湘黔汞矿带脉石矿物方解石稀土元素、碳氧同位素特征及其指示意义

Characteristics and Implications of REE,Carbon and Oxygen Isotopes of Hydrothermal Calcite from the Mercury Metallogenic Belt in Hunan and Guizhou Provinces,China

方解石是湘黔汞矿带的主要脉石矿物。湘黔汞矿带各矿床方解石的稀土配分模式均为轻稀土富集的右倾型,中段的大硐啦、茶田方解石和围岩的稀土配分模式比较相似,只是稀土总量有差别;南段的万山方解石和围岩的稀土配分模式则不一致,围岩的稀土总量反而要高于方解石。南段的万山方解石稀土具有弱的负Eu、负Ce异常;而中段的大硐喇、茶田方解石具有负Eu、正Ce异常。其中,作为示踪流体过程重要参数的Y/Ho比值在湘黔汞矿带南段与中段的方解石中也有着较大的差别。方解石的C、O同位素特征揭示南段万山汞矿的形成与古油藏的有机质有关,而中段大硐喇、茶田汞矿的形成则与有机质无关。这都说明了南段与中段无论是成矿物理化学环境还是成矿热液流体的性质等都存在着较大差别。

Hydrothermal Calcites are of main gangue minerals in the mercury metallogenic belt in Hunan and Guizhou Provinces, China. REE geochemical studies on hydrothermal calcites from three main mercury ore fields （Wanshan, Chatian and Dadongla） showed similar chondrite-normalized REE distribution patterns with LREE-enriched and right- inclined type. However, in comparison with host rocks, the total REE patterns are different with each other. In the middle section of mercury metallogenic belt, similar REE distribution patterns were observed between calcites and host rock from Chatian and Dadongla ore fields, although with the slightly difference in the total REE abundances. In the south section of the metallogenic belt, it showed not only distinct REE patterns between calcites and host rocks from Wanshan ore filed, but also higher REE abundances in host rocks compared with calcites. In addition, In the Wanshan ore field, calcites showed weak negative Eu and Ce anomalies; while in Dadongla and Chatian ore fileds, calcites showed negative Eu anomalies and positive Ce anomalies. The Y/Ho ratio of calcites from three ore fields, as the important parameter to trace ore fluid, also presented similar trend. Carbon and Oxygen isotopes of calcites revealed that the mineralization of the Wanshan ore field was closely related with organic matter of the ancient oil reservoirs, while it was decoupled between Mercury mineralization and organic matter of Dadongla and Chatian ore fields. Therefore, both physical chemical environment of mineralization and the nature of the ore-forming hydrothermal fluids are quite different in the whole Mercury ore belt as suggested in this paper.