Abstract

The Marysvale uranium district in central Utah is one of the principal examples of vein-type uranium deposits in the United States. The district hosts nearly vertical, northeast- and east-striking fissure veins that cut granitic and volcanic rocks in the eastern source area of the Miocene Mount Belknap Volcanics. The majority of the ore production came from an oval-shaped area 3000 feet long by 1500 feet wide located 3 miles north-northeast of the town of Marysvale in Piute County. The principal ore minerals are uraninite, coffinite, jordisite, and umohoite. Surface oxidation produced a variety of secondary uranium and associated molybdenum minerals. Uranium was discovered in 1947 in the area by a prospector seeking fluorite. Mining for uranium commenced in 1949 and continued through 1969. The principal operator in the district was the Vanadium Corporation of America. Records of the U.S. Atomic Energy Commission show that 12 properties produced a total of 307, 251 tons of ore with an average grade of 0.22 percent U₃0₈ (uranium oxide) and containing 1, 330,797 pounds of U₃0₈. The veins have been mined to a depth of 900 feet and drilling has indicated uranium mineralization is still present at a depth of 1400 feet.