甘肃拾金坡金矿床成因:来自^(40)Ar/^(39)Ar定年、成矿流体及H-O-S同位素证据  

Ore Genesis of the Shijinpo Gold Deposit in Gansu Province,NW China:^(40)Ar/^(39)Ar Dating,Ore-Forming Fluid and H-O-S Isotopes Constrains

作　　者：朱江[1] 吕新彪[1] 莫亚龙[1] 曹晓峰[1] 陈超[1] 

机构地区：[1]中国地质大学资源学院,武汉430074

出　　处：《吉林大学学报（地球科学版）》2013年第2期427-439,共13页Journal of Jilin University：Earth Science Edition

基　　金：国家科技支撑计划重点项目(2007BA25B04;2011BAB06B04-05)

摘　　要：甘肃拾金坡金矿床是北山造山带南部的一处重要中型金矿床。矿体以石英脉和蚀变岩形式产出,受东西向断裂控制,赋矿围岩为早泥盆世拾金坡二长花岗岩。矿石中主要金属硫化物为黄铁矿及少量方铅矿、闪锌矿和磁黄铁矿。石英脉两侧花岗岩发生强烈的硅化、黄铁绢英岩化和绿泥石化。热液蚀变绢云母40 Ar/39 Ar坪年龄为(364.6±3)Ma,表明成矿作用发生在晚泥盆世。矿石石英中流体包裹体可分为早晚两期:早期流体包裹体群包含不同气液比水溶液包裹体和含CO2包裹体,指示成矿过程存在流体沸腾作用,其均一温度集中在280～325℃,盐度(w(NaCl))为7.86%～9.21%;晚期流体包裹体群只发育水溶液包裹体,均一温度集中于160～230℃,盐度为9.47%～11.10%。成矿流体属中温低盐度、富CO2流体。流体从早阶段演化到晚阶段,温度降低约100℃,压力由约113 MPa骤减到约11 MPa。流体包裹体的δ18 OH2O值为1.39‰～3.39‰,δD值为-71‰～-99‰。氢氧投图中,石英脉和蚀变岩样品构成良好的线性关系,暗示初始成矿流体主要来自变质热液,晚期有强烈大气降水加入。矿石金属硫化物δ34S值变化范围为4.44‰～11.33‰,峰值为8‰～9‰,呈塔式分布。与区域S同位素资料对比分析表明,石英脉型矿石S主要来自前寒武系基底,蚀变岩型矿石S更多地继承了花岗岩围岩S。综合分析认为,拾金坡金矿床属于造山型金矿,形成于造山晚期挤压—伸展转换环境。The Shijinpo gold deposit is an important middle-size lode gold deposit in the Beishan orogenic belt, northwestern China. The gold mineralization is hosted in the early Devonian granite and consists primarily of auriferous quartz veins that are controlled by the EW-trending faults. Wall-rock alteration is dominated by sericite -＋- quartz q- sulfide assemblages in close proximity of gold veins. The pyrite is the predominant sulfide mineral, variably coexisting with minor amounts of galena, sphalerite and chalcopyrite. Laser incremental heating 40Ar/agAr analysis of hydrothermal sericite yields a plateau age of （364.6-＋-3） Ma （2a）, which suggests that the gold mineralization took place in the late Devonian period. The comprehensive fluid inclusion study shows that there are three major types of fluid inclusions in the early stage, liquid-rich, gas-rich aqueous and CO2-bearing fluid inclusions, with intermediate homogenization temperature （280 - 325 ~C ）, and low salinity （7.86 ~ - 9.21% NaC1 eqv）. The fluid boiling is evidenced by the co-existence of three types of fluid inclusions with similar homogenization temperatures. There is only liquid-rich aqueous fluid inclusions in the late stage, with hqmogenization temperatures and salinities varying from 160 ~C to 230 ~C, 9. 47o//oo to 11. 10~ Nacl equivalent. Fluid pressures declined from ca. 113 MPa to ca. 11 MPa through the early stage to the late stage, and the ore-forming fluids are assumed to undergo boiling in a transitional setting （from compression to extension）. Oxygen and hydrogen isotopic contents in the ore-forming fluid range from 1.39~//ooo to 3.39~//ooo and --71%0 to --99%o0, respectively, suggesting that the ore-forming fluid was mainly derived from the metamorphic water, and mixed by the meteoric water in the late stage. The measured ~4S values in sulfide minerals range from 4.44%0 to 11.33%o0. Both the Precambrian metamorphic rock and granitic wall-rock might be the sulfur sources. Based on the paper and the regional geologic

关 键 词：拾金坡 金矿 40Ar 39Ar定年 成矿流体 矿床成因 

分 类 号：P618.51[天文地球—矿床学]