Rio Grande Resources Corporation controls uranium operations and mineral resources acquired by GA from Chevron Resources in 1991. Included in this acquisition were mines in south Texas and New Mexico. In New Mexico, the Mt. Taylor project, a conventional underground mine that contains the largest uranium resource in the United States, is currently on standby.
Rio Grande Resources properties in south Texas included Palangana, Rhode Ranch and Panna Maria. All these properties have either been successfully reclaimed or are in final stages of reclamation. Due to the variety of operations that occurred on these properties, Rio Grande Resources has developed extensive expertise in reclamation of open-pit and in situ leach mines, as well as mill decommissioning and reclamation.
The Mt. Taylor uranium mine is located in northwestern New Mexico about 60 miles (100 km) west of Albuquerque. Uranium was discovered in the Mt. Taylor area in 1968 and delineation drilling identified an ore trend extending nearly 6 miles (10 km). Chevron Corporation began commercial production at Mt. Taylor in 1986, initially shipping the ore to Chevron's Panna Maria mill in south Texas for processing. More than 8 million pounds U3O8 (3,080 mtU) were produced from the Mt. Taylor mine before the mine was placed on standby in 1989.
Uranium mineralization in the Mt. Taylor deposit occurs within the Westwater Canyon sandstone of the Jurassic age Morrison Formation and is similar in form to trend-type deposits in the Ambrosia Lake uranium district. The deposit occurs at 3,000 feet (900 m) below the surface. Coffinite is the primary uranium mineral. Ore grades range from 0.15% to over 2.0% U3O8, and averaged 0.5% U3O8 during the production period. The Mt. Taylor mine contains an in-place resource of over 100 million pounds U3O8 (38,500 mtU). Presently, the deposit is being evaluated for development as an in situ leach operation.
Rio Grande Resources has been involved in reclaiming numerous properties in the South Texas uranium district, developing an extensive background in groundwater restoration, surface rehabilitation, and tailings disposal and monitoring.
At the Palangana property, in Duval County about 100 miles (160 km) south of San Antonio, Rio Grande reclaimed an in situ leach well field and recovery plant. Beginning in the late 1960s Palangana became, essentially, a test site for in situ leaching, a methodology then in the early stages of development. With Union Carbide as the operator, the project passed through various stages of pilot testing using various leaching solutions and flow techniques, as well as development and operation under multiple testing scenarios. Ultimately, the project was shut down in 1979, after producing only 314,000 pounds U3O8 (120 mtU) of the 5.6 million pound uranium resource (2,150 mtU) identified on the property. Restoration of the groundwater aquifer at Palangana was a complex process due to the history of chemicals used and the characteristics of the geologic formation. Final release from the State of all permits was achieved in 1999. The Panna Maria mill, with a design capacity of 2,500 tons (2,270 tonnes) per day, was completed by Chevron in 1979. Located 45 miles (75 km) southeast of San Antonio, the mill originally processed ore from the Panna Maria open pit mines. When mine reserves were exhausted in 1985, the mill was revamped to process ore from the Mt. Taylor deposit in New Mexico and, later, ore from the Rhode Ranch mine. After processing the last Rhode Ranch ore, Rio Grande Resources demolished the plant in 1992. Working with both the Texas Department of Health and the Nuclear Regulatory Commission, Rio Grande Resources successfully decommissioned, decontaminated and reclaimed the plant site, more than 290 acres (117 hectares) of holding ponds, and tailings from the mill operations.
Rio Grande also reclaimed two open-pit uranium mines, Rhode Ranch and Jack Pump. The Rhode Ranch mine was closed in 1991 after producing nearly 6.7 million pounds U3O8 (2,580 mtU). Mine reclamation at Rhode Ranch commenced in 1992 and was successfully completed in 1998 when the Texas Railroad Commission released the property from bonding. Rio Grande successfully completed the Extended Responsibility Period for the Jack Pump mine in 1999 and applied for bond release and permit termination, the final steps in approving the reclamation work.