Geochemical characteristics of biotite granite in the Guangming fluorite deposit in eastern Hunan, China: Implications to fluorite mineralization

Guangming fluorite deposit is located in the north of Xitian granite pluton in the eastern Hunan.Aiming to investigate the correlationship between the biotite granite and fluorite mineralization in the mining district, systematic geochemical studies of the rock mass and the orebody, as well as zircon LA-(MC) -ICP-MS U-Pb age, trace element and Hf isotopic characteristics of the biotite granite have been carried out.Biotite granite in the Guangming deposit is characterized by elevated SiO₂, Al₂O₃ and total alkali contents, with A/CNK ratios of 1.07~1.14, showing peraluminous.Low-U zircons from three samples yield weighted average ²⁰⁶Pb/²³⁸U ages from 215 Ma to 218 Ma, indicative of Indosinian emplacement.The granite has zircon ages ranging from 237 Ma to 133 Ma, yielding three relatively concentrated age peaks at 230~210 Ma, 190~170 Ma and 150~130 Ma, indicating the influence of multi-stage magmatic activity.The biotite granite has strong Eu negative anomaly with weak positive Ce anomaly, being enriched in LILE(Rb, Th, U) and depleted in Ba, Nb, etc.The fluorite has moderate negative Eu anomaly with relatively depletion of Rb, Ba, Nb, Sm, Hf, Eu and enrichment of U, La, Nd, Zr, Y.The granite has ε_Nd(t) values of -11.2 to -10.6 and the corresponding T_DM2=1793~1837 Ma, while the fluorite has ε_Nd(133 Ma) values of -11.3 to -10.0 and the corresponding T_DM2=1741~1848 Ma.Hafnium isotope compositions showing a large variation, ¹⁷⁶Hf/¹⁷⁷Hf=0.282234~0.282420, ε_Hf(133 Ma)=-16.70~-8.45, T_DM2=1756~2214 Ma, indicating the crustal model age of Paleo-Mesoproterozoic.The comprehensive analysis suggests that the biotite granite in the Guangming deposit originated from the dehydration melting of muscovite in the mature crust, experienced multiple magmatic activities from Indosinian to Yanshanian.The biotite granite experienced strong differentiation and finally formed in an environment with low oxygen fugacity.The Yanshanian granite and the fluorite have similar characteristics of rare earth and trace elements, as well as the identical Nd isotopic compositions, different from Indosinian biotite granite, suggesting that fluorite mineralization in the Guangming deposit is related to the Yanshanian magmatism in the area.The ore-forming fluid is dominated by magmatic hydrothermal with minor addition of meteoric water.