Abstract: Case History of Discovery of New Uranium Deposit, Ambrosia Lake District, New Mexico
David C. Fitch
Uranium ore deposits in the Ambrosia Lake district, New Mexico, are in fluvial sandstones in the Westwater Canyon Sandstone Member of the Jurassic Morrison Formation. Uranium mineralization is concentrated in humic matter which imparts a gray to black color to the host rock. The ore deposits in the district vary greatly in size and shape and are difficult drill targets.
A sequence of drilling led to the discovery of deposits comprising a part of the Johnny M mine owned jointly by Ranchers Exploration and Development Corp. and Houston Natural Gas Oil Co. The tract under consideration consists of a square mile (2.65 sq km) where three separate ore deposits were found at depths of approximately 1,350 ft (411 m). Initial exploration drilling consisted of holes on a random pattern where ore was intersected in the fifth hole drilled. Subsequent random drilling led to the discovery of a second deposit in the 109th hole drilled and a third deposit was located in the 169th hole. A total of 268 holes has been drilled on the section with ore-grade mineralization intersected in 48 holes. Drill-hole spacing ranged from several hundred feet (meters) during the exp oratory phase to as close as 75 ft (29 m) in blocking out ore deposits. Ore reserves are estimated at 350,000 tons (315,000 Mt) of ore containing 3,500,000 pounds (1,575,000 kg) of U3O8.
A review of the drill data shows no conclusive relation of uranium ore with any geologic feature other than humic matter. In some cases, low-grade mineralization extends away from ore whereas, in others, the ore boundary cuts off very sharply to barren ground.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC