新疆阿尔泰小土尔根铜矿岩浆-成矿流体作用与铜矿富集机制

The Altay orogenic belt, located in Xinjiang, is characterized by the development of VMS type copper-lead-zinc deposits, pegmatite type rare metal deposits, volcanic type iron deposits, and skarn iron deposits, but no porphyry deposit was discovered. The Xiaotuergen deposit in recent exploration is a porphyry copper deposit discoverd for the first time. The discovery of this deposit started a new direction of porphyry copper deposits exploration in Altay. Thus, anatomy of this deposit, including the mineralization and wall rock alteration zoning, ore-forming age, characteristics of ore-forming fluid, enrichment mechanism of copper, and ore deposit model is an important scientific question. This project aims at the survey of basic geological characteristics of Xiaotuergen copper deposit, study on the of ore-forming fluid and mineralization system, inclusion petrography and microthermometry of quartz from granodiorite porphyry associated with mineralization, as well as calcite, quartz, pyrite and other minerals in different stages of mineralization and metallogenic depth. Combined with the analysis of C, H, O, and He-Ar isotopes, precise mineralization age, we discuss the characteristic, evolution and source of the ore-forming fluids, copper sulfide accumulation precipitation mechanism, establishing the model of ore deposit. This study will add new content in the deposits in Altay, it can also provide a basis for exploration deployment of porphyry copper deposits in Altay.

新疆阿尔泰造山带以发育VMS型铜铅锌矿、伟晶岩型稀有金属矿、火山岩型铁矿和矽卡岩型铁矿为特色，最近勘查的小土尔根是历史上首次发现的斑岩型铜矿床。该矿床的发现开启了在阿尔泰地区寻找斑岩铜矿新方向。因此，该矿床解剖研究，包括矿化及围岩蚀变分带、成矿时代、成矿流体特征、铜富集机制、矿床模型都是一个亟待查明的重要科学问题。本项目拟在小土尔根铜矿地质特征调查基础上，重点开展成矿流体系统及成矿作用研究；通过对与成矿有关花岗闪长斑岩中石英斑晶、不同成矿阶段及成矿深度的方解石、石英、黄铁矿等矿物中的包裹体开展岩相学和显微测温，并进行C、H、O、He-Ar同位素分析，结合精确厘定成矿时代，探讨成矿流体性质、演化、成矿流体来源和铜硫化物聚集沉淀机制，构建矿床模型。本项目将为阿尔泰矿床研究增添新内容，同时也将为阿尔泰斑岩型铜矿床的勘查部署提供依据。

小土尔根是新疆阿尔泰首次发现的具有“斑岩型”特征的铜矿。本项目开展了矿区地质特征、年代学、地球化学及成矿流体研究，探讨成矿作用，建立矿床模型。矿体赋存于花岗闪长岩内接触带，矿化为浸染状、细脉状、细脉-浸染状、网脉状，围岩蚀变主要有钾化、硅化、碳酸盐化、绢云母化、黄铁矿化、绿泥石化、绿帘石等，其中硅化、碳酸盐化与成矿关系密切。成矿过程发生在岩浆热液期，包括4个成矿阶段。矿区出露诺尔特组火山沉积岩，凝灰岩锆石LA-ICP-MS U-Pb年龄为412Ma，其时代为早泥盆世。矿区侵入岩主要为花岗闪长斑岩、石英斑岩、黑云二长花岗岩、花岗斑岩，LA-ICP-MS U-Pb年龄分别为405.5Ma、399.7Ma、398.1Ma、397.3Ma和369.6Ma，表明矿区存在早期405～397Ma、晚期370Ma的多期次岩浆侵入活动，矿化与花岗闪长斑岩有关，成矿时代略晚于405Ma。花岗斑岩、花岗闪长岩和石英二长斑岩，以富钾为特征，属钾玄岩系列，黑云二长花岗岩以富钠为特征，属低钾拉斑系列，地球化学特征显示矿床形成于陆缘弧环境。成矿流体属于由高温演化到低温（155～374℃）、中低盐度（3.52～15.86%）的H2O-NaCl 体系，黄铁矿3He/4He为0.029～0.224Ra，与地壳流体组成比较接近，石英δD为-93.7～-64.9‰，δ18OSMOW为11～13.1‰，表明成矿流体主要来源于岩浆水，混合少量大气降水。硫化物ä34S为6.4～15.1‰，硫来源于花岗质岩浆，硫原位微区同位素显示黄铁矿δ34S值变化不明显，表明黄铁矿结晶环境比较稳定。黄铜矿Cu同位素暗示铜来自于花岗质岩浆。综上，成矿流体由中高温岩浆热液，经过中阶段流体沸腾、温度降低等过程演化为还原性流体，导致大量金属硫化物沉淀；成矿早期成矿流体以岩浆水为主，晚期混入大气降水；确定矿床成因类型为斑岩型，构建了矿床模型。