湘西-鄂西地区铅锌矿的大范围低温流体成矿作用研究

摘要

Studies on fluid inclusions in sphalerite, calcite, dolomite, and quartz from Shizishan lead-zinc deposit, Limei lead-zinc deposit, Naizibao lead-zinc deposit, Chatian lead-zinc deposit, Dagoudong lead-zinc deposit, Dongjiahe lead-zinc deposit, Tangjiazhai lead-zinc deposit in western Hunan, Bingdongshan lead-zinc deposit and Aizigang lead-zinc deposit in western Hubei, through the analysis of homogenization temperatures, salinity, gas compositions, liquid compositions by heating/freezing system, Laser Raman and Ion Chromatography, show that the temperature of ore-forming fluid is 80-230℃, the salinity is always greater than 15%, the density is greater than 1g/cm3, and the mineralization pressure is about 223×105-777×105Pa. The ore-forming fluid is highly concentrated solution containing mainly sodium and calcium chloride. It belongs to the low temperature, high salinity, high density and mineralized underground hot brine. The cations in ore-forming fluid are mainly Cl-, Na+, Ca2+, K+, Mg2+. The composition of hydrogen and oxygen isotopes show that the origin of ore-forming fluid is related to construction water, with possible infiltration of rainwater and little metamorphic water. There is organic matter in the fluid inclusions. CH4 is widespread in the fluid inclusions. Mineralization is probably related to organic matter. The organic matter in the ore-controlling structure leads to the reduction of sulfate and the deposition of lead and zinc ore. The homogenization temperatures of ore-forming fluid from typical lead-zinc deposits in Sichuan, Yunnan, Guizhou district is 90-280℃. The studied lead-zinc deposits in western Hunan and western Hubei show similar low temperatures and MVT. The lead-zinc deposits in both regions may be controlled by the same tectonic dynamics.%对湘西-鄂西地区狮子山、李梅、耐子堡、茶田、打狗洞、董家河、唐家寨、冰洞山、凹子岗等典型铅锌矿床中闪锌矿、方解石、白云石及石英等矿物进行了流体包裹体均一温度、盐度、流体包裹体气相成分、流体包裹体群体液相成分测定，结果表明：成矿流体温度主要分布在80~230℃，总盐度一般>15%，密度多>1g/cm3，成矿压力为223×105~777×105 Pa，是以钠和钙氯化物为主的高浓度溶液，属于低温度、高盐度、高密度的地下热卤水性质的含矿热水溶液。成矿流体阳离子成分主要为Cl-, Na+, Ca2+, K+, Mg2+，流体包裹体氢氧同位素组成表明成矿流体来源与建造水有关，后期可能有雨水和少量变质水的渗入。矿物流体包裹体中含有机质，流体包裹体气相成分中CH4普遍存在，表明成矿与有机质相关，处在控矿构造内容矿层中的有机质使矿床中的硫酸盐硫还原为还原硫，促使成矿流体中的铅、锌沉淀形成矿床。相邻的低温成矿域川滇黔地区典型铅锌矿床成矿温度约为90~280℃，湘西-鄂西地区铅锌矿与川滇黔铅锌矿相比，具有相同的低温成矿特征，矿床类型均为MVT型，两者可能受控于相同的动力学背景。