Geology And Genesis Of The Jiagangxueshan W-Mo Deposit,Tibet

Jiagangxueshan W-Mo deposit was the first example of greisen-type tungsten deposit identified in Tibet,which was associated with the peraluminous magmas.However,this deposit has not been well studied,and thus this paper has systematically studied on metallogeny,geochemistry and geochronology of this deposit and associated ore-forming intrusions.Geological relationships indicate that W-Mo mineralization is closely related to the monzogranites in the mining area.According to the different textural features,the monzogranites have been further divided into fine-grained,porphyritic and medium-grained monzogranite.Hydrothermal alteration in this doposit is dominated by greisenization,silicification and muscovitization,while it is evidently that the alteration degrees are positively related to the mineralization intensities.Orebodies are dominated by greisen-type,with minor quartz vein-type ore-bodies.The greisen-type ore-bodies are characterized by veinlet,which are usually hosted in greisen or greisenized monzogranite.Zircon U-Pb dating results of porphyritic monzogranite and medium-grained monzogranite are 18.1�0.1 Ma and 19.2�0.2 Ma,respectively,while muscovites separated from greisen ore have ⁴⁰Ar-³⁹Ar plateau age of 18.5�0.2 Ma.Diagenetic and metallogenic ages are consistent within the errors,indicating that this deposit is developed in Miocene.The ore-forming rocks have SiO₂ content of 71.5?76.3%.These rocks are enriched in LREEs and LILEs,and depleted in HREEs and Ba,Sr,Ti,show obviously negative Eu anomalies.These rocks yielded initial ⁸⁷Sr/⁸⁶Sr of 0.7137?0.7271,?_Nd(t)of-11.3?-10.6,and have T_DM2 of 1709?1816 Ma.Zircon?_Hf(t)values range from-13.8?-5.3,and T^C_DM ranges from 1439?1980 Ma.Homogenization temperatures of the fluid inclusions hosted in quartz from different types of ores are varying from 195 to 369?,while salinity?(Na Cleq)range from 5.7 to 13.5%,indicating that the ore-forming fluids are medium-high temperature and medium-low salinity.?¹⁸O and?D water values of quartz are 2.0�?4.3�and-131�?-90�,respectively,while?¹⁸O_V-SMOW(�)of the wolframites is 3.7?4.7,indicating that ore-forming fluids are dominantly derived from magmas.Sulfides have the?³⁴S values of+2.2�?+5.3�,which are relatively homogeneous,showing the magma-source features.Pb isotopic data show that Pb is derived from upper crust,which is the Proterozoic-Precambrian metamorphic base of the Central Lhasa Terrane.Mineralogical and geochemical characteristics of the three types of ore-forming rocks indicate that they are genetically associated,and are derived from the same source region.All of them are S-type granites,and have underwent intensively fractional crystallization of feldspar,biotite,monazite and orthite.They were derived from partial melting of metagreywacke in the Paleoproterozoic middle-upper crust.Jiagangxueshan W-Mo polymetallic deposit is closely related to peraluminous magma generated by the crustal shortening and thickening,indicating that the Lhasa terrane and even Tethys Himalayan have the potential to form tungsten deposits.