| The research region is located in the eastern part of the Central Asian Orogenic Belt, it's a tectonic-magmtic-metallogenic province experienced multiple congruence action such as the closure of the Paleo Asian Ocean, the Mongolia Okhotsk Ocean, the Pacific Ocean and Cenozoic discordgenic fault and so on. It also is a molybdenum ore resource base following the Qinling Metallogenic Belt in our country. According to the statistics, currently there are 4 super large Mo deposits have been explored, large and above more than 20, medium and small more than 70, the amount of resource is more than 7 million tons, the metallogenic type mainly is porphyry, the metallogenic epoch mainly occurred in the Mesozoic, and multi stage metallogenic characteristics exists and their intensity is different. In order to deeply reveal the constraints of the fluid in different stages, magmatism and geodynamics process in this research area on metallogenesis, we carried out the study of the geology, fluid inclusion, element and isotope geochemistry and geochronology on the Mesozoic different period porphyry Mo deposits in the research area and summarized the regional metallogenic regularity to provides the scientific basis for deep prospecting. The geodynamic model of diagenesis and metallogenesis is set up. The main progress and achievements are as follows.We identified two epochs of mineralization, which had five stages for the Mesozoic porphyry Mo mineralization in the area: the Indosinian comprising the Early-Middle Triassic(245-235Ma) and Late Triassic(209-200Ma), the Yanshanian comprising the Early-Middle Jurassic(189-167Ma), Late Jurassic-early Lower Cretaceous(151-125Ma) and late Lower Cretaceous(116-110Ma). The mineralization in Early-Middle Jurassic and Late Jurassic-Early Cretaceous is the strongest. The Early-Middle Jurassic Mo deposits mainly developes in the Lesser Xing'an Range-Zhangguangcai Range metallogenic belt and the Late Jurassic-early Lower Cretaceous Mo deposits mainly developes in the Great Xing'an Range.Through the analysis on the previous data of porphyry Mo and Cu deposits in the eastern of the Xing-Meng Orogenic Belt, the ore types of the porphyry Mo deposits in the area mainly disseminated, vein, fine-vein disseminated type and breccia type. The ore texture mainly includes euhedral-subhedral-anhedral texture, foliated-scalychrysanthemum texture and metasomatic texture. The ore structure comprises of fine vein-vein-stockwork structure and disseminated- fine vein disseminated- massive. Structure. The alteration zoning is obvious, large-scale metallogenesis is related closely with potassic alteration, silicification, sericitization.The characteristics of fluid inclusions indicates that the ore-forming fluid of porphyry Mo deposits in the research area exits critical high-salinity fluid in the early high-temperature stage; metallogenic stage has obvious symbiosis in middle-high temperature high-salinity and low-salinity fluid. In the late metallogenic stage, it is mainly the middle-low salinity fluid inclusion. The whole process of fluid evolution has experienced high-temperature vapor phase, middle-high fluid immiscibility or boiling and fluid hybrid process. The vapor phase, vapor–liquid two-phase and daughter minerals bearing polyphase are widespread, metallogenic process generally involved in CO2, the temperature of the main metallogenic stage is higher(>250?, generally more than 300?). The vapor phase composition in different epoch exists obvious differences, the Triassic Mo deposits characterized by the inclusions with rich CO2 aqueous-carbonic inclusions common development, while the Early-Middle Jurassic inclusions are common in the vapor phase composition containing CH4. In addition, Late Jurassic-early Lower Cretaceous exists both rich CO2 system and poor CO2 system, and the late Lower Cretaceous inclusions are common in the vapor phase composition mainly containing H2 O. The source of ore-forming materials is relatively complicated, crustal and mantle materials are involved.The metallogenic porphyry in the Early Triassic Modeposits is monzogranite porphyry-granite porphyry assemblage, belongs to high potassium calc-alkaline, metaluminous-peraluminous rock series, the magma originated from the partial melting of the ancient continental crust basement or the partial melting neogenic lower crust, and contaminating by ancient continental crust. The metallogenic porphyry of the Late