Hydrothermal evolution and W-Be-F mineralization in the Mahuaping deposit, SW China: insights from fluid inclusion compositions

The Mahuaping W-Be-F deposit in southwestern China is characterized by a unique metal association and two mineralization stages. However, the detailed evolution of the ore-forming fluids for Mahuaping deposit remains controversial, particularly whether mineralization was driven by a single evolving fluid or multiple fluid pulses during progressive magma fractionation. Here, we combine fluid inclusion microthermometry with in situ LA-ICP-MS analysis of individual inclusions throughout different mineralization stages to resolve this issue. Four inclusion types were recognized, namely pure liquid aqueous type, liquid-rich aqueous type, CO 2 -bearing type, and daughter mineral-bearing type. Primary CO 2 -bearing type and liquid-rich aqueous type inclusions hosted in quartz, beryl, and fluorite throughout all mineralization stages define a H 2 O-CO 2 -NaCl system. These inclusions record homogenization temperatures ranging from 132 °C to 378 °C, salinities between 0.2 wt% and 16.4 wt% NaCl equivalent, and high concentrations of ore-forming metal with W and Be reaching 463 ppm and 538 ppm, respectively. Elemental ratios such as K/Na, Rb/Na, and Ca/K of individual inclusions from all stages consistently fall within the range of magmatic fluid, confirming a predominant magmatic origin. Systematic variations in fluid composition reveal a clear break between Stage Ia and Stage Ib. Notably, W/(Na + K) ratios of Stage Ib are nearly one order of magnitude higher than those of Stage Ia, which is inconsistent with the progressive wolframite depletion in a single-fluid system. This together with the decoupled evolution of temperature and salinity provides compelling evidence for two discrete magmatic fluid pulses. The first pulse (Stage Ia) was exsolved from a less fractionated granitic magma and formed quartz-wolframite-beryl veins via fluid-rock interaction with Fe-rich slates. In contrast, the second pulse (Stage Ib) was originated from a more evolved, W- and F-enriched magma and produced scheelite-beryl-fluorite mineralization through interaction with Ca-rich marbles. Stage II represents the late-stage evolution of the second fluid pulse, characterized by decreasing Be/(Na + K) and W/(Na + K) ratios accompanied by lower temperatures and salinities. Ore precipitation in Stage I was mainly controlled by fluid-rock interaction, supported by the inverse relationship between Ca/(Na + K) and W/(Na + K) ratios and by pervasive greisen and fluorite alteration. We collectively conclude that the W-Be-F mineralization at Mahuaping was governed by a magmatic-hydrothermal system involving two discrete fluid pulses, fluid-rock interaction, and meteoric water input. These results clarify the hydrothermal evolution of Mahuaping deposit and provide new constraints on the genesis of W-Be-F system.