Print this pageAbstract: Iron-Sulfide Mineralogy and Morphology in Oil Shale and Marlstone, Green River Formation, Piceance Creek Basin, Colorado
Oil shale and marlstone from the Parachute Creek Member of the Green River Formation, Colorado, usually contain less than 2 weight % total sulfur. This sulfur is partitioned primarily into iron sulfide minerals; minor sulfur occurs in organic combination and as sulfate. X-ray diffraction of iron sulfide separates (N = 53) shows that pyrite is the dominant phase with marcasite second and pyrrhotite third.
Iron sulfide bodies in oil shale and marlstone occur in six dominant morphotypes: streaks, lenses, blebs, boudinage structures, patches, and blades. Framboidal pyrite is rare in oil shale. The size of the bedded sulfide bodies ranges from pods, streaks, blebs, and boudinage structures several centimeters thick and several tens of centimeters long, down to microscopic blades and patches. Size analysis of disseminated blades and patches indicates that most bodies are between 2 and 60 µ in maximum dimension, and the mean size is about 20 µ.
The most common iron sulfide morphotype is the blade. An aggregation of microscopic blades generally makes up the larger sulfide bodies (patches, blebs, lenses, streaks) that are visible to the unaided eyes. These larger sulfide bodies generally have inclusions of other mineral matter, commonly analcime and quartz. Reflected-light microscopy reveals that the interior parts of most blade structures are weakly anisotropic, indicating the presence of marcasite. The outer parts of such blades are isotropic and composed of pyrite. This suggests that much of the disseminated and stratified pyrite in oil shale formed from a marcasite precursor.
AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma