PDF《西藏甲玛铜多金属矿床成因研究》

486 地球学报第三十三卷 homogenization of the critical phase originated from the exsolution of fluid supercritical fluid. The fluid inclusions of the main stage were assemblages of boiling inclusions. Fluorescent effect of organic inclusions are notable. Microthermometry shows that the homogenization temperature of fluid inclusions in quartz phenocrysts from the magmatic-hydrothermal stage was 250C540℃, the salinity concentration of fluid inclusions with halite minerals was 35C61 (wt%)NaCl.eq, the salinity concentration of fluid inclusions of homogeneous phase was 3C29(wt%)NaCl.eq, the homogenization temperature in quartz vein from porphyry and hornfels after the magmatic stage was 210C410 , the salinity ℃ concentration was 33C41 (wt%)NaCl.eq, the salinity concentration of fluid inclusions in unmixing association with them was 5C25 (wt%)NaCl.eq. Homogenization temperature of skarn minerals was 130C360℃, the salinity concentration was 3C41 (wt%)NaCl.eq. The homogenization temperatures and salinity decreased step by step from the magmatic-hydrothermal transition stage to the quartz-sulfide stage. There were abundant chalcopyrite daughter minerals in fluid inclusions from quartz phenocrysts, suggesting the enrichment of metallogenic elements at the magma crystallization and differentiation stage. The results of Laser Raman show that the gas compositions were mainly CO2, CH4 and N2 in fluid inclusions from the early mineralization stage to the main mineralization stage. The gas compositions of fluid inclusions in minerals of various stages had close succession. Ore-forming fluids had high temperature and high salinity and were enriched in CO2 and CH4. The ore-forming fluids came from magma and were subsequently mixed with atmospheric water. When the magma-hydrothermal solution rose, high temperature ore-forming fluid experienced decompression and boiling due to the sudden release of pressure. Lots of CO2 and CH4 escaped, magmatic fluid was mixed with atmospheric water, causing the deposition of metallogenic elements. The deposit was genetically related to magmatic-hydrothermal mineralization. Key words: fluid inclusion;

characteristic;

genesis;

Jiama(Gyama);

Gangdese metallogenic belt;

Tibet 西藏甲玛铜多金属矿床位于西藏墨竹工卡县, 中国地质科学院矿产资源研究所从

2008 年起对该 矿床进行了全面的地质勘探与详细系统的研究工作, 取得了重大找矿突破, 是冈底斯成矿带上目前已探 明的超大型铜多金属矿床(唐菊兴等, 2009, 2010, 2012), 受到了地质界的广泛关注. 甲玛铜多金属矿床作为冈底斯成矿带一个重要 的代表性矿床, 前人对其进行了大量研究, 提出的 成因观点主要有: (1)海底沉积喷流成因(杜光树等, 1998;

潘凤雏等, 2002);

(2)岩浆热液充填交代成因 ( 冯孝良等,2001;

李光明等,2005;

佘宏全等,2006).近年来, 唐菊兴等(2009, 2010)、应立娟等 (2009)、郑文宝等(2010)、秦志鹏等(2011, 2012)通过 矿床勘探和综合研究认为矿床属 岩浆热液充填交 代成因 的典型的斑岩-矽卡岩型铜多金属矿.斑岩 成矿系统中岩浆体系演化为热液体系, 成矿流体在 出溶和演化过程中伴随着金属元素的富集和成矿 (Shinohara, 1994;

Webster, 1997;

Davidson et al., 2001;

Simon et al., 2004;

Halter et al., 2004;

Landtwing et al., 2005;

Hezarkhani, 2009), 本文拟通 过对甲玛铜多金属矿床流体包裹体的显微岩相鉴定, 冷热台显微测温、扫描电镜分析、激光拉曼光谱分 析, 研究流体包裹体从岩浆热液阶段演化到石英硫 化物阶段的特征变化, 找到矿床成因在流体包裹体 方面的 岩浆热液充填交代成因 证据, 探讨甲玛 铜多金属矿化与岩浆热液活动的关系, 这对甲玛矿 床的成因研究及指导找矿必将具有重要意义.