Aishan Granite And Regional Metallogenic Background Research In Jiaodong Peninsula

Jiaodong peninsula in Shandong province is the most important gold field in China,the majority of gold deposit hosted in Linglong and Guojialing Mesozoic granite,either as quartz-vein in the granitoids or disseminated in altered shear zones along the boundary of the granitoids and Archaean metamorphic rocks,showed a intimate space output relationship.But it has been discovered that Linlong granite formed in 150-160 Ma,Guojialing granite in 126-130 Ma,and the main gold deposit-forming time in 120±10 Ma,suggest that the ore granite is older then ore-forming time.Although Aishan granite located in Zhaoyuan-Laizhou metallogenic belt has no any space association with gold deposit,the study found it formed in 116 Ma,which close to the main gold deposit-forming time,and what the point is Aishan granite has no enough deep study.Zhaoyuan-Laizhou metallogenic belt in which Aishan located host the most majority gold deposit in Jiaodong peninsula,but the Mouping-Rushan metallogenic belt in which Haiyang granite located has only a little gold deposit,and the study found it is a typical A type granite.So what the purpose of this article is to investigate the petrologic feature of Aishan granite(include K-feldspar megacryst,plagioclase alteration and biotite alteration)and its formation mechanism,also to explore the geological setting of ore-forming processes compared with Haiyang granite.Aishan granite located in noth-central of Jiaobei uplift,intruded into Guojialing granite with a north-south direction.It mainly consists of Nangushan fine grained monzogranite,Zhuajishan densepatch monzogranite,Yushan corcovadite-quartz diorite porphyrite and Gongjiashan porphyraceous medium grained granodiorite.Mafic microgranular enclaves(MME)and abundant K-feldspar megacryst are widespread,and the mafic microgranular enclaves in granite generally have been considered is the typical results of magma mixing.The geochemical study has found that Aishan granite are metaluminous to weakly peraluminous(A/CNK=0.89-1.01,most of them are 0.89-0.99).In diagrammatize of SiO2-K2O,they almost all belong to high-k calc-alkaline series.Aishan granite are enriched in light rare earth elements(LREE)and the large ion lithophile elements(LILE),but significantly deplete high field strength elements(HFSEs),and are characterized by negative Nb,Ta,P and Ti anomalies,no Eu anomaly.We suggest that Aishan granite are formed by magma mixing,and the acidic end-member is mainly of Archean middle-lower continental crust,while the basic end-member mainly is enriched lithospheric mantle,and both of them are depleted in HFSEs,the negative anomaly of Nb and Ta may be mainly inherited from source region,and also partly affected by residual of rutile.Combine the study of Mesozoic tectonic regime in Jiaodong peninsula with detailed geological data of Aishan granite,we deduced that the reginoal geological environment when Aishan granite formed is asthenospheric upwelling and lithospheric thinning,and the formation of Aishan granite is also associated with subduction of the west pacfic plate.Although Haiyang A type granite and Aishan granite are both formend in a extension environment,but there existed some difference on metallogenetic mechanisim and tectonic setting between the Mouping-Rushan and Zhaoyuan-Laizhou metallogenic belt in which they respectively located,result in fifferences in enrichment and migration of metallogenic material,thus lead to a differences on the mineralization ability between them.