摘要:
舍索矿床位于西藏申扎县北部,属班公湖-怒江成矿带中段,为小型矽卡岩型铜多金属矿床。本文在野外地质调查和室内岩矿鉴定基础上开展了锆石LA-ICP-MS U-Pb法测年、主量与微量元素测试、H-O、C、S和Pb同位素、流体包裹体拉曼光谱、包裹体温度与盐度分析。矿区成矿岩体花岗闪长岩年龄为116Ma, A/CNK值在1.0附近,A/NK值在1.62~1.88之间,为准铝质与过铝质的过渡类型。微量元素蛛网图中,富集大离子不相容元素Rb、Th、Pb、Ti,贫Nb。稀土配分模式属于右倾型,重稀土部分的曲线形态平缓,∑REE=89.89×10-6~97.92×10-6,∑LREE/∑HREE=7.47~9.31,δEu=0.75~0.89,具有不明显的负Eu异常。矿床形成于班公湖-怒江洋向南(即冈底斯地块)俯冲碰撞闭合之前的岛弧环境。石英包裹体流体主要为岩浆水。方解石的δ13CV-PDB(‰)=-3.6~ -2.0;δ34SV-CDT(‰)=-10.3~2.7,以负值为主,出现-8.5‰与-3.5‰两个峰值,辉钼矿的δ34S 出现较大的负值。花岗闪长岩的锶钕同位素显示其源区为幔源,在上升过程中受到下地壳物质的影响。包裹体均为气液两相包裹体,气相成分主要为CO2,有少量的N2与CH4。气液比(%)为5~45,大小为3×6~33×20μm。测试的均一温度范围为130~290℃,主要介于180~260℃,盐度主要介于3%~6% NaCleqv和10%~18% NaCleqv,总体显示为低温低盐度特点。成矿物质由岩浆与地层共同提供。
Abstract:
Shesuo deposit is located in the north of Shenzha county, Tibet. It is near the Bangong Lake-Nujiang metallogenic belt, and a small skarn type copper-richen polymetallic deposit. This paper is based on the systemic field geological survey, indoor rock and ore appraisal, zircon LA-ICP-MS U-Pb dating, test of major and trace element, H-O, C, S and Pb isotopes, Raman spectra, temperature and salinity of fluid inclusions, and find out its chronology and geochemical characteristics. The age of granodiorites which is metallogenic rock is 116Ma, A/CNK value is near 1.0, A/NK value 1.62~1.88. The roceks belong to transition types between metaluminous and ultraluminum. In the spider diagram of trace elements, big ion incompatible elements Rb, Th, Pb and Ti are rich, and Nb is poor. The distribution pattern of rare earth elements is right-trending type, and the curve of heavy rare-earth elements is gentle, ∑REE is range from 89.89×10-6 to 97.92×10-6, ∑LREE/∑HREE=7.47~9.31, δEu=0.75~0.89, and namely it has no obvious negative Eu abnormalities. Bangong Lake-Nujiang oceanic crust subducts southward (Gangdes plot). The deposit formed in island-arc environment. Pb isotopes of granodiorites which are metallogenic rocks reflects that it belongs to crust source. The date of H and O isotopes of inclusions in sulfide-quartz veins shows that it mainly belongs to the magma water. The δ13CV-PDB of calcite ranges from -3.6‰ to -2.0‰; The δ34SV-CDT=10.3‰~2.7‰, and they are negative values, and mainly appear -8.5‰ and -3.5‰ two peaks, δ34S of molybdenum reflects larger negative values. In the structure model image, Sr-Nd isotope dates is located near the mantle,and is affected by lower crust. All inclusions are gas-liquid two phase inclusions, and the gas phase composition is mainly CO2 and a little with CH4 and N2. The ratio of gas to liquid is between 5% and 45%, and the size is of 3×6~33×20μm. Uniform temperature ranges from 130℃ to 290℃, and is mainly 180~260℃; and the salinity in mainly 3%~6% NaCleqv and 10%~18% NaCleqv, and overall it shows the low temperature and salinity characteristics. The ore-forming materials are provided by magama and strata together.
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