摘要
滇西兰坪盆地北部发育了一类受逆冲推覆构造控制的浅成热液Cu_Ag_Pb_Zn矿化 ,形成了白秧坪、富隆厂、吴底厂、麻栗坪及金满、科登涧等大_中型矿床和矿点 ,并存在矿化分带。文章利用这些矿化脉体的流体包裹体和热液方解石的碳氧同位素组成资料 ,研究成矿流体与矿化分带的关系。结果表明 ,成矿流体主要属于NaCl_H2 O成分体系 ,盐度w(NaCleq)为 2 %～ 1 1 % ,形成温度为 1 70～ 30 0℃ ,形成于 1 .8～ 3.8km深度内 ,这些相似性说明这类矿化的发生具有相似的流体性质和沉淀机制。热液方解石在δ1 3 C_δ1 8O图解中呈近水平线展布的型式 ,指示流体源自地壳浅部的地下水系统 ,与海相灰岩等围岩作用形成了溶解碳以 [HCO3 ]-为主的成矿流体 ,流体与岩石的相互作用可能是成矿流体沉淀的主要机理。从西到东 ,流体包裹体的盐度_温度由高到低变化与矿化分带和逆冲推覆构造的根带→中带→锋带相配套 ,显示重力驱动流动可能是主要的流体流动机制。成矿流体在不同构造部位流动的通畅及流体_岩石系统的封闭_开放程度等流体流动性质与矿化发生的强度和规模有关 ,兰坪北部逆冲推覆构造中带的流体通畅地流动及沉淀时处于相对开放状态 。
Controlled by the thrust_nappe structures, a series of epithermal Cu_Ag_Pb_Zn mineralizations occur in northern Lanping basin, western Yunnan, thus forming a large number of polymetallic deposits, such as Baiyangping, Fulongchang, Wudichang, Maliping, Jinman and Kedengjian, with the existence of mineralization zoning in the region. The fluid inclusion and C_O isotope data from 13 ore veins were used to study the relationship between the ore_forming fluids and the zoning of mineralizations. It is shown that 2_phase liquid_rich aqueous inclusions and single_phase liquid aqueous inclusions are most commonly seen, together with a few 3_phase solid_bearing aqueous inclusions and 3_phase CO 2_aqueous inclusions. The 2_phase liquid_rich aqueous inclusions belong to the NaCl_H 2O system, with salinity, trapping temperature and formation depth of 2_11 eq. wt% NaCl, 170～300℃ and 1.8～3.8 km, respectively. Therefore, there existed similar fluid characteristics and precipitation mechanism in these mineralizations. The δ 13 C and δ 18 O values of hydrothermal calcites fall within the ranges of -6.6‰～2.11‰ PDB and 6.46‰～17.05‰ SMOW, respectively. Nearly horizontal correlation array of C_O isotopes from hydrothermal calcites implies that the fluids came from the underground water system in the shallow part and that - was the dominant form of dissolved carbon in the fluids. From the west to the east of the basin the salinity and homogenization temperature of fluid inclusions gradually decrease, which is in consistent with the zoning of the mineralizations and the thrust_nappe structures (root zone→median zone→frontal zone), suggesting that the gravity_driven fluid migration might have acted as the major fluid flow model in this area. The continuous flow of fluids and the close_open degree in the interaction between the fluids and the wall rocks along the fault system are associated with the intensity and scale of the polymetallic mineralizations. The continuous flow and the good open state are favourable to the large_scale mineralization in the median zone of Lanping thrust_nappe structures.
出处
《矿床地质》
CAS
CSCD
北大核心
2003年第4期365-376,共12页
Mineral Deposits
基金
国家自然科学基金项目 (编号 :40 0 73 0 14 )资助
