贵州泥堡金矿床热液方解石地球化学特征及地质意义

已有研究表明，右江盆地卡林型金矿成矿期方解石具有独特的中稀土元素富集特点，但其成因还存在诸多争议。贵州泥堡金矿存在成矿期和非成矿期2种热液方解石脉，其中成矿期方解石脉多出现在矿化凝灰质细砾岩与凝灰质（粉）砂岩中，矿物组合为含砷黄铁矿+毒砂+石英+方解石；非成矿期方解石脉在未蚀变灰岩、矿化凝灰质细砾岩与凝灰质（粉）砂岩中均发育，且常穿切成矿期含硫化物方解石脉。文章通过对2种类型方解石脉开展稀土元素与碳、氧同位素、成矿期方解石脉内金属硫化物电子探针与微区原位LA-ICP-MS元素分析，发现与成矿期方解石脉共生的黄铁矿具典型的环带结构，黄铁矿环带和毒砂富Au、As、Sb、Hg、Cu、Co、Ni等元素。成矿期方解石脉显示中稀土元素富集模式和Eu正异常特征，表明金成矿流体为还原性流体，明显不同于非成矿期方解石脉的轻稀土元素富集模式和Eu负异常特征。泥堡金矿成矿期热液方解石的中稀土元素富集模式，与中国西南低温Au-Sb矿床成矿期方解石、萤石、磷灰石等矿物的稀土元素组成特征一致，酸性成矿流体的稀土元素组成可能是导致该金矿区成矿期方解石富集中稀土元素的主要原因。该区热液方解石特有的地球化学特征，使其在低温热液金矿床成矿年代学研究及深部找矿应用方面具有重要前景。

Geochemical and geological significance of hydrothermal calcite from Nibao gold deposit in Guizhou Province

It has been widely found that the hydrothermal calcite formed during mineralization in the carlin-type gold deposits in Youjiang basin shows distinguished enrichment of middle rare earth elements (MREE), but the genesis of the calcite vein is still controversial. Two kinds of hydrothermal calcite veins have been recognized in the Nibao gold deposit, one was formed during the gold mineralization and is mainly found in the mineralized tuffaceous fine-grained breccia, siltstone and sandtone, while the other is pre- or post metallogenic calcite and mainly found in unaltered limestone and mineralized tuffaceous clastic rock. The former calcite vein has a mineral association of arsenic pyrite, arsenopyrite, quartz, and calcite. In contrast, the latter is pure with single calcite mineral and commonly cuts through the former sulfides calcite vein. The rare earth element (REE) and C-O isotopic analysis of two kinds of calcite veins, Electron Probe Micro-Analysis (EPMA) and LA-ICP-MS analysis of sulfides were conducted in this paper. Pyrite in the calcite veins formed during gold mineralization shows typical zonal structure, and pyrite rim and arsenopyrite show enrichment of Au, As, Sb, Hg, Cu, Co and Ni. Furthermore, the ore-forming calcite shows distinguished enrichment of MREE and positive Eu anomaly, which is obviously opposite to the calcite formed pre- or post metallogeny, and indicates a reduced ore-forming fluid. REE pattern of ore-forming calcite in the Nibao gold deposit is similar to hydrothermal calcite, fluorite and apatite in the low-tempe-rature Au-Sb deposits in South China. Based on mineralogy and geochemistry of calcite, the authors hold that the REE composition of acid ore-forming fluid could be responsible for the MREE enrichment of calcite in the gold deposits in Youjiang basin. The distinguished geochemical features of the calcite in southwestern China make it possible to apply them to gold geochronologic study and deep prospecting in the low-temperature hydrothermal gold deposits.