Exsolution depth and migration pathways of mineralising fluids in porphyry deposit-forming magmatic systems

斑岩矿床形成岩浆系统中成矿流体的出溶深度及运移路径

• 批准号: 1930105
• 金额: --
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1930105
• 关键词: Exsolution; depth; migration; pathways; mineralising

Porphyry copper deposits provide around 75% of the world's copper and are an important source of gold and other metals. One aspect of porphyry deposit models that is poorly understood is whether the mineralising fluids from which they form are derived from: (i) high-level copper-rich porphyry magmatic stocks, (ii) feeder chambers at mid-upper crustal levels, (iii) a lower crustal magmatic reservoir, or (iv) a combination of these. The high level porphyry stock is often assumed to be the fluid source as it is invariably mineralised and can usually be temporally and texturally linked to the mineralisation. However, it is unlikely that enough fluid could be derived from such a limited magma volume. It therefore seems probable that much of the fluid comes from a deeper source, possibly 5 to 15 km, although how fluids are transported from such depths is poorly understood. The aim of the studentship is to identify textural and chemical evidence for the exsolution depth and migration pathways of mineralising fluids in materials from different levels within porphyry systems, e.g. enclaves, cumulates, minerals which crystallised at different depths and breccia clasts. Crystallisation depths will be assessed from a variety of mineral-based barometers, and the composition, including relative copper fertility and water contents, of the melt from mineral indicators, including plagioclase (1). Textural evidence for fluid exsolution will include miarolitic cavities and primary fluid inclusions in magmatic minerals. The deposits to be studied are in Nevada where, due to tectonic tilting, there is the rare opportunity to study well exposed sections through porphyry systems to palaeo-depths of >10 km (2). The student will carry out two fieldwork campaigns of around 4 weeks each. Analyses will be undertaken using state-of-the-art facilities including electron microprobe, SEM, laser ablation ICP-MS, cathodoluminescence, micro-CT scanning and fluid inclusion microthermometry at Camborne School of Mines and the Natural History Museum. New concepts from the project will inform models for porphyry deposit formation and as such aid in their discovery. References:1. Williamson B. J., Herrington R. J., Morris A., 2016. Porphyry copper enrichment linked to excess aluminium in plagioclase. Nat. Geosci. 9, 237-241.2. Seedorf E., Barton M. D., Stavast W. J. A., Maher D. J., 2008. Root zones of porphyry systems: extending the porphyry model to depth. Econ. Geol. 103, 939-956.

斑岩铜矿提供了全球约75%的铜，是黄金和其他金属的重要来源。斑岩矿床模型的一个鲜为人知的方面是，形成斑岩矿床的成矿流体是否来自：(I)高水平富铜斑岩岩浆库，(Ii)中上地壳水平的供给室，(Iii)下地壳岩浆储集层，或(Iv)这些的组合。高品位斑岩通常被认为是流体来源，因为它总是被矿化，通常在时间和结构上与矿化有关。然而，从如此有限的岩浆体积中提取足够的流体是不太可能的。因此，许多流体似乎很可能来自更深的来源，可能是5到15公里，尽管人们对流体是如何从这样的深度输送的知之甚少。该课程的目的是确定矿化流体在斑岩系统内不同层次的物质中的出溶深度和迁移途径的结构和化学证据，例如包体、堆积体、在不同深度结晶的矿物和角砾岩碎屑。结晶深度将通过各种矿物气压计进行评估，熔体的成分，包括相对铜丰度和水含量，将通过包括斜长石在内的矿物指标进行评估(1)。流体出溶的结构证据将包括岩浆矿物中的微晶石腔和原生流体包裹体。要研究的矿床位于内华达州，由于构造倾斜，这里有难得的机会研究从斑岩系统到10公里(2)以下的古深度的暴露良好的剖面。学生将进行两次为期约4周的实地考察活动。分析将在坎伯恩矿业学院和自然历史博物馆使用最先进的设施进行，包括电子探针、扫描电子显微镜、激光消融电感耦合等离子体质谱、阴极发光、微型CT扫描和流体包裹体显微测温。来自该项目的新概念将为斑岩矿床的形成模型提供信息，并因此有助于它们的发现。参考文献：1.Williamson B.J.，Herrington R.J.，Morris A.，2016。斑岩铜富集与斜长石中过量铝有关。纳特。吉奥西。9,237-241.2。主编：刘晓明，刘晓华，等.斑岩系统的根带：将斑岩模型延伸到深部。经济上。吉奥尔。103,939-956。