安徽北淮阳地区金矿化相关火山岩的形成年代和源区特征:锆石U-Pb定年和Hf同位素的制约

Formation age and characteristics of magma sources of volcanics related to gold mineralization in the Beihuaiyang zone,Anhui:Constraints from zircon U-Pb dating and Hf isotopes

安徽北淮阳地区发育中酸性陆相火山岩相关的金矿化,本次研究选取金矿化相关的新店河英安岩开展锆石LA-ICP-MS U-Pb年代学及LA-MC-ICP-MS Lu-Hf同位素研究。结果显示锆石Th/U比值为1.21~2.57,明显高于Th/U比值小于0.1的变质成因的锆石,为典型岩浆成因锆石。英安岩年龄加权平均值为(130±2)Ma(n=13,MSWD=1.4);结合锆石自形、发育岩浆环带等特点,该年龄是新店河英安岩的成岩年龄。锆石Hf同位素研究显示,新店河英安岩的ε_(Hf)(t)在-31.6^-26.3之间,两阶段模式年龄变化范围为2.82~3.15 Ga,为中—新太古代的基底部分熔融而成。新店河英安岩有较好的金矿化潜力,因此北淮阳地区金矿化可能形成于早白垩世后碰撞伸展环境,是大别造山带构造垮塌导致的大规模岩浆作用的产物。结合前人资料,北淮阳地区矿化可以划分为两个阶段:早期火山热液型金矿化(130 Ma)和晚期斑岩型钼矿化(114 Ma)。

This paper presents LA-ICP-MS zircon dating and zircon Hf isotopic data of the Xindianhe dacite related to gold mineralization in the Beihuaiyang zone, Anhui Province. The Th/U ratios of zircons range from 1.21 to 2.57, which indicated that they are magmatic zircons in origin. The Xindianhe dacite has weighted mean age of （130±2） Ma （n= 13, MSWD= 1.4）, which indicated it is the crystallization age of the Xindianhe dacite in consideration of euhedral texture and zonary structure of zircon mineral. The meas- urement of zircon Hf isotopes show that εHf（t） value ranges from -31.6 to -26.3 and corresponding two-stages ages are 2.82 to 3.15 Ga, which indicated that it was formed by the melting of the Meso-Arehean to Neo-Arehean basement. The gold mineralization in the Beihuaiyang region likely results from the large-scale magmatism related to the orogenic collapse which were formed in the post-colli- sional extensional setting in the post early Cretaceous period. In combination with previous data, two-stages of gold mineralization are i- dentified, i.e., early stage epithermal gold mineralization （about 130 Ma age） and late stage porphyry Mo mineralization （about 114 Ma age）. Therefore there is great prospecting potential for epithermal gold deposit in the Xindianhe region.