Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit, Yunnan, China: implication for migmatitic–hydrothermal fluid evolution and ore genesis

Yunlong tin deposit is a medial-sized hydrothermal deposit in western Yunnan province of China. This deposit is unusual because the tin mineralization occurs exclusively within the migmatite bodies. The genesis of the ore deposit has been hotly debated and various models have been proposed including granite-related magmatic–hydrothermal and migmatitic–hydrothermal origins. This paper reports a systematic trace and rare-earth elements (REE) geochemical study in tourmaline and cassiterite from the orebodies and associated migmatites from the Yunlong tin deposit. Tourmaline and cassiterite from this deposit show light REE (LREE)-enriched patterns with variable Eu and Ce anomalies consistent with hydrothermal fluids being derived from local high-grade metamorphism and migmatization. The data suggest that tourmaline and cassiterite were likely precipitated from migmatitic–hydrothermal fluids and indicate that the Yunlong tin deposit was probably formed during migmatitic–hydrothermal process. The high concentrations of transition metals (e.g., Sc, Ti, V, Cr, Mn, and Zn) in tourmalines are also consistent with this model. The high concentrations of Sn, Sr, and especially Sc, V, and Cr in tourmalines can be used to discriminate tourmaline from barren deposits relative to those associated with economic tin mineralization.