胶东金矿区高钾-钾质脉岩地球化学与俯冲-壳幔作用研究

Study on the geochemistry and subductioncrust mantle interaction of the high potassiumpotassium dike rocks in gold deposits concentration zone of east Shandong, China.

胶东金矿区与金矿成矿伴生的脉岩为一套高钾 -钾质脉岩。根据地质、岩相学及与金矿化的时空关系 ,将主要岩石类型划分为煌斑岩、安山玢岩、英安玢岩类 ,它们分别形成与金矿化早期、同期和晚期 ;主要元素成分以富碱高钾、低钛为特征 ,成分变异具同源岩浆结晶分异演化的一般规律 ,早期以辉石和橄榄石、中晚期以角闪石和斜长石为主的矿物相分离结晶控制岩浆的演化 ;岩石明显富 Ba、Sr、Rb、K、L REE等大离子元素、强烈亏损 Cr、Ni及相对亏损 Th、Nb、Ti、Y等高场强元素元素 ,体现初始岩浆起源于富集地幔源区 ;大量的挥发组分及强烈的富集 Ba、Sr及低的 Sr/ Nd比值 ,指示源区为以俯冲陆源沉积为主、有玄武质洋壳参与的脱水、脱气等作用交代早期地幔楔形成的富集地幔源 ,初始岩浆是在中生代印支期形成的富集地幔向燕山期亏损方向演化的特定阶段发生低程度熔融形成 (熔融程度为 6 %～ 8% ) ;

The paper mainly studied high potassiumpotassium dike rocks in gold concentration zone in Jiaodong of Shandong. The rocks can be divided into three kinds of lithologies, ~{*+~}i.e.~{*+~} (I) Lamprophyre, (II) Andesiteporphyrite, ~{*)~}(III) Dacite~{***2~}porphyrite on the basis of factors such as geologic attitude and lithologic character and timespace relationship of gold mineralization etc. These rocks were the products of early mineralization, synchronous and later mineralization, respectively. Advance on study of geochemistry shows that the geochemical compositionsvariations of the major oxides have vague general rules of homologous magmatic fractionalcrystallization, and the mineral facies (major component augite and olivine in early stage of transition from lamprophyre to Andesiteporphyrite hornblende and palgioclase by the later stage of the transition from andesiteporphyrite to daciteporphyrite) controlled the magmatic evolution process. The rocks takeof enriched alkali, high K2O, but lower TiO2, and commonly intensively enriched in LILE (such as Ba, Sr, Rb, K, LREE ~{*+~}et al~{*+~}.), intensively depleted in coherence elements (such as Cr, Ni ~{*+~}et al~{*+~}.), relatively depleted in high fields elements (such as Th, Nb, Ti, Y ~{*+~}et al~{*+~}.), which proved that magma was derived from thesource of enriched mantle. Enriched fugitive constituents and intensively enriched Ba, Sr and lower Sr/Nd component may be caused by mixing of main subduction terrigenous sediment and basaltic ocean crust by dehydration into mantle wedge. The lower partial melting degree (6%~8%) might have been formed at the special stage from IndoChinese epoch on in with an enrich mantle to a depleted mantle at stage of Yanshan, and emplacement environment may be the main causes of the different magmatic evolution in the quartz veintype and altered rocktype of gold deposits.