The Ophiolitic Tectonic Melange And Mineralization In The Yongzhu Area,Tibet

The study area is located in Bangor and Shenzha where belong to Naqu area in the northern of Tibet plateau hinterland.This paper based on the four 1?50 000 regional geological and mineral resources survey projects in southwest Bangor county in Tibet,collecting predecessors' information,developing field geological survey,using the theory of geology,petrology,metallogenic multidisciplinary and so on to research,we find the study area has the better metallogenic conditions and rich mineral resources,it is an important prospect area of resources exploration.This study chose Yongzhu ophiolite belt that was the better development and preserved intact,we found Langme-Duobusongguo ophiolitic tectonic melange in the southeast section of Yongzhu for the first time,and based on this research object,carried out geological mapping and the research of petrography,mineral chemistry,rock geochemistry and Zircon U-Pb dating.Langme-Duobusongguo ophiolitic tectonic melange developed units that included metamorphic peridotite,metamorphic gabbro,sheeted dike complex,pillow basalt and radiolarian chert.Mineral chemical and rock geochemical analyses showed that rock units was calc-alkaline series and had homologous evolution characteristics between rocks.Using gabbro samples of sheeted dike complex to test zircon U-Pb age,the results showed that zircon formation was magmatic origin,zircon U-Pb harmonic age and weighted average age were 162.8±1.8Ma and 164.5±25.3Ma respectively,we initially determined the diagenetic age of sheeted dike complex was middle Jurassic.The dosage points for tectonic environment and cause the illustration of rock units were located on the ridge or the transitional area between ridge and island arc.Comprehensive indoor research and field observations,Langme-Duobusongguo ophiolitic tectonic melange was formed in the back-arc(arc)basin,which belonged to SSZ-type ophiolite.The study area was located between two giant suture zone,and experience the complex tectonic magmatic evolution between the late Triassic(or middle Jurassic)to the late cretaceous.Tectonic units were devided into one level there tectonic unit and four level four tectonic units,the one was Yongzhu ophiolitic melange belt,the four were Bugacuo Paleozoic fault-uplift,Langme-Duobusongguo ophiolitic tectonic melange,Quelong-Longjiao Paleozoic fault-uplift and Chagong-Jiangxiqu early cretaceous magmatic arc belt.The study of tectonic units would enriched the evolution history of Shiquanhe-Yongzhu-Jiali ophiolitic melange.Mineralization in study area had close relationship with sedimentary,magmatic and metamorphic,using all kinds of mineralization and alteration information,and determined metallogenic types and age preliminary.We found twelve ore occurrences in and around Yongzhu ophiolitic melange belt,and nine ore occurrences formed in Yongzhu ophiolitic melange belt,and others had a certain relationships with Yongzhu ophiolitic melange belt in time and space.Analyzed metallogenic regularity of these ore occurrences,we could delineated preliminarily five metallogenic prospect area of Bugacuo boron,Bugacuo lead polymetallic,Bulaer-Gongma-Xiawunongba boron,Buqiela iron and copperand Placer gold and Mangrelongba copper in the study area.