西南天山阿沙哇义金矿载金矿物地球化学特征及地质意义

阿沙哇义金矿床是中国新疆西南天山目前探明的第二大金矿,是中亚造山带南缘“亚洲金腰带”的重要组成部位。野外构造调查表明,研究区在古生代期间经历了由挤压变形发展为走滑伸展两次构造作用,成矿发生在挤压变形到走滑伸展转换时期。运用矿相学、电子探针、扫描电镜及S同位素等方法确定矿床载金矿物、金的赋存状态、成矿物质来源等,结果表明:阿沙哇义金矿载金矿物主要为含砷黄铁矿、部分毒砂。含砷黄铁矿分为沉积成岩期(Py1)、成矿早期(Py2)、成矿期(Py3);Py2、Py3富As、Te,亏S、Fe,S、As呈明显负相关;Co/Ni比值显示黄铁矿属沉积-热液成因。Au以纳米级“可见”自然金(Au0)形式存在于含砷黄铁矿中。黄铁矿、辉锑矿δ34 S为9.5‰~16.3‰,显示成矿流体中硫为海相硫酸盐热化学还原产物,成矿物质来自赋矿地层。矿床属典型的中浅成造山型金矿,矿床埋藏较浅,矿区深部具有很好的找矿潜力。

Geochemical characteristics of gold-bearing minerals and its geological significance in the Ashawayi gold deposit in the southwestern Tianshan Orogen

Ashawayi gold deposit, the second largest gold deposit in the southwestern Tianshan Orogen, NW China, is located at the southern margin of the Central Asian Orogenic Belt of the "Asian Golden Belt". Detailed field observations showed that the regional area experienced two tectonic processes from early compression to lately strike-slip extension during the Paleozoic, and the mineralization was related to the transition from compression to extension. By the methods of mineragraphy, EMPA, SEM and S isotope analysis, the gold-bearing minerals in the ore deposit, the occurrence state of gold, the source of ore-forming materials, were determined in this paper, suggesting that gold-bearing minerals should be mainly composed of arsenian pyrite and some arsenopyrite. The formation of arsenic pyrite can be divided into three stages, i.e. sedimentary diagenesis stage (Py1), early ore-forming stage (Py2), and main ore-forming stage (Py3). The Py2 and Py3 are rich of As-Te, and deficit of S-Fe, while the content of S and As is significantly negatively correlated. The ratio value of Co/Ni indicates that the pyrite should be the origin of deposit-hydrothermal. The gold is mostly hosted in arsenic pyrite as the form of nano-scale "visible" natural gold (Au0). The δ34S value of pyrite and stibnite changes from 9.5‰ to 16.3‰, suggesting that the sulfur in ore-forming fluid should be a thermochemical reduction product of marine sulfate and ore-forming material probably resourced from the stratum. Therefore, the Ashawayi gold deposit should be a typical medium-shallow orogenic-type gold deposit, and the buried depth of ore-bodies is relatively shallow, suggesting a favorable prospecting potential in the deep.