Mineralogical Characteristics of Zhibula Skarn-Type Cu Deposit in Tibet and Their Geological Significance

Xu Jing; Zheng Youye; Sun Xiang; Jiang Junsheng; Geng Ruirui; Shen Yahui

doi:10.3799/dqkx.2014.062

Abstract：The Zhibula skarn-type Cu deposit is located about 2 km away from the south of Qulong super-large porphyry Cu-Mo deposit in Gangdese metallogenic belt,Tibet.The skarn and ore body are mainly distributed as layer-stratoid in the tuff and marble of Yeba Group in Lower Jurassic,which show zoning characteristics:tuff-garnert tuff-garnet skarn-pyroxene skarn-(wollastonite)marble.From early to late stages,or from tuff to marble,the colors of garnets change from dark brownish red to brownish red,followed by green(brown),and pale brownish yellow These garnets are mainly grossular and andradite.The end members of pyroxenes are dominated by diopside,with minor johannsenite.Garnets near tuff have higher Al,Ti contents, whereas those nearthe marble have relatively more enriched Fe,Mn contents.Garnets show distinctive light and dark oscilla-tory-zoning.Light zoning is distinctively enriched withcalcium-iron components,and dark zoning is enriched with calcium-aluminum components.These garnets generally show increasing calcium-iron components and relatively reducing calcium-aluminum components from the core to outer zones.The Zhibula layer-stratoid skarn-type ore body are developed due to thedeep buriedore-bearinghy drothermal migration with differential magmatic crystallization along the interface,or migration along fractured rock bands driven by temperature and pressure differences.In addition,selective metasomatic alteration between tuff and marble or crystalline limestone contributed to the formation of this ore deposits.Therefore,this ore deposit belongs to the magmatic hydrothermal contact metasomatic type rather than stratabound or exhalative forming layer skarn-type, and has the same forming mechanism with Qulong porphyry Cu-Mo deposit.