滇西北兰坪盆地金满脉状铜矿床成矿流体特征及其成矿意义

滇西北兰坪盆地西缘发育大量沉积岩容矿脉状铜多金属矿床,矿体的分布受逆冲推覆系统控制,金满是其中储量最大、品位最高的铜矿床。成矿过程可分为3个阶段:成矿前(不含矿化石英-铁白云石脉)、主成矿阶段(含铜硫化物石英脉)、晚成矿阶段(少硫化物方解石+石英脉)。流体包裹体岩相学和显微测温结果表明:成矿前和主成矿期石英中流体包裹体特征变化不大,成矿前和主成矿期石英中均存在3种类型的包裹体,以水溶液包裹体为主,含CO_2水溶液包裹体次之,富CO_2包裹体较少出现。含CO_2水溶液包裹体测温结果也差别不大,均一温度都集中在240320℃,盐度(w(NaCl))集中在1%4%。水溶液包裹体均一温度变化也不大,集中在160 230℃,明显低于含CO_2水溶液包裹体;盐度却存在较大的变化,主成矿期盐度变化范围明显较大,且峰值高于成矿前。晚成矿阶段则仅出现水溶液包裹体,均一温度和盐度都明显降低,均一温度集中在120185℃,盐度集中在1.4%9.3%。结合其他证据,笔者认为金满铜矿床包含两种不同性质的流体:深源流体,以中高温、中低盐度、富含CO_2为特征;盆地卤水,以中低温、中高盐度、贫CO_2为特征。成矿过程中未发生明显的沸腾和相分离作用,深源流体和盆地卤水的混合可能是导致Cu等成矿元素沉淀的重要机制。

Ore-Forming Fluid Characteristics of the Jinman Vein-Type Copper Deposits in the Western Lanping Basin and Its Metallogenic Significance

A large number of sediment-hosted vein-type copper deposits controlled by a thrust-nappe system have been discovered in the west part of the Lanping basin, among which, the Jinman deposit is the largest in tonnage scale and with the highest Cu grade.The mineralization process of this deposit can be divided into three stages, including the early stage (pre-ore quartz-ankerite vein stage), the major stage (massive polymetallic sulphide-quartz vein stage), and the late stage (carbonate-quartz stage).The detailed studies of fluid inclusions distinguishes three types of fluid inclusions dominated by aqueous water in both pre-ore and syn-ore quartz from the Jinman deposit, including aqueous water, CO2-bearing, and pure CO2 inclusions.There is no obvoius difference between pre-ore and syn-ore quartz in terms of the type of fluid inclusions and microthermometric parameters of their CO2-bearing inclusions.The homogenization temperatures of CO2-bearing inclusions in both pre-ore and syn-ore quartz vary from 217 to 334 ℃(peak at 240～320 ℃), with corresponding salinities ranging from 1% to 4%.The homogenization temperatures of aqueous inclusions in both pre-ore and syn-ore quartz vary from 143 ℃ to 239 ℃(peak at 160～230 ℃), much lower than those of CO2-bearing inclusions.However, the salinities of aqueous inclusions show significant difference between pre-ore (3.1%～18.0%) and syn-ore quartz (4.1%～22.8%).Quartz-calcite vein in the late mineralizing stage only have aqueous inclusions, with homogenization temperature of 120～185 ℃, and salinities of 1.4%～9.3%.The fluid inclusion characteristics, together with other evidence, indicate that (1) there are two fluid systems responsible for Cu mineralization in the Jinman deposit one is deep crustal fluids, characterized by high CO2 content and relatively low salinities, and the other is basin brine, characterized by relatively high salinities and low temperatures.(2)The fluid mixing, without boiling or phase separation, might be the major precipitation mechanism.