Study On The Genesis And Metallogenic Potential Of The Late Cretaceous Xueru Rock Mass In The Bangor Area, Northern Tibet

The main body of the late Cretaceous Xueru rock mass in the Bangor area is a set of porphyritic monzogranite,Locally develocped dioritic inclusions.The rock mass is located at the Bangor-Basu magma arc,It is adjacent to the Bangong Lake-Nujiang Ophiolite Mixed Zone belt in the north and adjacent to the Shiquanhe-Namco Ophiolite Mixed Zone belt in the south.This paper studies on the LA-ICP-MS zircon U-Pb chronology,in-situ zircon Hf isotope,whole rock geochemistry and Sr-Nd isotope composition of the host granite and dioritic enclaves of Xueru rock mass,These data are used to confirm the emplacement age of Xueru rock mass,identify the genetic type and material source of the rock,discuss the regional tectonic background and its metallogenic potential,provide new evidence for the tectonic evolution of Bangong Lake-Nujiang Ocean and North Lhasa terrane,constrain the metallogenic dynamic background,and provide more abundant theoretical support for the follow-up regional prospecting and exploration.The result of zircon U-Pb chronology testing shows: The ages of various rocks in Xueru rock mass are 75.91±0.95Ma(Porphyritic monzonitic granite),74.0±0.76 Ma(Medium-finegrained monzonitic granite)and 75.2±1.3 Ma(Dioritic inclusion).Which indicate that the age of emplacement of Xueru rock mass is late stage of late Cretaceous epoch;The whole rock geochemistry result shows: The host rocks of Xueru rock mass generally show the characteristics of rich silicon,high aluminium,rich alkali and low magnesium.They belong to the high potassium calc-alkaline series,have the characteristics of quasi-aluminous and weak peraluminous,and belong to moderately differentiated I-type granit;The enclaves belong to the series of high-potassium-calcium-alkaline-potassium rocks with quasialuminum characteristics.The host rock and the inclusion body have similarities in rare earth elements and trace elements.Both are enriched in LREE and LILE(Rb?Th?U?K),and depleted in HREE and HFSE(Nb?Ta?P?Ti),with moderate-weak Eu negative anomaly;Geochemistry,Sr-Nd isotope and Hf isotope characteristics of zircon indicate that the host rocks and the enclaves originate from homologous magma.Magma evolution may undergo the following process: the first batch of the parent magma evolved into the second magma chamber of dioritic enclaves,the first batch of the first magma in the parent magma evolved into a secondary magma chamber of the diorite inclusion,which was entrapped in a semi-plastic state and ascended together by the slightly later magma.Isotope characteristics show that Nd-Hf isotope decoupling occurs in Xueru rock mass.Based on the whole-rock geochemistry results and Sr-Nd isotope characteristics,it is inferred that Xueru rock mass magma originated from the mixing of crustal and mantle materials,and mainly from the middle-lower crust,and there is residual garnet in the source area.Based on the geochemical characteristics and the regional geological background,this paper proposes that the Xueru rock mass may be formed in the stage of syncollision.Skarn-type mineralization is widely developed in the contact zone between intermediate-acid magma and limestone in Xueru rock mass.The main minerals are garnet,diopside and actinolite.Geochemical characteristics indicate that Xueru rock mass has good ore-bearing property,and has the potential to form Cu,W,Sn,Mo deposits.Further,according to the grade analysis of main ore-forming elements in the samples of mineralization points in the study area,it shows that they have the potential of Cu,W mineralization.