摘要:
铁格隆南是一个超大型的斑岩-高硫化型浅成低温热液Cu-Au矿床,该矿床位于中国西藏班公怒江成矿带多龙矿集区内.为了更好地限制该矿床在成矿过程中的物理条件,本次研究主要选择了流体包裹体群进行显微测温.在斑岩系统中,Qz-Cpy脉主要捕获了富液相流体,其NaCl盐度为9.2%~12.9%,捕获温度为330~360℃,压力为121~170 bars,对应古深度为1.21~1.70 km.采样位置为地表以下1.03~1.07 km处,推算该处剥蚀深度为0.18~0.67 km.石英斑晶中流体包裹体以高盐度(LVS)和富气相流体(VL)为主,高盐度流体的NaCl盐度为29.3%~35.8%,最低捕获温度为330~350℃.在浅成低温热液系统中,Qz-Aln-Py-Tn-Cv脉和石英斑晶主要捕获了高盐度(LVS)和富气相(VL)包裹体,其中LVS在矿化脉和石英斑晶中的NaCl盐度分别为30.7%~32.4%和29.3%~35.8%,两者最低捕获温度一致,为310~320℃,对应最小压力为74~84 bars,最小古深度为0.74~0.84 km.采样位置为地表以下183.8~188.1m处,因此推算该处的最小剥蚀深度为0.55~0.65 km.通过拉曼光谱分析,发现在斑岩系统中,石英斑晶捕获的流体包裹体所包含的金属矿物主要为黄铜矿、赤铁矿,与斑岩系统的金属矿化类型一致;在浅成低温热液系统中,石英斑晶捕获的流体包裹体所包含的金属矿物为黄铁矿、铜蓝,也与蚀变岩中的金属矿物组合一致.同时,石英斑晶捕获的流体包裹体大部分定向穿切石英斑晶,并且与含矿石英脉具有一致的均一温度峰值.上述流体特征表明石英斑晶捕获了大量成矿流体.此外,这些流体包裹体中的金属矿物在高盐度流体和低密度流体中都存在,因此,这两种流体都具有搬运Cu的能力.通过以上研究认为,流体相分离、均一温度、盐度、流体包裹体所包含的金属矿物能够指示斑岩-浅成低温热液系统的矿化条件,并且这些流体确实能够搬运成矿物质,与铁格隆南斑岩-浅成低温热液矿化直接相关.
Abstract:
The giant Tiegelongnan porphyry-high sulfidation epithermal Cu-Au deposit is located in the Duolong ore concentration area of the Bangong–Nujiang metallogenic belt in Tibet. To better confine the physical conditions of ore forming process, the authors used fluid inclusion assemblages to do microthermometry. In the porphyry system, fluid inclusions in the quartz-chalcopyrite vein are dominated by aqueous fluid containing 9.2 wt to 12.9 wt percent NaCl equiv at temperatures between 330℃ and 360℃. The temperatures correspond to the trapping pressures of 121~170 bars and the paleo-depth of 1.21~1.70 km. The cores were sampled at the depth of 1.03~1.07 km, and it is thus estimated that the erosion depth at the spot is about 0.18~0.67 km. Fluid inclusions in quartz phenocrysts are dominated by LVS and VL fluid inclusions and the high-salinity fluid contains 29.3~35.8 wt percent NaCl equiv at the lowest trapping temperatures between 330~350℃. In epithermal system the Qz-Aln-Py-Tn-Cv vein and quartz phenocrysts contain hypersaline inclusions as well as vapor rich inclusions, the hypersaline inclusions contain 30.7~32.4 wt and 29.3~35.8 wt percent NaCl equiv, respectively, and the lowest trapping temperatures of the two subjects both range from 310℃ to 320℃. The lowest trapping temperatures correspond to the lowest trapping pressures of 74~84 bars and the minimum paleo-depth of 0.74~0.84 km. These samples were collected at the depth of 183.8~188.1 meters and hence the minimum eroded depth should be about 0.55~0.65 km. Raman spectroscopic analysis indicates that chalcopyrite and hematite mainly exist in fluid inclusions of quartz phenocrysts in the porphyry system, which is consistent with the metallic mineral composition in the system. In addition, Raman spectroscopic analysis also implies that pyrite and covellite exist in fluid inclusions of quartz phenocrysts in the epithermal system. Besides, inclusions contained in qurartz phenocrysts cut through their hosts and generally distributed in the similar direction. Together with the fact that the homogenization temperatures of fluid inclusions in quartz phenocrysts correspond with those of the mineralized veins, the authors hold that fluid contained in quartz phenocrysts was directly related to mineralization. Meanwhile these metallic grains can be observed in both vapor rich and hypersaline inclusions, which implies that both the vapor rich and the hypersaline fluids were capable of carrying Cu. It is considered that the varieties of liquid phase, homogenization temperatures, salinities and minerals contained in fluid inclusions can represent the conditions of mineralization in porphyry and epithermal systems, and these fluids could indeed carry metallogenic elements and were responsible for the formation of the Tiegelongnan porphyry-epithermal deposit.
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