西秦岭早子沟金矿黑云母成分特征及成岩成矿指示意义

Composition characteristics of biotite and its implications for diagenesis and mineralization in Zaozigou gold deposit,Western Qinling

甘肃省夏河-合作矿集区是西秦岭造山带中重要的金矿富集区之一,早子沟金矿为其中最为著名的特大型矿床,矿区中酸性脉岩极为发育,与成矿具有密切联系。本次在早子沟金矿床野外调研的基础上,针对矿区主要脉岩中的黑云母进行了电子探针分析。结果表明,早子沟金矿中酸性脉岩中主要为岩浆黑云母,黑云母中FeO_(t)含量为19.71%~29.84%,MgO含量为9.54%~13.51%,兼有镁质、铁质黑云母的特点;黑云母的结晶温度为776.61~799.65℃,结晶压力为131~283 MPa,氧逸度lg f_(O2)为-14.85~-13.11,表现为高温、低压、较高氧逸度的特征。通过黑云母化学成分特征分析表明早子沟金矿脉岩属钙碱性花岗岩,为壳幔混源成因。早子沟金矿脉岩黑云母的这些矿物化学特征及其所指示的地质背景,揭示了早子沟脉岩代表的该套岩浆为形成大型热液矿床创造了有利条件。

The Xiahe-Hezuo Mining area in Gansu Province is one of the important gold deposit dense areas in the West Qinling orogen.The Zaozigou gold deposit is the most famous giant gold deposit in this area.The veined intermediate to acid magmatic rocks are commonly developed in the Zaozigou gold mining area,which are closely related to mineralization.Based on the field investigation of the geological characteristics of the Zaozigou giant gold deposit,the electron microprobe analysis of the biotite was carried out on the veined intermediate to acid magmatic rocks in the mining area.The detailed results show that the FeO_(t) contents of biotites range from 19.71% to 29.84%,and the MgO contents range from 9.54% to 13.51%.They show the characteristics of both magnesian biotite andiron biotite.The crystallization temperatures of biotite are 776.61℃ to 799.65℃,the crystallization pressures rangefrom 131 MPa to 283 MPa,and the oxygen fugacity lgfO2are-14.85 to-13.11.The biotites are characterized byhigh temperature,low pressure and relatively high oxygen fugacity.The geochemical composition characteristics ofbiotites show that the veined magmatic rocks in the Zaozigou gold deposit belongs to calc-alkaline granite,which isderived from mixed crust and mantle origin.The mineral chemical characteristics of biotite of the veined magmaticrocks of Zaozigou gold mine and the geological background revealed that the magmatism which the Zaozigou veinedmagmatic rocks represented contribute to the mineralization of the giant gold hydrothermal deposit.