by Petr Hykš
Will the Wyoming Uranium Province Rival Canadas Athabasca or Australias Northern Territories?
Geology is 90 percent terminology and 10 percent science, laughed Ray E. Harris, one of Wyomings leading geological theoreticians, having been with the Wyoming Geological Survey since 1982. He died on March 7th. Two weeks earlier, we met with and interviewed Mr. Harris. Everyone we met in Wyoming, and who was interested in uranium mining, had, at one time or another, passed through his office, which was adjacent to the University of Wyoming in Laramie.
Ray Harris traveled the world, investigating and studying uranium deposits. He was well versed on the geology of every significant uranium deposit on earth and was also involved in the exploration, development and mining of uranium. In a Geological Survey of Wyoming Public Information Circular, published in 1986, Ray Harris presented a unique, and possibly controversial, thesis, The genesis of uranium deposits in Athabasca, Canada and Northern Australia Wyoming exploration significance. In his introduction, Harris wrote:
Wyoming has some uranium occurrences in geological environments similar to those of Australia and the Athabasca Basin, and appears to have the potential for a uranium deposit similar in magnitude to those deposits.
Harris acknowledged in his paper, Reported reserves for these two regions are 436,360,000 tons of U3O8, or one quarter to one third of the noncommunist worlds proven reserves. At the same time, the total 1982 U.S. uranium reserves at /pound stood at 203,000 tons. Wyomings piece of that mineable pie stood at 32,700 tons. His was a bold statement, open to debate it not outright dispute and dismissal.
Perhaps there may be truth in Harris claim. In 1981, E.S. Cheney published an article in American Scientist, entitled The Hunt for Giant Uranium Deposits, where he explained a giant deposit would contain more than 100 million pounds of recoverable U3O8. But can the parts amount to more than a single giant uranium deposit? William Boberg in his 1981 article, Some Speculations on the Development of Central Wyoming as a Uranium Province, published in the Wyoming Geological Association Guidebook, wrote, The Wyoming Uranium Province consists of several uranium districts (Gas Hills, Shirley Basin, Crooks Gap, Red Desert, Powder River Basin and Black Hills) each of which is made up of a few to numerous individual uranium deposits. In Part 2 of this Wyoming Series, uranium savvy Senator Robert Peck speculated there were 50 to 60 million pounds of recoverable uranium in the Gas Hills proven by previous drilling.
Warren Finch in U.S. Geological Survey Bulletin #2141 (1996, US Government Printing Office, Washington), wrote in his paper, entitled Uranium Provinces of North America Their Definition, Distribution and Models, that provinces are identified by the distribution of major uranium clusters, generally of a size of 500 tons and more U3O8 Since January 1970, when S.H.U. Bowie described how to go about defining uranium provinces and searching for major uranium deposits in a paper he presented tot the International Atomic Energy Agency in Vienna, geologists have been eager to compare similar geological settings between geographically diverse uranium deposits, and more accurately define uranium provinces.
Ray Harris wrote in his previously quoted article, There are no producing ore bodies in the United States similar to those of the Athabasca Basin and Northern Australia, but two deposits, not currently being mined, may be of similar genesis. These are the deposits near Chatham, Pittsylvania County, Virginia, and at Copper Mountain, Fremont County, Wyoming. (Editors Note: According to the Strathmore Minerals website, the companys Copper Mountain property, previously drilled by Anaconda Uranium Corp through 1997, lists an historical contained resource of more than 38 million pounds of U3O8. Strathmore has not done sufficient work to verify this resource estimate.)
Harris explained that a high-grade uranium deposit in the United States, of geological similarity to an Athabasca Basin grade deposit, could not be quickly ruled out. He cited the Chatham, Virginia uranium deposit, grading four pounds per ton of ore, and which he believed might contain 30 million pounds of uranium oxide. He wrote, the setting is similar to non-conformity uranium deposits on first glance, it seems to have formed similarly to the Athabasca and Northern Australian deposits. Unfortunately, the Virginia legislature voted to ban uranium mining, which offers a temporary setback on this deposit. That is not the case in mining-friendly Wyoming, where in Part One of this series, the state governor is urged companies to bring uranium projects and money to his state.
Wyomings Geology Potential for U.S. Utilities
It is known that Wyoming has multiple roll-front uranium deposits in its sandstones. A pro-mining state, prolific numbers of roll-front uranium deposits, and a rising spot uranium price in a uranium bull market all combine to make Wyoming the U.S. center for in situ leach mining (ISL), also known as solution mining. However, as Ray Harris had suggested during our interview there may be larger uranium source, possibly one that may be competitive with Athabasca Basin or Northern Australia. It is a premise he had argued in the 1980s, in the previously quote work, and again in 1993, Harris paper, entitled Geological classification and origin of radioactive mineralization in Wyoming.
In his 1986 work, Harris concluded, Given the impressive length of exposure, the relatively shallow subcrop depths of favorable nonconformities in Wyoming, and the great amounts of uranium available for mobilization, a nonconformity-related uranium deposit should exist somewhere in Wyoming. One possibility, as Harris suggested, may be in Fremont Countys Copper Mountain area. Harris wrote that at the Copper Mountain area, Uranium occurs in fractured and faulted Precambrian rocks and in the nonconformably overlying Eocene Tepee Trail Formation. The uranium occurrence is subeconomic but of promising grade and size. He added, The uranium is spatially related to fractures and subsidiary faults associated with the Laramide North Canning fault. Rocky Mountain Energy Company has conducted detailed drilling on the North Canning deposit.
