Hydrothermal beryllium mineralization in the Qingtian volcanic-intrusive complex, southeast China

Abstract

Hydrothermal Be mineralization in igneous-related systems is controlled by magma composition, physical conditions (e.g., temperature and pressure), hydrothermal fluid properties, and the host rocks. However, the transport, concentration, and mineralization of Be in volcanic-intrusive complexes remain poorly understood. We report the petrography, mineralogy, and geochemistry of the Qingtian volcanic-intrusive complex (Zhejiang Province, southeast China), to investigate the concentration and mineralization of Be during the hydrothermal alteration of subvolcanic rocks. The granite porphyry dikes (subvolcanic rocks), granite, and the host tuff have similar chemical, mineralogical, and isotopic compositions, and comprise one volcanic-intrusive suite. The Be mineralization in the Qingtian volcanic-intrusive complex corresponds to variable hydrothermal alteration of the granite porphyry dikes, and extensive Be mineralization mainly occur in Shawan, Huangshanlong and Tuoliao. The formation of the Shawan Be ore is likely related to the F-rich metasomatism of the granite porphyry dike after albitization, the Huangshanlong Be ore was resulted from hydrothermal alterations between granite porphyry dike and host tuff by Be-rich fluids, and the Tuoliao Be ore was formed by the hydrothermal alteration of the granite porphyry dike by evolved F− and (CO3)2−-rich fluids. Fluorine plays a key role in hydrothermal Be mineralization in these Be ores, but (CO3)2− and S2− increase the diversity of Be mineralization. The chemical compositions of Be-bearing minerals (bertrandite, phenakite, and helvine-group minerals) reflect the metasomatic alterations of the granite porphyry dike by Al-poor hydrothermal fluids. Low Be contents of the granite porphyry dike and the surrounding granite, and widespread high Be contents of the altered tuffs in Qingtian area suggest that Be may have been derived from the later hydrothermal alteration of the surrounding tuff. These results not only provide an example of the exploration of Be resources in volcanic-intrusive complexes but also suggest the potential for significant Be resources in the volcanic rocks along the southeast coast of China.