Temporal-spatial variations in Li-Fe mica compositions from the Weilasituo Sn-polymetallic deposit (NE China): Implications for deposit-scale fluid evolution

Spatial-temporal compositional variations in hydrothermal mica from different mineralization stages were determined across a single cross-section at the Weilasituo tin-polymetallic deposit, Northeast China. Hydrothermal mica from the magmatic-hydrothermal transitional stage (unidirectional solidification textures), hydrothermal tin-tungsten stage, molybdenum stage and copper-zinc stage was analysed in situ for major and trace element composition. Weilasituo mica is enriched in Li, Rb, Cs and Zn, has a moderate W and Sn content and a low Cu content. The temporal variation in mica composition shows that the Li content decreases slightly from the early to the late stage, while Zn concentration shows the opposite trend. Other elements in mica are relatively constant between stages, with only Sn, Rb and Cs being slightly enriched in the hydrothermal tin-tungsten stage mica. According to the spatial variations in mica composition, mica with a high W, Sn, Nb and Ta content occurs in granite, while mica enriched in volatile elements like Li and F is distributed within the main tin ore vein, or adjacent to the breccia pipes. The results suggest that mica W-Sn-Nb-Ta enrichments are genetically related to an early high-temperature magmatic fluid linked to the granitic intrusions at Weilasituo, while volatile elements were enriched by successive evolution of lateral fluid migration. The trace-element content of the Weilasituo mineralizing fluid (estimated from mica composition and rough estimates of mica-fluid partition coefficients) suggests that the fluid related to different mineralization originated from the same source, and does not support obvious magmatic-meteoric fluid mixing. Finally, the results suggest that spatial-temporal variations in mica compositions can be taken as a potential indicator of ore fluid compositional evolution in a hydrothermal system.