拉斑玄武质岩浆角闪石氧逸度计实验模拟及其在造山带铜镍矿床中的应用

Oxygen fugacity controls the status of sulfur in magma, and thus some scholars believe that the magma transition from high oxygen fugacity to low oxygen fugacity controls the formation of Ni-Cu deposits in orogenic belts. However, due to the lack of key evidence and case studies, the debate is rather controversial. Amphibole, which is a ubiquitous mineral in rocks of these Ni-Cu deposits, record important information such as magmatic water content and oxygen fugacity. However, the existing empirical formulas of amphibole were derived from the calc-alkaline basaltic-andesites experiments and cannot be applied to tholeiitic basalts which were closely associated with Ni-Cu deposits in orogenic belts. This project intends to carry out the amphibole fractional crystallization experiments on water-bearing basalt (including picritic and high-Mg basalt). The results, combined with the existing experimental data, will be used to establish an amphibole oxygen barometry suitable for Ni-Cu deposits. Then, the amphibole and other oxygen barometers will be applied to the Huangshan and Huangshandong deposits, which consist rocks varying from gabbro to lherzolite, to reveal oxygen fugacity evolution during multiple stages of magmatic emplacement, fresh magmatic recharge, in-situ contamination, and fractional differentiation. By analyzing the evolution of oxygen fugacity in the two deposits, it is expected that the relationship between oxygen fugacity and formation of Ni-Cu mineralization in orogenic belts will be further restricted. Meanwhile, comparing the calculation results and errors of each oxygen fugacity barometer to find out the scope of application of different oxygen fugacity barometer in Ni-Cu deposits. The results of this project also have implications for other basic-ultrabasic rock related deposits.

氧逸度控制岩浆中硫的状态，有学者认为岩浆从高氧逸度转变为低氧逸度控制造山带铜镍矿床的形成，但因缺少关键证据与实例支持，仍存争论。角闪石是造山带铜镍矿床的贯通矿物，记录岩浆水含量、氧逸度等重要信息，但现有角闪石经验公式来源于钙碱性玄武安山岩的实验，并不适用于拉斑玄武质岩浆相关的铜镍矿床。本申请拟开展含水玄武质岩浆（涵盖苦橄质和高镁玄武质）的角闪石分离结晶实验，结合已有实验数据，建立适用于铜镍矿床的角闪石氧逸度计。以东天山黄山和黄山东两个岩相丰富的矿床为例，结合角闪石和其他氧逸度计，揭示这两个矿床在多期岩浆侵位、新鲜岩浆补给、就地混染、结晶分异等过程中氧逸度的变化，探讨氧逸度演化与成矿的联系，对比各氧逸度计的计算结果与误差，明确它们在铜镍矿床中的适用范围。通过剖析两个矿床的氧逸度演化，可望进一步限定氧逸度与造山带铜镍成矿的关系。本申请的研究结果对其他基性-超基性岩相关矿床研究也具借鉴意义。

该项目的研究目标为通过实验岩石学揭示拉斑玄武质岩浆温度、压力和氧逸度等参数与其结晶角闪石之间的联系，以中亚造山带典型铜镍矿床为实例检验角闪石氧逸度计，并查明黄山和黄山东矿床在多期岩浆活动、岩浆补给、就地混染等多种过程中的氧逸度变化，并对东天山铜镍矿床的角闪石成分及其记录的成矿过程与条件进行对比。截止2022年底，本项目总体研究目标基本完成，其中1项研究目标为初步完成，其他为已经完成和超额完成；预期2023年底全部达成。项目总体上按计划执行，但是受疫情影响，部分岩石学实验从2019年调整至2022年，部分调整至2023年，预计2023年完成全部岩石学实验与所有研究任务，并将相关数据与论文整理成稿。项目开展研究内容主要有：1）拉斑玄武质岩浆角闪石氧逸度实验研究；2）实验产物的成分分析；3）黄山矿床成矿过程的氧逸度演化；4）东天山（喀拉通克）区域基性-超基性岩体的氧逸度研究与对含矿性评价的指示。取得的重要进展有：1）通过实验岩石学，初步探讨了拉斑玄武质岩浆的分异过程，为后期实验与进一步研究提供了依据；2）揭示了混染过程的氧逸度变化与斜方辉石结晶机制，明确了黄山矿床成矿过程的氧逸度演化；3）论证了晶间过程对元素的改造，验证了相关氧逸度计在铜镍矿床中的适用范围与使用条件，展示了再平衡过程对相关氧逸度计具有直接影响；4）通过大量角闪石结晶实验Melts模拟，通过东天山和喀拉通克铜镍矿床角闪石成分反演了岩浆氧逸度与成矿过程。研究成果发表于Journal of Petrology、Contributions to Mineralogy and Petrology、Economic Geology、Lithos等国际权威期刊发表SCI论文4篇（两篇为第一标注），国内SCI论文1篇（岩石学报），后期还有1-2篇国际SCI论文刊出；参加国内会议交流3次，国际会议1次（2023年7月），与其他项目共同培养博士研究生2名，项目负责人入选中科院青促会会员。已经在论文发表和人才培养方面超额完成了任务。