极富CO_2流体的造山型金矿:苏丹哈马迪金矿  

Extremely CO_2-rich fluid inclusions in an orogenic gold deposit:Hamadi gold deposit of Sudan

作　　者：徐九华[1] 王建雄[2] 向鹏[2] 李闫华[2] 肖星[1] 张辉[1] 成曦晖 

机构地区：[1]北京科技大学资源工程系,北京100083 [2]中国地质调查局武汉地质调查中心,武汉443000

出　　处：《岩石学报》2015年第4期1040-1048,共9页Acta Petrologica Sinica

基　　金：中国地质调查局工作项目(1212011220911);国家自然科学基金项目(41372096)联合资助

摘　　要：哈马迪金矿位于苏丹东北部,矿床产于阿拉伯-努比亚地盾新元古界变质岩系中,属于受剪切带控制的造山型金矿床。金矿体赋存在角闪片岩内近南北向的片理化蚀变带中,围岩蚀变主要为黄铁绢英岩化,以及绿泥石化和碳酸盐化等。在含矿石英细脉中赋存有大量的极富CO2的碳质流体包裹体。这些包裹体几乎不含水,含有少量CH4(XCH4=0~0.10)。脉石英中碳质流体包裹体既有孤立或随机分布的原生包裹体,也有呈线性分布的次生包裹体,最晚期还有次生水溶液包裹体的分布。碳质流体包裹体的三相点(Tm,CO2)范围变化不大(-58.4^-57.0℃),但均一温度(Th,CO2)范围变化较大(-19℃^+29℃)。捕获的P-T条件可由LCO2包裹体的ρ值或Th,CO2值,以及与其伴生的CO2-H2O包裹体最终均一温度Th,TOT值,从有关相图中估算。早期碳质流体包裹体的捕获P-T条件范围为280~360℃、80~320MPa。金矿化发生在变质峰期之后的退变质作用晚期。广泛发育的热液蚀变说明碳质流体并非来自单一的流体源,寄主石英变形很弱也不能解释水从H2O-CO2-盐流体包裹体中优先淋失、残留大量的CO2±CH4包裹体。碳质流体包裹体可能的成因是:在金成矿的退变质时期,来自深部的H2O-CO2-盐流体,由于P-T下降而发生不混溶,H2O在热液蚀变中被大量消耗,而CO2则以碳质流体包裹体的形式被得捕获在脉石英中。The Hamadi gold deposit,hosted in the metamorphic strata of the Arabian-Nubian Shield（ ANS）,is a shear zonecontrolling orogenic gold deposit. Ore bodies occur in foliated alteration zone striking south to north within hornblende schist,which were mainly altered by beresitization,as well as chloritization and carbonatization. Fluid inclusion studies by microthermometry and laser Raman microspectroscopy revealed that the quartz veinlets in ores is dominated by primary population of extremely CO2-rich（ carbonic） fluid inclusions with no visible water and small amount of CH4（ XCH4= 0 - 0. 10）. Primary carbonic inclusions in vein quartz either occur as isolated or as random distribution,whereas secondary carbonic inclusions orientate in tiny fissures. Secondary aqueous inclusions can be found in the latest fissures. The solid CO2 melting temperatures（ Tm,CO2） of carbonic inclusions have a narrow range of- 58. 4 - - 57. 0℃,whereas the homogenization temperatures（ Th,CO2） vary widely（- 19℃ - ＋ 29℃）. According to the densities or the Th,CO2 of carbonic fluid inclusions and the final homogenization temperatures（ Th,TOT） of associated CO2-H2 O inclusions,the trapping P-T conditions of carbonic inclusions can be estimated to be 280 - 360℃ and 80 - 320 MPa. Gold deposition may occur in late retrogress metamorphism after the peak regional metamorphism. Carbonic inclusions might not be a single CO2 source because of widely distributed alteration,while post-trapping leakage of water from original H2O-CO2-salt fluids and consequently forming carbonic inclusions is also not accepted due to weakly deformed host quartz. The reasonable interpretation for the origin of carbonic inclusions in the Hamadi gold deposit is that unmixing might happen in an immiscible aqueous-carbonic mixture during retrogress metamorphism because of decreasing of P-T conditions; H2O was depleted in hydrothermal alteration,and CO2 was trapped as carbonic inclusions in vein quartz.

关 键 词：碳质流体包裹体 造山型 哈马迪金矿 苏丹 

分 类 号：P618.51[天文地球—矿床学]