Geochemical Characteristics And Mineralization Of The Bayandulan Copper Deposit,East Ujimqin Banner,Inner Mongolia,China

The Southern Gobi-East Ujimqin Metallogenic Belt,which across the border between China and Mongolia,is an important copper-polymetallic metallogenic belt in the Central Asian Orogenic Belt(CAOB).The Bayandulan high-mesothermal vein-type copper deposit is a newly discovered deposit in the East Ujimqin Banner metallogenic belt.Based on detailed field and indoor work on the strata,rock mass,ore features,the author presented the lithogeochemistry,zircon geochronology and Sr-Nd-Hf isotopes analysis for the granite in the Bayandulan copper deposit.And then,the metallogenic epoch,the source of ore-forming and the tectonic setting of the copper deposit were determined combined with the S-Pb isotopes of sulfide ores.Finally,the mineralization of the Bayanduan deposit and regional copper metalllogeny were discussed.The main conclusions are as follows:The laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)U-Pb dating yields the crystallization ages of(300.2±2.2)Ma and(300.0±2.0)Ma for biotite monzogranite.The granite is rich in Si,high potassium calc-alkali,weakly peraluminous,together with highly enriched the light rare earth element(LREE),Rb,K and other large-ion lithophile element(LILE),depleted Sr,Nb,Ta and other high field-strength element(HFSE).The granite has a narrow Sr-Nd isotopic ratio range which Isr values from 0.70375 to 0.70546,?Nd(t)values from 2.5 to 3.6,and two-stage model ages(TDM2)values from 765 to 858Ma,the zircon Hf isotopic analysis shows high positive ?Hf(t)values of 6.1-10.7 and TDM2 of 632-924 Ma.The Sr-Nd-Hf results reveals that granites are mainly derived from the partial melting of young accreted lower crust converted from the subduction of oceanic crust and surrounded mantle.The values of?34S of sulfide is between+2.3‰ to+3.5‰,values of 206Pb/204Pb from 18.211 to 18.438,values of 207Pb/204Pb from 15.514 to 15.624,values of 208Pb/204Pb from 37.901 to 38.389.The S-Pb isotopic composition of Sulfide indicate that the source of ore-forming material are closely related to mantle derived matter,and suggest the same source region of magmatic sourceThe author inferred that the regional mineralization is mainly related to the tectonic evolution of the late Paleozoic paleo-Asian Ocean as well as the superposition of Mesozoic Peri-Pacific tectonic evolution.The formation of the Bayandulan copper deposite is mainly affected by late Paleozoic tectonomagmatic activity.The tectonic setting has been entered the post-orogenic stage and gradually turned to widely extension setting,since the Hegenshan back-arc basin closed between late Carboniferous and early Permian.During this period,the lithosphere delamination effected after collision and the upwelling of the mantle material under tension mechanism,which resulted in the young accreted lower crust reactivation.Then acidic magma mixed with mantle source material brought sufficient metal elements and hydrothermal fluids,the Bayandulan copper deposit formed subsequently.