Plet, Chloe1, Siegel, Coralie1, Noble, Ryan1
1CSIRO Mineral Resources, Kensington WA 6151, Australia
In Australia, the presence of a thick transported cover on ~70 % of the continent has hindered the discovery of new world-class mineral deposits. To overcome this challenge, novel approaches are developed. Gases, with their high mobility, are thought to hold great potential as pathfinders for mineral exploration through cover. Previous investigations of gases detected at the soil surface have shown varying degrees of success in revealing the presence of buried mineralisation.
Here we investigate gases produced during laboratory weathering of sulfides. The experiments were run under sterile and non-sterile conditions. Carbon dioxide (CO2) and carbon disulphide (CS2) were the most abundant gases detected in all experiments. Non-sterile experiments produced more abundant gases than their sterile equivalents highlighting the importance of microbes in the weathering of sulfides.
In addition, the results of sterile experiments were compared to equilibrium thermodynamic predictions. In all experiments, as predicted, CO2 was the most abundant gas detected. However, some sulfur gases predicted by thermodynamic modelling were not detected in the laboratory (e.g. S2, H2S, CH3SH and C2H6S). Moreover, the most abundant sulfur gas predicted, carbonyl sulfide (COS) was only detected at trace levels. These results indicate that the experiments did not reach equilibrium.
Further soil gases experiments should include characterisation of the microbial communities. These would permit to gain a better understanding of the processes by which microbes impact the gases and improve the reliability of both techniques in the search for buried mineral deposits.
Chloe Plet obtained her PhD in organic and isotope geochemistry at Curtin University in 2017. In 2018 she joined CSIRO Mineral Resources, where her work largely focuses on investigating the potential of soil gases as a medium for mineral exploration.