Mineral Leases on Navajo Land: Navajo Reservation land, closed to mineral claim location and prospecting by the Secretary of the Interior (March 1936), was reopened by a Congressional Act of May 1938, which let the Tribal Council lease Navajo land under the new regulations with approval of the Secretary of the Interior. Six vanadium leases were approved (1939-mid 1940s) around the Carrizo Mountains in Arizona and New Mexico. Several vanadium mines opened in 1942: by 1947, 38 were producing. Most had closed when the Federal Government’s program under the Metals Reserve Company ended in early 1944. Several of the vanadium mines later produced uranium under U.S. Atomic Energy Commission procurement programs that began in January 1947.
(See report at footnote 3: Chenoweth, 1991)

A private effort was begun in summer 1951 to map and sample mineral occurrences in the Salt Wash Member in the ore belt area on the northeastern face of the Lukachukais. The results of the study showed excellent potential for additional ore to be developed in that area. In August 1951, the newly formed Navajo Uranium Company (NUC) of Cortez, Colorado, acquired the F.A. Sitton, Inc., firm and the leases it held by assignment. Data from the new study along with the positive results from the AEC’s exploratory drilling program prompted the NUC to propose a 300 ton-per-day mill at Shiprock, New Mexico. The proposed mill was not approved by the AEC; however, it did approve the building of an ore-buying station at Shiprock. The buying station was opened in January 1952 and was operated by American Smelting and Refining Company under contract to the AEC. The Shiprock station provided a market for all non-VCA controlled uranium ore mined in the northeastern Arizona and northwestern New Mexico areas.

On the Colorado Plateau in the early 1950s, the lack of a system of all-weather roads for transporting ore materials was a major drawback to the Federal uranium procurement program. By 1951, the importance of the Carrizo-Lukachukai deposits to the fledgling Federal uranium procurement effort was recognized. The uranium-exploration areas were at best served by poorly constructed dirt-surfaced roads that could become impassable in wet periods. New mining areas typically had no roads or were served only by primitive jeep trails. Under AEC’s authority to justify construction of roads into uranium mining areas and with the cooperation of the Bureau of Public Roads and various state agencies, the agency began in 1951 a region-wide project to investigate and recommend improvements on the most urgently needed routes. Under this project, the former Indian Service road from US Highway 666 in New Mexico through Red Rock Trading Post, Arizona, to the camp at Cove, Arizona, was improved to an all-weather haulage road. The grading of the old dirt road was improved and gravel was applied. From the Red Rock Trading Post, the former wagon road northward to Oak Springs, which is near the East Reservation leases, was also improved under the AEC program.¹⁷

Navajo Uranium Company continued to mine in the Lukachukais into early 1952. It was acquired in May 1952 by Kerr-McGee Oil Industries, Inc.,¹⁸ which also acquired the 75 percent interest in the Navajo mining leases. Kerr-McGee also acquired the Shiprock ore-buying station that was leased to AEC by Navajo Uranium. The firm also signed operating agreements with several other Navajos who held individual leases in the Lukachukais. Kerr-McGee opened new mines and soon increased uranium production from its properties. In 1953, Kerr-McGee formed the Navajo Uranium Division that included the Shiprock buying station and its mining operations in the Lukachukai Mountains.

In August 1953, Kerr-McGee Oil Industries, Inc., signed a contract with the AEC for a uranium processing mill to be built at Shiprock near the AEC ore-buying station. Construction began in the fall of 1953 and the mill started up in November 1954. When the mill was started up, the firm also assumed operation of the AEC buying station. Kerr-McGee eventually purchased from the AEC a total of 186,035 tons of ore averaging 0.31 percent U₃O₈ and 1.02 percent V₂O₅, including the AEC-purchased ore stockpiled at the Shiprock buying station. The U₃O₈ recovered from this ore in the Shiprock mill was sold to the AEC under the agency’s uranium concentrate procurement contracts.¹⁹

In March 1963, Vanadium Corporation of America (VCA) purchased the Shiprock mill and the Lukachukai mines of Kerr-McGee and continued its operation until August 1967, when VCA was merged into Foote Mineral Company. Foote then operated the mill (then known as the Navajo mill) until it was closed in May 1968.²⁰

Originally designed as a 300 tons-per-day (TPD) throughput-capacity mill, the Shiprock mill’s capacity was later raised to 500 TPD by addition of new equipment and process modifications. The ore was crushed and ground and then leached in a two-stage bath of hot sulfuric acid plus oxidant to solubilize uranium and vanadium. Pregnant solution was recovered from leached solids by countercurrent washing in classifiers and thickeners, then treated by separate solvent extraction circuits to first recover uranium and then vanadium. Precipitation of uranium from the strip solution was accomplished by increasing the acidity and boiling to expel the carbonate, followed by neutralization with magnesia.²¹ Over the mill’s operating life, a total of about 1.53 million tons²² of ore was processed, and some 7.42 million pounds U₃O₈ and 20.46 million pounds V₂O₅ in concentrate were produced. Uranium recovery averaged about 94 percent and vanadium about 58 percent.²³ Nearly all (99.98 percent) of the uranium concentrate product was purchased by the AEC. The vanadium concentrate was sold into the commercial market.

