西藏雄村斑岩型Cu-Au矿集区I号矿体富CH4成矿流体演化过程研究

The Xiongcun district, located in the southern margin of the Gangdese, belt, is the only known porphyry copper-gold district associated with the Neo-Tethys oceanic subduction. The applicants have conducted a preliminary study on the inclusions of the No.I deposit in the Xiongcun district, and consider that the ore-forming fluid of the No.I deposit is the methane-rich fluid. This research based on accurate division for the mineralization stages and guided by thermodynamics. Fluid inclusions microscopic observation as the main research means in this study. Through systematic research of the fluid inclusions in the quartz phenocrysts of the ore-bearing and typical hydrothermal minerals of the different mineralization stages, this project will find out the composition, nature, origin and evolution of methane-rich ore-forming fluid. This research will reveal the genesis of the CH4, and discusse the relationships between the methane-rich fluid and the alteration and mineralization. The methods of this study include fluid inclusion thermometry, laser Raman microprobe and C-H-O and He-Ar isotope analysis. This research will provide a new thought for the genesis study of the methane-rich porphyry deposits.

西藏雄村矿区是冈底斯成带目前发现的唯一与新特提斯洋俯冲期成矿作用有关的斑岩型铜金矿集区。本申请拟在申请者和前人研究工作基础上，针对雄村I号矿体中的流体包裹体发现大量CH4的地质事实，以最新的包裹体热力学理论为指导，采用最新的流体包裹体显微观测和成分测试技术，通过对I号矿体含矿斑岩石英斑晶以及不同成矿阶段特征热液矿物中的熔融、流体包裹体岩相学特征、显微温、压和盐度测定、单个包裹体激光拉曼光谱分析，以及C、H、O和He-Ar同位素等的系统研究，查明岛弧型斑岩铜（金）矿床富CH4成矿流体组成、性质、来源及演化过程，厘定成矿流体中CH4的成因，揭示富CH4成矿流体演化及其与蚀变、矿化的耦合关系，为该类矿床的成因研究提供科学依据。

本项目以西藏冈底斯带南缘雄村矿区富CH4成矿流体的I号矿体为解剖对象，以岩浆-流体演化为切入点，主要开展了I号矿体成矿流体来源、成矿流体中CH4成因和成矿流体演化与蚀变、矿化的耦合关系的研究。取得了如下成果：①查明了I号矿体成矿期成矿阶段，准确划分了矿物的生成顺序，查明了不同阶段成矿流体的物理化学性质（成分、温度、压力、氧逸度）；②查明了成矿流体不同阶段H-O、He-Ar同位素组成（δ18OH2O = -3.2 – +3.6 ‰, δD = -106 – -89.9 ‰；3He/4He = 0.11–0.96 Ra, 40Ar/36Ar = 418.7–2920.2），反映成矿流体主要来自于地壳流体，并且明显有大气降水的加入的特点；③查明了成矿流体中C同位素组成（δ13Cfluid = -26.3 – -28.2 ‰）和矿区含碳地层的分布情况，表明成矿流体中CH4来自于含碳地层有机质的热分解过程；④精细刻画了I号矿体流体演化过程。通过本项目的研究，丰富了还原型斑岩型矿床的研究案例，补充和完善了冈底斯成矿带侏罗纪俯冲作用相关的斑岩型铜（金）矿床的成矿理论。