西藏尼玛县达查金矿床同位素地球化学研究

西藏达查金矿的成矿物质来源问题一直存在很大的争议。达查金矿床矿物中硫、铅、硅同位素及包裹体水中的氢、氧同位素研究表明 ,矿区内黑色炭质板岩、浸染状黄铁绢英岩化闪长玢岩和石英黄铁矿脉中的δ3 4SCDT值分布范围为 1 1‰～ 1 6‰ ,平均为 1 4‰ ,与陨石硫或深源岩浆硫接近。地层铅、岩浆岩铅和矿石铅在构造模式图上主要落在造山带线附近。石英包裹体的均一温度为 44 0 8～ 5 0 1 8℃ ,δDV -SMOW 值为 - 12 6‰～ - 98‰ ,δOV -SMOW 在 2 0 8‰～ 8 84‰之间 ,为典型的岩浆水 ;矿石中热液石英的硅同位素δ3 0 SiNBS -2 8　　　值的极差主要集中在 - 0 5‰～- 0 6‰之间 ,与成矿密切相关的硅质可能来源于基性或中基性岩浆岩。岩金矿的成矿物质可能有 3个主要的源区 :一是木嘎岗日群第二、三岩组 ,该岩组的海底热水沉积物含有大量的成矿物质 ;二是深部隐伏的原来特提斯海底的基性或中基性岩浆岩 ,它是金与硅的主要供给者 ;三是本区的中酸性岩浆岩 ,它是多种成矿物质最终集中成矿的主要中介。本区的成矿流体主要为受到大气降水或海水强烈改造的岩浆热液

ISOTOPE GEOCHEMISTRY OF DACHA GOLD DEPOSITS IN TIBET

Based on the studies of S, Pb, Si isotopes and H,O isotopes of water in the fluid inclusions from Dacha gold deposits in Tibet, the range of δ 34 S CDT value is 1 1‰-1 6‰ with average 1 4‰,which close to meteoric sulphur and depth origin magma sulphur; the leads of stratum, magma rock and ore are located around orogen belt in the pattern of tectonic; the temperatures of homogenization of quartz veins range from 440 8 to 501 8℃, δ D V-SMOW from -126‰ to -98‰ , δ O V-SMOW from 2 08‰ to 8 84‰, that means the water in fluid inclusion is typical magmatic water; the δ 30 Si NBS-28 ranges from -0 5‰ to -0 6‰,and the silicon possibly come from the basic and intermediate basic magma rocks. Three sources are recognized for the metallogenic material of the primary gold deposits in Dacha area,Tibet. The first source is the second and third formations of the Mugagangri group, the marine thermal water sediments which bear a lot of metallogenic material. The second source is deep buried basic and intermediate basic magmatic rocks which occur in Tethys bed and provide most of the gold and silicon for the gold deposits. The third one is intermediate acid magmatic rocks which are the main rocks providing various matellogenic material. The main matellogenic fluid of this area is the magmatic hydrothermal fluid reformed strongly by meteoritic water or sea water.