新疆阿希金矿床黄铁矿标型特征及其地质意义

Typomorphic Characteristics and Geological Significance of the Pyrites from Axi Gold Deposit,Xinjiang,China

新疆阿希金矿床为西天山一典型的形成于晚古生代的与火山岩有关的大型浅成热液金矿床。电子显微探针微区成分分析结果显示,该矿床黄铁矿具有富砷贫硫的特点,w(Co)/w(Ni)比值主要介于1.79～4.61之间,反映出成矿流体以岩浆热液为主,而其比值在环带结构富砷黄铁矿核部(>5)及环带(<1)中的变化规律则进一步反映出成矿早期火山-次火山热液和后期大气降水的参与。As在成矿早期还原条件下以毒砂矿物形式存在,在后期氧化条件下则以类质同像形式进入黄铁矿形成富砷环带,而Au很可能是以不可见的超显微金形式赋存于该环带中。黄铁矿热电系数及其参数、导型的垂向变化规律等表明:成矿温度主要介于196.0～278.3℃之间,为中低温热液金矿床;矿体已剥蚀掉1/4,在1 341m中段深部矿体仍有约349m的延伸,矿体剥蚀浅并在深部仍具有一定的找矿前景。

Axi gold deposit,existing in West Tianshan Mountain,Xinjiang,is a type of large volcanic-related epithermal gold deposit formed in the Paleozoic era.Electron microprobe（EMP） analysis shows that the pyrites are characterized by being rich in As and poor in S.That the Co/Ni of pyrites varies mainly from 1.79 to 4.61 suggests the ore fluids come mostly from magmatic hydrothermal solution probably.Furthermore,the ratio variation from the cores（5） to the rims（1） of the zoned arsenopyrites suggests the participation of volcano-subvolcano hydrothermal solution in earlier stage and of meteoric water in later stage.The major As modes of occurrence are arsenopyrites in the early reducing ore-forming stage,but in the late oxidizing ore-forming stage As scatters as mixed isomorphism matter in the pyrites and forms the As-rich rims,where Au occurs as invisible nanometer-size gold.The vertical changes of thermoelectric coefficient,parameters and conduct types of pyrites indicate that the mineralization temperature varies from 196.0 ℃ to 278.3℃ and the ore body has been denudated by 25% while the deep ore body at 1 341 m mining level is found to extend for 349 m.This proves that this is a low temperature hydrothermal gold deposit with low denudation and should be expectable for a prospecting potential.