Jon Spencer Presents:
Federal lands and mineral resources: Colorado Plateau uranium deposits and the Sonoran Desert Heritage
Many times during Arizona’s 100-year history, federal lands have been reclassified in ways that prevent further mineral exploration and mining. This AGS talk will outline mining and mineral-resource issues associated with a recent federal-land reclassification intended to stop uranium mining in three areas in northern Arizona, and a reclassification that is under consideration that would prevent mining in parts of western Arizona.
A 2012 decision by former U.S. Interior Secretary Ken Salazar to remove a million acres of federal land in northern Arizona from new mining claims for 20 years was based significantly on concerns about contamination of Colorado River water by runoff from areas of uranium mining (none of this land is within the Grand Canyon, which is already protected). More than a thousand circular features on the Colorado Plateau in northwestern Arizona have been mapped as breccia pipes or possible breccia pipes. Some breccia pipes are known to contain economic uranium deposits. Total current and historic production is approaching 15,000 tons of U3O8 from about ten pipes. The deposits are typically small, deep, dry, and high grade. The deposits are mined underground and the ore is trucked to Utah for milling. Post-mining restoration involves filling the mine shafts with rubble and restoring the land to its approximate original form. Concerns about contamination of the Colorado River are overblown. Trucks hauling 30 tons of 1% uranium ore (0.3 tons U3O8), even if they poured their entire load directly into the river and all the ore dissolved, would add trivially to the natural dissolved-uranium river load of approximately 60 tons per year.
A proposal to withdraw ~750,000 acres (~1170 square miles) of western Arizona federal land from drilling and mining, as currently envisioned in the “Sonoran Desert Heritage” plan, is being prepared for consideration by Congress without evaluation of mineral-resource potential. (The 2001 creation of the 496,400-acre Sonoran Desert National Monument under the Antiquities Act was done without Congressional consent and without an assessment of mineral-resource potential, as was the 2000 creation of Ironwood Forest National Monument which includes 128,700 acres of federal land.) The geology of almost all of the land within the Sonoran Desert Heritage proposal area was mapped by geologists at the Arizona Geological Survey during the past 30 years. An evaluation of mineral resource potential based on mapping and related studies, as well as past mining activity, indicates that the Harquahala – Big Horn Mountains area has high potential for future base and precious metal mineralization, high quality aggregates, and manganese.
BIOGRAPHY- Jon Spencer
Jon Spencer received his Ph.D. in Geology from M.I.T. in 1981. He has been at the Arizona Geological Survey in Tucson for the past 30 years and has been Senior Geologist for the past 13 years. His research has focused on geologic mapping in the Basin and Range province, extensional tectonics, structural aspects of mineralization, evolution of the Colorado River, and a variety of other topics that reflect diverse issues addressed by a small State Geological Survey in a big and geologically complex state.