甘肃早子沟金矿矿床成因——来自流体包裹体及H-O-S同位素的证据

Genesis of the Zaozigou gold deposit in Gansu Province:evidences from fluid inclusions and H-O-S isotopes

对早子沟金矿床进行了流体包裹体测温和H-O-S同位素分析.研究结果显示,包裹体的均一温度范围为120.8~257.5℃,主要集中于150~230℃(平均为178.0℃),冰点温度介于-3.6^-0.1℃(平均为-1.6℃).由此计算得到盐度介于0.18%~5.86%(平均2.61%),密度介于0.78~0.97 g/cm3(平均0.91 g/cm3).对6件石英样品的氢氧同位素测试结果显示,δ(DV-SMOW)介于-99.8^-91.40,δ(18OH2O)介于-2.53~4.08,表明成矿流体可能由岩浆水或变质水与大气降水或地下水混合形成.黄铁矿样品的δ(34S)均为负值,具有较窄的分布区间,介于-14.2^-7.6,说明成矿物质可能由区域内的岩浆岩或变质岩所提供.早子沟金矿可能形成于晚三叠世秦岭造山带后碰撞的伸展构造环境中,此时岩石圈拆沉导致软流圈上涌,引发下地壳大规模的岩浆作用,岩浆作用晚期热液携带成矿物质向上运移,经受了大气降水或地下水的混合作用,最终,含矿热液在构造破碎带中沉淀、富集成矿.

A fluid inclusion temperature testing and H-O-S isotopic analysis was performed of the Zaozigou gold deposit and the results showed that its homogenizing temperature ranged from 120.8℃to257.5℃,mainly concentrating at 150-230℃(178.0℃on average),and the freezing temperature rangedfrom-3.6℃to-0.1℃(-1.6℃on average).Accordingly,the salinity was calculated as from 0.18%to5.86%(2.61%on average)and bulk densities from 0.78 to 0.97 g/cm3(0.91 g/cm3 on average),respectively.Theδ(DV-SMOW)andδ(18 OH2O)values of quartz from six samples ranged from-99.8 to-91.40 and from-2.53 to 4.08,respectively,indicating that the ore-forming fluid was probably magmatic or metamorphic in origin with contaminations of meteoric waters.Theδ(34S)values were all negative and ranged from-14.2 to-7.6 within a narrow distribution range,implying that the ore-forming materials were probably derived from magmatic or metamorphic rock.Together with previous studies,it was considered that the metallogenesis of the Zaozigou gold deposit was most likely associated with the post-collision extensional tectonic setting of the Qinling Orogen during the Late Triassic.The ore-forming processes can be summarized as the follow:the upwelling of asthenospheric mantle material caused by lithosphere delamination triggered a large-scale magmatism at the lower curst,and the late stage magmatic fluid carried ore-forming materials and moved upward.The ore-forming materials precipitated and settled in the fractures at the shallow crust.