OPTICAL AND GEOCHEMICAL CLASSIFICATION OF PINE POINT BITUMENS AND EVIDENCE FOR THEIR ORIGIN FROM 2 SEPARATE SOURCE ROCKS

Mississippi Valley-type mineralization occurs within Middle Devonian c arbonates at the Pine Point lead-zinc mining property, Northwest Terri tories, Canada. A highly diverse suite of natural bitumens, ranging fr om liquid heavy oils to solid bitumens, is found in proximity to and d istant from the ore bodies on the property. In this study, the bitumen s are divided into different types based on qualitative observations i n reflected white and fluorescent light. Five texturally distinct bitu mens are distinguished: one homogeneous and four heterogeneous forms. Geochemical analyses (elemental analysis, solvent extraction and fract ionation, gas chromatography, gas chromatography-mass spectrometry, an d pyrolysis-gas chromatography) indicate that one of these bitumen typ es has a contribution from a source other than the ''F''facies, which previously had been considered to be the source of all the Pine Point bitumens. Other factors besides source that have caused the variations in the properties of Pine Point bitumens are thermal alteration, biod egradation, and possibly thermochemical sulfate reduction. Study of Pi ne Point bitumens suggests that bitumen classification schemes should include a combination of geochemical and optical parameters, rather th an depending on only one type of analysis.