Geochemical Characteristics And Ore Genesis Of The Shangjiazhuang Molybdenum Deposit In Jiaodong Metallogenic Province,China

Jiaodong Metallogenic Province is famous for its great reservoir of gold.Researches have always focusing on the ore genesis of gold deposits while rarely pay attention to the molybdenum deposits which are similar to the gold deposits in tectonic settings and space time.This paper chooses the Shangjiazhuang Molybdenum as the subject to study its lithogeochemical characteristics,fluid inclusion,metallogenetic,epoch and mineral deposit geochemistry.The results of this study provide a good example for themetallogenetic mechanism analysis of regional Molybdenum deposits,and also provide theory basis for the regional prospecting.The petrogeochemistry analysis of Yashan Granite shows that the host granodiorite are rich in silicon,aluminum,alkali,suggesting a type I granite with high K-Ca-alkali contents.The primitive mantle normalized spider diagram of trace elements reveals enriching LILE of Rb,Ba,U,Th,K and Pb and lacking of HFSE of Nb,Ta,P,Ti.The spider diagram of REE shows weak negative Eu anomaly and intensive REE fractionation with LREE/HREE ratio of 18.83?22.63.It is also characterized of high Sr,low Y and Yb,similar to those typical of adakite and high Ba-Sr suggests a pattern of Hi Ba-Sr granite.The granodiorite were derived from partial melting of crust and influenced by magma mixing.The arc-like patterns of trace elements,old zircon cores and Hf model ages suggest that the granodiorite is the result of old crust materials' reworking.The lithospheric thinning and extension during the Early Cretaceous caused the eruption of I-type Yashan granodiorite.In this study,we obtain one molybdenite Re-Os isochron age of 117.1 ± 1.4Ma,which consists with the age of the granodiorite and the eruption gold mineralization.The hydrothermal stage can be divided into three stages which is the qtz-mot stage,the qtz-ccp-py-mot stage,and the qtz-py stage.The qtz-ccp-py stage can be further more divided into I,II stage.The hydrothermal belongs to the NaCl-H2O system.The homogeneous temperatures of I stage ranges from320??380?,and the homogeneous temperatures of II stage ranges from 200??230?.The H-O isotope shows that the juvenile water dominated during the I stage while the atmospheric water increased during the II stage.The metallogenetic mechanism of Shangjiazhuang molybdenum may be as follows:The lithospheric thinning and extension during the Early Cretaceous caused the eruption of I-type Yashan granodiorite.During the postmagmatic stage,the mineralizing fluid came from the magma.Then the fluid formed the deposit through filling and repolacement.