二密还原性斑岩铜矿多期岩浆过程氧逸度示踪与岩石成因研究

The relationship between porphyry Cu deposits and oxidation state of magma has been a topic of considerable interest in the field of ore genesis and development. Most researchers agree that porphyry copper deposits are closely related to relatively oxidized magmas, although the nature of redox state associated with magmatic processes is still controversial. On base of detailed analysis, however, we found this viewpoint still cannot explain well on formation of reduced porphyry Cu deposits, such as the ore-forming magma, whether it is oxidized or reduced. Based on the results of our pilot study, this project will attempt to investigate the typical reduced porphyry copper deposit – Ermi which located in southern Jilin Province, NE China. The main objective of this research proposal is to establish genetic links between the redox state of magmatic processes and the specific controls on formation of reduced porphyry Cu deposits. To accomplish this objective, we propose using petrology and geochemistry characteristics of intrusions to identify the relation and distinction between, and petrogenesis of, causative porphyries and ilmenite-series rocks. Based on the study of oxygen fugacity for zircon and other mineral, we will make a detailed examination in polyphase composite rock body from Ermi deposit, revealing the genetic links between variation in oxygen fugacity with multiphase magmatic processes and mineralization of reduced porphyry Cu deposits. Through the above work, we will make comparison with the similar research results in the world, aiming to provide more detail metallogenic theories about reduced porphyry copper deposits.

岩浆氧化状态对斑岩铜矿形成的制约已成为当今矿床学研究领域的前沿课题，尽管存在一些争议，大量学者认为斑岩铜矿与相对氧化的岩浆有密切的成因联系。剖析前人研究结果发现，上述结论并不能很好的解释还原性斑岩铜矿成矿地质过程，例如其成矿岩浆究竟是氧化性还是还原性熔体等方面仍存在许多争议。本项目将在已有研究的基础上，选取吉林二密还原性斑岩铜矿开展研究工作，探讨岩浆氧逸度演化与还原性斑岩铜矿之间的成因联系。本次研究将在甄别成矿斑岩前提下，从岩石学、地球化学角度探讨钛铁矿系列岩石与成矿斑岩的岩石成因、联系及差异；通过对二密矿区复式岩体中锆石及其他矿物氧逸度的研究，刻画多期次岩浆的氧化还原状态，揭示多期次岩浆氧逸度变迁如何制约还原性斑岩铜矿的形成。在此基础上与国际同类研究成果作对比，以期完善还原性斑岩铜矿成矿理论。

岩浆氧化状态对斑岩铜矿形成的制约已成为当今矿床学研究领域的前沿课题，大量学者认为斑岩铜矿与相对氧化的岩浆有密切的成因联系。剖析前人研究结果发现，上述结论并不能很好的解释还原性斑岩铜矿成矿地质过程，例如其成矿岩浆究竟是氧化性还是还原性熔体等方面仍存在许多争议。本项目将在已有研究的基础上，选取吉林二密还原性斑岩铜矿开展研究工作，探讨岩浆氧逸度演化与还原性斑岩铜矿之间的成因联系。本次研究在二密矿区识别出两种类型岩石，及钛铁矿系列岩石（闪长岩，石英闪长岩，花岗闪长岩）和磁铁矿系列岩石（石英二长岩，花岗闪长斑岩，花岗斑岩）。LA-ICP-MS锆石U-Pb精确定年这些岩石的结晶年龄分别为96.4，95.0，94.0，93.0，92.7和92.0 Ma。岩石地球化学特征表明上述岩石具有弧岩浆地球化学属性，如富集大离子亲石元素，亏损高场强元素，同时拥有相似的Sr-Nd同位素组成；并揭示其起源于交代的岩石圈地幔经分离结晶作用形成，且岩浆演化过程中没有发生明显的地壳物质混染。结合前人的研究，本研究认为二密铜矿的成岩成矿作用发生在晚白垩世早期，形成于太平洋俯冲作用背景下的伸展环境下。本次研究系统揭示了二密矿床岩浆氧逸度的变化情况。研究发现二密矿床岩浆氧逸度存在明显的波动；早期岩浆拥有较低的氧逸度，而随着岩浆的演化其氧逸度有明显升高的趋势，特别是与成矿关系密切的花岗斑岩。高氧逸度的暗色闪长质包体所代表的中基性岩浆进入上地壳浅部岩浆房可能是造成岩浆房中氧逸度明显变化的重要因素。本次研究表明二密还原性斑岩铜矿成矿岩浆为高氧化性的熔体，同时揭示了高氧逸度岩浆与还原性斑岩铜矿之间的成因联系。

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