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Geophysical logs from uranium drill holes in the Grants region are a valuable source of information on coal resources. Coal occurs in the southern San Juan basin of New Mexico in the Upper Cretaceous Gallup Sandstone, Crevasse Canyon Formation, and Menefee Formation. Uranium has been mined from the Upper Jurassic Morrison Formation that underlies the coal-bearing Cretaceous formations and is separated from them by approximately 1,000 ft (300 m) of section.
Permission was obtained from Santa Fe Mining, Inc., Pathfinder
Mines Corp., and Ranchers Exploration and Development Corp. to examine their uranium drill logs for information on coal. Over 1,400 logs spudded above the base of the Gallup formation were examined, and depth to coal, coal thickness, and coal stratigraphic horizon were determined for coal beds at least 3 ft (1 m) thick. Coal isopachs have been drawn, and depth from the surface to the first coal have been contoured for the Crevasse Canyon and Menefee Formations. Data from an earlier study, which used geophysical logs from petroleum test borings, has been incorporated. The relationship between the coal resources determined from uranium drill holes and known coal deposits and mines in the southern San Juan basin is discussed.
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