Transport and deposition of uranium in hydrothermal systems at temperatures up to 300°C: geological implications

Volcanogenic uranium deposits: Geology, geochemical processes, and criteria for resource assessment

“…Carbonate complexes have been advocated for neutral to alkaline conditions and low temperatures (Hostetler and Garrels, 1962;Langmuir, 1978). Fluoride forms stable complexes with U +6 and possibly U +4 at low pH (Romberger, 1984), if there is sufficient F in the environment. More recently, chloride complexes have been proposed for high salinity fluids (Komninou and Sverjensky, 1996;Cuney and Kyser, 2009), which seems appropriate for basin brines and some volcanic systems.…”

Geologic characteristics of sediment- and volcanic-hosted disseminated gold deposits - Search for an occurrence model

“…Gold is soluble to varying degrees in aqueous sulfide solutions, in which the solubility depends on pressure, temperature, and sulfur concentration. Gold is most soluble when the pH is nearly neutral or slightly alkaline Casadevall, 1976;Romberger, 1982). If a rising hydrothermal solution containing gold in a bisulfide complex, such as Au(HS)2, were to reach a water table in which boiling was occurring ( fig.…”

“…The relation between boiling and ore deposition has been emphasized recently by many authors (Ewers and Keays, 1977;Kamilli and Ohmoto, 1977;Cunningham, 1978;Buchanan, 1980;Clifton and others, 1980;Bodnar, 1981;Drummond, 1981;Berger and Eimon, 1982;Romberger, 1982;Heald-Wetlaufer and others, 1983), but the interdependence of boiling and gold deposition has not been conclusively demonstrated. In this chapter I propose two models that illustrate specific aspects of this complex process.…”

“…Gold is soluble as a chloride complex under conditions of low pH, intense oxidation, high chloride activity (Romberger, 1982), and low total sulfur content (R. J. Bodnar, written commun., 1982).…”

“…Romberger, oral commun., 1981). Romberger (1982) summarized the conditions favoring gold deposition as follows: "* * * If gold were transported as chloride complexes, deposition occurs with increased pH, reduction, dilution and/or cooling," and "* * * if gold were transported as bisulfide complexes, oxidation, dilution, pH changes, and/or precipitation of base metal sulfides result in gold deposition." Gold deposition is particularly likely to occur where ascending solutions boil as a result of decreasing hydrostatic pressure, because there is a simultaneous loss of dissolved sulfide, decrease in temperature, and change in pH as volatile constituents, such as H2S and CO2, partition into the evolving gas (mostly steam) phase.…”