Origin of the Early Cretaceous Be mineralization in the Tongbai-Dabie orogen, central China

Abstract

The Niangniangding Be deposit is a Be-only deposit in the Tongbai-Dabie orogen. The Be mineralization is hosted in albitized granite in the contact zone between biotite monzogranite and metasedimentary rocks. Genthelvite, a Zn-rich helvine-group mineral, is the major carrier of Be. The Niangniangding biotite monzogranite and albitized granite were emplaced at 769–766 Ma and were derived from reworking of Paleoproterozoic crust in a Neoproterozoic continental-rift setting. Hydrothermal monazite coexisting with genthelvite yields an in situ U-Pb age of 126.7 ± 1.6 Ma, demonstrating that the Be mineralization is genetically unrelated with the Niangniangding granite that was albitized by Early Cretaceous ore-forming fluids. The albitization caused an increase of Al, Na, Mn, Fe, Zn, Be and Sr contents and a decrease of Si, K, Rb and Ba contents, reflecting in the formation of spessartite, albite, genthelvite and calcite and the consumption of quartz, K-feldspar and biotite. Petrographic and geochemical evidences hint that ore-forming fluids and metals (e.g., Be, Zn, Mn) may be sourced from non-exposed Cretaceous intrusions and metasedimentary wall rocks (the Huangmailing Formation). The Early Cretaceous intrusions are related to crustal extension due to the rollback of Paleo-Pacific plate. The close spatial relation between genthelvite, calcite, and albitization indicate that the fluid composition (the availability of Na+ and CO2– 3) may have crucially controlled the precipitation of Be. Our study indicates that the Tongbai-Dabie orogen has potential for Early Cretaceous extension-related Be deposits.