Geology,Geochemistry And Genesis Of The Youmapo Deposit In Guangxi Province

Bobai-Cenxi fault belt in Guangxi is located in the southern section of Qinzhou Bay-Hangzhou Bay(Qin-Hang)metallogenic belt.It is not only a long-term active boundary fault zone,but also a W-Mo-Sn-Pb-Zn-Sb-Au-Ag polymetallic metallogenic belt with frequent magmatic activities.Based on detailed field study of Youmapo skarn type tungsten molybdenum deposit,using some methods such as geochemistry of Youmapo deposit,stable and radioactive isotope measuring,this thesis explains its genesis.The main conclusions are as follow:1)The mineralization in Youmapo deposit is skarn tungsten mineralization.The wall rock alteration includes skamization,silicification and marbleization.2)There are three types of fluid inclusions in the main metallogenic stage about the Youmapo deposit,including aqueous inclusions,CO2 inclusions and liquid inclusions.The analytical results show that the temperature varied from 157.9? to 444.5? and the peak is 300.0? to 325.0?.The average temperature is 318.9?.The salinity of ore-forming fluid varied from 5.11% to 13.51% and the peak is 7.0% to 10.0%.The average fluid density is 0.87g/cm3.Those results show that the ore-forming fluids belong to medium-high temperature and low-middle salinity.3)Hydrogen and oxygen isotope results show that the ore-forming fluids are dominated by magmatic water.The ?18OV-SMOW varied from 11.8� to 13.7� and the ?DV-SMOW varied from 53� to-71�.The ?18OH2O varied from 5.62� to 7.52�.The sulfur isotope values of ?34SV-CDT varied from 0.5� to 4.1� and the average value is 2.45�.The sulfur shows the features of deep-seated magma.4)The LA-ICP-MS U-Pb dating results show that the zircon U-Pb age of the dark grey granite porphyry,grey biotite granodiorite and greyish muscovite granite are(479.7�3.9)Ma,(109.7�1.1)Ma,(103.3�1.2)Ma,respectively.The molybdenite Re-Os dating was also carryied out for metallogenic epoch,the result is(97.4�1.9)Ma.These high precision dating data suggest that the Youmapo stock is a multiple stock,which are consist of granite porphyry in Early Ordovician(Caledonian),biotite granodiorite and muscovite granite in Early Cretaceous.Biotite granodiorite makes up the bulk of Youmapo stock.The W-Mo deposit was formed in the late Early Cretaceous(i.e.late Yanshanian),and closely related to biotite granodiorite and muscovite granite.