Over its history, the mill treated raw uranium ore, dried processed slime concentrates, chemical precipitates, bulk uranium-vanadium precipitates from heap-leach piles, stockpiled vanadium-bearing sand tailings, purchased vanadium liquor, and cleanup materials from the Durango and Naturita mills after they were shut down. Contractor-controlled mines in the Navajo Nation and other widely located areas of the Colorado Plateau region contributed slightly more than one-half of the uranium ore milled at the Shiprock mill. About one-third of the ore was purchased by the mill’s operators from independent mining firms, and the remainder came from contractor-controlled mines and through purchases the uranium ore that had been stockpiled at AEC buying stations.²⁴

When Shiprock milling operations ended in 1968, the mill, offices and other buildings, a raffinate pond area, and about 1.7 million tons of mill tailings contained in two adjacent piles near the San Juan River remained at the 230-acre mill site. The larger pile (46 acres) was not stabilized. The smaller pile (26 acres), stabilized with 0.5 to2.0 feet of pit-run soil and gravel, eventually developed a natural vegetative cover. Earthen dikes were constructed across the toe of the piles to prevent the spreading of tailings toward the San Juan River.

Control of the former mill site reverted to the Navajo Nation in 1973, when the Foote Mineral Company’s lease for the land expired. The Navajo Engineering Construction Authority (NECA) then used about 40 acres of the site, including mill offices and buildings, as a training facility to instruct students to operate and maintain earthmoving heavy equipment. The larger tailings pile was used as a practice ground for earthmoving equipment.²⁵ In January 1975, NECA began decontamination of the former mill site under an Environmental Protection Agency plan in order to reduce the radiological exposure to NECA employees and trainees. Tailings material that had been moved by wind action was loaded and returned to the piles. NECA removed contaminated material from the mill site and ore-storage areas and placed it in the larger tailings pile. That pile was then covered with earthen material taken from the site during the decontamination activities. A broadcast-type irrigation system was installed on the relatively flat top of the larger pile in an attempt to reduce further wind erosion of the tailings material.

UMTRA Surface Remediation:   The Shiprock former mill site is situated on an elevated river terrace adjacent to a steep escarpment that slopes down to the flood plain of the San Juan River. At the site, natural surface and local groundwater contamination resulted from the milling of uranium-vanadium ores. In 1983, the U.S. Department of Energy (DOE) and the Navajo Nation entered an agreement for cleanup of the Shiprock mill site.²⁶ At the start of the cleanup project, radioactively contaminated materials that remained at the site included uranium and vanadium mill tailings; radium, thorium, and uranium residues mixed locally with soil; a pond area that at one time stored spent process liquids from milling of ore; a few buildings; and construction debris. In the cleanup, all radioactively contaminated materials at the Shiprock former mill site were identified and consolidating into one pile. Contaminated materials from 15 vicinity properties (residences, commercial buildings, and open land areas) were also excavated and placed in the pile. The pile was then stabilized in place as the permanent disposal cell structure. The project was begun in October 1984 and completed in October 1986. In May 1991, DOE received concurrence from the U.S. Nuclear Regulatory Commission (NRC) that cleanup of the former mill site conformed with pertinent Federal standards.

Disposal Structure:   About 2.8 million cubic yards of residual radioactive materials (RRM) from the site and the vicinity properties were entombed in a 77-acre on-site disposal cell. The cell’s cover is a three-layer, engineered structure 8.5 feet thick. The low-permeability infiltration/radon barrier, placed directly atop contaminated material in the cell, consists of a compacted sandy, silty soil layer that is 6.4-feet thick on the top slopes and 7 feet-thick on the side slopes of the encapsulated RRM. The barrier is covered by a 6-inch thick bedding layer of granular rock material designed to promote rapid runoff of precipitation and to prevent percolation through the cell. A system of rock-lined drainage ditches collects surface-water runoff and diverts it away from the completed cell structure.

Responsibility for Remediation:   U.S. Department of Energy, 100 percent.

Stewardship:  The U.S. Department of Energy (DOE) is responsible for long-term stewardship tasks at the former Shiprock former mill site, including groundwater monitoring. The DOE maintains data relating to site characterization, design parameters for site restoration, and current and historical site monitoring data for the remediated site. In 1996, NRC issued a general license to the Shiprock Site for custody and long-term care of residual radioactive material in the disposal cell.

Groundwater Program:   A plume of contaminated groundwater is present in the shallow alluvial material and weathered and fractured bedrock beneath the former mill site. The plume contains about 1.2 million cubic yards of groundwater contaminated with cadmium, nitrate, radium, selenium, uranium, and net gross alpha. It extends beyond the former mill site boundaries and covers an irregularly shaped area about 1.6 miles long by about 0.75 miles wide at its broadest dimensions.²⁷ The DOE has proposed a combination of active remediation on the river terrace area, to be completed in 2012, and natural flushing in the broader flood plain area to clean up the contaminated groundwater plume. Natural flushing action of the groundwater is anticipated to clean the flood plain aquifer within a period of 75 years, after which the DOE will continue monitoring the aquifer in perpetuity to demonstrate the integrity of the disposal cell and its compliance with remediation standards.²⁸

(We would like to acknowledge the generous contributions by the following persons to the preparation of this article. William L. Chenoweth, Grand Junction, Colorado, Consulting Geologist and Research Associate, New Mexico Bureau of Mines and Mineral Resources, provided detailed information on about early vanadium-uranium mining activities and Federal Government procurement programs and reviewed the final draft for historical and technical content. Craig Goodknight, Geologist, S.M. Stoller Corporation, Grand Junction Projects Office, Grand Junction, Colorado, also reviewed the final draft and provided information relating to the environmental remediation project at the former mill site.)