Sulfur and CO2 gases emitted during weathering of sulfides: Role of microbial activity and implications to exploration through cover
Chloé Plet, Coralie Siégel, Martijn Woltering, Ryan Noble, Anaïs Pagès, Robert Thorne, Sam Spinks, Ravi Anand
Abstract
In mineral exploration, a thick cover is challenging and can hinder the discovery of new world class mineral deposits. Traditional surface geochemistry techniques are virtually “blind” in areas where the cover exceeds a few meters. Therefore, alternative surface geochemistry approaches such as the detection of soil gas anomalies over buried mineral deposits have been investigated and developed. This study investigates the source and potential of soil gases for mineral exploration by comparing equilibrium thermodynamic models with gases detected during weathering of “pure” sulfides and sulfide ores in the laboratory. Weathering experiments were conducted under moist settings, both for sterile and non-sterile conditions, and under water-saturated settings for non-sterile environments. Gaseous hydrocarbons were below detection limits, suggesting that any hydrocarbons produced during sulfide oxidation would only reach low abundances. Thermodynamic models undertaken in both moist and water-saturated conditions predict CO2 as the dominant gas produced. However, CS2 is the dominant sulfur gas produced in laboratory experiments, contradicting thermodynamic predictions. This suggests that experiments did not reach equilibrium. Sulfide weathering under non-sterile conditions produce greater relative abundance of gases than sterile experiments. This suggests that microbes play an important role in the weathering of sulfide to produce gases. Thus, the mechanisms involved in the production of gases from microbes-sulfide interactions must be considered in soil gas geochemical studies applied to mineral exploration.