| There have developed multiple Triassic molybdenum deposits in the eastern Tianshan-Beishan area,such as Baishan,Donggebi,Huaheitan,Xiaohulishan.This paper focuses on Xiaohulishan molybdenum deposit,on the basis of the detailed study of geological characteristics and petrography,and further to carried out EPMA,rock geochemistry,zircon U-Pb dating,isotope geochemistry,and fluid inclusion studies.The formation process of Xiaohulishan granites,and the genetic relationships between magma,fluid and mineralization were systematically studied.Comparing the diagenetic and metallogenic background of molybdenum deposits in eastern Tianshan-Beishan area,obtains the main knowledge is as follows:(1)In addition to the Xianshuihu group andesite(489±11Ma): and late silurian andesitic porphyrite(419±5.4Ma)in the surrounding rock of Xiaohulishan mining area,which was first reported in Silurian volcanic activity for the mining area.Andesitic porphyrite is calc-alkaline series of metaluminum,which was formed in the island subduction arc background,its melt was probably formed from partial melting of lower crust with mantle materials addedtion and which has experienced strong assimilation contamination.(2)The Early Paleozoic magmatic rocks in Xiaohulishan area showed similar characteristics in chronology,geochemical and formation background with magmatic rocks in Hanshan microcontinent and Mazongshan island arc belt,which are located in sourth of Xiaohulishan.It suggests that all of them belong to island-arc accretion zone between the Siberia and the Tarim plates.(3)The zircons of K-feldspar granite porphyry was intruded 198 ~ 215 Ma in Xiaohulishan deposit,corresponding to the late Triassic.Intrusion shows characteristics of high-silicon,weakly peraluminous and high-K calc-alkaline,the geochemical and mineralogical characteristics of granite porphyry are similar with A1 type granite.Parental Magmas derived from partial melting of the neogenic lower crust caused by the underplating of mantle-derived magma under the background of intraplate extension.(4)The ore-forming fluid of Xiaohulishan deposit can be divided into three stages:potassium silicate stage(400 ~ 250 ?),quartz-sulfide stage(300 ~ 100 ?)and quartz carbonate stage(200 ~ 100 ?): the main ore-forming temperature is between 400 ~150 ?,the pressure is less than 400 MPa and metallogenic depth is less than 2.5 km,the type of molybdenite is 3R.This is a typical porphyry molybdenum deposit,the precipitation of molybdenite is mainly caused by the sudden drop of temperature.(5)The Triassic molybdenum deposits in the eastern Tianshan-Beishan area were mainly formed in the intraplate extensional background.The molybdenum-bearing magma originated from partial melting of neogenic lower crustal materials.(6)Porphyry deposits are the main type of molybdenum-bearing deposits in Tianshan-Beishan area,and show gradually younger from West to the East when it time to their spatial and temporal distribution features.In terms of metallogenic scale,the location of Contact Zone of the eastern Tianshan,Xinjiang and Beishan,Gansu has the greatest metallogenic potential.In conclusion,the eastern Tianshan-Beishan area has a great potential for forming Triassic molybdenum deposits.The research results of Xiaohushan deposit provide a reliable basis for theoretical research and production exploration of Triassic molybdenum deposits in eastern Tianshan-Beishan area. |
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