Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland.
Sci Rep. 2017 Mar 15;7:44523. doi: 10.1038/srep44523.
Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > 0.5 GPa) during ≥2-3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits.
斑岩矿床是我们铜的主要来源，也是钼、铼和金的重要来源，它们与中酸性火成岩一起形成于汇聚边缘。尽管人们普遍认为铜是由这些岩浆释放的流体携带和沉淀的，但导致经济矿床形成的岩浆过程仍然难以捉摸。在这里，我们通过蒙特卡罗岩石学和地球化学模拟来定量地将地壳岩浆过程和岩浆的地球化学特征（即 Sr/Y）与不同规模的斑岩铜矿床的形成联系起来。我们的分析表明，经济矿床（特别是最大的矿床）可能仅在与中下地壳（P > 0.5 GPa）中积累的岩浆相关联的情况下形成，在长达 ~2.0 Ma 的时间内转移到上地壳并脱气。在较浅的深度（<0.4 GPa）处的岩浆积累和演化会大大降低岩浆系统产生经济矿床的潜力。我们的模型还预测了最大斑岩矿床与相关岩浆岩特定 Sr/Y 间隔（~100 ± 50）的关联，这与巨型斑岩铜矿床中测量的值几乎相同。
