Petrogenesis Of The Paleozoic Granites And Associated Uranium Mineralization In The Eastern Segment Of The North Qinling Orogen

The voluminous granites with different age can record the multi-stage evolution processes of the Qinling orogen.Voluminous Early Paleozoic granites in the eastern part of North Qinling are closely related to granitic pegmatite and U deposits.The seven thousand pegmatite veins developed within the dome,which was surround by the Early Paleozoic leucogranites.The pegmatite-type Uranium ore deposit was located in the widely developed pegmatite vein within the contacted belt.This paper focused on the typical Early Paleozoic granites(e.g.,Kuanping pluton,Qiushuping pluton,Duiwo pluton,Luoziping pluton,Huangmiaogou)and related granitic pegmatite veins(Yanwugou Uranium-bearing pegmatite veins).Based on the detailed field observation and geochemical analysis,we try to discuss the genetic links between the Early Paleozoic granites and Uranium mineralization in this area..The main conclusions as following:(1)By analizing precedent data,combined with the result reveled from the LA-ICP-MS zircon U-Pb data,three stages of granitic magmatism were formed in the study area.Among them,the last two stages are considered closely related to local Uranium mineralization.The early stage was represented by the Ordovian-Silurian Kuanping,Qiushuping and Duiwo plutons,mainly composed of gneissic monzogranites.Their associated Uraninites was occurred within the tectonic alteration zone.The late stage includes the Silurian-Devonian Huanglongmiao and Luoziping garnet-bearing leucogranites,and their associated uranatemnite was mainly occurred within the biotite pegmatite in the contact zone.(2)The second stage of early granites can be subdivided into two substages:(a)the Kuanping gneissic granites was formed ca.450Ma,it is high-K calc-alkaline and metaluminous.(b)the Qiushuping-Duiwo-Kuanping porphyritic granites was ca.430-421Ma,it is strongly peraluminous.The first substage granitoids were formed by muscovite dehydration melting of pelite-rich metasedimentary rocks at low temperature condition.The K-and Rb-rich granitic magmatism was generated at the early stage of the syn-collision setting.The later substage monzogranites were derived from biotite dehydration melting of metagraywacke at relatively high-temperature condition,which represents the products of transitional extension setting.(3)The late stage Huanglongmiao-Luoziping leucogranite have LA-ICP-MS zircon U-Pb ages of 415.2±2.0Ma and 430.7±9.3Ma,indicating the tectono-magmatism from Late Silurian to Early Devonian.They display high Si and K,low Fe-Mg contents,and significantly negative Eu anomalies.The variable whole-rock Sr-Nd isotopic compositions suggest hetergeneous source region.it was derived from anateixs of pelite-rich gneiss in the Qinling group,which represented that products of late-stage extension setting.(4)Pegmatite-type uranium mineralization was developed in the complex zone between biotite pegmatite or pegmatite and Qinling Group.In the mineralization,the uranatemnite was predominated industrial minerals.Most was dispersive distributed within the interstitial of biotite and feldspar.Their mineralization age was ca.416-404Ma,which was younger than the age of garnet-bearing leucogranites.(5)After the formation of Uranium ore body,an exhumation took place in the area.In the first stage,the leucogranites were exposed as the form of stocks,the uranium-bearing pegmatite was outcrop around the exposed small stocks,thus represents as a large scale Guangshigou type Uranium ore deposit;the second stage of the exhumation,caused by the incresing local uplift orogenesis tectogenesis,the leucogranites were exposed as the form of batholiths,the uranium-bearing pegmatite was outcrop in the intrinsic zone of batholiths,thus represents as a small scale Chenjiazhuang type uranium ore deposit.(6)In the magmatic differentiation evolution,due to the constraint of oxygen fugidity,uranium mainly enters the secondary minerals such as crystalline uranium ore and zircon with U⁴⁺.With the increasing differentiation,uranium continues to be enriched,laying the material foundation for uranium mineralization at the later stage.Geochemical characteristics indicate that Luoziping leucogranite has a good mineralization potential.