LA-ICP-MS Zircon U-Pb Age, Geochemistry and Tectonic Implications of Metamorphic Dacite from Huaniushan Group in Beishan Area, Gansu, China

By using the zircon LA-ICP-MS U-Pb dating, the obtained ages of metamorphic dacite from Huaniushan Group are (454.7 ±0.87)Ma (MSWD=0.28), which belong to the early stage of Late Ordovician.This age can provide a new basis for accurately determining the depositional age of Hunshan Group, thus the age of Hunshan Group has been revised as Upper Ordovician.This metamorphic dacite have high alkali and high Al, obvious enrichment of Rb, Th, U, K, Pb, negative anomalies of Nb, Ta, Ti, no obvious δEu anomaly, showing the typical volcanic magma characteristics.According to the regional geological data, the metamorphic dacite is formed in the active continental margin,which is related to the addition of subduction fluid or subduction sediments and is different from the formation of massive sulfide deposits in the Huaniushan Pb-Zn deposit.Therefore, it is considered that the Huaniushan Group is not the ore-bearing strata of Huaniushan Pb-Zn deposit.