大湖塘和园珠顶热液铜钼成矿作用中Cu、Mo同位素组成及其地质意义

The geochemical behaviors of metal elements in the ore-forming process is one of the hot issues in the study on the magmatic hydrothermal ore systems. Cu and Mo isotopic compositions can be used to trace ore-forming fluids which is becoming the research frontier for ore deposit study. We discovered a negative relationship between δ65Cu and δ97Mo in the Dahutang W-Cu-Mo ore field and a similar trend in the Yuanzhuding Cu-Mo deposit. What geological significance does this trend indicate for the ore-forming process? How and why Cu and Mo isotopes fractionate in hydrothermal Cu-Mo mineralization system? To understand these scientific questions, this project is planned to investigate the above two deposits. On the basis of detail investigating ore deposit geology, we will measure Cu-Mo isotopic compostions of the potential source rocks (including host rock and multiple and polyphasic granitoids), chalcopyrites and molybdenites from different ore-forming stages. In combination with the work on fluid inclusion, element geochemistry, H-O isotope geochemistry, we will distinguish how Cu and Mo isotopes fractionate in the hydrothermal Cu-Mo mineralization system and what constrain their variations. This project will approach to reveal the mechanism and geological significance for negative relationship existing between δ65Cu and δ97Mo in Dahutang and Yuanzhuding. The results may help us to trace the geochemical behaviors of Cu and Mo in the ore-forming process and to better understanding the mechanisms of hydrothermal mineralization.

成矿作用中成矿元素的地球化学行为是热液成矿系统研究领域中的前沿课题。Cu、Mo同位素可直接示踪铜钼在热液成矿作用中的地球化学行为，是当前研究热点。申请者初步研究发现大湖塘钨铜钼矿田δ65Cu和δ97Mo存在明显的负相关，在园珠顶铜钼矿床也发现类似趋势。这些趋势的成矿地质意义何在？热液铜钼成矿作用中Cu、Mo同位素组成的制约因素有哪些？本项目拟以大湖塘和园珠顶为研究对象，在精细矿床地质解剖的基础上，查明围岩地层、不同期次花岗岩、不同阶段黄铜矿和辉钼矿的Cu、Mo同位素组成；并结合流体包裹体、元素及H-O同位素地球化学方法，判别热液铜钼成矿作用中Cu、Mo同位素组成和变化的制约因素，揭示δ65Cu和δ97Mo负相关的内在机制和其指示意义，初步建立热液成矿中Cu、Mo同位素的示踪体系。这不仅可以探索Cu、Mo等成矿元素在成矿过程中的地球化学行为，还可为深刻理解热液矿床成矿机理提供新的思路。

赣西北大湖塘超大型钨铜钼矿床和粤北园珠顶斑岩型铜钼矿床是典型的热液铜钼矿床，是开展热液铜钼矿床中铜钼同位素组成的理想对象。本项目开展了赣西北大湖塘超大型钨铜钼矿床的成矿流体性质、来源及演化，认为大湖塘矿床至少存在两个阶段的流体成矿系统；通过成岩成矿时代的研究，首次提出长达20Ma的持续性成矿作用是形成大湖塘超大型矿床的关键因素之一；通过LA ICP-MS锡石U-Pb定年，获得浙东南洋滨斑岩型锡矿床的成矿年龄为101.0 ± 3.1Ma；通过热液矿床中锡石和黄锡矿的锡同位素研究，认为氧化还原反应是控制锡同位素组成的主要因素；该项目还开展了锡石的锡同位素测试方法研究，探测了大湖塘钨铜钼矿床的深部地球物理特征，总结了钼同位素地球化学研究进展及其在成矿作用研究中的应用。通过粤北园珠顶斑岩铜钼矿床黄铜矿的铜同位素和辉钼矿的钼同位素及花岗岩体、围岩地层的的铜钼同位素研究，发现粤北园珠顶斑岩型铜钼矿床的铜钼同位素相关性与大湖塘钨铜钼矿床的铜钼同位素之间的相关性非常类似。