Study On Geological And Geochemical Characteristics And Metallogenic Time Of Baogutu Porphyry Copper Deposit

The No. V intrusion, which is the main ore containing body of the newly found Baogutu porphyry copper deposit, are composed of granodiorite and granodiorite-porphyry, and is located at the west margin of Junggar basin and to the south of Dalabute fault. Studies on petrochemistry, geochronology of diagenetic and ore formation, mineralization and ore assessment of Baogutu porphyry copper deposit were done.Primarily veinlet-disseminated mineralization was found by observations on samples of the No. V intrusion. The ore has typical potassic alteration zone, quartzification -sericitization zone and greenitized propylitization zone likes many other porphyry copper deposits, and has a laumontite alteration zone seldom found in others. The main sulfide minerals are pyrite, chalcopyrite, molybdenite, sphalerite, arsenopyrite, and minerals composed of Te and Bi.The No. V intrusion has characters of adakitic rocks. The trace elements, such as Rb, Ba, Sr, Th and U, are characterized by relative enrichment while Nb, Ta, Ti, La, Ce, Pr, Nd and Sm are depletion. The total contents of rare earth elements are low that are between 38.19μg/g ~ 132.80μg/g. Distinct fractionations of light rare earth elements and heavy rare earth elements are existent and the values of La/Yb are between 4.8~33.2. Theδ34S of chalcopyrite and pyrite are varying between -2.4‰~ -0.8‰and -2.7‰~ +0.7‰, respectively, indicate sulfur of the ore came from mantle.There are multi-types of fluid inclusions in the ore. They are liquid-rich two-phase inclusions, vapor-rich two-phase inclusions and inclusions containing a halite daughter phase and a gas bubble. Their homogeneous temperatures are between 130℃~ 450℃and the salinities are between 0.5 wt% ~ 39 wt%. The data show the temperatures of the main mineralization epoch are between 180℃~ 450℃and under the pressures between 10 bar ~ 90 bar.In order to confirming the diagenesis and metallogency ages of the ore, SHRIMP U-Pb ages of zircons, K-Ar ages of whole rocks and biotites, and Re-Os ages of molybdenites are determined. The weighted mean value of 206Pb/238U ages of 11 spots of zircons, 337±6 Ma, is interpreted as emplacement age of the No. V intrusion; the model age of molybdenites, 310±4 Ma, as metallogency age of the ore. Comprehensive researching considers the metallogenic process is as follows: The No. V intrusion has experienced two epoches ore-forming fluid activities in addition after the diagenesis of the adakitic magma come from the mantle for about 20 Ma. The early epoch can be divided into four phases and sulfides of Cu, Fe, Mo, Zn were formed. Four stages of mineralization were distinguished according to mineralization types and cutting relation of mineral veins. In the late epoch, compound minerals of Cu-Te-Bi-Au-Ag were formed.