Tectonic Setting And Genesis Of The Jienagepu Gold Deposit In Zhaxikang Ore Concentration District,Tibet

The large-scale mineralization caused by the collision between India and Asia generate abundant typical antimony and gold deposits?spots?in Tethys Himalaya tectonic belt in Southern Tibet,which constitutes the distinctive Southern Tibet Antimony Gold Polymetallic Metallogenic Belt.In the Belt,it possesses superior metallogenic geological conditions for epithermal gold deposits,but most researchers think that the gold deposits found at present are orogenic gold deposits.Zhaxikang Pb-Zn polymetallic Ore Concentration District,located in the southeast of Southern Tibet Antimony Gold Polymetallic Metallogenic Belt,which is an important part of the Belt.Jienagepu gold deposit,as the first epithermal deposit found and evaluated in Southern Tibet,which is of significant academic and economic values.Through the detailed geological analysis,we can perfect the mineralization sequence surrounding the Cuonadong leucogranite,enrich the genetic type of the deposit,and provide an example for studying the mineralization during the post-collisional extension stage in Qinghai-Tibet Plateau.Ore bodies of Jienagepu gold deposit,quasi-bedded or lenticular,are strictly constrained by compresso-shear faults trending in EW direction and the secondary fault in flanks of isoclinal fold.Two different kinds of ore types identified:quartz vein type and altered rock type,and the gold in quartz vein type ore exists in the form of native gold,while the altered rock type ore is solid solution gold.Wall rock alterations are typical mesothermal and epithermal alterations,mainly including beresitization,arsenopyritization,chloritization and carbonation.The mineralization can be divided into 2 stages,namely native hydrothermal mineralization period and the supergene weathering?oxidizing?period.There are mainly 3 kinds of fluid inclusions,including type?-1 aqueous,type?-2 CO₂-aqueous,and type?-1 aqueous-liquid CO₂-gaseous CO₂ fluid inclusions.Homogenization temperatures of fluid inclusions in the main metallogenic stage concentrates at 211.9²80.4?,with the salinities of 0.18⁶.74 wt%NaCl.eqv and the densities of 0.77⁰.90 g/cm³.Combined with the analysis results of LRM,we conclude that the ore forming fluid belong to the H₂O-NaCl-CO₂±CH₄±N₂ system,with the characteristics of middle-low temperatures,low salinities,low densities and rich CO₂.The ore forming fluid of the deposit mainly derived from circulatory meteoric water and magmatic water,but the former is dominant.The sources of minerogenic substances are of polyphyly,and mainly root in adjacent rock stratum and Cuonadong leucogranite.In summary,Jienagepu gold deposit is a typical intermediate sulfidation?IS?epithermal deposit.The mineralization sequence indicates that the deposit formed during 20¹2Ma.Jienagepu epithemal gold deposit is a vital part of Pb-Zn-Sb-Au metallogenic system,which is closely related to the extensional crustal detachment after the collision between India and Asia plate,and it is restrained by post collision extension setting.The meteoric water migrated along the faults,mixing with the magmatic water richening ore forming material,and the fluid were driven by the heat of Cuonadong leucogranite,forming the circulatory fluid migrating upward,during which it extracted the ore forming material continuously in wall rock.When the fluid migrated into the faults,with the sharp decreasing of pressure,the ore forming fluid boiled,and the solubilities of ore forming material reduced quickly,then precipitated and mineralized.