Skarn Characteristics, Genesis And Mineralization Of Jiama Copper Polymetallic, Tibet

As a typical porphyry-skarn copper polymetallic deposit in Gangdise belt, Tibet,Jiama has a rich mineralization especially in skarn ore body with much metal element,high grade and diversity of miners. Thus the feature, genesis of skarn and the relationto mineralization are of great theoretical and practical significance to Jiama deposit.This paper is based on sufficiently pre-information and outcome, Then do someresearch on typical composition, zonation, evolution, fluid inclusions and isotopiccharacteristics of skarn minerals.The research suggests that the skarn minerals in Jiama are mainly distributed inthe expansion space of marble and hornfels, its formation mainly result frommagmatic fluid flowing through replacing marble and hornfels. Also its mineralspecials and assemblages are abundant and diverse. The garnet is mostly andradite-grossular series and pyroxene typically belongs to diopside series at the skarn center,which represent the typical calcium-skarn composition.There is obvious vertical and horizontal zonation of skarn minerals in Jiama.Zonation of ore minerals is also closely related to skarn minerals. Vertically, skarnminerals which next to hornfels is mainly garnet in the upper side whereas in thelower part near marble is wollastonite. Ore minerals are mainly characterized like thatthe upper part is the assemblage of chalcopyrite±molybdenite and in the lower part ischalcocite±tetrahedrite±bornite. Horizontally, wollastonite generally distributed inthe distal skarn; and garnet and wollastonite are near to stock. The abundance ofgarnet and diopside decreases from close to stock to remote from it. Metal mineralsare molybdenite, chalcopyrite near the stock; with decrease abundance of garnet andpyroxene, there begins to outcome tetrahedrite, chalcocite, bornite; however whenremoted from the stock, wollastonite skarn mainly contains bornite.Oxygen and hydrogen isotope geochemical features of Skarn minerals indicatethat hydrothermal solution of early skarn minerals is magmatic fluids. Then meteoricwater joined in the late alteration. Skarn are caused by magmatic fluids replacing ma -rble and hornfels. The stock that offered fluids is granite porphyry, monzonite porph-yry, and granodiorite porphyry in Jiama. We all find garnet in three types of porphyry, indicating a complicated formation process of skarn in Jiama, and it is related tothe three sorts of magma. Meanwhile with the process of metasomatism, hornfelsmay provide partial quantity of Si,Mg,Fe.Floor marble which in the bottom provide alot of calcium.That is to say, in upper side of skarn there mainly appears garnet anddiopside while wollastonite in the lower part.