Geochronology evidence of Mesozoic metallogenesis and Cenozoic oxidation at Hongshan HS-epithermal Cu-Au deposit, Kalatage region, eastern Tianshan, and its tectonic and paleoclimatic significances

Abstract

Located in the Paleozoic uplift along the southern margin of Tu-Ha basin in eastern Xinjiang,the newly discovered Hongshan HS-epithermal to porphyry Cu-Au deposit occurs in the superimposed Mesozoic volcanic basin upon the north section of Late Paleozoic Dananhu-Tousuquan accretionary arc.Hongshan Cu-Au deposit,on the edge of the desert,is one of the driest areas in eastern Tianshan.Moreover,the highest temperature has been up to 60℃,and the average rainfall receives only 34.1mm/y.The light rainfall and rapid evaporation in the vicinity of this deposit have allowed the formation of a great variety of water-soluble sulfates. Oxidization zone of this deposit lies on the upper part of primary sulfide orebodies appearing with a depth of 50m～60m,which is dominant in sulfate minerals.The Hongshan Cu-Au deposit is controlled by the tectonic,stratum,magma activity and volcanic apparatus,whereas Cu-Au mineralization is closely related to volcanic activity in Mesozoic and sub-volcanic intrusive rocks.K-Ar isotopic ages of biotite and hornblende from the wall rock-quartz diorite,biotite granite and monzonite granite are 296.5±6.7Ma, 232.0±3.5Ma and 217.10±6.41 Ma respectively.And Ar-Ar isotopic age of biotite from biotite granite is 238.0±2.4Ma.The ore- bearing rhyolitic breccia lava contains breccia of the biotite granite,which indicates the volcanism,and related Cu-Au mineralization occurred later than the granite,possibly in Mesozoic.K-Ar ages of granitoids in Sanya,Baishiquan and Hongliugou area and Molybdenite Re-Os age of Baishan Mo deposit all are in Triassic.Besides Late Paleozoic magmatism,Mesozoic magmatic event was widespread in eastern Tianshan.The K-Ar age dating indicates that the K-Ar age of Voltaite occurred below surface lm is 56.0± 4.OMa,K-Ar age of Ferricopiapite occurred below surface 1.5m is(8.6±1.1) Ma,K-Ar age of Yavapaiite occurred below surface 14m is 4.1±0.4Ma,and K-Ar age of voltaite occurred below surface 10m is (14.3±1.7) Ma.So the age interval of oxidation zone is between 60～3.4Ma in Hongshan Cu-Au deposit.Oxidization and weathering occurred at Cenozoic era (from 65Ma) in oxidation zone, which can be identified through comparing with different deposits.The oxidation ages of Hongshan not only coincide with collision of India-Asia and multistage uplifting of Qinhai-Tibet Plateau subsequently,but also is the effect and record of collision and uplifting of Tibet Plateau.The predecessor did much research through biota,isotopes,and susceptibility in PETM event.This paper tries to use different sulfate minerals demonstrating climatic change.