Abstract

Solid bitumens, the residues of migrating hydrocarbons, may contain authigenic minerals closely comparable to those in organic-rich siliciclastic rocks. The minerals include quartz, feldspars, illite, and pyrite. Authigenic feldspars are of orthoclase or albite composition. In vanadium-rich bitumens, roscoelite is the dominant silicate phase. The minerals are recorded in bitumens from host rocks of Precambrian to Tertiary age. Silicate inclusions are particularly developed in large bitumen veins, which occupy major fluid-migration pathways. At a megascopic scale the bitumens appear to be pure hydrocarbon deposits, but the silicates indicate a major aqueous component in the hydrocarbon-bearing fluids. The sulfur-isotope systematics of fractionated bitumen samples are similar to those of sediments during early diagenesis, composed of 34 S-depleted pyrite and 34 S-enriched organic sulfur.

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