准噶尔北缘老山口铁铜金矿床成矿流体及成矿机制

老山口铁铜金矿床位于准噶尔北缘,铁铜金矿化主要呈块状、团块状、脉状、角砾状、细脉浸染状产于闪长(玢)岩和玄武质火山岩的接触带中。矽卡岩阶段石榴子石以发育熔融包裹体和流体包裹体为特征,退化蚀变阶段绿帘石主要发育液相包裹体,石英-硫化物-碳酸盐阶段的方解石主要发育液相包裹体、含子矿物包裹体和含CO2三相包裹体。早期矽卡岩阶段流体包裹体均一温度变化于205~550℃及大于550℃,主要集中在220~470℃和大于550℃,盐度w(NaCleq)介于7.02%~17.96%,峰值为7.5%和16%,密度为0.60~1.00 g/cm3。退化蚀变阶段,均一温度变化于212~510℃,峰值为220℃,盐度w(NaCleq)介于6.16%~21.04%,密度为0.60~0.95 g/cm3。石英-硫化物-碳酸盐阶段,均一温度变化于150~380℃,在160℃和220℃出现峰值,盐度w(NaCleq)介于13.4%~18.47%,密度为0.75~1.10 g/cm3。石榴子石和方解石的δ18OSMOW值为5.2‰~17.8‰,δ18O水值为-2.4‰~3.5‰,δDSMOW值变化于-144.0‰~-84.0‰,表明成矿流体主要为混合的岩浆水和大气降水。方解石的δ13CPDB值变化于-6.8‰~-3.5‰,δ18OSMOW值为11.6‰~17.8‰,暗示成矿流体中碳主要来自闪长质岩浆,少量来自碳酸盐岩。黄铁矿δ34S值集中在0~3‰,结合稀土元素特征,表明硫主要来自于与矿体空间关系密切的闪长质岩浆。结合野外地质特征,认为铁矿成矿作用与矽卡岩的退化变质作用有关。

Ore-forming fluids and mineralization mechanism of Laoshankou Fe-Cu-Au deposit in northern margin of Junggar

The Laoshankou ore district is located in the northern margin of Junggar Basin.The Fe-Cu-Au minerals mainly occur in the massive,lumpy,veinlike,brecciaed and veinlet-disseminaed forms in the diorite porphyrite and basaltic volcanic rocks.Garnets of the skarn period are characterized by the development of melt inclusions and fluid inclusions.Fluid inclusions in epidote of the retrogressive metamorphism stage are liquid inclusions.Fluid inclusions in calcite of the quartz-sulfide-carbonate period mostly contain liquid inclusions,daughter mineral-bearing inclusions and three-phase CO2-bearing inclusions.Homogenization temperatures of fluid inclusions at the early skarn stage vary from 212℃ to 550℃ and are even higher than 550℃,mostly in the range from 220℃ to 470℃.Salinity w(NaCleq) ranges from 7.02% to 17.96%.Ore fluid density ranges from 0.60 g/cm3 to 1.00 g/cm3.Homogenization temperatures of fluid inclusions at the retrogressive metamorphism stage vary from 212℃ to 510℃,with the peak around 220℃.Salinity w(NaCleq) ranges from 6.16% to 21.04%.Ore fluid density ranges from 0.60 g/cm3 to 0.95 g/cm3.Fluid inclusions in the quartz-sulfide-carbonate period have homogenization temperatures from 150℃ to 380℃,with the peaks around 160℃ and 220℃.Salinity w(NaCleq) ranges from 13.4% to 18.47%.Ore fluid density ranges from 0.75 g/cm3 to 1.10 g/cm3.The δ18OSMOW values of garnet and calcite range from 5.2‰ to 17.8‰,with the corresponding δ18OH2O values between-2.4‰ and 3.5‰,and δDSMOW values of fluid inclusions between-144.0‰ and-84.0‰.These isotopic data imply that the ore-forming fluids were mainly derived from magmatic fluids and meteoric water.The δ13CPDB values of calcite define a narrow range of-6.8‰ to-3.5‰,and δDSMOW values of fluid inclusions vary between 11.6‰ and 17.8‰,indicating that the carbon in the ore fluids was mainly derived from the diorite magma closely related to the ore bodies,with a minor part from carbonate rock.The δ34S values of pyrite mainly range from 0 to 3‰,indicating that the sulfur was derived from diorite magma closely related to the ore bodies.In combination with the geological characteristics of the Laoshankou deposit,the authors hold that the ore-forming process was related to the retrogressive metamorphism of the skarn.