西天山卡特巴阿苏金矿床黄铁矿特征研究及其对成矿机制的指示

Tracing the mineralization physical chemical condition in the complicated ore-forming process by characteristics of pyrite is the forward topic on metallogenic mechanism of hydrothermal gold deposits. Kateba’asu gold deposit located in Xinjiang Province,was a a newly discovered large deposit in the western Tianshan, charactered multiple phases and different types of mineralization , proving the Asian Gold Belt extend to west Xinjiang Tianshan and becoming a ideal research object of gold mineralization in western Tianshan.Pyrite is the most important Au-bearing mineral of Kateba’asu gold deposit. Firstly,Based systematic field work and microscopic examination , the occurrence and forming phase(stage,generation) of the pyrites will be identified .By studying the physical characteristics (crystal morphology, cell parameters, thermoelectricity)and its time-space variation law, the ore-forming temperature,oxygen and sulphur fugacity of hydrothermal solution will be obtained.With LA-ICP-MS in situ microanalysis ,studying the compositions,contents, distribution characteristics of trace element in pyrite , and the migration regularities of trace element in hydrothermal activities,to constrain the chemical composition and evolution characteristics. Combining with REE and S,Pb isotope of ore minerals and wall rocks,the sources of metallogenic materials and fluids will be deeply discussed.By researching the the mechanism of the deposition and enrichment of ore forming elements, to clarify the relationship between the Skarn type and altered rock type mineralization ,revealing the ore-.forming mechanism of Kateba’asu gold deposit.This research has important significance for metallogenic theory and exploration of the gold deposits in western Tianshan and even Central Asian Metallogenic Region.

黄铁矿特征对复杂成矿过程的成矿环境理化条件的示踪是当前热液金矿床成矿机制的前沿课题。新疆卡特巴阿苏金矿床是我国西天山新发现的大型金矿床，具有多期成矿且发育多种矿化类型的成矿特殊性，黄铁矿是矿床内的主要载金矿物。本项目拟通过系统的野外调查和镜下鉴定，查明黄铁矿的产状类型和期次阶段世代。通过研究黄铁矿的物理特征（晶体形态、晶胞参数、热电性）及其时空变化规律，反演成矿温度、热液氧逸度及硫逸度等性质的演化过程。采用原位微区分析，查明黄铁矿的微量元素组成、含量及分布特征，研究热液活动过程中微量元素的迁移规律，进而约束成矿热液的化学成分及演化特征；结合矿石矿物和围岩的稀土元素及S、Pb同位素特征，探讨不同期次矿化的物质和流体来源。从而确定成矿元素的沉淀富集机制，厘清矿区矽卡岩型矿化和蚀变岩型矿化的内在联系，揭示卡特巴阿苏金矿床的成矿机制。这对西天山乃至中亚成矿域金矿床的理论研究和勘查具有重要意义。

卡特巴阿苏金矿床是西天山新发现的大型金矿床，已探明黄金资源量80余吨，以蚀变岩型矿化为主，受断裂控制明显。前人对成矿成因还存在争议。黄铁矿是矿床内的主要载金矿物，与金矿化密切相关。本项目选择黄铁矿为研究对象，通过分析不同阶段黄铁矿的晶体形态、晶胞参数和微量元素，揭示成矿的物理化学条件，进而约束成矿热液的化学成分及演化特征。通过野外调查及显微观察，划分出黄铁矿-石英-绢云母、石英-黄铁矿、金-多金属硫化物和石英-碳酸盐等成矿阶段，形成4个阶段黄铁矿。从早到晚，黄铁矿形貌具有粗粒自形-半自形→中粒自形-半自形（以{100}为主）→中细粒半自形-他形单晶及集合体（以{100}、{210}、{111}为主）→晚期细粒自形单晶（以{100}为主）的演化特征，指示成矿流体温度逐渐降低。成矿早期处于温度较高、低过饱和度、低氧逸度及低硫逸度的环境，主成矿阶段具有较高的氧逸度、硫逸度和过饱和度。早期黄铁矿的Co、Ni含量明显较高，主成矿阶段Ag、Se、Te、As、Cu、Zn、Sb等含量稍高。大部分黄铁矿Co/Ni为1～10，Au/Ag小于1，指示岩浆热液成因。矿床内发育含铋、含碲矿物，Au和Bi、Te具有较好的正相关性，而与As之间相关性较弱，说明Bi、Te对Au的富集有明显作用，而与As关系不大。主成矿期黄铁矿相对于早期黄铁矿稀土元素总量呈减小趋势，且Eu负异常更明显。不同阶段黄铁矿Ce异常均不明显，说明成矿体系主要呈还原状态。石英δDH2O为-80.7‰～-107.0‰，平均为-93.8‰。δ18OH2O为1.6‰～11.0‰，平均为4.8‰，表明成矿流体为岩浆水和大气降水混合来源。黄铁矿δ34S值为5.8‰~12.15‰,平均9.37‰，具“塔式”效应，表明硫源较为单一，说明成矿流体的硫主要来源于深部岩浆，在运移过程中可能混入地层等物质。黄铁矿206Pb/204Pb为18.106～18.896，207Pb/204Pb为15.557～15.647，208Pb/204Pb为37.954～38.851，说明矿石铅具有壳幔混合来源，二长花岗岩以及地层对成矿也有一定的贡献。综合黄铁矿矿物学、同位素地球化学特征及前人研究成果，初步认为卡特巴阿苏金矿床为岩浆热液矿床，并建立了矿床的成因模式。