New LA-ICP-MS U-Pb Ages, Lu-Hf Systematics and REE Characterization of Zircons from a Granitic Pluton in the Betare Oya Gold District, SE Cameroon

摘要

A combination of whole rock geochemistry, Ti-in-zircon thermometry, geochronology and Lu-Hf isotope composition of zircon is employed in this study to depict the source of a granitoid from the Bétaré Oya Gold District, its formation temperature, age of emplacement and evaluate the role of petrogenesis and magmatic evolution of the granitic melt in hydrothermal fluid circulation and primary gold precipitation. In this contribution, zircon grains from a granitic pluton were analyzed for their internal structures using cathodoluminescence imagery and dated by U-Pb technique using LA-ICP-MS. Based on the zircon internal structure, magmatic and metamorphic zircons are distinguished. The granitoid reveal a mean age of 635 Ma similar to those obtained from granitic intrusions along the Central African Shear Zone (CASZ) in Cameroon. This age defines a narrow Pan African emplacement age for the pluton and a unique melting event synchronous with magmatism and deformation. It also depicts a new and older mineralization along the CCSZ at 620-635 Ma for the Bétaré Oya Gold District, SE Cameroon. Ti-in-zircon thermometry indicates their emplacement at a modal temperature range between 625°C and 775°C. Based on whole rock geochemistry alongside trace and REE composition of zircon, the pluton shows a granodioritic to tonalitic affinity. The granitoid is sub alkaline with a high K calc-alkaline affinity, peraluminous and of I-type. REE in zircon patterns display high Ce concentrations, negative Eu anomalies, HREE enrichment, 176Lu/177Hf ratio < 0.022 and negative Hf values that range from -5.29 to -0.12. Positive Hf values suggest a mafic crustal contribution. Across the Atlantic into NE Brazil, mineralization is often associated to late Pan African event. We disclose an early mineralization event at 635-620Ma in the region.