胶东地区笏山金矿床黄铁矿微量元素特征及其成矿指示意义

Trace element characteristics of pyrite from the Hushan Gold Deposit in the Jiaodong Region and its metallogenic significance

胶东地区一直是金矿研究的热点,但大部分研究集中在胶西北和牟乳成矿区,而蓬莱—栖霞成矿区研究较少。笏山金矿床位于蓬莱—栖霞成矿带的南部,受北东向台前—陡崖断裂控制。笏山金矿床主要载金矿物为黄铁矿,根据黄铁矿结构、形态特征,成矿阶段可分为早成矿阶段和晚成矿阶段。通过采用LA-ICP-MS对笏山金矿床不同成矿阶段的黄铁矿进行原位微区成分分析,结果显示:黄铁矿中w(Co)最大值为502.57×10-6,平均值为137.56×10-6,指示其属于中低温型黄铁矿。早成矿阶段w(Co)/w(Ni)值要大于晚成矿阶段,说明成矿过程中温度逐渐降低。笏山金矿床中金元素主要以可见金的形式存在,显微镜下可观察到大量可见金颗粒。元素含量关系图显示:Au含量均在Au最大溶解度曲线以下,说明黄铁矿中不可见金主要以晶格金的形式存在。Au与As呈正向相关,暗示Au富集受As影响。早成矿阶段As对黄铁矿晶胞中S的替代,为Au富集提供了便利条件。到了晚成矿阶段,成矿热液从相对还原态向相对氧化态过渡,成矿流体减压使成矿热液中的金沉淀下来,最终形成可见金颗粒。

The Jiaodong Region has always been a hot spot for gold deposit research,but most of the research focuses on Northwest Jiaodong and Muping-Rushan metallogenic zone,while the Penglai-Qixia metallogenic zone is basically undeveloped.The Hushan Gold Deposit is located in the southern part of the Penglai-Qixia metallogenic zone and is controlled by the NE-trending Taiqian-Douya fault.The main gold-bearing mineral in the Hushan Gold Deposit is pyrite.According to the structural and morphological characteristics of the pyrite,it can be divided into two stages:early metallogenic stage and late metallogenic stage.In this study,the in-situ microzone component analysis of the pyrite from different metallogenic stages of the Hushan Gold Deposit is carried out by LA-ICP-MS.The results show that the maximum value of w(Co)in pyrite is 502.57×10^(-6),and the average value is 137.56×10-6,which indicates that it belongs to medium-low temperature type pyrite.The w(Co)/w(Ni)in the early metallogenic stage is higher than in the late stage,indicating the temperature gradually decreased during the metallogenic process.The gold element in the Hushan Gold Deposit mainly exists in the form of visible gold,and a large number of visible gold particles can be observed under the microscope.According to the element content relation diagram,all the gold contents are below the maximum solubility curve of Au,indicating that the invisible gold in the pyrite mainly exists in the form of lattice gold.The data shows that there is a positive correlation between Au and As,suggesting that the enrichment of Au is affected by As.The substitution of As for S in the unit cell of pyrite in the early metallogenic stage facilitates the enrichment of Au.In the late metallogenic stage,the ore-forming hydrothermal fluid transited from the relatively reduced state to the relatively oxidized state.The pressure decrease in the ore-forming fluids precipitated the gold in the ore-forming hydrothermal fluids,which eventually formed visible gold particles.