Formation and evolution of multistage hydrothermal fluids in the Baishitouwa quartz-wolframite vein-type deposit in the southern Great Xing'an Range tungsten belt, NE China: Constraints from individual fluid inclusion LA-ICP-MS analysis

Revealing hydrothermal evolution from the early oxide to late carbonate stages for quartz-wolframite vein-type deposits is essential for understanding the ore-forming process. In this study, we choose the Baishitouwa tungsten polymetallic deposit located in the southern Great Xing'an Range tungsten belt as a case study, and pre-sent detailed deposit geology and in situ fluid inclusion (FI) analyses including micro-thermometry, laser Raman spectra, and LA-ICP-MS microanalysis to address this issue. Four stages of hydrothermal activity were identified: (1) quartz-wolframite (I), (2) quartz-wolframite (II)-pyrite-chalcopyrite, (3) quartz-polymetallic sulphides, and (4) quartz-carbonate. Four types of FIs were recognized: CO2-rich, CO2-bearing, liquid-rich, and brine inclusions. Microthermometric data showed that the homogenization temperatures and salinities from the early to late stages are 380-460 degrees C, 7.4-17.3, and 29.3-43.2 wt% NaCl equiv., 300-390 degrees C and 7.1-17.0 wt% NaCl equiv., 220-320 degrees C and 2.7-8.1 wt% NaCl equiv., and 150-250 degrees C and 0.5-4.8 wt% NaCl equiv., respectively, suggesting a decreasing trend. Geochemically, all stage fluids contained high Rb and Mn concentrations, high Rb/Na, Cs/Na, Li/Na, K/Na, Rb/Sr, low K/Rb, and consistent Cs/Rb and Cs/(Na + K) ratios, indicating that the mineralizing fluids originated from a common source & mdash;an underlying, geochemically uniform, and highly fractionated granitic magma. Fluid immiscibility and cooling are the main mecha-nisms for wolframite precipitation, whereas greisenization is subordinate; the incursion of meteoric water into the hydrothermal system initiated at the sulphide stage, and fluid mixing is the dominant mechanism for sulphide precipitation.