Speciation and Transport of Metals and Metalloids in Geological Vapors

Sulfur radical species form gold deposits on Earth

“…This breakdown induces precipitation of a portion of the gold, consistent with numerous observations in different types of deposits where fluid unmixing occurs (29)(30)(31)(32)(33)(34)(35)(36), with the balance constrained by the vapor phase as volatile complexes with hydrogen sulfide (4,17) or chloride (37), depending on the fluid H 2 S and HCl content, acidity, temperature, and depth of the vapor-liquid separation. For example, vapor-liquid partitioning coefficients for Au in S-rich (∼1 wt% S) acidic (pH < 5) systems at 400-500°C are above 1 (17,36), suggesting an important contribution of the vapor phase to Au transport. Once such H 2 S-SO 2 vapor ascends and condenses to liquid below the water critical temperature, S − 3 and its complexes with Au may reform again, along with AuðHSÞ − 2 .…”

“…Third, the selective affinity of S − 3 for Au may induce gold fractionation from Cu, Zn, and Pb that do not bind to S − 3 (SI Appendix). Thus, along with other multiple factors evoked so far, such as selective vaporphase transport (10,(36)(37)(38), specific metal sources (7,8), and silicate and sulfide melt evolution at depth (3,41,42,44), S − 3 binding to Au and, possibly, to other sulfur-loving metals and metalloids (e.g., Ag, Sb, Te) may be responsible for the particular ore signatures of Carlin, orogenic and intrusion-related gold deposits enriched in the Au-As-Sb-Tl-Te (±W±Mo) suite, with little Cu, Zn, and Pb (Fig. 4).…”

Geochemical identification of episodes of gold mineralisation in the Barberton Greenstone Belt, South Africa

“…However, gold may participate into the vapour phase if sufficient concentrations of sulphur are available (Pokrovski et al, 2013). Compositions of hypersaline fluid inclusions (Kouzmanov & Pokrovski, 2012;Pokrovski et al, 2013) imply a strong tendency for gold to partition into the vapour phase.…”

“…However, gold may participate into the vapour phase if sufficient concentrations of sulphur are available (Pokrovski et al, 2013). Compositions of hypersaline fluid inclusions (Kouzmanov & Pokrovski, 2012;Pokrovski et al, 2013) imply a strong tendency for gold to partition into the vapour phase. Weatherley & Henley (2013) found that cavity expansion during an earthquake generated such extreme reductions in pressure that fluids expand to a low-density vapour, resulting in the rapid co-deposition of silica together with a variety of trace elements to form gold-enriched quartz veins.…”

Chalcophile and platinum-group element distribution in pyrites from the sulfide-rich pods of the Lac des Iles Pd deposits, Western Ontario, Canada: Implications for post-cumulus re-equilibration of the ore and the use of pyrite compositions in exploration

“…Given the stability field of pyrite at b750°C (Kullerud and Yoder, 1959) and the progressive greenschist alteration down to 350°C (Boudreau et al, 2014), the main ligand capable of transporting Pt (and possibly Pd) during pyrite growth was either HS − or S 3 − (e.g., Hanley, 2005;Pokrovski and Dubrovinsky, 2011). Under these conditions As, Bi and Sb were more likely transported as uncharged hydroxide species (e.g., Pokrovski et al, 2013 and references therein).…”