Geochemical Characteristics And Genesis Of Enlightenment Of Hahaigang W-Mo Polymetallic Deposit In Tibet

The Hahaigang W-Mo polymetallic skarn deposit is located in the central of the eastern section of the Nyainqentanglha belt and south edge of Gangdese tectonomagmatic belt,Tibet.Ore bodies are confined within the Dalong fault zone.The present research is limited to the geology of ore deposit geology,rock-and ore-forming ages.This paper mainly reports the geological characteristics of deposit,the determining of ore-forming rock and its geochemical characteristics,and the tracing of metallogenic materials.The goal was to contrast with other deposits of Gangdese tectonomagmatic belt and research for diagenetic-metallogenic mechanism and summarize the regional metallogenic regularity.Based on field investigation and ore microscopic,we have divided into period skarn and quartz-sulfide for the Hahaigang mineralization,including early skarn stage,later skarn stage,quartz-molybdenite and quartz-pyrite-chalcopyrite-galena-sphalerite sulfide stage.Previous studies showed that the age of granodiorite(56.1Ma)and monzogranite(57.02-58.66Ma)are later than the molybdenum age(63.2Ma),but we found that disseminated scheelite and molybdenite is developed in granodiorite and quartz-molybdenite vein in monzogranite.Therefore,we tested the age of mineralized rocks again,and the zircon U-Pb ages of granodiorite are 194.5±1.8Ma and 63.82±0.7Ma,and monzogranite is 64.63±0.8Ma.According to the phenomenon of mineralization,rock-forming ages and ore deposit zonation,we think the paleocene granodiorite or monzogranite is ore-forming rock,which show highly fractionated I-type granite features.S-Pb isotopic compositions of metal sulfide and surrounding rock show that ?34SCDT values of sulfide are 2.7‰-5.4‰,average 4.08‰.Studies found it would be possible for sulfur is ore-forming magmatic rock origin,and contaminated by surrounding rock.Pb isotopic ratio is relatively stable with ranges less than 0.1‰.In the diagram of tectonic environment evolution,the Pb isotopic value of metal sulfide fall on the upper crustal evolution line and concentrated evenly distribution,suggest major ore-forming materials comes from the upper crustal.In conclusion,metallogenic material of Hahaigang W-Mo polymetallic skarn deposit mainly comes from crust mixed with part of mantle magma.