会泽铅锌矿床成矿流体浓缩机制  

Concentration Mechanism of Ore-Forming Fluid in Huize Lead-Zinc Deposits, Yunnan Province

作　　者：张振亮[1] 黄智龙[1] 饶冰[2] 管涛[1] 严再飞[1] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学开放实验室 [2]南京大学地球科学系内生金属成矿机制研究国家重点实验室,江苏南京210093

出　　处：《地球科学（中国地质大学学报）》2005年第4期443-450,共8页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.40372048);云南省省院省校科技合作项目(No.2000YK-04).

摘　　要：云南会泽铅锌矿床位于扬子板块西缘川-黔-滇铅锌银多金属成矿域的中南部,严格受断裂带的控制.长期以来,对于该矿的成矿流体来源存在着较大的争论.研究表明,矿石中脉石矿物方解石的C、O同位素组成相对均一,其δ13C(PDB)为-2.1×10-3～-3.5×10-3、极差-1.4×10-3、均值-2.8×10-3,δ18O(SMOW)为16.7×10-3～18.6×10-3、极差1.9×10-3、均值17.7×10-3,不同矿体(不同标高)、不同产状以及相同矿体不同产状方解石的C、O同位素组成不具明显差别;除了纯液相包裹体(L)和富液相的气液两相包裹体(L+V)外,还存在含子晶的三相包裹体(S+L+V)和不混溶的CO2三相包裹体(VCO2+LCO2+LH2O),流体包裹体均一温度介于110～400℃之间,具有双峰现象;矿床的(87Sr/86Sr)0(0.713676～0.717012)不仅明显高于地幔(0.704±0.002)和峨嵋山玄武岩(0.703932～0.707818;85件样品)的(87Sr/86Sr)0,也相对高于矿区赋矿地层(C1b)的(87Sr/86Sr)0(0.70868～0.70931;3件样品),但明显低于基底岩石的(87Sr/86Sr)0(0.7243～0.7288;5件样品),且成矿过程中流体基本没有发生Sr同位素分馏现象.因此,成矿流体为均一流体,是不同性质流体的混合产物,具有多源性.而从气液两相包裹体盐度-均一温度图解可以看出,在300～400℃区间,包裹体盐度基本被孤立为两群:一群为5%～6%(w(NaCl)),另一群为12%～16%(w(NaCl)).而在100～300℃特别是150～250℃区间,包裹体盐度则基本均匀分布在7%～23%(w(NaCl))之间.断裂带形成压力为(50～320)×105Pa,矿体上覆岩石压力为(574～640)×105Pa,矿床成矿压力为(145～754)×105Pa.流体在上升到断裂带后压力的剧降,导致了沸腾作用的发生.在混合作用和沸腾作用的双重影响下,受狭窄断裂带控制的成矿流体高度浓缩,金属矿物得以大规模地从流体中沉淀出来,形成品位极高的铅锌矿石.The Huize Pb-Zn ore deposits, Yunnan Province, located in the southern-center of the Sichuan-Yunnan-Guizhou Pb-Zn-Ag multimetal mineralization district, are strictly controlled by faulted zones. There has long been controversy about the sources of ore-forming fluid in these ore deposits. Calcite is one of the gangue minerals in the ores of these ore deposits. Their δ13 (PDB) values vary from -2.1 × 10-3 to -3.5 × 10-3, and their δ18O (SMOW) values are 16.7 × 10-3 to 18.6 × 10-3. There are no obvious difference in the δ13C (PDB) values and the δ18O (SMOW) values of calcites from different ore-bodies, different occurrences and different elevations. Besides pure liquid inclusions (L) and gas-liquid inclusions with rich liquid (L+V), three-phase inclusions containing a daughter (S+L-V) and immiscible three-phase CO2 inclusions (VCO2 + LCO2 + LH2O) occur in the minerals. The homogenization temperatures of all these inclusions vary from 110°C to 400°C, and have two peaks. (87Sr/86Sr)0 ratios of these ore deposits (0.713676-0.717012) are obviously higher than those of the mantle (0.704 ± 0.002) and Emeishan basalt (0.703932-0.707818; 85 samples), and slightly higher than those of the Baizuo Formation of Huize lead-zinc ore deposits (0.70868-0.70931; 3 samples). But all these ratios are lower than the ones of the basement rocks (0.7243-0.7288; 5 samples). The (87Sr/86Sr)0 ratios of these ore deposits also show that the isotopic fractionation of Sr does not occur in the ore-forming fluid during the precipitation of minerals. So, the ore-forming fluid is homogeneous and a product of different fluid mixing. Gas-liquid inclusions can be obviously separated into two groups in the range of 300-400°C according to their salinities: a group with the salinity of 5%-6% (w(NaCl)) and the other group with the salinity of 12%-16% (w(NaCl)). However, the salinities of inclusions vary from 7% to 23% (w(NaCl)) in the range of 100-300°C, especially the range of 150-250°C. The pressures of faulted zones are 50 × 105-320 × 1

关 键 词：混合流体 沸腾作用 降压 高品位 

分 类 号：P618.1[天文地球—矿床学]