A Study On The Relationship Between Late Mesozoic Magmatism And Contemporaneous Mo-Au Mineralization And Its Prospecting Target In The Xiong'ershan Polymetallic Mineralized Concentration Area

The Xiong'ershan ore concentration area is located in the East Qinling Orogenic Belt(EQOB)and preserves abundant molybdenum and Au resources.The most important molybdenum and Au metallogenic events in this area occurred in the Late Mesozoic,producing a number of Mo and Au deposits.The Late Mesozoic magmatic activity is also very frequent,forming numerous granitic batholiths and small porphyry stocks in this area.It remains unclear for i)the magma source,petrogenesis and geodynamic background of the Late Mesozoic magmatic rocks in the Xiong'ershan area;ii)ore genesis and ore-forming process of Mo and Au deposits,and iii)the relationship between magmatism and Mo-Au mineralization.Based on summary of the systematic research results of the Late Mesozoic magmatism,Mo and Au mineralization in the EQOB,this study focuses on the typical Late Mesozoic granite plutons,the Shapoling Mo deposit and the Qiyugou Au deposit.This study applies integrated modern diagenesis-mineralization theory,and systematic analyses of integrated whole-rock geochemistry,zircon U-Pb-Hf-O isotopes and trace elements,geochemistry of rock-forming minerals,and in situ trace element and sulfur isotope analysis of pyrite from the Shapoling Mo deposit and Qiyugou Au deposit.All data were performed to carry out research on the Late Mesozoic magmatism and its relationship with Mo-Au mineralization,and the origin and metallogenic processes of Mo-Au deposits.Furthermore,this study summarizes the ore-controlling factors,constructs the prospecting models and proposes the prospecting prospects.Four major results are listed below.1.This study establishes the geochronological framework of Late Mesozoic magmatism in the Xiong'ershan area and proposes that the Late Mesozoic tectono-magmatic evolution and the corresponding geodynamic background in the Xiong'ershan area can be divided into three stages.(1)Late Jurassic(160?145Ma):partial melting of the thickened lower crust in the post-collision stage of the Qinling Orogenic Belt formed typical adakitic granites with high Sr and low Y feature;(2)Late Jurassic to Early Cretaceous(145?125 Ma):due to the westward subduction of the Paleo-Pacific plate,the North China Craton was destroyed and the regional tectonic regime changed from compression to extension.Upwelling of the asthenosphere led to partial melting of the enriched lithospheric mantle and thinning of the crust.The granite intrusions in this stage show variable geochemical characteristics;(3)Early Cretaceous(125?110Ma):the Qinling Orogenic Belt was in an extensional background with completely removed continental lithospheric mantle,forming the granites without the characteristics of adakitic rocks.2.According to the research on the magma source and magmatic evolution of the typical Late Mesozoic intrusions in the Xionger'shan area,this study reveals the relationship between the Late Mesozoic granitoids and the Mo-Au mineralization.Large-scale crustal thickening caused by intra-continental subduction led to partial melting of the thickened lower crust in the post-collision stage of the Qinling Orogenic Belt;the subsequent destruction of the North China Craton led to the thinning of the lithosphere and the upwelling of the asthenosphere.During the transition from compression to extension,partial melting of the ancient lower crust and enriched mantle,and strong crust-mantle interaction occurred.The whole-rock geochemistry and zircon Hf-O isotopic features of the Late Mesozoic granitoids indicate that their parental magma were originated from the mixing of partial melting of the Taihua Group and the enriched lithospheric mantle.Upwelling of the asthenosphere led to the destruction of the sulfides in the enriched lithospheric mantle and lower crust,inducing the enrichment of incompatible metals such as Mo and Au in the silicate magma.The magma carries ore-forming fluids and metals rapidly ascending to the upper crust.3.This study analyzed the in-situ trace elements and sulfur isotopes of pyrite from the Shapoling Mo deposit and Qiyugou Au deposit.The results reveal the types,genesis and material sources of pyrite,ascertain the occurrence status of Mo and Au in pyrite and discuss the ore-forming process and genesis of the Mo and Au deposits in the Xiong'ershan area.Mo mainly occurs as independent molybdenite and Mo-bearing inclusions in pyrite.Pyrites,which are porous,broken and rich in inclusions,show higher Mo content.The?³⁴S values of pyrite are mainly concentrated between-2.5‰and 0‰,and the Co/Ni ratio is also consistent with the range of magmatic hydrothermal pyrite,indicating that Mo mineralization is the product of regional second-phase magmatic-hydrothermal activity.Au exists as invisible nano-scale natural gold particles or gold-bearing minerals in pyrite,rather than the form of solid solution.The features of trace element and sulfur isotope indicate that explosive breccia hosted and porphyry Au mineralization are the products of the same magmatic-hydrothermal system.Furthermore,the explosive breccia-type and porphyry Au mineralization represent the early-stage and the late-stage products of magmatic-hydrothermal system,respectively.4.On the basis of research on the Late Mesozoic magmatism and the Mo-Au mineralization,this study summarizes the ore-controlling factors prospecting criterias,constructs the prospecting models in the Xiong'ershan area.In combination with geological,geophysical and geochemical anomalies,this study suggests that concealed pluton could be developed in the deep level of the western part of the Xiong'ershan area.The identified Ag-Pb-Zn deposits and some Au deposits are mainly distributed on the shallower level and periphery of the concealed pluton which present as the intrusive center.The concealed pluton has prospecting potential for porphyry Mo and Au deposits.The eastern section has the potential to find Au-Ag-Pb-Zn deposits at the periphery of porphyry Mo deposits and porphyry Au deposits by locating the porphyry stocks with metallogenic potential.