Geological, Geochemical Characteristics And Genesis Of The Lamuyouta Sb (Au) Deposit, South Tibet

Lamuyouta Sb (Au) deposit in Tibet is located at the eastern of the Lhagoi Kangri passive continental margin basin of Himalayan block tectonically and is a typical Sb (Au) deposit in the Sb-Au metallogenic belt of southern Tibet. Combining with achievements done by former scientists and the detailed results of field geological survey, both fluid inclusion and isotope geochemical characteristics of this very deposit have been further studied, meanwhile the properties of ore-forming fluids and the source of ore-forming materials in this ore deposit have been revealed in this paper as well. At last the genesis of this ore deposit has been discussed while the metallogenic model has also been initially established on account of specifically regional tectonic evolution and geochronological data.The ore bodies of Lamuyouta Sb (Au) deposit occurred in the fracture belts or the contact zones between the Early Cretaceous altered neutral-mafic dykes and the Middle Jurassic Zhela Formation stratum or the nearby regions of the contact zones, sometimes intersperses with veins or Zhela Formation stratum. The ore-bearing wall rocks are dominated by neutral-mafic dykes and Zhela Formation sandy slate. Metallic minerals are mainly stibnite, along with a very small amount of arsenopyrite, galena, pyrite, sphalerite and chalcopyrite, occurring a limited quantity of antimony oxide (valentinite) and limonite near the earth's surface; nonmetallic minerals are dominated by quartz, calcite, sericite and so on.The ores are mostly disseminated, breccia, agglomerate and massive in structure, while some of them are granular, idiomorphic-subhedral, scaly, poiklitic and with common crystallization textures. The alterations of wall rocks related with mineralization are basically silicification, carbonatation, sericitization, chloritization, and argillization, but alteration zone is not obvious. The mineralization process can be divided into three stages, that is, quartz stage→quartz + antimonite stage→quartz + calcite + antimonite stage.The neutral-mafic dykes are mainly typical gabbro and diabase in this mining area, which have the characteristics of OIB-type basalt in terms of major, trace and REE elements.And their sources are mantle peridotite which enriches garnet and clinopyroxene,thus it can be inferred that their formation maybe have some link with Early Cretaceous large Comei igneous province in southern Tibet.The main types of fluid inclusions within quartz and calcite are aqueous inclusions, homogenization temperature is 150～340℃, its average is 253℃; salinity is 0.53~9.61wt%NaCl, its average is 3.84wt%NaCl; density is 0.55~0.93g/cm~3, its average is 0.76g/cm~3, which reflect the metallogenic process is under mid-low temperature conditions and ore-forming fluid is low salinity and low density type. H,O isotopic studies have shown that the ore-forming fluids sourced from the precipitation.S,C,Pb isotopic studies have suggested that the sulfur source and the carbon resource are derived from the neutral-mafic dikes of the mining area or nearby region, the lead source came from the ancient metamorphic crystalline basement of the upper crust,which imply that the ore-forming materials may have two approaches.The ore-forming age analysis of typical Sb(Au)deposit in the mineralization belt suggested that the Lamuyouta'a Sb(Au)deposit which is likely formed in the Miocene is a structurally controlled meteoric water type hydrothermal ore deposit and it have some relationship with the extension of the North Himalayan tectonic belt in Post-collsional environment.