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The economic Jewel Seam forms part of the Lower Cretaceous Gates Formation and has a stratigraphic thickness of about 10 m. Its depositional setting was on a coastal plain, well removed from marine clastic influences. These peat deposits were likely dominantly planar, low lying, and formed under seasonal wet (relatively dry) conditions. Shortening by subsequent folding and thrusting of the strata amounted to 50 percent, often resulting in structural thickening of the Jewel Seam along the hinges of folds.

Mineral matter and sulfur and maceral contents are largely determined by the original sedimentary environment. Vertical profiles with an upward increase in ash yield and low ash zones through the center of the seam can be explained by the chemical environment of the swamp. The average finely disseminated ash yield is 14 percent (dry basis); however, in places it is higher because of Laramide tectonic shearing. Sulfur contents are low compared to many other coal deposits and average 0.3 percent (dry basis). Sulfur often shows slightly elevated values at the base, and to some extent at the top of the seam. Volatile matter and vitrinite reflectance are largely controlled by depth and duration of burial and to some extent by deformation. These coals have relatively high inertinite contents, which probably result from seasonally dry forest swamp conditions.

Rank of the Jewel Seam ranges from high to medium volatile bituminous, where the highest rank is found in the central part of the study area. The intersections of isorank surfaces with the Jewel Seam indicate components of syndeformational coalification. A good linear correlation between maximum vitrinite reflectance and volatile matter (dry and ash free) is observed, enabling volatile matter to be estimated from vitrinite reflectance. A contoured map of vitrinite reflectance predicts rank and volatile matter of the Jewel Seam for unexplored parts of the coalfield.

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