Characteristics of ore-forming fluid and metallogenesis of the Tongkengzhang porphyry molybdenum deposit,Jiangxi Province

Tongkengzhang molybdenum deposit is a newly discovered deposit,which is mainly hosted by the Cretaceous granitic porphyry.Based on mineral assemblage and vein crosscutting relationships,the ore-forming process could be divided into three mineralization-alteration stages:Potassic stage,fluorite-biotite(muscovite)-K-feldspar-molybdenite stage,sericite-quartz-carbonate stage.The study of fluid inclusions shows that early ore-forming fluids are high salinity magmatic fluids,containing alkalic components and volatile phase,which formed in condition of high pressure(～1000bar)and high temperature(550～600℃),and were separated to multiphase high salinity fluid inclusions and lower salinity vapor-rich fluid inclusions by boiling.With cooling of oreforming fluids(420～440℃)and release of pressure(320～360bar)led to re-boiling of ore-forming fluids,which caused precipitation of molybdenite.Give the evidence of widespread occurrence of high salinity(29.58%～44.12%NaCleqv)fluid inclusions in the sericite-quartz alteration related veins,indicating that the fluids caused the later alteration was dominated by the magmatic fluids,only a few quartz veins are primarily occupied by aqueous inclusions suggesting the mixture of magmatic fluids and meteoric fluids.Meanwhile,the Laser Raman and SEM measurements detected Fe 2 O3,SO 2 in the early fluids,indicating the early fluids were highly oxidized,the abundance of K-feldspar suggests alkalic environment.The existence of CH 4and intergrowth of molybdenite and muscovite reveals fluids were in a relative reduced environment,suggesting redox potential fluctuations and the change of pH value could lead to deposition of molybdenite.