安徽姚家岭锌金多金属矿区花岗闪长斑岩锆石U-Pb年龄和Hf同位素特征及其地质意义

U-Pb Age and Hf Isotopic Characteristics of Zircons from Granodiorite Porphyry in the Yaojialing Zn-Au-Polymetallic Mine,Anhui Province and Their Geological Significance

姚家岭锌金多金属矿床位于铜陵矿集区东部,其形成与小青塘花岗闪长斑岩密切相关.然而,前人对该岩体的研究仍较少,为了深入认识姚家岭矿区的成矿作用,利用岩石地球化学的方法,对花岗闪长斑岩及锆石特征进行研究,结果表明:花岗闪长斑岩具有较高的SiO2,K2O/Na2O比值为0.68~1.02,为I型花岗岩,属于高钾钙碱性系列;锆石具有明显的环带结构,Th/U比值为0.34~1.20,为典型的岩浆锆石;锆石的206Pb/238 U加权平均年龄为141.0±1.7 Ma,说明花岗闪长斑岩形成于早白垩世;锆石的εHf(t)为-22.5^-9.2,Hf同位素两阶段模式年龄为1 639~2 620Ma,表明形成花岗闪长斑岩的岩浆是古元古代地壳岩石部分熔融的产物.此外,研究还表明,花岗闪长斑岩的结晶温度为558~739℃,成岩压力为50~250MPa.

The formation of the Yaojialing Zn-Au-polymetallic deposit located in the eastern of Tongling ore deposit concentration area is closely related with the granodiorite porphyry.However,the previous studies on the rock is still less,in order to further understand the diagenesis and mineralization of the Yaojialing deposit,this paper carried the analysis of the characteristics of granodiorite porphyry and the study zircon,and shows that the granodiorite porphyry belongs to high-K calc-alkaline series with relatively higher content of SiO2(67.08%-68.57%),and it is of I-type granite(the ratios of K2O/Na2O are 0.68-1.02).The zircons display oscillatory zoning with ratios of Th/U at 0.34-1.20,which suggests they are zircons of magmatic origin.The weighted average 206Pb/238 U age for the zircons is 141.0±1.7Ma,which shows that the granodiorite porphyry was formed in early Cretaceous.ZirconεHf(t)values are-22.5to-9.2,indicating that the magma of the granodiorite porphyry was derived from partial melting of the rock in the crust.The zircons Hf isotopic two-stage model ages are 1 639-2 620Ma,showing the time of the differentiation of crustal rock from the mantle is Paleoproterozoic.In addition,our study finds that the crystallization temperature and the diagenetic pressure of the granodiorite porphyry are 558-739℃and 50-250MPa respectively.