Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland.
Univ. Lyon, UJM-Saint-Etienne, UBP, CNRS, IRD, Laboratoire Magmas et Volcans UMR 6524, F-42023 Saint Etienne, France.
Sci Rep. 2017 Jan 12;7:40566. doi: 10.1038/srep40566.
Porphyry deposits are copper-rich orebodies formed by precipitation of metal sulphides from hydrothermal fluids released from magmatic intrusions that cooled at depth within the Earth's crust. Finding new porphyry deposits is essential because they are our largest source of copper and they also contain other strategic metals including gold and molybdenum. However, the discovery of giant porphyry deposits is hindered by a lack of understanding of the factors governing their size. Here, we use thermal modelling and statistical simulations to quantify the tempo and the chemistry of fluids released from cooling magmatic systems. We confirm that typical arc magmas produce fluids similar in composition to those that form porphyry deposits and conclude that the volume and duration of magmatic activity exert a first order control on the endowment (total mass of deposited copper) of economic porphyry copper deposits. Therefore, initial magma enrichment in copper and sulphur, although adding to the metallogenic potential, is not necessary to form a giant deposit. Our results link the respective durations of magmatic and hydrothermal activity from well-known large to supergiant deposits to their metal endowment. This novel approach can readily be implemented as an additional exploration tool that can help assess the economic potential of magmatic-hydrothermal systems.
斑岩矿床是由岩浆侵入体在地球地壳深处冷却时释放的热液中金属硫化物沉淀形成的富含铜的矿体。寻找新的斑岩矿床至关重要，因为它们是我们最大的铜来源，而且还含有其他战略金属，包括金和钼。然而，由于缺乏对控制其规模的因素的了解，巨型斑岩矿床的发现受到阻碍。在这里，我们使用热模拟和统计模拟来量化冷却岩浆系统释放的流体的时间和化学性质。我们证实，典型的弧岩浆产生的流体在组成上与形成斑岩矿床的流体相似，并得出结论，岩浆活动的体积和持续时间对经济斑岩铜矿矿床的储量（沉积铜的总质量）具有一级控制作用。因此，初始岩浆中铜和硫的富集虽然增加了成矿潜力，但对于形成巨型矿床并非必需。我们的结果将从著名的大型到超大型矿床的岩浆和热液活动的各自持续时间与其金属储量联系起来。这种新方法可以很容易地作为一种额外的勘探工具来实施，有助于评估岩浆-热液系统的经济潜力。
