藏南拆离系锑金成矿特征与成因模式

Metallogenic Characteristics and Genetic Model of Antimony and Gold Deposits in South Tibetan Detachment System

藏南拆离系是一条重要的锑、金成矿带,呈东西向平行于变质核杂岩带展布。通过对典型矿床成矿特征的研究,识别出3种主要矿床类型:1沙拉岗式锑矿床:受南北向正断层和东西向层间断层控制,矿体为石英-辉锑矿脉,围岩蚀变较弱;2马扎拉式锑-金矿床:主要受间断层控制,局部与南北向断层相关,矿体主要由含金石英-辉锑矿脉体群组成,硅化、绢云母化、绿泥石化和碳酸盐化等围岩蚀变发育;3浪卡子式金矿床:位于变质核杂岩周缘,受剥离断层和正断层控制,矿体呈石英细脉和蚀变岩构成的透镜体,硅化、绿泥石化和绢云母化蚀变强烈。石英流体包裹体测温表明,流体主要为低温和低盐度流体。氢、氧、硫同位素研究显示,沙拉岗式锑矿床具有西藏地热水的特征(δD值为-140‰^-166‰),而马扎拉式锑-金矿床为岩浆水与大气降水的混合,两者的硫同位素大多具有岩浆硫的特征。矿床的形成与变质核杂岩驱动的地热系统密切相关,在变质核杂岩附近形成浪卡子式金矿床,向外形成马扎拉式锑-金矿床,远离核杂岩形成沙拉岗式锑矿床。

The south Tibetan detachment system, located at the convergence belt between Indian and Asia continents, is one of the most important antimony and gold metallogenic belt in southern Tibet. The belt is composed of more than 50 antimony and gold deposits and occurrences, and parallel to the metamorphic core complex belt extending west--east. Based on the metallogenic characteristics of several deposits, three main types of deposit can be recognized as follows. ① Shalagang type antimony deposit, orebody is quartz-stibnite vein filling in the NS-strike normal fault and EW-strike bedding fault with weakly wall-rockalteration;② Mazhala type antimony-gold deposit, orebody consists of gold containing quartz-stibnite vein swarm filling in fault, cleavage and joint with wall-rock alteration of silicification, sericitization, chloritization and carbonatization; ③ Langkazi type gold deposit： lenticular orebody is composed of quartz vein and altered rock with strong wall-rock alteration of silicification, chloritization and sericitization, and controlled by detachment fault and normal fault along the margin of the metamorphic core complex. Microthermometric results of fluid inclusions in quartz from Shalagang type antimony deposits and Mazhala type antimony-gold deposits show low homogenization temperature （peak value of 200C and low salinity （1. 23-6. 16 NaCl%）. Hydrogen- and oxygen- isotopic compositions of quartz indicate that the fluid of Shalagang type antimony deposit （6＇D between --166‰ and --140‰, δ18OH2o between --11.5‰ and 12.3‰） is similar to the geothermal waters in southern Tibet, whereas the fluid of Mazhala type antimony-gold deposit （6＇D between-- 108‰ and -- 73‰, δ18OH2O between 5. 4‰ and 11. 2‰） is likely to be the mixture of magmatic and meteoric waters. The regional distribution of deposit from the metamorphic core complex to the outside is in turn from Langkazi type gold deposit, to Mazhala type antimony-gold deposit, and finally to the Shalagang type antimony deposit, suggesting a close relationship between the ore-forming process and the geothermal system driven by the metamorphic core complex.