表明其是交代化的下地壳成因。