Geochemistry And Ore Bearing Evaluation Of Mesozoic Intrusive Rocks In Huma Area,Heilongjiang Province

The huma area in Heilongjiang Province is located in northeast of Great Xing’ an Range,between the border of Erguna and Xing’ an block.It has experienced many tectonic events,such as micro block splicing,paleo Asian Ocean closure,Mongolia-Okhotsk ocean closure,the Great Xing’ an Range orogeny and so on.In this paper,Mesozoic intrusives were studied by means of petrology,geochronology and whole rock geochemistry.Petrogenesis and tectonic settings of intrusives were revealed,ore bearing property of intrusives were evaluated.Mesozoic intrusives in this area can be divided into early Jurassic acid rocks and early Cretaceous neutral rocks.Diagenetic times were 176.3± 0.8～ 177.7 ± 1.1Ma and 118.7 ± 0.9 ～121.3 ± 1.2Ma,respectively.The early Jurassic intrusivs are peraluminous rocks of high-K calc alkaline series.REE curves shows a right dipping pattern,with no obvious negative Eu anomaly.They are enriched in large ion lithophile elements(LILE)such as Rb,K,Sr and Ba,but depleted in high field strength elements(HFSE)such as Nb,Ta,Ti,P and Zr.They belong to I-type granites,whose magma source are mainly derived from the continental crust,with the addition of mantle derived components.These rocks,speculated to be related to the southward subduction of Mongolia-Okhotsk ocean,were formed in volcanic arc tectonic environment.The early Cretaceous intrusives are calc alkaline to high-K calc alkaline series of quasi aluminous to weak peraluminous rocks.REE curve shows a right dipping pattern,with weak positive Eu anomaly.Cobweb map of trace elements shows enrichment of K,Sr,Ba and other large ion lithophile elements(LILE),but depletion of Nb,Ta,Ti,P and other high field strength elements(HFSE).These rocks have high Sr/ Y,Mg#,Cr and Ni values,showing a characteristics of adakitic rocks.They were formed in extensional tectonic setting,suggesting mantle derived materials brought by lithospheric delamination then underplating and dominated to form magmatic activities.Compared with the early Cretaceous intrusives,the early Jurassic intrusives have higher evolution degree and medium redox conditions,and mostly located in ore bearing and sub ore bearing areas.Through the mixed distribution screening of 1: 50000 stream sediment datas and the factor analysis after ILR transformation,it is found that Au,W and Mo have a characteristics of multi-mode mixed distribution and high correlation,which have a prospecting potential.