兰坪盆地白秧坪铅锌铜银多金属矿床成矿流体及成矿物质来源

Baiyangping Pb-Zn-Cu-Ag Polymetallic Deposit in Lanping Basin:A Discussion on Characteristics and Source of Ore-Forming Fluids and Source of Metallogenic Materials

白秧坪矿床位于滇西北兰坪盆地北部,是一沉积岩容矿的铅锌铜银多金属矿床,矿体赋存于中生代地层中,受断裂构造控制明显.通过成矿期方解石、石英、闪锌矿中流体包裹体研究,以及方解石的C、O和含硫矿物的S、Pb同位素研究,来探讨成矿流体性质及其来源和成矿物质来源.研究表明,白秧坪矿床包裹体一般小于10μm,气液两相为主,成矿流体体系为Ca2+-Na+—K+-Mg2+-Cl--F--NO3-卤水体系,矿床矿物中冰点温度范围为-26.4～-0.2℃,平均为-14.6℃,均一温度集中于120～180℃,盐度为0.35%～24.73%(NaCleq),平均值16.9%(NaCleq),成矿流体密度在0.84～1.11g/cm3之间,平均值1.04g/cm3,成矿压力为28.0～46.9MPa,平均37.6MPa,对应的成矿深度约1058～2452m,平均1555m,集中于1200～1800m;碳质的来源较为均一,矿石中热液方解石中碳源自地层中碳酸盐岩溶解,成矿流体属于盆地流体系统,有大气降水的加入;成矿物质硫来自硫酸盐的热化学还原作用,或者含硫有机质的热分解,金属成矿物质来自沉积地层和盆地基底.

Located in Mesozoic strata of northern Lanping basin,Northwest of Yunnan Province,Baiyangping deposit is a sediment-hosted Pb-Zn-Cu-Ag polymetallic deposit controlled by fracture.In this paper,a study is carried out on the fluid inclusions in ore-forming stage calcite,quartz,sphalerite and C,O isotope of calcite and S,Pb isotope of sulfur-bearing minerals,on basis of which the character and source of ore-forming fluids and the source of ore-forming materials are discussed.The fluid inclusions of Baiyangping deposit are generally less than 10 μm,main gas-liquid phase.The ore-forming fluid system was Ca2+-Na+-K+-Mg2+-Cl--F--NO3-brine system.The freezing temperature of fluid inclusions in mineral deposits ranges from-26.4 to-0.2 ℃,with an average of-14.6 ℃;the homogenization temperature is concentrated in 120-180 ℃,and the salinity varies from 0.35% to 24.73%(NaCleq),with an average of 16.9%(NaCleq).ore-forming fluid density is between 0.84 g/cm3 and 1.11 g/cm3,with an average of 1.04 g/cm3,mineralization pressure is between 28.0 MPa and 46.9 MPa,with an average of 37.6 MPa;the corresponding mineralization depths is between 1 058 m and 2 452 m,with an average of 1 555 m,concentrated in 1 200 m to 1 800 m;Carbon and oxygen isotope data indicate a homogeneous carbon source,and the carbon in hydrothermal calcite is derived from the dissolution of carbonate rock strata.The ore-forming fluid belongs to the basin brine fluid system,which is mixed with the precipitate water;S isotope data show that sulfur in sulfides and sulphosalts is derived from thermochemical sulfate reduction,or the thermal decomposition of sulfur-bearing organic matter;the metal mineralization material is from sedimentary strata and basement.