Metallogenesis Of Orogenic Gold Deposits In Zhaxikang Ore Concentrated Area,Eastern Tethys Himalaya Belt

The first discovery and report of the Miocene orogenic gold deposit in the Zhaxikang ore concentrated area,eastern Tethys Himalayan belt confirmed that the orogenic gold deposit not only occurred in the main collision-extruded tectonic environment,but also developed in the post-collision-extensional tectonic environment.This paper focused on the Mazara gold deposit and the newly discovered Mingsai and Jainakepu gold deposit,analyzed the geological features,traced the metallogenic fluids and material sources,identified the ore-controlled factors,determined the metallogenic epoch and tectonic settings,established the metallogenic model,discussed the gold mineralization,which enriched and improved the theory of continental colliding gold mineralization and owned the guiding significance for regional prospecting.The orogenic gold deposits in the Zhaxikang ore concentrated area were formed in 19?17 Ma during the post-collision extension stage of india-eurasia?<25 Ma?.The ore body are strictly controlled by extensional fault structure.Metallic minerals are mainly natural gold,pyrite,toxic sand,galena,sphalerite,with a minor of magnetite,arsenic nickel,tetrahedrite.Nonmetallic minerals are mainly quartz,sericite,iron dolomite,calcite,chlorite and kaolinite.The wall rock alteration are mainly pyritization,toxoarenization,silicification,sericite and carbonization.The main gold bearing minerals are pyrite and arsenopyrite,followed by quartz and clay minerals.Microscopic temperature measurement and Laser Raman component analysis of fluid inclusions show that the fluid inclusions in Mazara,Mingsai and Jainakepu gold deposits are mainly CO₂-H₂O inclusions,and the homogenization temperature are concentrated at 270?290?,230?270?and 230?260?,respectively.The average salinity are 3.8 wt%Na Cl.eqv,3.4 wt%Na Cl.eqv and 3.6 wt%Na Cl.eqv,and the average density are 0.82 g/cm³,0.84 g/cm³ and 0.85 g/cm³,which is of CO₂-rich H₂O-Na Cl-CO₂-?CH4-N₂?system with medium temperature,low salinity and low density.The ore-forming pressure and depth are 73.88 Mpa,6.98 km,64.90 Mpa,6.50 km,62.84Mpa,6.39 km,respectively.Multiple isotope geochemical tracers indicate that the metallogenic fluid is derived from crust-source metamorphic fluid and the metallogenic material is derived from the deep source.The comprehensive analysis shows that the crustal stress state is changed by the extension of the southern Tibet detachment system?STDS?and the extension of the Cuonadong gneiss dome,which inducing the strong regional thermal dynamic metamorphism defluid in the lower crust,forming metamorphic fluid rich in CO₂.The metallogenic materials from deep source migrated to the shallow part of the crust along the north-south rift in the form of Au?HS?₂^-complex,mixing with modified atmospheric saturated water or construction water,while migration to the tensile space,such as the interbedded fracture zone and the high-angle normal fault in the north-south direction,the pressure drops sharply,resulting in fluid boiling and phase separation,which induces the rapid and efficient precipitation and mineralization of Au.Through comparative analysis with typical orogenic gold deposits in the Indus Yarlung Zangbo Suture Zone?IYS?,it is found that there are significant differences in ore-controlling structure,geochemistry and metallogenic tectonic settings.Based on the regional geological evolution,it can be concluded that there are two gold mineralization processes related to the collision orogenic process between India and Eurasia in Himalayan belt.That is,the main collisional extrusion setting in Eocene,the gold mineralization related to the rollback and breakoff process of subducted tethys oceanic crust plate,and the post collision extension setting in Miocene,the gold mineralization related to the extension of the southern Tibetan detachment system?STDS?and the resulting gneiss dome-forming extension.