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，如铼和硒。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是什么尚不清楚：软流圈地幔、俯冲玄武岩地壳、俯冲沉积物，或者可能是上板块的地壳。我们将通过实验确定在俯冲带条件下榴辉岩、元沉积物和含水流体之间Cu、Mo、Ag、Au和W的分配来解决这个问题。这些高压实验将允许定量预测俯冲玄武岩地壳或俯冲沉积物对斑岩矿床金属平衡的贡献程度。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，这将有助于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.