Geochemical characteristics, chronology and geological significance of the dacite in the Mazhala deposit, southern Tibet

Located in Northern Himalaya metallogenic belt, the Mazhala deposit is the most representative gold deposit in the Zhaxikang integrated exploration area. In this study, the authors carried out comprehensive researches including petrochemistry and zircon U-Pb dating analysis of the dacite in the Mazhala deposit, Comei County, southern Tibet. Chemical analyses show that the dacite is characterized by high Si (SiO₂=66.86%~71.84%), low alkali (Na₂O+K₂O=3.79%~4.60%), low Mg (MgO=0.50%~0.94%), strong peraluminous nature (A/CNK=1.55~2.23), enrichment of LILE such as Rb, U and depletion of HFSE such as Ta, Ti and Zr. The rocks also exhibit high total REE content (ΣREE=295.71×10^-6~343.82×10^-6), enrichment of LREE and obvious differentiation (LREE/HREE=10.5~15.22), with moderately negative Eu anomalies (δEu=0.39~0.48) and no cerium anomaly. LA-ICP-MS zircon UPb chronology indicates that the Mazhala dacite was emplaced at 138.2±1.6Ma, being the product of the Early Cretaceous magmatic activity. According to regional geology and related data, it is considered that the dacite was formed on the Himalayan passive continental margin and may be a part of Comei-Bunbury large igneous province.