Geochemical Study Of Mineralized Intrusions In Baoyintu Molybdenum Deposit,Inner Mongolia

Baoyintu molybdenum deposit, in western Inner Mongolia, is a part of the giant multi-metallogenic belt which is located in Sino-Mongolian border. A lot of achievements have been obtained about this deposit since 2008 it has been discovered.The research is short of the ore intrusive, and it becomes a key problem for the deep exploration. On the basis of the implementation of the Inner Mongolia Geological Exploration Project（NMKD2008-01）,the author made the “Geochemical Study of mineralized intrusions in Baoyintu Molybdenum Deposit,Inner Mongolia” as a doctoral thesis with important scientific significance and the value of mining.According to field geological survey work and the indoor analysis, which is including measuring 40 km geological section,logging 60 drilling and collecting 320 pieces of rock and mineral specimens, the paper has obtained the following understanding and progress:The mineralized intrsion is the composite granitoid pluton composed of plagiogranites, onzoniticgranites,K-feldspar granites and graniteaplites.Zircon U-Pb ages of（225.9±4.4） ^258.8±3.3Ma for each stage samples indicate that composite intrusion formed during Hercynian-Indosinian epoch. Re-Os dating of molybdenite samples from Chaganhua ore block in this research yield an isochron age of（239.2±5.8）Ma, which is during the diagenetic stage of K-feldspar granites with the age of（236.8±4.5） ^244.3±4.2Ma.The compositions of granites vary in the sequence of plagiogranite�' onzoniticgranite�'K-feldspar granite�'graniteaplite. The chemical variation during the magmatic evolution process is in favour of mineralization,especially the late-stage K-feldspar granites.The chemical variation during the magmatic evolution process is in favour of mineralization,especially the late-stage K-feldspar granites and graniteaplites enriched in Cl,F,B,Cu and Mo.Based on analyses of REE distribution patterns, characteristic values（including ∑REE-LREE/HREE and δEu-LREE /HREE） and petrochemical compositions, comparisons with REE compositions of mantle-derived magma and Nanling granites, authors deduce that genesis of ore-forming granites is related to melting of the continental crust.Elements have experienced differentiations in different stages. Petrochemical compositions show the characteristics of peraluminous and rich-K, and K2O/Na2 O of the aplite in the late stage is the highest,while K2 O and Ca O is negative correlation.Comparisons with Sr/Ba-Zr/Y of main magmatic belts in the world show that they are different from the characteristics of the granites derived from melting of subducting oceanic crust,but they are in accordance with the characteristics of the magmatites in the Yanshan belt and Qinling orogeny. And they are similar to the hosting rocks of Proterozoic metamorphic rocks with geochemical characteristics.Therefore, the metallogenic granites in this area indicate that they belong to the S-type granites.