Uranium Mining in Arizona—High Grade and Safe

Dr. Karen J. Wenrich*, Geologist
CrystalUnlimited@aol.com

The uranium industry has made a dramatic turn-around in the past two years that even the most optimistic economist was not willing to predict during the uranium downswing of the 1990s. Uranium reached a 30-year low in February 2001 of $6.50/lb. By the end of February 2006 it had soared to $38.50/pound. This nearly 600% increase in the uranium spot price within 4 years dwarfed the increase in gold price that has barely mustered a 100% increase. The initial slow rise from $6.50 in February 2001 to $10.75 in April 2003 was primarily driven by the decrease in the value of the dollar. Since then several factors have contributed to the soaring price: (1) The awakening of many to the simple fact that uranium supply has not met demand for several years and that the world’s stockpiles are being drawn down, (2) How sharply this fragile supply can be impacted by disasters at the world’s major uranium production facilities, such as a) the flooding of the McArthur River Mine in the spring of 2003, b) fires at Olympic Dam, c) the potential that Rossing, with an annual capacity of 4000 tones uranium might close by 2007, (3) the withdrawal of Tenex from the HEU (highly enriched uranium) feed agreement, and (4) the announcement by the Chinese of their intent to build 30 new nuclear reactors.

Figure 1. Graph of uranium price in dollars per pound of U3O8 from January 2003 to November 2007. Data from The Ux Consulting Co, LLC. Website: www.uxc.com.

The race for military nuclear supremacy during and following World War II resulted in the rapid development of a worldwide uranium production industry. The adage, ‘haste makes waste’, created this legacy. The frantic pursuit of these early military programs created environmental hazards and health risks throughout the world that left a multi-billion dollar Cold War uranium production legacy. Lessons learned from this legacy have had a profound influence on modern uranium production, thereby minimizing long-term environmental impact and health risks during uranium exploration, mining and milling. The industry has come a long way from the time when tailings were left unprotected and allowed to be transported by water and wind into nearby streams and rivers. The mining industry has since learned to embrace the philosophy that it is more effective to prevent pollution than to clean it up.

This soaring uranium price has brought about a flurry of mineral exploration activity that has not been witnessed in the US since the 1849 gold rush. Uranium economics have a significant impact on the state of Arizona. The highest-grade uranium deposits in the United States (average grade close to 1%) occur in a breccia pipe environment in northwestern Arizona. In fact, these deposits are higher grade than most uranium deposits elsewhere in the world, with the exception of the Canadian deposits (that grade up to 20% uranium). However, the word uranium brings fear to many who live in Arizona because of the uranium legacy that was left behind on the Colorado Plateau over 50 years ago. Yet, these breccia pipe mines are different—the uranium is deep beneath the plateau surface, the mines are underground, and nothing extraneous is left on the surface after mine closure. The breccia pipe deposits were so successfully mined and reclaimed in the 1980s and early 1990s that few people even realize that there were eight producing mines in the Arizona Strip near the end of the 20^th century. Today even uranium geologists can no longer find the location of the three former producing uranium mines that are located in Hack Canyon (figs. 6-7).

click image to enlarge

Figure 2. The Bat Cave Breccia Pipe is eroded and well-exposed along the canyon walls. It is about 200 feet in diameter and extends over 600 feet in elevation before its top was truncated by erosion. The pipe formed by solution collapse of overlying sandstone, shale and limestone into a cavern within the Redwall Limestone. This collapse process left a cylindrical column of broken rock above the cavern. Photo by Karen Wenrich.

So, what is a breccia pipe? A breccia is a coarse-grained rock composed of large, angular, broken rock fragments that are cemented together in a finer grained matrix (fig. 3). Breccia is an Italian word for broken rock. A breccia pipe is a vertical pipe-like column of broken rock (fig. 2). Because of the coarse-grained and initially porous nature of these breccia pipes, mineralizing fluids that passed through some pipes deposited a large suite of metallic minerals. When geologists think of a breccia pipe they immediately think of volcanic rock, such as a diatreme. However, there are no volcanic rocks associated with these geologic features. Many of the 500 ft-high sheer walls of the Grand Canyon are formed by the massive Mississippian Redwall Limestone, which is one of the most extensive karst-forming limestones in the U.S. (Wenrich and Sutphin, 1994). The Redwall Limestone karst development was so extensive as to permit brecciation of overlying sandstones, shales and limestones into thousands of pipe-shaped columns of breccia. This occurred when sedimentary strata collapsed into solution caverns in the underlying Mississippian Redwall Limestone. Upward stoping through the upper Paleozoic and lower Mesozoic strata, involving units as high in the section as the Triassic Chinle Formation, produced vertical, rubble-filled, pipe-like structures (fig. 2). A typical pipe is approximately 300 ft in diameter and extends upward as much as 3000 ft.(Wenrich and Sutphin, 1989).

click image to enlarge	Figure 3. Breccia. Breccia is an Italian word for broken rock. Note the vuggy nature of the rock, which permits pore space for mineral-bearing fluids to create an orebody. Within the breccia the broken pieces are multi compositional. Photo by Karen Wenrich.

A significant number of the pipes contain U-mineralized rock as well as anomalous concentrations of Ag, Co, Cu, Mo, Ni, Pb, V, and Zn. Mapping studies on the Hualapai Indian Reservation show that approximately 8% of the pipes show some exposed mineralized rock, either as recognizable copper-bearing minerals, or anomalous gamma radiation (Wenrich and others, 1996). Uraninite is the primary ore mineral for the breccia pipes (fig. 4), but colorful secondary minerals form of uranium, copper, and other metals associated with the uraninite, when the orebodies have been exposed to oxidation by erosion in the canyons (fig. 5) and high on the cliffs.

