桂西北百勇金矿、百蓬金矿粗粒黄铁矿和毒砂的矿物学特征  

Mineralogical characteristics of coarse-grained pyrites and arsenopyrites in the Baiyong and Baipeng gold deposits, Northwest Guangxi, China

作　　者：马克忠 陈懋弘[1] MA Ke-zhong;CHEN Mao-hong(Institute of Mineral Resources,Chinese Academy of Geological Science,Beijing 100037,China)

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《矿物学报》2020年第5期601-614,共14页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(批准号:41572072);国家重点基础研究发展计划973课题(编号:2014CB440902);广西找矿突破战略行动地质矿产勘查项目(编号:20180302)。

摘　　要：桂西北百勇金矿和百蓬金矿为小型卡林型金矿床,与同一地区的明山、金牙金矿对比,最大特点是载金矿物黄铁矿和毒砂晶体颗粒粗大,黄铁矿最大者直径可达10~15 mm,毒砂最大直径在15 mm左右。百勇金矿电子探针结果显示黄铁矿表现为高As(0.63%~2.35%)、低S、Fe的特征,As与S呈负相关关系,与一般的卡林型金矿类似,但含砷黄铁矿为均质结构,未形成明显的元素分带,表明百勇金矿粗粒黄铁矿是在比较稳定的热液流体环境下形成。百蓬金矿含砷黄铁矿具有环带结构,核部低砷,环带高砷(2.309%),且环带宽大(100~200μm),不同于明山金矿黄铁矿形成细小密集的环带(5μm左右),表明百蓬金矿黄铁矿的形成环境可能处于百勇金矿与明山金矿之间,暗示热液活动周期比较长,且补给充足,从而形成粗大的环带。电子探针分析结果表明,百勇金矿和百蓬金矿中的Au是以固溶体(Au+)的形式存在于含砷黄铁矿和毒砂中,且成矿流体中的Au呈不饱和状态。由于含砷黄铁矿的生长环境较为稳定,流体充足,导致黄铁矿表面空位以及晶格缺陷较少,金没有足够的空间进入。另外,地层中存在大量的铁白云石为成黄铁矿的形成提供了大量的Fe,进一步减小了黄铁矿形成过程中形成空位以及晶格缺陷的可能,最终使得黄铁矿中金含量很少。同时,含砷黄铁矿中As的含量普遍低于典型卡林型金矿的含砷黄铁矿,导致Au进入黄铁矿缺乏"催化剂",从而导致百勇金矿和百蓬金矿品位较低,暗示粗粒黄铁矿和毒砂对形成卡林型金矿不太有利。The Baiyong and Baipeng gold deposits are two small Carlin type gold deposits in the Northwest Guangxi. Compared with Mingshan and Jinya gold deposits in the same area, they are characterized by the gold-bearing minerals of coarse-grained pyrites and arsenopyrites with their sizes of pyrite and arsenopyrite grains up to 10-15 mm and about 15 mm, respectively. Coarse arsenopyrite is often disseminated or intersected with pyrite. Electron microprobe analytical results show that pyrites of the Baiyong gold deposit are characterized by high As contents(0.63%-2.35%), low contents of S and Fe, and negative correlation between As and S, similar to those of the common Carlin type gold deposits. However, the arsenic-bearing pyrite has homogeneous structure with no obvious element zoning, indicating that the coarse-grained pyrite in the Baiyong gold deposit was formed in a relatively stable environment of hydrothermal fluid. The arsenic-bearing pyrite in the Baipeng gold deposit has zoning structure with low arsenic content in the core and high arsenic content(2.309%) in the 100-200 μm wide rim, which is different from those(narrow and dense zones of about 5 μm in width) of the pyrite in the Mingshan gold deposit. It indicates that the pyrite of the Baipeng gold deposit may be formed in an environment between the formation environment of the Baiyong gold deposit and that of the Mingshan gold deposit, suggesting that the wide high-arsenic zone of pyrite in the Baipeng deposit could be formed due to the relatively long activity cycle and sufficient supply of the hydrothermal fluid. The results of EPMA analysis show that Au in the Baiyong and Baipeng gold deposits occurred in arsenic-bearing pyrites and arsenopyrites in the form of solid solution(Au+), and the Au in ore-forming fluid was unsaturated. Because the growth of arsenic-bearing pyrite is under relatively stable environment in sufficient fluids, there are fewer vacancies and lattice defects on the surface of pyrite crystals without enough room to be occupied by gol

关 键 词：百勇金矿 百蓬金矿 金的赋存状态 矿物学 

分 类 号：P575.1[天文地球—矿物学] P572[天文地球—地质学]