Metal transfer in CO2-rich geological fluids
|Leitung:||PD Dr. Nuo Li|
|Förderung durch:||Humboldt foundation|
CO2 is one of the most ubiquitous volatiles in crustal fluids and vapors. The role of CO2 in the transport of metals has been ignored owing to the fundamental assumption that most base and chalcophile metals cannot directly bind with the non-polar CO2 and thus metals are not soluble enough in the CO2-rich phases. On the other hand, the supercritical CO2 (>31 °C) is extensively used as solvent in industry for purification of organics and metal extraction from aqueous solution. Experimental study also verifies the capability of CO2 in dissolving and mobilizing metals at low temperature and pressure (60 °C, and up to 160 bar). It remains unknown, however, whether a similar solvation phenomenon may operate in natural fluid systems for metal forming sulfide complexes. Recent advances in fluid inclusion studies of hydrothermal Mo(±Cu±Au±W±Fe±REE) deposits from the Qinling-Dabie Mo belt, Central China, reveal enriched CO2 in the ore-forming fluids, with exceptional concentration attaining 50 to >95 mol% (Fig. 1). This finding evokes the possibility of enhanced metal (e.g. Mo, Au, Cu, W, Fe, Pb and REE) transfer in CO2-rich fluids or vapors. To present rigorous interpretation of the geological phenomenon and hence better understanding the role of CO2 on metal transfer and precipitation, a combined study based on LA-ICP-MS analysis of fluid inclusions and solubility experiments would be employed. The present study seeks to: (a) quantify the metal concentrations in natural CO2-rich inclusions from typical hydrothermal Mo(±Cu±Au±W±Fe±REE) deposits; (b) determine experimentally the metal solubility in CO2-rich fluid systems typical of hydrothermal ore deposit; (c) re-evaluate the role of CO2 in the transport of metals.