Mesozoic Metallogenetic Granitoids In The Eastern Jilin-heilongjiang Provinces:Petrogenesis And Molybdenum Mineralization

The eastern part of Jilin and Heilongjiang provinces?EJHP?,part of the Xing'an–Mongolian Orogenic Belt?XMOB?of China,is located between the Siberian and North China cratons.The tectonism recorded in this area includes not only the late Paleozoic-early Mesozoic closure of the Paleo-Asian Ocean but also the Mesozoic-Cenozoic subduction events associated with the Paleo-Pacific plate.Historically,the tectonic evolution of the EJHP was thought to involve the amalgamation of micro-continental massifs,including the Songliao,Jiamusi-Khanka and Nadanhada massifs/terranes.The unique and complex geological evolution and multi-structural magmatism in this study area can provide well metallogenic environments for the generation of porphyry Mo deposit.In order to investigate the formation and distribution of porphyry Mo deposit in this area,zircon LA-ICP-MS U-Pb data are reported for the metallogenetic granitoids.These U-Pb data,combined with the existing molybdenite Re-Os isotope dates,show that the granitic magmatism was coeval with the porhyry Mo mineralization.Furthermore,we recognize that the studied granitoids were mainly emplaced in three periods,i.e.,Early Jurassic?193¹76 Ma?,Middle Jurassic?172¹65Ma?and Early Cretaceous?111 Ma?.Whole-rock major and trace elements,together with zircon Hf-O isotope data,are reported for the metallogenetic granitoids in the EJHP,in order to investigate their petrogenesis,sources and tectonic implications.This thesis first introduces the Mo isotope for the molybdenite from four?Luming,Daheishan,Fuanpu,and Baoshan?porphyry Mo deposits.Combining published data of the ore-forming fluid in the EJHP,we accordingly investigate the source of molybdenite,the Mo isotope fractionation and their transport processes.1.Age and distribution of Mesozoic metallogenetic granitoidsMesozoic metallogenetic granitoids in the EJHP were mostly emplaced during the Early Jurassic to Early Cretaceous.The zircon U-Pb geochronology of the present study indicates that the Luming monzogranite and the metallogenetic monzogranite porphyry formed at 197.1±1.6 Ma and 182.9±2.2 Ma,respectively.The Fuanpu monzogranite porphyry and quartz diorite were also emplaced in the Middle Jurassic with ages of 170.4±2.1 Ma and 168.6±1.9 Ma,respectively.The Jidetun monzogranite?170.8±1.9 Ma?and quartz diorite?170.7±0.9 Ma?were emplaced during the Middle Jurassic.The Baoshan granodiorite and quartz diorite were emplaced at 164.4±1.9 Ma and 165.2±1.7Ma,respectively,indicating the Baoshan granitoids formed in the Middle Jurassic.The Kanchuangou granodiorite was emplaced in the Early Cretaceous?111.8±1.4 Ma?.The Liushengdian non-metallogenetic monzogranite porphyry was formed in 252.2±1.6 Ma.Collectively,the Early Jurassic metallogenetic granitoids exposed in the Lesser Xing‘an Range and Yanbian region,with rock types consisting of monzogranite,granodiorite and quartz monzonite.The Middle Jurassic metallogenetic granitoids are distributed in the Zhangguangcai Range and Yanbian region,with rock types consisting of monzogranite and granodiorite.The Early Crtaceous metallogenetic granitoids are distributed in the eastern EJHP,with rock types consisting of granodiorite.2.The sources of Mesozoic metallogenetic granitoids and tectonic implicationsThe Early Jurassic metallogenetic granitoids have high SiO₂,Y,Yb and HREE contents and low MgO,Fe₂O₃,CaO and Sr contents,and display the features of LILE-enriched,HFSE-depleted.Most of the Early Jurassic Luming metallogenetic granitoids have positive?_Hf?t?values with Hf two-stage model ages of 831¹328 Ma,indicating that the primary magmas of these rocks were derived from partial melting of Meso-Neoproterozoic crustal source.The Early Jurassic Luming metallogenetic granitoids have positive?_Hf?t?values with Hf two-stage model ages of 762⁵54 Ma,indicating that the primary magmas of these rocks were derived from partial melting of Neoproterozoic crustal source.The Luming and Jiapigou metallogenetic granitoids have high?¹⁸O values?5.72‰±0.2‰and 6.1‰±0.14‰?,indicating that their source rocks were affected by the incorporation of high ¹⁸O crustal materials.The Middle Jurassic metallogenetic granitoids have high SiO₂,and low MgO,K₂O,contents,insignificant Eu anomalies,together with the features of high Sr and low Y and Yb contents,suggesting that they are adakite-like granitoids.The Middle Jurassic Fuanpu monzogranite porphyry and Jidetun monzogranite in the Zhangguangcai Range have low?¹⁸O values?4.64‰±0.19‰and4.64‰±0.19‰?,suggesting that the source materials was previously significantly modified by interaction with slab-derived fluids.The Middle Jurassic Baoshan granodiorite in the Yanbian region have?¹⁸O=5.51‰±0.12‰,together with the Hf isotopic compositions(?_Hf?t?=+6.1⁺10.0;T_DM2=575⁸25Ma),suggesting that the Baoshan granodiorite originated from the partial melting of a dominantly Neoproterozoic lower crustal source.Based on the new geochemical data and Hf isotopic compositions(?_Hf?t?=+3.8⁺9.8;T_DM2=542⁹28 Ma),we propose that The Early Cretaceous Kanchuangou granodiorite originated from the partial melting of the Neoproterozoic crustal source.The Kanchuangou granodiorite contains high?¹⁸O values?7.05‰±0.19‰?,suggesting that the source was affected by the incorporation of high ¹⁸O crustal materials.Combining these geochemical data with the geology of the study region,it is indicated that the Mesozoic metallogenetic granitoids were generated as a result of the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.3.The Mo sources of molybdenite and the variations of molybdenite in ore-forming fluidCombining the existing hydrogen and oxygen isotope,S isotope,Pb isotope and fluid inclusion data,we propose that the hydrothermal fluid is mainly originated from magmatic melts,with input of minor meteoric water.The?^98/95Mo of molybdenites ranges between0.17‰and 1.49‰,which is in agreement with the values of the representative molybdenites.The?^98/95Mo values of the molybdenites were slightly higher than those of the crustal granites,indicating that the Mo originated from the crustal magma.In contrast,samples from uniform porphyry Mo deposit have different?^98/95Mo values,indicating that Mo isotope fractionation?0.38‰⁰.79‰?is significant.The Mo isotope fractionation is more effective in a medium-high temperature,and high salinity fluid?0.56‰⁰.79‰?condition.The transport and mineralization are influenced by the temperature and salinity in ore-forming fluid.We propose that fractionation of the Mo is impacted by high temperature Rayleigh distillation and oxidation in ore-forming fluid.