Core drilling for data on uranium-bearing lignite in the Mendenhall area, Harding County, S. Dak. , was conducted by the U. S. Bureau of Mines during the period October 1952 to July 1953. Forty-two core holes totaling 9, 683 feet drilled in an area of about six square miles indicate a reserve of about 127/000,000 tons of lignite of which about 49,000,000 tons contain an average of 0.005 percent uranium or more. The Mendenhall area is near the center of the Slim Buttes, which are about 30 miles long from north to south. The uranium-bearing lignite averages, 5. 4 feet in thickness and occurs in the Ludlow member of the Fort Union formation of Paleocene age. Fuel analyses of about 130 samples indicate that the lignite contains about 15 percent ash, 36.7 percent moisture, 24r percent fixed carbon, 23.9 percent volatile matter, and 1.5 percent sulfur and has heating values of about 5,800 btu (as received). Uranium analyses of about 700 samples of lignite core indicate that about 2, 790 tons of uranium are present in the Mendenhall area. Inferred uranium reserves of 2,335 and .1. 050 tons are indicated by grade cutoffs of 0. 005 and 0. 01 percent uranium in the lignites, and 2, 065 and l s 35Stons are indicated by grade cutoffs of 0.03 and 0.05 percent uranium in the lignite ash. The above grade cutoffs have been incorporated on maps showing areal distribution:
and thickness of mineralized beds.