西藏甲玛斑岩铜多金属矿铜钼同位素特征对铜钼分离机制约束

The Jiama copper polymetallic deposit, located in the Gangdise metallogenic belt of Tibet, is one of the largest porphyry copper deposits being mined in China. The mineralization separation of copper and molybdenum in the deposit is ubiquitous. This phenomenon also exists in many porphyry copper-molybdenum deposits at home and abroad. The separation mechanism of copper and molybdenum has always been the research focus. Most studies draw clues from fluid inclusions, melt inclusions or experimental petrology. The main factors affecting the separation of copper and molybdenum are oxygen fugacity, pH, temperature, or different sources of materials, different complexes proxies for metal transporting, and etc. The study of Cu-Mo isotopes signature in Jiama deposit may provide new sight on the mechanism of copper and molybdenum separation. The separation mechanism of copper and molybdenum in Jiama porphyry copper deposit is an important scientific issue. This paper intends to make a preliminary study on the feature of Cu-Mo isotopes in typical cross-sections to reveal Cu-Mo separation mechanism. This study is mainly focused on two factors: temperature and oxygen fugacity. Copper and molybdenum both have variable valence, and the fractionation is greatly affected by temperature. And isotopical values between different phases is likely to be distinguished within the range of errors. This paper attempts to discuss the separation mechanism of copper and molybdenum from fractionation mechanism of copper and molybdenum isotopes in the different isotope zonation. The potential of copper-molybdenum isotope zoning in exploration targeting is then further discussed. The applicant plans to study the copper-molybdenum isotopes of the metal minerals (molybdenite, chalcopyrite, etc.) in the typical cross-sections of the Jiama cu polymetallic deposit, providing a new basis for the study of the separation mechanism of copper and molybdenum in the porphyry copper-molybdenum deposit.

西藏冈底斯成矿带的甲玛铜多金属矿床，是我国正在开采的超大型斑岩-夕卡岩型铜多金属矿之一，具有典型的铜钼矿化分离现象。该现象亦多见于国内外诸多斑岩型铜钼矿床，其铜钼分离机制一直是关注焦点。基于流体、熔融包裹体或实验岩石学的研究表明，氧逸度、pH、温度的变化，或物质来源、搬运方式的不同可能是导致铜钼分离的原因。针对甲玛矿铜钼分离机制这一重要科学问题，本项目拟对2条典型的十字剖面产出的角岩型、矽卡岩型、斑岩型矿石的金属矿物（辉钼矿、黄铜矿等）开展系统的铜钼同位素组成研究，探讨温度、氧逸度等成矿因素与样品铜钼同位素组成的关系，继而制约铜钼空间分离的控制因素。铜钼皆为变价元素，其同位素分馏受温度、氧逸度影响较大，不同相态间有可分辨的分馏值。本项目可为铜钼分离机制研究提供新的视角和研究方法，并可进一步探讨铜钼同位素特征在指导矿床勘查方面的可能性。

在甲玛斑岩成矿系统的综合研究中，前人对传统地球化学特征等的研究广泛深入，随着新的仪器分析精度进步，非传统同位素地球化学研究热点进入矿床应用，其主要目的是示踪成矿过程、成矿流体来源及成矿条件等，目前对直接的成矿金属的同位素研究较少。.本研究综合前人研究资料，完成深钻岩芯采集工作，室内开展的系统矿床地球化学分析测试分析。对于硫化物原位分析得到，金属元素分布特征以及原位硫同位素数据。甲玛硫化物硫同位素特征范围变化有限，显示典型岩浆热液来源。甲玛钻孔薄片硫化物原位硫同位素比值变化范围-4到1.5‰之间。对甲玛地区钻孔不同深度的斑岩、矽卡岩、角岩型矿石（黄铜矿、斑铜矿、黝铜矿等矿物）进行系统的铜同位素分析，并系统对不同矿物铜同位素分馏变化进行研究。对铜山含矿闪长玢岩岩体与矽卡岩接触带硫化物矿物对进行分析测试，尝试建立甲玛三维铜同位素模型，甲玛铜同位素分析主体数据特征表现出岩浆同位素组成，表明其为高温原生条件形成的铜同位素特征。角岩中不同期次硫化物铜同位素变化范围均较大，前两期受到第三期矿化明显叠加改造，从而使得三期硫化物没有显示系统变重的趋势。榍石定年结果为16±1.3Ma，甲玛独居石、榍石Nd同位素比值变化范围-5到0‰之间，与甲玛锆石氧同位素特征反映的成矿信息一致，综合多种地球化学特征信息，均显示甲玛铜多金属矿床为典型的斑岩铜矿特征。.本研究主要研究对象为冈底斯带甲玛超大型斑岩铜矿，具有典型性和代表性，为非传统稳定同位素在勘查领域的示范，形成了良好的案例研究。