Harris explained that mineralization occurs in the Precambrian granite and enclosed metasediments. The mineralization is said to be primarily low-temperature pitchblende and coffinite. Harris compared the North Canning deposit to nonconformity- related uranium deposits. He wrote, It is likely that the deposit formed by processes similar to those that operated in the Athabasca and Northern Australian regions. We checked with David Miller of Strathmore Minerals (TSX: STM; Other OTC: STHJF) about their Copper Mountain holdings. He responded by email, We own all the federal minerals in the area that covered uranium mineralization: about 75 percent of the gross uranium resources. The Canning Deposit is owned about 60 percent by us and 40 percent by Neutron. Strathmore Minerals has around 100 mining claims in the area.
The source of Wyomings roll-front uranium deposits are open to debate and have yet to be clarified. In 1981, William Boberg wrote, The major deposits of Wyoming occur in the Lower Cretaceous Inyan Kara Group of the Black Hills, in the Paleocene Fort Union Formation in the Powder River Basin, in correlative Eocene sandstones in all of the major uranium districts. Warren Finch later described Wyomings roll-fronts, in his previously quoted work, The predominant type of uranium deposit is the roll-front sandstone deposit in Tertiary continental fluvial basis developed between uplifts. These ore deposits were formed by oxidizing uranium-bearing ground waters that entered the host sandstone from the edges of the basins. Two possible sources of the uranium were (1) uraniferous Precambrian granite that provided sediment for the host sandstone and (2) overlying Oligocene volcanic ash sediments. Ray Harris appeared to lean more toward the former. William Boberg has argued more toward the latter explanation for a uranium source.
Boberg wrote, It appears that currently available evidence is in support of a hypothesis calling for combined sources of Precambrian granites and volcanic ash falls which produce a unique, uranium-rich, ore-forming liquid that invades very porous and permeable young sediments to form large altered tongues and discrete deposits in a geologically short period of mineralization. It has been calculated that a typical altered tongue would take 700,000 years to form; a typical roll-front uranium deposit could be formed over 50,000 years.
Boberg speculated it was the numerous and extensive uranium-enriched ash falls from Middle Eocene volcanism, which was responsible for these deposits. He wrote, Of greatest importance is the fact that a series of volcanic events from a variety of extrusive centers began about 50 million years ago generating tremendous volumes of ash, which was distributed across Wyoming and adjacent states for greater than a 40-million year span of time.
His explanation of the volcanic ash provides a valuable insight into how Wyomings uranium deposits were formed:
The volcanic ash, when flushed by the first rainfall, produced a unique fluid, which was acidic and charged with ions. The chemical reaction of the buffering on this fluid on contact with the Precambrian granites, the ash and other rocks brought the pH back to approximately neutral but leached additional uranium from the granites and probably the ash. The high rainfall and climate assured a steady supply of dissolved oxygen to the fluid resulting in the formation of a unique, oxidizing, uranium-enriched fluid, which entered the unconsolidated, reduced sediments oxidizing them and carrying the uranium to the eventual maximum extent of oxidation.
Boberg explained the development of the roll-fronts, writing, Fluid flow through the very porous and permeable sediments would be relatively fast allowing for the development of large oxidized tongues with the young sediment as well as scattered uranium deposits at the redox (oxidized reduction) interface within approximately a million years. Deposits formed near the granitic highlands would be larger and of higher average grade because of the proximity to the dual source of granite and ash.
J.D. Loves uranium discovery in Tertiary sandstones, in 1951, was a near-surface roll-front type of redox deposit. A roll-front deposit follows a sinuous linear trend, often C-shaped. Colorado and Utah miners began calling the cross-sectional configuration a roll in the early 1940s. Roll-fronts occur in sandstones, bordered above and below by less permeable shales. In Wyoming, the rolls are bordered by altered and unaltered sandstone. It is generally concave from altered ground and convex into unaltered ground. Harris idealized roll-front uranium deposit would have uranium concentrations decrease abruptly away from the concave boundary, and concentrations gradually decrease away from the convex boundary in reduced rock.
Uranium is not always present everywhere along a roll front. It may be unevenly distributed and there are often other elements, such as vanadium, selenium, molybdenum, copper, silver, lead and zinc. Geologists look for where coarse-grained sandstones grade into finer grained or clay-bearing equivalents as indicators for uranium ore. As uranium geologists know with roll-front deposits, it may be mined as long as it is below the water table. Once deposits are brought above the water table, the uranium concentration can be eroded and severely modified.
It is not the roll-front uranium deposits, which interested Harris, but the tabular redox uranium occurrences found in many parts of Wyoming. He found those most prominently in the Cretaceous Inyan Kara Group in the Black Hills. Harris explained, The uranium mines in New Mexico and many other parts of the Colorado Plateau are also tabular deposits. The tabular bodies, Harris noted, describe their irregular tabular form, and are found parallel to bedding, dissimilar to roll-front mineralization, which crosses bedding. Harris believed some of the tabular bodies in Tertiary rocks were the limbs and detached limbs of roll fronts left in less permeable rocks at fluvial channel margins. He also said that tabular bodies could be preserved in oxidized rock due to high concentrations of other rock, such as coal or pyrite.
In any event, Harris agreed with other geologists that Wyoming is a uranium province with uranium occurring in nearly all major time divisions in the state. He concluded, Uranium was available for mobilization during every major weathering period related to the nonconformities. In our final minutes together, he was convinced that many of the uranium development companies should sink more funds into exploration and find the elephant uranium deposits, which he pointed out in three different parts of uranium. To his way of thinking, that was more exciting that the simple ISL extraction of uranium from previously drilled areas. As with others interviewed, few of those areas will hold surprises, but instead offer the steady, cash-producing uranium extraction that help develop budding companies. Thats what U.S. utilities, and utilities from other countries, are eagerly seeking right now. Wyoming uranium could fuel many of the U.S. nuclear reactors as more companies commence ISL uranium operations.
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