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In southwest Alabama, deep-basin lignite with economic potential occurs in the Oak Hill Member of the Naheola Formation. This middle Paleocene lignite is the thickest (2 to 11 ft, 0.6 to 3.3 m) and most extensive lignite in the southwest Alabama region. The Oak Hill lignite deposit accumulated in lower delta plain coastal marshes located in interchannel areas behind of a barrier system. The source area for the deltaic sediments was probably to the west and/or northwest of Choctaw County, Alabama. The lignite occurs in a clay-dominated sequence. Oak Hill interdistributary bay ripple-laminated clays are interbedded with ripple-laminated, crevasse splay sands generally < 15 ft (5 m) in thickness. The glauconitic sands of the overlying Coal Bluff Member of the Naheola Form tion represent marine encroachment into the interchannel basin area.
An estimated 8 billion short tons of hypothetical Oak Hill deep-basin lignite may be available in southwest Alabama. The lignite is of good quality and is characterized on an "as determined basis" as having 20 to 27% moisture, 8 to 10% ash, 0.8 to 3.0% sulfur, 0.1 to 1.0% pyritic sulfur, 30 to 39% volatile matter, and 28 to 36% fixed carbon. The calorific value of the lignite is 9,070 to 9,970 Btu/lb and averages 9,530 Btu/lb. Presently, this deep-basin lignite resource is beyond the depth for effective surface mining and, therefore, must be recovered by underground mining or in situ gasification or liquefaction recovery methods.
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