Au-As-S多元流体交代菱铁矿形成载金黄铁矿的矿物学证据

The mineralogical evidence for the formation of gold-bearing pyrite through the metasomatism of siderite by the Au-As-S multicomponent fluids

成矿流体与含铁围岩反应可生成大量黄铁矿并伴随金的高效沉淀,然而含Au-As-S的多元流体交代含铁碳酸盐围岩形成载金黄铁矿的矿物学过程还有待揭示。本文运用水热实验模拟了Au-As-S多元流体交代菱铁矿的成矿过程,采用X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)和电子探针显微分析(EPMA)等方法表征了菱铁矿蚀变前后的矿物学特征。结果表明,含Au-As-S的多元热液流体交代菱铁矿可生成载金黄铁矿,且黄铁矿的平均颗粒尺寸受控于初始溶液的As浓度;当初始溶液As浓度从0升至100×10^(–6),黄铁矿的平均颗粒尺寸减小约56%;初始溶液As浓度越高,进入黄铁矿结构中的As则越多,也更有利于流体中的Au以不可见金的形式进入黄铁矿;所形成的载金黄铁矿的Au与As含量呈现显著的正相关性,即存在As-Au耦合关系,与已报道的载金黄铁矿中的现象一致。该研究不仅深入剖析了菱铁矿在含Au-As-S的多元流体蚀变前后的矿物学演化特征,还有助于对载金黄铁矿中Au-As耦合关系成因的认识。

The reaction between ore-forming fluids and iron-bearing wallrocks can generate a large amount of pyrite accompanied by efficiently precipitated gold.However,the mineralogical process for the formation of gold-bearing pyrite through the replacment of iron-bearing carbonate wallrocks by the Au-As-S-bearing multicomponent fluids remains to be revealed.In this study,hydrothermal experiments were conducted to simulate the ore-forming process of gold-bearing pyrite through the metasomatism of siderite by the Au-As-S multicomponent fluids,and mineralogical characteristics of siderites before and after the hydrothermal alteration are investigated by using the X-ray diffraction(XRD),Raman spectroscopy(Raman),Scanning electron microscopy(SEM),and Electron probe microanalysis(EPMA)methods.The results show that the gold-bearing pyrite can be formed through the metasomatism of siderite by the Au-As-S-bearing multicomponent fluids,and the average particle size of formed pyrites is controlled by the arsenic(As)concentration of the initial solution.When the As concentration of the solution was increased from 0 to 100×10–6,the average particle size of pyrites was decreased by approximately 56%.The higher the As concentration of the initial solution,the more As entered into the pyrite structure.This is more conducive to the entry of Au of the fluid into the pyrite in the form of invisible gold.The Au and As contents of the formed gold-bearing pyrites are significant positively correlated,indicating that there is an As-Au coupling relationship which is consistent with the phenomenon observed in previously reported gold-bearing pyrites.This study not only provides an in-depth analysis of the mineralogical evolution characteristics of siderite before and after alteration by the Au-As-S-bearing multicomponent fluids,but also contributes to the good understanding of the genesis of the Au-As coupling relationship in gold-bearing pyrites.