斑岩成矿系统岩浆-热液阶段Cu、Mo、Au和S配分行为与赋存形式实验研究

Porphyry copper deposits are the huge enrichment of Cu, Mo, Au and S in upper crust, where the contents of metals and sulfur in giant porphyry copper systems can reach tens million and one billion tons respectively. Fluid exsolution and extracting metals as well as sulfur from magma are crucial processes affecting mineralization or not and the scale of formed porphyry copper deposits. And oxygen fugacity, aluminum content in melts and depth of fluid exsolution also have significant effect on porphyry mineralization potential and types. This extraction process and partition and complexing behaviors of ore-forming components at magmatic-hydrothermal stage have not yet been completely revealed. In particular, there is a lack of systematic experimental studies on melt composition, e.g. aluminum content in melts, and depth of fluid exsolution effecting on behaviors of the ore-forming components, which partially limits understanding of the anomalous enrichment process of ore-forming components during porphyry copper formation. In this study, an improved method of high-temperature and high-pressure experiments will be conducted to simulate process of fluid exsolution from melt in porphyry copper systems and in-situ micro-analysis of products will be applied to investigate mechanisms of above factors as well as oxygen fugacity effecting on partition coefficients and extracting efficiency of Cu, Mo, Au and S at magmatic-hydrothermal stage, which is designed to reveal favorable conditions of fluid exsolution for mineralization and complete huge enrichment mechanism of metals and sulfur in porphyry copper deposits. At the same time, the main complexing forms and valence states of Cu, Mo, Au, and S in the melt and fluid will be identified, which can provide more micro-scale evidences for the partition mechanism of ore-forming elements and give important clues for mechanism of reduced sulfur formation during hydrothermal mineralization in porphyry copper systems.

斑岩铜矿是上地壳Cu、Mo、Au和S发生巨量富集的载体，巨型斑岩铜矿金属和硫的富集量分别高达数千万吨和近十亿吨。岩浆-热液阶段流体出溶和萃取成矿物质的能力是控制斑岩能否成矿的关键，而氧逸度、熔体铝饱和度及流体出溶深度等对斑岩成矿潜力和矿化类型也有重要影响。目前对影响成矿元素萃取效率、配分和赋存形式的因素和机制尚未厘清，尤其缺乏熔体铝含量和流体出溶深度制约成矿元素行为的实验研究，限制了对斑岩系统成矿元素巨量富集机制的认识。本项目拟采用改进的高温高压实验技术模拟斑岩系统流体出溶过程，借助多种元素微区测试手段，探究氧逸度、熔体铝饱和度和流体出溶深度等对Cu、Mo、Au和S配分系数和赋存形式的影响，限定流体出溶的有利条件和控制萃取效率的因素，揭示斑岩铜矿床成矿元素巨量富集机制。在此基础上，查明不同相中成矿元素的赋存形式和价态，从分子尺度揭示控制元素配分的微观机理，阐明热液成矿过程还原硫的形成机制。

斑岩铜矿是上地壳Cu、Mo和Au发生巨量富集的载体，而岩浆-热液阶段流体出溶和萃取成矿物质的能力是控制斑岩能否成矿的关键。本项目对熔体铝饱和度、流体盐度以及HCl含量对流体萃取熔体中成矿物质的影响展开了系统的实验研究。实验和模拟计算结果显示中-酸性岩浆出溶低盐度流体时，熔体ASI，HCl含量以及流体盐度均会影响Cu, Mo, Au的分配行为，这也会影响不同金属之间的相对富集程度，并影响之后的热液矿化类型。偏碱质熔体，中等HCl浓度和低盐度流体更有利于形成Cu-Au矿化，偏铝质熔体，低HCl浓度和高盐度流体更有利于Cu-Mo矿化。当中-酸性岩浆出溶低盐度流体时，均会有效的的萃取岩浆中的Cu和Au；而对Mo的萃取效率较低，这表明形成富Mo的斑岩铜矿则需要规模更大且结晶程度更高的岩浆房。