太行山北段石湖金矿区中生代岩浆岩中单颗粒锆石的稀土元素特征及启示

Characteristics of Rare Earth Elements of Zircon from Mesozoic Magmatic Rocks in Shihu Gold District,North Taihang Mountain,North China

对太行山北段中生代岩浆岩中的锆石稀土元素进行了分析,结果表明,花岗岩和花岗闪长岩样品中锆石的ΣREE分别为747.08×10-6,704.84×10-6,δEu的均值分别为0.47,0.49,(Lu/Gd)N均值分别为23.55,24.12,锆石的稀土特征有着很强的一致性,反映岩体的中心相和边缘相有明显的亲缘性;而闪长岩和石英闪长玢岩样品中锆石的ΣREE分别为989.69×10-6,560.00×10-6,δEu的均值分别为0.56,0.75,(Lu/Gd)N均值分别为20.59,17.49,锆石的稀土特征有着明显得差异性,反映二者可能起源于不相同的岩浆源区,故岩体和脉岩的形成机制可能存在着差别。研究表明,(Lu/Gd)N和δEu是相对稳定的、是有指示意义的两个重要参数,∑LREE的值变化范围较大,尤其是La的丰度变化范围较大,所以∑HREE/∑LREE和(Sm/La)N的指示意义并不明显。结合锆石测年结果和CL特征,可以认为该区与胶东等超大型金矿的形成具有一致的背景,即华北克拉通大规模岩石圈减薄及壳幔相互作用;相对起源最深的石英闪长玢岩岩浆携带深部含金流体(透岩浆流体)迁移上升,与低fO2的花岗质岩浆期后流体和地下水混合,在围岩片麻岩的裂隙中沉淀成矿。

Rare earth elements of single zircon from Mesozoic magmatic rocks in north Taihang Mountain were analyzed by LA-ICP MS. The result reflect that average values of ∑REE, δEu and （Lu/Gd）N of the zircons from granite and granodiorite were 747.08 × 10^-6 and 704.84 × 10^-6, 0.47 and 0.49, 23.55 and 24.12 respectively. A strong consistency of the zircons rare earth characteristics indicated that the central face was coincident with marginal face of the rock body, their two faces could originate from the same magma source. However, average values of ∑REE, δEu and （Lu/Gd） N of the zircons from the diorite and quartz diorite porphyrite were 989.69 × 10^-6 and 560.00 × 10-4, 0.56 and 0.75, 20.59 as well as 17.49 respectively. The obvious differences of the zircons rare earth characteristics indicate that the two kinds of dikes can originate from the different magma source triggered by sults showed different formation mechanism. The rethat the （Lu/Gd）N and δEu were two iraportant parameters which were relativley stable but some ratios of the rare dement related with La （or LREE） eg. 2 HREE/∑ LREE and （ Sm/La ） N were unstable in determining the characteristics of zircon as ∑LREE especially La usually changed in a lager scope. Combining the results above with isotopic dating resulted and CL imaged, the geodynamic ground of this region was consistent with super-large gold deposit in eastern Shandong, which was largescale lithosphere thinning of North China Craton and interaction of crust and mantle. The higher fO2 of gold-bearing deep fluid （transmagmatic fluids） carried by quartz diorite porphyrite that originate from the deepest mix with lower fO2 of post-magmatic hydrothermal and underground water, and at last resulted in the formation of gold veins in the fracture of genesis as host rocks.