Geochemistry of oil inclusions in sulfide-related calcites—fingerprinting the source of the sulfate-reducing hydrocarbons of the Pb–Zn carbonate-hosted Jubilee deposit of Nova Scotia, Canada

Sulfide precipitation in the context of carbonate-hosted base metal deposits has been previously explained by numerous processes including SO4 reduction in the presence of hydrocarbons. This model has been suggested for numerous deposits although clear criteria to support the model have not been systematically provided. Numerous oil-inclusions are encompassed by fibrous calcite crystals in finely laminated Carboniferous limestone at the base of the Windsor Group, a unit that hosts numerous base metal occurrences in Nova Scotia, particularly the hydrocarbon-rich Jubilee Pb–Zn deposit in Cape Breton Island. Oil from two inclusion-rich samples from this deposit have been characterised by gas chromatography, gas chromatography–mass spectrometry, gas chromatography–isotope ratio mass spectrometry and bulk stable C isotopes. As established in the authorsʹ former publications, the Jubilee deposit is a clear metallogenic case for which the ground preparation and mineralisation stages involved reduction of SO4 by hydrocarbons. Here, the question of potential sources of these hydrocarbons is addressed. It is postulated that the hydrocarbons that were trapped in the sulfide-related calcites at the deposit, correlate with previously characterised oil seeps, and it is demonstrated that their source is not the marine host-carbonates but stratigraphically deeper lacustrine formations of the Horton Group.