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矿床地质:2018,Vol.>>Issue(6):1337-1348

厄立特里亚Koka金矿床成矿流体特征及其地质意义
中国地质调查局武汉地质调查中心, 湖北 武汉 430205,中国地质调查局武汉地质调查中心, 湖北 武汉 430205,中国地质调查局武汉地质调查中心, 湖北 武汉 430205,中国地质调查局武汉地质调查中心, 湖北 武汉 430205,中国地质大学丝绸之路学院, 湖北 武汉 430074
Characteristics of ore-forming fluids of Koka gold deposit in Eritrea and their geological significances
ZHAO Kai,YAO HuaZhou,WANG JianXiong,XIANG WenShuai,Ghebsha Fitwi Ghebretnsae
(Wuhan Center, China Geological Survey, Wuhan 430205, Hubei, China;College of Silk Road, China University of Geosciences, Wuhan 430074, Hubei, China)
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投稿时间:2018-07-04   修订日期:2018-09-03      网络发布日期:2019-01-09
中文摘要:厄立特里亚Koka金矿床产于努比亚地盾新元古代浅变质岩系中,矿体主要赋存于Koka微晶花岗岩内,受剪切构造控制,是在该国发现的大型造山型金矿床。矿床含金石英脉中石英中赋存的原生流体包裹体分为富CO2包裹体、CO2-H2O包裹体和H2O包裹体共3种类型,以大量发育富CO2包裹体与CO2-H2O包裹体为特征。成矿流体具有富CO2、中低温(210~360℃)、中低盐度(w(NaCleq)=2.24%~8.51%)的特征。流体中阳离子主要为Na+与少量K+,阴离子为Cl-与少量SO42-,气相成分主要为CO2与H2O,基本不含其他气体组分,流体属于NaCl-H2O-CO2体系。成矿流体密度变化范围较大(0.597~0.969 g/cm3),其中高密度的富CO2包裹体捕获的最小P-T条件为260~360℃、100~270 MPa,形成于区域变质作用时期。成矿流体的δDV-SMOW范围为-57‰~-50.1‰,δ18O范围为1.4‰~3.2‰,表明Koka金矿床成矿流体主要来源于变质热液,并伴有大气降水的混入。成矿流体中CO2-H2O包裹体气相分数变化范围很大(15%~80%),与之共生的H2O包裹体具有相似的盐度以及较低的均一温度,表明初始的CO2-H2O型流体发生了不混溶作用,导致相分离,产生的大量富CO2流体,并使金大量沉淀。
Abstract:Located in the metamorphic strata of the Nubian Shield, the Koka gold deposit is a large orogenic gold deposit in Eritrea. The orebody hosts in the Koka aplitic granite, controlled by shear structure. The primary fluid inclusions in gold-bearing quartz veins can be divided into three types, i.e., extremely CO2-rich inclusions, CO2-H2O inclusions and H2O inclusions, with CO2-rich inclusions and CO2-H2O inclusions being dominant. The oreforming fluid is characterized by rich CO2, medium-low temperature (210~360℃) and low salinity (w(NaCleq)=2.24%~8.51%). In the liquid phase components, the cations mainly include Na+ and a little K+, the anions contain Cl- and a little SO42-, the gaseous content of the fluid inclusion is primarily CO2 and secondly H2O, almost without any other gaseous content, and the fluids belong to NaCl-H2O-CO2 system. The density of ore-forming fluid has a large variation (0.597~0.969 g/cm3), and the trapping P-T conditions of CO2-rich inclusions characterized by high density can be estimated to be 260~360℃ and 100~270 MPa, usually formed in regional metamorphism period. δDV-SMOW of the fluid is between -57‰ and -50.1‰, whereas δ18OH2O of the fluid is between 1.4‰ and 3.2‰, which suggests that the source of the ore-forming fluid for Koka gold deposit came mainly from metamorphic water mixed with meteoric water. The filling degree of CO2-H2O inclusions has a large variation (15%~80%), and symbiotic H2O inclusions have similar salinities and lower uniformity temperature, indicating that the original CO2-H2O fluid experienced fluid immiscibility, which resulted in the phase separation that formed a mass of CO2-rich fluid and caused gold precipitation.
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中图分类号:P618.51     
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基金项目:中国地质调查局项目“埃及及邻区矿产资源潜力评价”(编号:DD20160109)项目资助
引用文本:
赵凯,姚华舟,王建雄,向文帅,Ghebsha Fitwi Ghebretnsae.2018.厄立特里亚Koka金矿床成矿流体特征及其地质意义[J].矿床地质,37(6):1337~1348
ZHAO Kai,YAO HuaZhou,WANG JianXiong,XIANG WenShuai,Ghebsha Fitwi Ghebretnsae.2018.Characteristics of ore-forming fluids of Koka gold deposit in Eritrea and their geological significances[J].Mineral Deposits37(6):1337~1348
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