Porphyry copper mineralization triggered by sulfate reduction and alkali metasomatism: Constraints from an experimental investigation
Porphyry copper mineralization triggered by sulfate reduction and alkali metasomatism: Constraints from an experimental investigation
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硫酸盐还原和碱交代作用引发的斑岩铜矿化：实验研究的限制
DOI：
10.1130/b36435.1
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发表时间：
2023-01
影响因子：
4.9
通讯作者：
Huayong Chen
中科院分区：
文献类型：
--
作者：
Jianping Li;Weihua Liu;Long Su;Dengfeng Li;Shitao Zhang;Huayong Chen
钾硅酸盐蚀变带是世界范围内斑岩铜矿的主要赋矿带。认识斑岩铜矿化过程中的元素行为是提高对斑岩铜矿化认识的基础，但目前对斑岩铜矿化过程中元素行为的认识还不够。在这项研究中，我们反应合成富Cl流体，含有K，Na，Cu，Mo，Zn等，与安山岩在一个复杂的实验系统中模拟浅部斑岩铜矿化过程。本文旨在填补简单实验研究与复杂自然体系之间的差距，评价硫酸盐还原作用对斑岩成矿的贡献及其与早期碱交代作用的关系。结果表明，温度升高（300 ~ 500 °C），钾硅酸盐蚀变作用增强，钾长石主要由斜长石经溶解-再沉淀过程转化而成。在相同温度下，低矿化度的气相比液相具有更强的钾硅酸盐蚀变能力。此外，将温度从300 °C升高至500 °C有利于硫酸盐还原以进一步增强金属硫化物沉淀。流体中还原硫的有限可用性导致Cu-（Mo）硫化物的优先沉淀，而大部分Zn可溶于流体中，并且Cu作为硫化物在蒸气中沉淀比在共存液体中更有效。斑岩铜矿中钾硅酸盐蚀变带与硫酸盐还原触发的矿化之间的重叠受几个伴生因素控制，相对高的温度（例如，在400−500 °C下）、蒸汽形成和减压。此外，钾硅酸盐蚀变通过改变流体成分，例如，从流体中除去K。
The potassium silicate (K-silicate) alteration zone is the main ore contributor in porphyry copper deposits worldwide. Knowledge of element behaviors in the alteration and mineralization processes is essential for an improved understanding of porphyry copper mineralization, but they are still not well understood. In this study, we reacted synthetic Cl-rich fluids, containing K, Na, Cu, Mo, Zn, etc., with andesite in a complex experimental system to simulate the shallow porphyry copper mineralization process. We aimed to bridge the gap between simple experimental studies and complex natural systems and to evaluate the contribution of sulfate reduction to porphyry ore formation and its relationship with early alkali metasomatism. The results show that increasing temperature (from 300 to 500 °C) enhances the K-silicate alteration by promoting ion-exchange reactions, and the K-feldspar is mainly formed by the transformation of plagioclase via a dissolution-reprecipitation processes. The low-salinity vapor phase has a stronger capacity for K-silicate alteration than the liquid phase at similar temperatures. In addition, increasing temperature from 300 to 500 °C favors sulfate reduction to further enhance metal sulfide precipitation. The limited availability of reduced sulfur in the fluid causes preferential precipitation of Cu-(Mo) sulfides, while most of the Zn is soluble in the fluid, and Cu precipitation as sulfides in the vapor is much more efficient than in the coexisting liquid. The overlap between the K-silicate alteration zone and the mineralization triggered by sulfate reduction in porphyry copper deposits is controlled by several concomitant factors, e.g., relatively high temperature (e.g., at 400−500 °C), vapor formation, and decompression. Moreover, K-silicate alteration would further promote mineralization by changing fluid compositions, e.g., removing K from the fluid.