Geochemistry And Metallogenic Significance Of Dahongshan Granites In Northern Altun

Northern Altun area is located between Tarim and Qaidam block,the area has developed NE trending Altun sinistral strike-slip faults and EW trending Northern Altun fracture,its northeast side connect to Qilian orogenic belt,and occupy an important tectonic position.Dahongshan granite is located in northwestern of Aksai County in Northern Altun,in recent years,a number of large-medium iron,copper,gold and other metal deposits have been found in the study area,and showed good metallogenic prospecting,but the overall extent of geology and mineral resource research are relatively low.Thus,it has a great significance to identify granite types and its tectonic setting by studying petrology and geochemistry of Dahongshan granite,it can help promoting geological prospecting work and studing crustal evolution in the region.The research in this paper achieved the following main results and understanding:(I)Dahongshan rock are mainly composed of five small rock bodies,including moyite,gneissic adamellite,biotite adamellite,medium-fine adamellite and fine adamellite.(2)Dahongshan gneissic granite and moyite are composed by quartz,potassium feldspar,plagioclase,biotite and amphibole.They have characteristics of high Si2O(between 71.14%to 75.85%),and low MgO(0.05%-0.13%),Al2O3(11.99%-13.13%),CaO(0.74%-1.33%),enriched potassium and depleted sodium(Na2Ocontent was 3.15%-4.58%,K2Owas 4.95%-5.47%,K2O/Na2O=1.12-1.65),with higher Nb(52.6×10-6-145×10-6),Ta(4.14×10-6-7.02×10-6),Y(62×10-6-220×10-6),Yb(6.26 ×10-6-23.5 ×10-6),and lower Sr(12.2×10-6-79.3×10-6),(Zr+Nb+Ce+Y)=724 × 10-6-1534 × 10-6,A/NCK=0.82-0.98,A/NK=0.92-1.15,it belongs to metaluminous K calc-alkaline series.(3)On the spider diagram,Dahongshan granite relatively enriched in Rb?Th?K,strongly depleted in Sr?P?Ti,with highly Rb/Sr ratios(1.06-10.54).REE patterns were slightly tightist "Seagull",relatively enriched LREE,LREE and HREE have certain fractionation,the distribution of HREE was relatively flat,with obviously negative Eu anomaly(? Eu = 0.08-0.30).Combined with 104Ga/Al and Sc/Nb-Y/Nb diagram,judged as Al-type granites,indicated that Dahongshan granite formed in intraplate rift environment,diagenetic materials are parimarily from the lower crust.(4)By collecting granite's geochronology research achievements in northern Altun and its adjacent areas,combined with regional tectonic evolution of Altun region,we initially concluded that Dahongshan rock formed in Neoproterozoic,it is likely to be the product of partial melting of the lower crust caused by mantle plume underplating related with Rodinia supercontinent breakup underplating.(5)Dahongshan granite rich in niobium,tantalum and other rare mineral resources,this area has good prospecting.The rare minerals have been found in the region closely associated with magmatic activity,indicating magma activity provide rich source of material and heat.it will promote geological prospecting and mineralization research work in northern Altun by summarizing the regional metallogenic features.