Characteristics Of The Qurugou Pluton And Mineralization Of The Jiawu Gold Deposit In Qinghai Province

Western Qinling orogenic belt is a major part of the central orogenic belt,which is one of the most important gold-polymetallic ore belts in Qinghai province.TheQurugou pluton is located in the western part of the western Qinling orogenic belt in Qinghai province.Based on petrology,zircon U-Pb isotope geochronology and geo-chemistry of the Qurugou pluton,combining with the geological and geochemical characteristics of the Jiawu gold deposit,this work discussed the petrogenesis of the Qurugou pluton and the relationship between magmatism and gold mineralization.This study is also important for the regional ore exploration.The main work and con-clusions are listed as follows:?1?Geological characteristics indicate that the Jiawu gold deposit can be classified as the fine disseminated gold deposit,which is directly controlled by the structural alteration zone and has a genetic relationship with sedimentation and magnetism.Fluids inclusion results show that the ore-forming fluids have middle-low temperature and low salinity.Rare earth elements compositions show that ores inherited some constituents from wall rocks.Sulfur isotope compositions demonstrate that S mainly originated from magma and strata.Hydrogen and oxygen isotopic compositions indicate that the ore-forming fluids are mixtures of magmatic and metamorphic fluids.?2?The Qurugou pluton,occurred as fine-grained massive granodiorite,intruded in the Triassic Longwuhe group.Geochemical data indicate that the pluton is characterized by high-K cale-alkaline,high SiO₂,Na-rich I-type granites.This pluton has rare earth element contents ranging from 99.41×10^-6 to 154.85×10^-6 with LREE/HREE=7.23¹2.85.Rare earth element patterns show that the pluton has LREEs enrichment and weak negative Eu abnormity.This pluton is also enriched in LILE?Cs,Rb,Ba,Th?and depleted in HSFE?Nb,Ta,P,Ti?.Trace element characteristics of this pluton are similar to those of magmatic arc or collision-related granites.?3?The element discrimination diagram shows that the Qurugou pluton formed in the post-collision setting.Petrogenesis study shows that the magmatic source is metamorphosed basic rocks in lower crust.Delamination of lithospheric mantle leads to mafic magma underplating and then results in partial melting of metamorphosed basic rocks in lower crust.Variable crust-mantle magma mixing could also occur during this process.LA-ICP-MS zircon U-Pb dating reveals that the crystallization age of Qurugou pluton is 224.1±2.4Ma?MSWD=2.4?,indicating the pluton formed in the Late Triassic.?4?The study indicates that the high temperature magmatism caused gold hosted in the wall rock migration and enrichment.The deep hydrothermal fluids transported the metals along fractures and folds up to the shallow surface.Formation of the Jiawu gold deposit was related to transition of the structural system from compression to extension.