A GEOCHEMICAL STUDY OF SOLID BITUMEN IN AN EOCENE EPITHERMAL DEPOSIT - OWEN LAKE, BRITISH-COLUMBIA, CANADA

The Owen Lake deposit (British Columbia, Canada) is an epithermal polymetallic deposit related to Eocene volcanic activity and igneous intrusions. The deposit contains both solid and liquid hydrocarbons generated during early and late stages of ore deposition. GC-MS, Py-GC, Rock-Eval(R), electron microprobe as well as carbon isotope, fluid inclusion and optical techniques have been applied and the results integrated into a deposit model incorporating fluid flow, fluid source and thermal structure of the volcanic terrane. Most solid bitumen examined is of the albertite variety and is related to the latest stage of mineral deposition. Gas chromatography of saturated hydrocarbons yielded n-alkanes from C-15 to C33, with a maximum at n-C23. Steranes and diasteranes are of low abundance relative to n-alkanes, terpanes and hopanes. Regular steranes dominate over rearranged steranes. Hopanes dominate over tricyclic terpanes and gammacerane is a significant component. Aromatic compounds are very low in abundance and are represented mainly by triaromatic steroids. These results together with carbon isotope values suggest a mixed marine-terrestrial organic source of the bitumen with saline or hyper-saline conditions prevailing during deposition or very early diagenesis of the source rock. Based on the geological framework of the deposit, two possible sources of the solid bitumen together with the fluid path are suggested.