Contemporary Mineralization And Dynamic Mechanism Of The Molybdenum And Gold Deposits In Jiaodong Metallogenic Area,eastern China

The Mesozoic Mo mineralization in Jiaodong,which is a part of the Mesozoic Mo mineralization event in eastern China,shares similar patterns of ore forming ages and tectonic environment with the giant gold accumulation in Jiaodong.In this contribution,geochronology,rock geochemistry,isotopic geochemistry,fluid inclsions are presented for a selection of Mo and Au deposits in Jiaodong.The magma source of the Mo ore-causative grantoids were studied from the perspective of the crustal architecture in collision belt,by using a combination of rock and isotopic geochemistry features.A comparison of Mo mineralization in Jiaodong and Dabie region has been made and the cause of the differences is discussed.Finally,the coexist mechanism of Mo and Au deposits were attempted to explain based on the metallogenic dynamics in Jiaodong.Mo deposits are mainly skarn,quartz-vein and porphyry type in Jiaodong,which predominated formed in the late Jurassic(160-150Ma),early stage(ca.125Ma)and late stage(120-110Ma)of the Early Cretaceous.The ore-forming fluids are medium-high temperature H₂O-Na Cl with a magmatic origin.The ore-causative grantoids are High-K calc-alkaline and metaluminous to peraluminous I type rocks.They are adakite-like rocks derived from melting of thickened ancient continental crust.Their zircon?¹⁸O values of 6.84‰to 8.84‰are similar to the normal values of granites.Mesozoic and Cenozoic granulite xenoliths are found along the southeastern margin of the North China Craton(NCC)and the Sulu Orogen.Their zircon ages recorded three main thermal events of ca.2.5Ga,2.3-2.0Ga and 2.0-1.85Ga,which mirror the evolution fo the Jiao-Liao-Ji Belt.Thus the lower crust beneath the region show NCC affinity.The NCC provid the main source for the ore-causive granitoids which may lead the differences between Mo mineralization in Jiaodong and Dabie region.Au mineralization in Jiaodong are fault controlled“gold-only”deposits which extensively contain no molybdenite.They mainly formed during 126-120Ma and show similar patterns of mineral assemblges,alteration and isotopic values.The ore-forming fluids are low salinity,CO₂rich and the characteristic of ore fluids can be consistent with in large horizontal and vertical interval.In contrast,Mo mineralization are genetic related to granitoids with the ore-forming fluids of H₂O-Na Cl.The 120-110Ma Mo mineralization are simultaneous or slightly younger than the Au deposits but no gold has been found in them,also in the Jurassic deposits.This special temporal and spatial distribution of the Au and Mo mineralization indicated their entirely distinct ore-forming source and processes.The Mo mineraliztion is caused by the granitoids derived by melting of ancient crust,however,the Au may come from the subcontinental source which can be the subducted Pacific Plate or metamorphic lithospheric mantle.