北祁连西段牛毛泉东金矿地质特征、成矿时代及成因分析

牛毛泉东金矿位于北祁连造山带与阿尔金断裂的结合部位,该地区被誉为西北的"金三角"。牛毛泉东金矿为该地区近年来新发现的受脆韧性剪切带控制的金矿床,金矿体产于阴沟群安山质凝灰岩、安山质凝灰熔岩中的近东西向脆韧性剪切蚀变带,矿化受构造控制显著,成矿具有多阶段性,金主要形成于硫化物-石英-金矿化阶段。矿脉两侧热液蚀变强烈,与成矿有关的蚀变主要为硅化。通过石英流体包裹体测得金矿石中流体包裹体的均一温度112～191℃;成矿流体盐度0.35%～7.86%,平均4.77%;密度为0.92～0.96 g/cm^3,平均0.95 g/cm^3,显示成矿流体具有浅层低温热液特征。对黄铁绢英岩型矿石中绢云母⁴⁰Ar-³⁹Ar测年获得坪年龄为(296.7±2.8) Ma,对应于北祁连陆内伸展拉张构造演化过程。矿床的地质特征及成矿时代与邻近的寒山金矿类似,并受同一条韧性脆性断裂构造带控制,均为低硫浅成低温热液型金矿,主成矿时代为华力西晚期。牛毛泉东金矿的发现及成因研究对指导区域找矿方向具有重要的意义。

Geological Characteristics,Metallogenic Age and Genesis of Niumaoquan East Gold Deposit in the Western North Qilian

Niumaoquan East gold deposit is located at the intersection area where the North Qilian orogenic belt and the Altun fault converged, which is known as the “Golden Triangle” in Northwest China. Niumaoquan East gold deposit is a newly discovered gold deposit in the area controlled by fragile-ductile faults. The gold ores occurred in EW-striken ductile faults developed in the andesite tuff and andesite lavas of Yingou Group. Gold mineralization apparently was controlled by ductile faults, featured by multistage mineralization. Most of gold was deposited at sulfide-quartz-gold stage. The wall rocks around gold lodes and ores have shown intensive hydrothermal alteration, gold mineralization is mainly related with silicification. Homogenization temperatures of fluid inclusions for the quartz in gold ores are 112-191 ℃, the salinity is 0.35%-7.86% with an average of 4.77%, the density is 0.92-0.96 g/cm³ with the average of 0.95 g/cm³, all of which are showing typical characteristics of epithermal gold deposits. The⁴⁰Ar-³⁹Ar dating of the sericite collected from wall rocks yields plateau age of (296.7±2.8)Ma corresponding to the inner continental extension stage of the North Qilian belt. The geological characteristics and metallogenic age of Niumaoquan East gold deposit is quite similar with that of Hanshan gold deposit located in nearby area, both of the two deposits are controlled by the same NWW trending of ductile-brittle fault zones, should belong to low-sulfidation epithermal deposit formed in late Variscan period. The discovery of the gold deposit and the study on the genesis are of great significance for guiding regional prospecting.