西秦岭温泉斑岩钼矿床复式岩体岩浆氧逸度对成矿的制约

温泉斑岩钼矿床位于西秦岭东段，是该区发现的一个具有大型矿前景的斑岩型钼矿床。围岩温泉复式岩体发育5个岩相单元(Ⅰ~Ⅴ)，钼矿体(化)主要赋存于复式岩体Ⅱ单元富含镁铁质包体的黑云母二长花岗斑岩和Ⅲ单元富含镁铁质包体的似斑状二长花岗岩及其接触带内，其余岩相(包括单元Ⅴ似斑状正长花岗岩)很少发育矿化。该研究使用全岩地球化学数据和锆石微量元素含量数据，计算得到不同岩相单元的氧逸度。Ⅱ单元和Ⅲ单元含矿斑岩相对氧逸度ΔFMQ分别为1.35和1.38。Ⅰ单元黑云母花岗岩和Ⅳ单元二长花岗斑岩相对氧逸度ΔFMQ分别为-0.61和-0.73，明显低于含矿斑岩。富集地幔物质的加入与否可能是造成不同岩相之间氧逸度差异的主要原因。高氧逸度的熔体可以将秦岭地区古生代富钼沉积物中的钼氧化萃取出来，并使钼与高价态硫络合，不断在熔体中高度富集，最终成矿。氧逸度较低的熔体很难萃取和保存足够的钼，因而很少发育矿化。

Constraints of magmatic oxidation state on mineralization in the Wenquan porphyry molybdenum deposit,West Qinling,China

The Wenquan porphyry Mo deposit, containing 0.12 Mt Mo at average Mo grade of 0.048%, is closely associated with the concentrically zoned multiphase Wenquan batholith in the West Qinling Orogen. The Wenquan batholith consists of five units: biotite granite(Ⅰ), biotite monzogranite porphyry(Ⅱ), porphyritic monzogranite(Ⅲ), monzogranite porphyry(Ⅳ) and porphyritic syenogranite(Ⅴ). The disseminated and veinlets Mo mineralization is genetically associated with the biotite monzogranite porphyry and porphyritic monzogranite phases and hosted mafic enclaves. We calculated the oxygen fugacity (f(O2)) of the multiphase Wenquan batholith by using a relation for cerium redox equilibria in silicate melts and an internally-consistent model for zircon-melt partitioning of Ce. The ore-bearing porphyries had average f(O2) of ΔFMQ=1.35 and ΔFMQ=1.38 for units Ⅱ and Ⅲ, respectively, while the barren porphyries had lower f(O2) values of ΔFMQ=-0.61 and ΔFMQ=-0.73 for unit Ⅰ and Ⅳ, respectively. We therefore proposed that oxidized magmas can be associated with enriched mantle. Molybdenum can be extracted from high oxygen fugacity melt in the Paleozoic Mo-rich sediments in the Qinling Orogen. The increasing of oxygen fugacity is furthermore beneficial to concentrating Mo in the residual melt, favorable for Mo mineralization.