西秦岭大水金矿岩浆岩年代学、地球化学特征

摘要

西秦岭大水金矿床与其周围伴生的中酸性小岩体的成因关系，直接影响矿床成因的划分和深部资源的开发。中酸性岩浆岩的成因、源区性质及岩体规模对金矿成矿有重要影响。大水金矿岩浆岩地球化学研究结果显示：岩浆系列属于高钾钙碱性系列；岩体球粒陨石标准化稀土元素配分模式具有轻稀土元素富集、重稀土元素亏损、Eu正异常的特征；岩体洋中脊花岗岩标准化微量元素蛛网图显示其富集大离子亲石元素K、Rb、Ba、Th等，亏损高场强元素Nb、Ta、Hf、Zr、Sm、Y、Yb等，花岗岩的w（Sr）-w（Yb）分类属于高Sr、低Yb“C”型埃达克岩。LA-ICP-MS锆石U-Pb法测年获得大水金矿格尔括合岩体和竖井941岩脉的锆石U-Pb年龄分别为（215.8±1.3）、（202.9±1.5）Ma；成矿热液蚀变叠加在脉岩之上，成矿年龄应晚于202．9 Ma的脉岩年龄。Sr-Nd 同位素组成具有高初始N（87 Sr）/N（86 Sr）值、低εNd的特点，模式年龄为1．29～1．47 Ga。εSr（t）-εNd（t）图解表明岩浆源区为下地壳；εNd （t）初始N（87 Sr）/N（86 Sr）图解暗示西秦岭存在统一的岩浆源区。因此，西秦岭大水金矿在成因上与高Sr、低Yb“C”型埃达克岩密切相关。%The genetic relation between Dashui gold deposit in West Qinling and the surrounding associated small intermediate-acid rocks directly affects the classification of deposit genesis and deep resources development.The genesis,source property and rock scale of intermediate-acid magmatic rock have great influence on gold mineralization.Geochemistry of magmatite in Dashui gold deposit indicates that the magmatic series belong to high-K calc-alkaline series;chondrite-normalized REE patterns of rocks have the characteristics of LREE-riched,HREE-depleted and Eu positive anomalies;ORG-normalized trace elements spider diagrams of rocks indicate have the characteristics of LILE-riched (K,Rb,Ba,Th,etc.)and HFSE-depleted (Nb,Ta,Hf,Zr, Sm,Y,Yb,etc.);the classified diagram of w (Sr)-w (Yb)shows that the granite belongs to“C”-type adakite with high Sr and low Yb.The ages of Geerkuohe rocks in Dashui gold deposit and dyke in No.941 vertical shaft are (215.8±1.3)Ma and (202.9±1.5)Ma by the means of LA-ICP-MS zircon U-Pb dating;the ore-forming hydrothermal alteration superimposes on the vein rock,so that the metallogenic age should be later than that of the vein rock (202.9 Ma).The Sr-Nd isotopic compositions have the characteristics of high initial N(87 Sr)/N(86 Sr)and lowεNd ,and the model ages are 1.29-1.47 Ga.Diagram ofεSr(t)-εNd(t)indicates that magmatic source is lower crust;diagram ofεNd (t)-initial N(87 Sr)/N(86 Sr)implies that there is unified magmatic source in West Qinling.In general,the genesis of Dashui gold deposit in West Qinling is closely related to“C”-type adakite with high Sr and low Yb.