Subduction fluids and the source of metals in porphyry deposits

斑岩矿床是铜和钼的主要经济来源，也是其他一些金属和元素的主要来源，包括稀有材料Re和Se。它们总是在俯冲带环境中形成，但这些矿床中金属的最终来源尚不清楚：软流圈地幔、俯冲的玄武岩地壳、俯冲的沉积物，或者可能是上板块的地壳。我们将通过实验确定俯冲带条件下铜、钼、银、金和钨在榴辉岩、变质沉积物和水相流体之间的分配来解决这个问题。这些高压实验将使定量预测俯冲的玄武岩地壳或俯冲的沉积物对斑岩矿床的金属收支有多大的贡献。如果沉积物是主要的金属来源，如果俯冲沉积物中的金属含量变化很大，这将允许预测哪个弧段最有可能容纳主要矿床。正如我们在提案中指出的那样，有强有力的地球化学证据表明，钼也是如此，但其他元素的行为也需要进一步研究。

Porphyry deposits are the main economic source of copper and molybdenum and a major source of some other metals and elements, including rare materials like rhenium and selenium. They always form in a subduction zone environment, but it is not known what the ultimate source of metals in these deposits is: The asthenospheric mantle, the subducted basaltic crust, subducted sediments, or perhaps the crust of the upper plate. We will address this question by experimentally determining the partitioning of Cu, Mo, Ag, Au, and W between eclogite, meta-sediments, and aqueous fluids under subduction zone conditions. These high-pressure experiments will allow quantitative predictions to what extent the subducted basaltic crust or subducted sediments contribute to the metal budget of porphyry deposits. If sediments are the main metal source and if the metal contents in subducted sediments are highly variable, this would allow predicting which arc segment is most likely to host major deposits. As we note in the proposal, there is strong geochemical evidence that this is so for molybdenum, but the behavior of the other elements also requires further investigation.