Xu, LQ; Liu, C; Deng, JF; Li, N; Dai, M; Bai, LB
Through the study of petrology and geochemistry, the volcanic rocks of Tamulangou Formation in Erentaolegai silver deposit have the characteristics of high SiO2 (>57%), Al2O3 (> 16%), alkali especially K2O (>3%) and belong to HKCA series. The content of REE is medium (187 × 10-6 ∼ 240 x 10-6), (La/Yb)N ratio is from 18.6 to 27.9, Yb values are less than 1.90 × 10-6, Y values are less than 18.0 × 10-6, and δEu is from 0.85 to 0.96. REE fractionation is strong, apparently loss of heavy rare earth and No or slightly negative Eu anomaly. Trace element is relative enrichment of LILE such as Rb, Ba, Th, U, K, loss of HFSE such as Nb, Ta, Ti, HREE, and similar to the characteristics of active continental margin. The characteristics of andesitic volcanic rocks in Tamulangou Formation indicate the andesitic magma comes from the base of the thickened crust (>50km), the residues are garnet, clinopyroxene and amphibole, partial melting and later evolution process of magma are not equilibrium with plagioclase. Andesitic volcanic rocks in Tamulangou Formation are the partial melting of CA or HKCA metamorphic Okhotsk Ocean. SHRIMP zircon U-Pb age of quartz porphyry, which was considered close with Erentaolegai silver deposit, is 138.6 ±2.3Ma and is the digenetic age. So further restrict Erentaolegai silver deposit formed at early stage of Early Cretaceous. Through the comparison between quartz porphyry and Tamulangou volcanic rocks from forming age and the study of characteristics of deposit, the silver deposit type is magmatic hydrothermal.