Add time:08/25/2019         Source:sciencedirect.com

Quartz-vein-type wolframite deposits are a primary type of tungsten deposits. Traditionally, F and Cl were considered as important agents in tungsten transportation during ore formation process. However, ore-forming fluids enriched in CO2 were commonly observed in natural fluid inclusions associated with quartz-vein-type wolframite deposits, indicating that carbonate or CO2 could be important for their formation. In this paper, we report experiments of the dissolution and crystallization of huebnerite in the MnWO4-Li2CO3 (or Na2CO3)–H2O system using a hydrothermal diamond-anvil cell (HDAC). The results showed that MnWO4 dissolved in alkali-carbonate aqueous solutions and, in some cases, in associated carbonate melts during heating, and subsequently, huebnerite crystallized into needle and column shaped crystals during cooling. In situ Raman spectra obtained during heating of the experimental charge in the sample chamber of the HDAC showed that WO42− was the only tungsten-bearing ion detected in the carbonate melt or aqueous solution. The dissolution of MnWO4 mainly attributed to the alkaline environment in the alkali-carbonate aqueous solution. Furthermore, the weak alkali condition in the carbonate solutions enhanced the crystallization of huebnerite when the temperature and pressure were decreased. The experimental results indicate that although the crystallization temperature–pressure conditions of huebnerite vary in a wide range, conditions lower than approximately 200 MPa and 450 °C are not favorable for huebnerite crystallization. Our experimental results also suggest that the alkali-carbonate aqueous solution could serve as a medium for the transport of tungsten in the ore-forming process.

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