Fig. 2. Fluid inclusions in representative black barites from the Dresser mine.

a, b Thin section images (reflected light) showing primary fluid inclusion trails parallel to barite crystal growth bands (marked by black arrows). c Thin section image (transmitted light) showing primary fluid inclusions which are dispersed or oriented parallel to barite crystal growth bands (exemplified by dashed line). The image also shows a minor secondary inclusion trail (marked by black arrow). d Thick section image (transmitted light) of an aqueous carbonic-sulfuric fluid inclusion containing three volatile phases (including H₂S), plus pyrite, native sulfur, and strontianite as solid phases. e Thick section image (transmitted light) of a non-aqueous fluid inclusion bearing a vapour phase, native sulfur, and kerogen. These fluid inclusions are usually rich in H₂S. V vapour/gas, Lw liquid H₂O, L other liquid (e.g. CO₂). Organic compounds and gases preserved in these primary fluid inclusions could have provided a substrate to primordial microbial life in the Dresser Formation.