Origin, biodegradation, and water washing of bitumen from the Mishraq Sulfur Mine, northern Iraq

摘要

Bitumens from Middle Miocene Fat'ha Formation at Mishraq Sulfur Mine were investigated to determine their sources and the extent to which they may have been diagenetically altered. For these purposes, fourteen bitumen samples were subjected to detailed biomarker analysis using gas chromatography-mass spectrometry (GC-MS). Stable carbon and deuterium isotopes were also measured on chromatographic fractions. These bitumens are present in cavities and fractures of limestone from the native sulfur productive series. Polar fractions accounts for about half of the bitumen composition. These bitumens are showing a partial removal of n-alkanes; whereas their terpanes and steranes are intact. In addition, dibenzothiophene (DBT) and phenanthrene (Phen.) concentrations and DBT/Phen. ratio are variable among the samples. Most deuterium isotope values of asphaltene and resin fractions are similar to those of non-biodegraded bitumen seeps from the Qaiyarah area. These criteria suggest that bitumens of Mishraq mine are slightly affected by biodegradation and they are water washed to different extents but are not affected by abiotic oxidation. The biodegradation of these bitumens is mainly due to sulfate-reducing (anaerobic) bacteria.