藏北商旭金矿床成因研究:流体包裹体及氢-氧同位素证据  

Genesis of the Shangxu Orogenic Gold Deposit in Northern Tibet:Constraints from Fluid Inclusions and Isotopic Compositions

作　　者：裴英茹[1,2] 杨竹森[2] 赵晓燕[1,2] 张雄[1,3] 徐玉涛[1,3] 马旺[1,3] 毛敬涛[1,3] 庄亮亮[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院矿产资源研究所,北京100037 [3]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2015年第10期1814-1825,共12页Acta Geologica Sinica

基　　金：国家重点基础研究发展计划(973计划)(编号:2011CB403104);地调项目子课题(编号:12120113037901)联合资助的成果

摘　　要：商旭金矿床处于班公湖-怒江缝合带中段南侧,位于藏北双湖县境内,是班公湖-怒江缝合带已发现的可能是造山型的金矿床。矿体赋存于中-下侏罗统木嘎岗日群浅变质复理石中,受北西西向断裂构造控制,金矿化与石英脉密切相关。含矿石英脉中见较多黄铁矿、黄铜矿、方铅矿、闪锌矿等硫化物,自然金沿石英裂隙分布,少量分布在黄铁矿裂隙中。岩相学特征和激光拉曼测定结果显示,商旭金矿床中存在两类流体包裹体:1富液相包裹体(L型);2含CO2包裹体(C型),此类包裹体主要为CO2三相包裹体,见CO2两相包裹体。显微测温结果表明:1L型包裹体的均一温度为89.6~409.8℃,盐度ω(NaCleq)为0.35%~9.34%,流体密度为0.55~0.98g/cm3;2C型包裹体的均一温度为264.3~395.2℃,盐度ω(NaCleq)为4.62%~9.74%,流体密度为0.66~0.81g/cm3。商旭金矿床成矿流体具有富CO2、中低温度、低盐度、低密度的特征,与典型造山型金矿成矿流体特征相似。同时,商旭金矿床成矿流体的氢氧同位素组成分别为δD=-108‰^-89‰、δ18 O=-0.8‰~5.8‰,表明成矿流体主要来自变质水与建造水的混合。综合流体包裹体和氢氧同位素证据,进一步论证商旭金矿床为造山型金矿。The Shangxu gold deposit locates to the south of the middle part of the Bangong-Nujiang suture zone in northern Tibet.The gold ore bodies,hosted in the Middle-Lower Jurassic metamorphic flysh Mugagangri Group,are controlled by NWW-trending faults.The mineralization of gold is closely related to quartz veins.Auriferous quartz veins contain lots of sulfides,such as pyrite,chalcopyrite,galena and sphalerite.Natural gold is mostly distributed in cracks of quartz,with minor in cracks of pyrite.Laser Raman analysis shows that the Shangxu gold deposit contains two types of fluid inclusions：1 NaCl-H2 O inclusions（type L）;2 CO2inclusions（type C）,which can be subdivided into two-phase and three-phase inclusions.Microthermometric measurements indicate that：1 NaCl-H2O inclusions are characterized by homogenization temperature of 89.6to 409.8 ℃,salinity of 0.35 % to 9.34 %,and density of 0.55to0.98g/cm3;2 CO2 inclusions are characterized by homogenization temperature of 264.3to 395.2 ℃,salinity of 4.62 %to 9.74 %,and density of 0.66 to 0.81g/cm3.The ore-forming fluid of the Shangxu gold deposit is characteristic of CO2-rich,low to moderate homogenization temperature,low salinity and low density,which are similar to those of typical orogenic gold deposits.MeasuredδD values for the goldbearing quartz range between-108and-89 per mil,the estimatedδ18 O fluid values range from-0.8to 5.8per mil.The result of hydrogen and oxygen isotopes suggests that the ore-forming fluid is mainly derived from the mix of metamorphic fluid and formation water.Fluid inclusions and isotopic composition features imply that the Shangxu gold deposit may be an orogenic gold deposit formed under collisional orogenic belt.

关 键 词：流体包裹体 氢-氧同位素 造山型金矿 班公湖-怒江缝合带 西藏商旭 

分 类 号：P618.51[天文地球—矿床学]