新疆阿尔泰造山带南缘巴斯铁列克钨铜矿成矿机制研究

Xinjiang Altay hosts abundant deposits, which is characterized by Devonian volcanic-hosted iron, copper, gold and lead-zinc deposits, Permian- Triassic rare metal deposits, Permian Orogenic Au deposits and magmatic Ni-Cu sulfide deposits. Recently, Bastielake W-Cu skarn deposit associated with Permian biotite monzonitic granite had been discovered, which is tungsten polymetallic deposit discovered for the first time in Xinjiang Altay. Some important issue about metallogenesis associated with prospecting exploration need to be study, including the mineralization and wall rock alteration zoning, ore-forming age, characteristics of ore-forming fluid, enrichment mechanism of tungsten and copper. Moverover, the paragenesis mechanism between metallic elements with considerable different geochemical characteristics is an important issue in metallogeny. The paragenesis mechanism of tungsten (W)-copper(Cu) in the skarn deposits remains an enigma. The newly discovered Bastielake W-Cu skarn deposit is one of the best candidates to solve this issue. Our project will focus on the host rocks and ore-forming fluid related to the Bastielake deposit. The major element, trace element and Sr-Nd isotopic for the host rocks, the composition of the magmatic apatite, biotite and zircon, will be used to discuss the nature of magma source, differentiation index and oxygen fugacity of host rocks associated with the mineralization. Systematic investigation for, the composition of minerals (e.g., scheelite, pyrite, chalcopyrite and garnet and the isotopes; melt-inclusions from quartz in intrusion, melt-fluid and fluid inclusions hosted in scheelite, pyrite, garnet, epidote and quartz from different hydrothermal mineralization stages, will be used to decipher the correlation between physicochemical properties (pressure, temperature, pH and volatile fugacities) and the ore-forming fluids. All information will be employed to analyze the transfer and precipitate of tungsten and copper during magma evolution, exsolution from magma and hydrothermal evolution to provide the crucial constraints for the W-Cu parageneis. Our research results will be benefit to extend knowledge of skarn deposit theory, but also help to provide a theoretical basis of prospecting exploration for tungsten and copper deposit in the Xinjiang Altay.

新疆阿尔泰以发育泥盆纪与海相火山岩相关的铁、铜、金、铅锌矿、二叠-三叠纪伟晶岩型稀有金属矿、二叠纪造山型金矿和岩浆铜镍硫化物矿床为特色。近年来,克兰盆地发现了首例二叠纪矽卡岩型钨铜矿床，其矿化及围岩蚀变、成矿流体、钨铜富集过程和主要控制因素、矿床模型等亟待查明的重要科学问题，直接关系到找矿勘查工作，也为钨与铜等地球化学性质差异大的金属元素共生机制这一矿床学研究的重要科学问题提供了实例。本项目拟以巴斯铁列克钨铜矿为对象，通过与成矿相关花岗质岩体系统的矿物学、岩石学和地球化学研究，揭示岩浆来源和演化与钨铜富集关系；通过包裹体（熔融包裹体、熔流包裹体和流体包裹体）系统研究，结合矿物（石榴子石、白钨矿和黄铁矿）成分和同位素，确定含矿流体演化轨迹及钨和铜在流体中迁移沉淀过程，阐明钨铜共生机理，建立成矿模型。本项目将丰富矽卡岩型矿床成矿理论，拓展阿尔泰找矿方向，对区内矽卡岩型钨铜矿勘查部署提供依据。

巴斯铁列克矿床是近年来在新疆阿尔泰造山带南缘发现的首例中型钨多金属矿床，矿体赋存于花岗质复式岩体与康布铁堡组接触带的矽卡岩，发育独立钨矿体、钨铜矿体，是研究钨铜等元素富集沉淀和钨矽卡岩矿床成矿机制的理想对象。本项目以巴斯铁列克矿床为对象，开展了矿区侵入岩形成时代、岩浆来源和演化、成矿时代、成矿流体、成矿物质来源及成矿机制研究。LA-ICP-MS U-Pb定年法获得矿区花岗岩锆石年龄介于284～275Ma，矽卡岩热液锆石年龄为279.7±6.6Ma和249.8±2.5Ma，热液榍石下交点年龄介于250～252Ma，表明矿化与早二叠世岩浆活动相关，并受晚二叠世热液活动影响。矿区花岗岩地球化学特征与黑云母成分研究结果表明，这些岩体是来自不同岩浆体系的I-A过渡型岩石。不同的岩浆源区和演化分异程度是导致岩体含矿性差异的主要因素，钨铜矿化与不同岩体有关，高分异程度有利于钨矿化不利于铜矿化，高幔源组分与铜矿化有关。与黑云母平衡岩浆流体，在黑云母花岗岩中有最高的log f (HF) /f (HCl)值（－0.59~－0.81）和最低的log f (H2O)/f (HF) 值（4.18~4.52），在二云母花岗岩有最低的log f (HF) /f (HCl)值（－1.13~－1.25）和最高的log f (H2O)/f (HF) 值（4.64~4.96），表明黑云母花岗岩与钨矿化更为密切，二云母花岗岩与铜矿化相关。巴斯铁列克矿床白钨矿主要分布于矽卡岩中，黄铜矿和闪锌矿主要分布于石英-硫化物脉。不同类型白钨矿有不同的结构和成分。所有矽卡岩阶段白钨矿均呈右倾型稀土配分模式和强烈的Eu负异常（δEu=0.40-0.71），暗示流体来源于二叠纪岩体，并且至少有两种不同岩浆流体的参与。结合流体包裹体特征，成矿流体在演化过程中有大气降水混入。硫化物（黄铜矿、磁黄铁矿和闪锌矿）的δ34S集中于-0.16‰～1.53‰，峰值为0.5‰，表明成矿物质来源于幔源岩浆。巴斯铁列克矿床是还原性矽卡岩型矿床，是早二叠世多期岩浆流体注入、大气降水以及流体沸腾导致的多期钨多金属矿化，在晚二叠世受区域构造作用影响。