The effect of gold scavenging by bismuth melts is investigated using equilibrium thermodynamic modeling of an aqueous solution-mineral-melt system. The calculations for the Au-Bi-Na-Cl-S-H-O system, performed at temperatures between 300 and 450 °C, demonstrate that Au concentrations in the melt are several orders of magnitude higher than in the coexisting fl uid, indicating the possible formation of economic gold deposits from undersaturated aqueous fl uids, in which mineralization would not be expected in the absence of a bismuth melt. The model applies to any deposit where a Bi melt is stable and coexists with a hydrothermal fl uid; examples of such deposits are known from skarn, intrusion-related, orogenic, and volcanogenic massive sulfi de (VMS) gold systems. In sulfur-poor systems the partitioning curves presented here can be used directly to correlate the gold concentration in the fl uid and the Au grade in the ore (e.g., Escanaba Trough VMS deposit). These results also illustrate important principles generally applicable to understanding magmatic-hydrothermal and metamorphic deposits that may have contained signifi cant volumes of more complex polymetallic melts.

No abstract

No abstract

International audienceThe structure of Bi(III) clusters in aqueous concentrated acidic perchlorate solutions has been studied by means of X-ray absorption spectroscopy (XAS). The XAS data show that the polynuclear [Bi6O4(OH)4]6+ complex with a cage structure predominates at room temperature in acidic Bi-rich solutions. This complex breaks down to form mononuclear complexes with increasing temperature to 428 K. This behavior is consistent with theoretical predictions based on considerations of the electrostatic repulsion, which increases sharply as the dielectric constant of the solvent decreases with increasing temperature

No abstract