西南天山阿沙哇义金矿床流体包裹体和H-O同位素地球化学特征与造山型金矿成因

Geochemical characteristics of fluid inclusions and H-O isotopes of the Ashawayi gold deposit in the Southwest Tianshan Orogen and its orogenic-type gold deposit

【研究目的】阿沙哇义金矿位于西南天山,处在“亚洲金腰带”的中南缘,是最近几年新探明、中型规模的金矿,矿床基础研究程度较低。【研究方法】通过野外地质调查,室内开展流体包裹体岩相学、成分分析、测温、H-O同位素等研究。【研究结果】提出矿床的含矿地层为上石炭统喀拉治尔加组,矿体产于NEE走向逆冲推覆构造系统的次级断裂内;成矿可分为3阶段,早—中阶段发育H_(2)O溶液型、CO_(2)-H_(2)O型及纯CO_(2)型三种流体包裹体,但晚期仅发育纯H_(2)O溶液型包裹体。其中早期均一温度236~386℃,盐度1.6%~9.7%NaCl eqv.;中期均一温度225~301℃,盐度1.4%~12.5%NaCl eqv.;晚期均一温度139~222℃,盐度1.4%~7.3%NaCl eqv.;流体包裹体激光拉曼图谱显示液体成分为H_(2)O和CO_(2),含CH_(4)和N_(2);表明成矿流体具中低温、富CO_(2)、含CH_(4)和N_(2)、低盐度的变质流体特征;根据CO_(2)-H_(2)O型包裹体估算早—中期压力分别为140~180 MPa和130~160 MPa,对应的静岩压力深度分别为5~7 km和5~6 km;石英的H-O同位素结果显示成矿流体从早期深源变质流体,经中期变质流体与大气降水混合流体,晚期向浅源大气降水热液演化。【结论】综合分析认为,压力降低,流体不混溶或沸腾,CO_(2)、CH_(4)等气体逃逸,发育硫化、碳酸盐化这一过程是阿沙哇义金矿床金快速沉淀的主要机制,矿床属于典型的中浅成造山型金矿床。

This paper is the result of mineral exploration engineering.[Objective]The Ashawayi gold deposit,located at the central and southern margin of the"Asian Gold Belt",is a newly discovered medium-sized gold deposit in southwestern Tianshan Orogen,NW China.[Methods]Through field geological survey,indoor research on fluid inclusion petrology,fluid inclusion composition analysis,fluid inclusion temperature measurement,H-O isotope and so on is carried out.[Results]The deposits are hosted in Kalazierjiao Group,Late Carboniferous,and ore bodies are produced in secondary faults of the NEE-trending thrust nappe system.According to the relationship between vein cutting and mineral metastasis,the mineralization process can be divided into three stages.Microscopic observation analyses of inclusions in quartz showed that there were three compositional types of fluid inclusions,i.e.pure CO_(2),CO_(2)-H_(2)O and NaCl-H_(2)O in the early and middle stage,but only pure H_(2)O inclusions in the latest.Measurement of inclusions trapped in quartz revealed that the total homogenization temperatures were 236-386℃in the early stage,225-301℃in middle and 139-222℃in last,respectively,with corresponding salinities of 1.6%-9.7%,1.4%-12.5%,and 1.4%-7.3%NaCl eqv..The laser Raman spectrum of fluid inclusions showed that the liquid was composed of H_(2)O and CO_(2),a few of CH_(4)and N_(2),indicating that the ore-forming fluid was a kind of medium-low temperature,rich of CO_(2),bearing few of CH_(4)and N_(2),and low-salinity metamorphic fluids.The estimated pressures based on CO_(2)-H_(2)O type inclusions are 140-180 MPa in the early stage and 130-160 MPa in the middle,corresponding a depth of 5-7 km and 5-6 km,respectively,under the static rock pressure.The content of H-O isotopes of quartz showed ore-forming fluids changing from a kind of deep-source metamorphic fluid in the early stage,to a metaphase and atmospheric precipitation mixed fluid in the middle,and to a hydrothermal fluid of late-seasonal precipitation in the last.[Conclusions]Comprehensive analysis suggested that the fluid system stress reduction,immiscible or boiling,the escape of CO_(2)-CH_(4)and other gases,and the development of vulcanization and carbonate,should result to the rapid precipitation of the gold and the deposit is a typical medium-shallow orogenic-type gold deposit.