Breccia pipes extend across most of the Colorado Plateau in northwestern Arizona and into the Basin and Range Province wherever the Redwall Limestone and overlying sandstones and shales have been preserved (Wenrich and others, 1989). The potential for additional economic uranium mineralized breccia pipes is enormous and is greatest beneath the flat plateaus where erosion and oxidation of the ore have been minimized. It is only on the Colorado Plateau, with its history of tectonic stability, that the uraninite has been preserved. Along the edges of the plateau and in the canyons, the ore-bearing minerals are usually oxidized to colorful secondary minerals.

click image to enlarge</a>	Figure 4. Uraninite, UO2, is the primary ore mineral for the breccia pipes. Photo by Lou Perloff.

Mining activity in the Grand Canyon breccia pipes began during the nineteenth century, although at that time production was primarily for copper with minor production of silver, lead, and zinc. It was not until 1951 that uranium was first recognized in the breccia pipes. Despite periods of depressed uranium prices, the breccia pipes commanded considerable exploration activity in the 1980’s because of the high-grade nature of their uranium ore. During the period 1956-69, the Orphan Mine produced 4.26 million lb of U₃O₈ with an average grade of 0.42% U₃O₈ (Chenoweth, 1986). The Orphan Mine is located within Grand Canyon National Park where the head frame projects above Powell Point commemorating our US heritage through mining history. This history includes one of Teddy Roosevelt’s Rough Riders packing his burro down the trails of the Grand Canyon to his Orphan mine where he dug for copper and silver during the end of the 19th century. In addition to uranium, 6.68 million lb of copper, 107 oz of silver, and 3400 lb of V2O5 (vanadium oxide) were recovered from the ore (Chenoweth, 1986). Between 1980 and 1988 four breccia pipes (Pigeon, Hack 1, Hack 2, Hack 3) were mined for uranium in northern Arizona with grades averaging 0.65% U₃O₈ and total production of 13 million lbs of U₃O₈ (Mathisen, 1987). During the end of the period of breccia pipe mining by Energy Fuels Nuclear, they had refined their mining methods and the average grade of ore production approached 1% (I.W. Mathisen, oral commun., 1990). Although these uranium grades are dwarfed by those of the Athabasca Basin unconformity deposits in Canada, it is significant that (1) the breccia pipe mining costs are significantly less for the Arizona deposits, and (2) these ore grades of 0.4-1% are as high or higher than any other global uranium-deposit type.

The uranium production industry is well aware that they are faced with the environmental legacy of early uranium production. The uranium industry has undergone a significant evolution in the level of environmental understanding and management practices over the past 30 years. Experience has shown that there has been, and continues to be, ongoing development of enhanced environmental management practices in order to the meet the call from the public and the regulatory agencies for long-term environmental protection, and socio-economic benefits sharing with communities adjacent to the operations. Failure to incorporate best environmental practices in initial mining and milling plans can lead to such uranium legacies as we have witnessed in the past. The nuclear industry knows they cannot afford any more environment-damaging legacies.

click image to enlarge	Figure 5. Metatorbernite, Cu(UO2)2(PO4)2·8H2O. This uranium-copper-phosphate forms in oxidized zones above the breccia pipe orebody. Photo by Sugar White.

Mine safety for employees was strictly enforced in the breccia pipe mines of the Arizona Strip. During the previous mining operations of the 1980s and 1990s there were never any mine fatalities. Ventilation within the mines was excellent, so there was minimal exposure of miners to radon gas and its daughter products. Smoking was strictly prohibited within the mines. Radon in itself is not the problem with its 3.8-day half-life; the miner breathes it in and breathes it out. It is actually the radon alpha emitting progeny (lead and polonium) in the form of aerosols that are the nasty devils. They attach themselves to various areas of the respiratory system. Epidemiological studies have shown that the lung cancer risk to smokers is 10-20 times greater than “never” smokers at exposures to environmental levels of radon (such as 20-150 Bq/m³). The uranium industry now understands this increased risk that smoking miners have, and have adjusted their operations accordingly.

Higher grade deposits, such as the breccia pipes, produce more uranium with less environmental footprint. The environmental footprint duration for each mine is short as the life for each mine in the past was only 5-7 years. The water table is deep, well below the level of mining. There is no circulation of major northern Arizona aquifers within any of the mining levels so there is essentially little chance of any contamination to the ground water. Waste rock and tailings can always be, and have been, back-filled into the abandoned mine shafts and tunnels. Even the concrete from the former mining structures was broken up and backfilled into the old mine workings. There is no greater testimony to the mining and environmental success of these breccia pipe operations than a view of the previous operations in comparison to the current environment of the terrain (figs 6-9). This former mining company followed the modern mining philosophy: “It is more effective to prevent pollution during mining operations than to clean it up later”.

click image to enlarge	Figure 6. The Hack 1 Mine during mining (Hack Canyon, Arizona Strip). This was an underground mine that was in production during the 1980s. Note how little waste rock is sitting on the surface even during mining. As mining is closing the waste rock is backfilled into the drifts and stopes. Photo taken June, 1985 and courtesy of Pam Hill.

click image to enlarge	Figure 7. Hack 1 mine, after reclamation. During the reclamation the company also cleaned up debris that was left from early copper/uranium mining prior to 1950. Note that there are no longer any waste rock or tailings piled up on the surface, and in fact no evidence that mining ever occurred at this location. Photo taken October, 1989 and courtesy of Pam Hill.

click image to enlarge	Figure 8. Pigeon Mine during production, November, 1989. The mine was located on the north side of Snake Gulch. Photo courtesy of Pam Hill.

click image to enlarge	Figure 9. The Pigeon Mine after reclamation, October 5, 1993. Photo courtesy of Pam Hill.