Triassic Cu(Mo) deposits is mainly granodiorite porphyry, belongs to high potassium calc-alkaline, peraluminous rock series, and the magma was formed by the partial melting of the subduction oceanic crust. The metallogenic porphyry of the EarlyMiddle Jurassic Mo deposits is mainly porphyritic monzonitic granite- monzogranite porphyry and a small amount of granodiorite porphyry combination, belongs to shoshonite-high potassium calc-alkaline series, metaluminous-peraluminous rock series, the magma originated from the partial melting of thicken lower crust. the Late Jurassic-early Lower Cretaceous Mo deposits,of which rocks closely related to metallogenesis is granodiorite porphyry-granite porphyry assemblage, belongs to high potassium calc-alkaline series,metaluminous-peraluminous rock series, the magma originated from the partial melting of Neoproterozoic young lower crust materials by depleted mantle accreting or ancient lower crust. The late Lower Cretaceous Mo deposits, of which rocks closely related to metallogenesis is granodiorite porphyry and a small amount of granite porphyry assemblage, belongs to the calc-alkaline, sodium and peraluminous rock series, originated from the young underplating lower crust.Molybdenum deposits in different stages formed from different structural setting, Early-Middle Triassic Mo deposits formed in the extensional environment under the North China Plate and the Siberian Plate collision orogenic setting, and the Late Triassic copper molybdenum deposits formed in the subducting pericontinental arc environment. The formation of the Early-Middle Jurassic Mo deposits is closely related to the Pacific Plate subduction, only a few deposits(such as Wunugetushan) affected by continental collision system after the closure of the Mongolia Okhotsk Ocean. The Late Jurassic-early Lower Cretaceous Mo deposits experienced the conversion of Paleo-Asian Ocean structural domain to the Circum-West Pacific Ocean structural domain, intracontinental extension and the large-scale thinning of lithosphere occurred in this region. However, the metallogenesis in the late Lower Cretaceous should form in the continental arc setting which is related to tectonic exhumation period after the Izanagi Plate subduction. Porphyry Mo(Cu) deposits usually developes in the squeezing continental arc and continental collision orogenic belt setting, the basement most is ancient continental crust or young continental crust and oceanic crust. While porphyry Mo deposits more occurs in extensional plate subduction-behind arc-post orogenic setting, the basement can be neogenic continental crust or residual oceanic crustal, the metallogenic favorable site is intersections of two or more groups of faults, meanwhile the cryptoexplosive breccia development site is fine ore hosting and conducting site.In Early-Middle Triassic the North China Plat and the Siberian Plate collided, the lower crust was thicken in the collision, the thicken lower crust was partial melting, then formed early-middle Triassic Mo mineralization in the central-south of the Great Xing'an Range-Xilamulun River Belt. While in the Early-Middle Jurassic the subduction of Pacific Plate had thicken the lithosphere(continent) in the Xing-Meng Orogenic Belt, then the velocity of crustal and mantle materials interaction was accelerated by the thicken lithosphere, made the eastern of Jilin and Heilongjiang Provinces occurred large-scale molybdenum mineralization, which is the mainly reason of the early-middle Jurassic magma holding the crust- mantle mixing characteristics. The lithosphere was gradually thickening with the subduction then into the Late Jurassic-early Lower Cretaceous, the tectonic setting was converted to extrusion setting by squeezing setting, then the lithosphere began delaminating and thinning, during which the aesthenosphere materials upwelling accelerated the lower crust partial melting, leading to the large-scale Late Jurassic-early Lower Cretaceous molybdenum mineralization in the Great Xing'an Range. In the late Lower Cretaceous the homologous-adakitic rock developed by the secondary lithosphere mantle partial melting during the tectonic exhumation period after the Izanagi plate subduction, the Cu(Au) mineralization was formed by crystallization and differentiation and the molybdenum mineralization by mixing with the lower crustal remelting magma with the invasion process. |
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