西秦岭TTG质脉岩地球化学特征及其与金矿化的关系

Geochemical Characteristics of TTG Dick Rock and the Relation with Gold Mineralization in West Qinling Mountain

选取西秦岭夏河-合作断裂以南广泛发育的中酸性脉岩进行岩石学、岩石地球化学分析研究:研究区脉岩具有低硅低镁(SiO_2占55.14%～68.42%,平均64.13%;MgO占0.101%～1.02%,平均0.633%);高钠低钾(Na_2O/K_2O=0.63～2.92>0.5);高铝高钛(Al_2O_3含量大于15%;TiO_2占0.462%～0.806%,平均0.566%)特征。轻稀土元素(LREE)富集(LREE为195.89×10^(-6)～223.95×10^(-6),平均215.85×10^(-6)),重稀土元素(HREE)严重亏损(HREE为10.45×10^(-6)～14.56×10^(-6),平均11.86×10^(-6)),轻重稀土元素分馏明显,具弱的负铕异常(δ_(Eu))(δ_(Eu)=0.61～0.97,平均0.75);微量元素组成与埃达克岩类似,高Sr、低Y,高场强元素Th、U、Zr、Hf正异常,大离子亲石元素K、Ba、Sr负异常。脉岩具有奥长花岗岩-英云闪长岩-花岗闪长岩(TTG)岩套的性质,脉岩产生于晚三叠世洋壳俯冲消减活动大陆边缘弧环境。脉岩与金矿化是同一构造-岩浆旋回内区域壳幔相互作用的系列产物,金成矿与脉岩不仅在时空上密切伴生,而且物质成分上具有相同的来源和继承演化的成因联系。

The petrology and petro-geochemical analysis of the widely developed intermediate-acid dike rocks in the south of Xiahe-Hezuo fault in the West Qinling was investigated.The result shows that the dike rocks in the study area are characterized by low silicon and low magnesium(SiO2=55.14%~68.42%,average is 64.13%;MgO=0.101%~1.02%,average is 0.633%),high sodium and low potassium(Na2O/K2O=0.63~2.92),high aluminum and high titanium(Al2O3>15%;TiO2=0.462%~0.806%,average is 0.566%).The light rare earth elements(LREE)are enriched(LREE=195.89×10-6~223.95×10-6,average is 215.85×10^-6),and the heavy rare earth elements(HREE)are severely depleted(HREE=10.45×10^-6~14.56×10^-6,average is11.86×10^-6),and there is an obvious fractionation between HREE and LREE and a weak negative uranium anomaly(δEu)(δEu=0.61~0.97,average is 0.75).The composition of trace elements of the dike rocks is similar to that of adakite,which has a high Sr content and low Y content and a high field intensity element anomaly and a large lithophile element negative anomaly.The dike rocks have a property of trondhjemite-tonalite-granodiorite(TTG)rocks suite,and are originated in the late Triassic oceanic crust subduction active continental margin arc environment.Dike rocks and gold mineralization are the products of the interaction between crust and mantle in the same tectonic-magmatic cycle.Gold mineralization and dike rocks are not only closely associated in time and space,but also have the same origin and genetic relationship of inheritance and evolution in material composition.