青海铜峪沟铜矿床成矿流体特征及矿床类型探讨

Characteristics of ore-forming fluid and discussion on deposit type of Tongyugou copper deposit,Qinghai

青海省铜峪沟铜矿床位于东昆仑东西向构造岩浆带与鄂拉山北西向构造岩浆带的复合部位.依据矿物共生组合、交代与穿插关系可将铜峪沟铜矿成矿过程分为3个阶段：矽卡岩阶段、石英—多金属硫化物阶段及石英—方解石阶段.对不同阶段包裹体进行了包裹体岩相学、显微测温学和包裹体成分分析.研究结果表明,流体包裹体主要为液相包裹体（L型）、气相包裹体（G型）及含子矿物包裹体（S型）.其中矽卡岩阶段以含子矿物包裹体（均一温度为322℃～＞600℃,盐度为32.92％ ～＞ 73.97％ NaCleqv）和液相包裹体（均一温度为231℃～＞600℃,盐度为10.74％～21.68％ NaCleqv）为主.石英—多金属硫化物阶段以液相包裹体（均一温度为176℃～ 381℃,盐度为2.74％ ～ 21.96％NaCleqv）和气相包裹体（均一温度为127℃～419℃,盐度为4.49％ ～ 8.81％ NaCleqv）为主.石英—方解石阶段仅发育液相包裹体（均一温度为143℃ ～ 201℃,盐度为5.25％ ～9.21％ NaCleqv）.计算得到流体压力、密度变化范围分别为0.37 ～132.2 MPa、0.53 ～ 1.17 g/cm^3.成矿流体具有从高温高盐度向低温低盐度的演化特征.矽卡岩阶段发生了流体的混合作用,石英—多金属硫化物阶段发生了流体的减压沸腾作用导致了大量金属硫化物沉淀,成矿晚阶段流体可能来源于大气降水.分析认为,铜峪沟铜矿为岩浆热液层矽卡岩矿床.

Tongyugou copper deposit is located at the intersection part between the eastern Kunlun E-W direction tectonic magmatic belt and Elashan N-W direction tectonic magmatic belt.On the basis of the mineral assemblage and metasomatic alteration intercalation,the process of ore-forming can be divided into three phases：skarn stage,quartz-polymetallic sulfides stage and quartz-calcite stage.The results of petrographic,microthermometric and composition studies on the fuild inclusions show that Tongyugou copper deposit have three types of fluid inclusions：aqueous inclusions （type L）,gas phase inclusions （type G） and daughter mineral brine inclusions （type S）.In skarn stage,fluid inclusions are characterized by mainly daughter mineral brine type with 322℃ ～ ＞ 600℃ in homogenization temperature and 32.92％ ～ ＞ 73.97％ in NaCl salinities,and aqueous inclusions type with 231℃ ～ ＞600℃ in homogenization temperature and 10.74％ ～21.68％ in NaCl salinities.In quarts-polymetallic sulfides stage,fluid inclusions are aqueous type with 176℃ ～381℃ in homogenization temperature and 2.74％ ～21.96％ in NaCl salinities,and gas phase inclusions type with 127℃ ～419℃ in homogenization temperature and 4.49％ ～ 8.81％ in NaCl salinities.Inclusions of the quartz-calcite stage only contain aqueous phase type with 143℃ ～201℃ in homogenization temperature and 5.25％ ～ 9.21％ in NaCl salinities.The calculation of fluid pressure and density indicates that these values range from 0.37 to 132.2 MPa and from 0.53 to 1.17 g/cm^3.The ore-forming fluid is characterized by the evolution from the high to low in temperature and salinity.Fluid mixing occurred in the skarn stage,quartz-polymetallic sulfides stage had a fluid decompression boiling resulted in great amount of metal sulfide precipitation.The low temperature and low salinity aqueous phase inclusions of late mineralizaion stage may be derived from meteotic water.On the basis of features and the geological characteristics,the genetic type of Tongyugou copper is defined as magmatic hydrothermal stratabound skarn deposit.