February 22, 2012


Chamois Andersen
Communications & Public Outreach
(307) 766-2286 x231

Successful Uranium Exploration Model in the Shirley Basin Used Worldwide Today

Memoir 6 In the early 1960s, when uranium mining in Wyoming represented a large portion of the state’s extractive energy industry, geologists discovered what has become an industry standard used worldwide for locating sandstone-type uranium ore deposits. The “roll-front” model, which represents the underground shape and orientation of uranium ore deposits within sandstone, was discovered as an effective way to pinpoint where the best ore was located.

The Wyoming State Geological Survey (WSGS) has published a report entitled “The Shirley Basin Mine and the Development of the Roll-Front Model of Uranium Ore Deposits: A Historical Perspective” that details the geologic mapping program when the underground mine was in operation in the 1960s, and documents the successful use of the roll-front model for identifying uranium ore locations and trends.

“The roll-front model was a major breakthrough in knowledge and for understanding the nature of uranium deposits, particularly in sandstone deposits,” said Robert Gregory, a WSGS geologist and co-author of the report. “Mapping efforts led to the discovery of the roll front, which was then successfully applied to exploration and development drilling, as well as to ore projections ahead of mine workings and to reserve estimates in the mine,” he said.

The publication includes photos, maps, and graphics of the underground cross sections that illustrate where the roll fronts were located, revealing the best ore. “Many miners have never seen what these look like in place because nowadays the majority of uranium mining is done from the surface,” Gregory said. The geologists at the Shirley Basin Mine, while working underground, took the opportunity to photograph the various cross section views to illustrate mineralized and non-mineralized features, he said.

The process began with exploration drill holes for mapping the location of the sands that were considered the best suited for uranium deposits to occur. Considered as "legacy data," today many of these holes are being redrilled to link new measurements with the old uranium ore projections. The industry also uses gamma-ray logging and a device called a scintillometer to measure radiation levels to determine the amount of uranium at the various drill hole sites. Ultimately the legacy data and other studies will be used to determine where to reopen uranium production efforts in the Shirley Basin.

Uranium was discovered in 1955 at what then became the Shirley Basin Mine, in Carbon County. The Utah Construction and Mining Company began production in 1960 from underground and eventually in open-pit mines. Mining by in-situ leaching began in the early 1960s, which was the first in-situ leach mining of uranium in the United States.

Shirley Basin Mine geologist R. V. Bailey said the mine provided an excellent opportunity to study in detail the uranium deposits that occur in the Eocene Wind River Formation. “Our mapping efforts led to the discovery that ore existed at discreet and well-defined contacts between oxidized sands, which were called ‘altered’ and reduced or ‘unaltered’ sands,” said Bailey, a world-renowned geologist on mining, and co-author of the report that he originally developed in the 1960s.

The term “roll front” or geochemical interface came to be used to describe the “C” shaped terminal ends of the bodies of altered sands, as detailed in the report. The roll-front theory was demonstrated by the successful discovery and delineation of uranium ore in locations where the roll fronts occurred, Bailey said.

“Our objective was to illustrate the nature and configuration of the roll fronts,” Bailey said. Maps and cross sections were created to illustrate ore body configuration and major geological features observed during the course of the mapping program.

These maps and cross sections are also featured on a CD included with the report, resources that can be used to learn how “roll front location” can be identified and projected within the two distinct sand types, known as Sage Sand and Turtle Sand in the Shirley Basin. The paper also includes a brief review of mining techniques and a discussion on the evolution of uranium mining mapping techniques.

Uranium is an accessory element found in minerals like zircon, tourmaline, and feldspar, all of which are common minerals in granitic and other igneous rocks. Uranium is concentrated in bodies of ore. Ground water migrating through fractures and pore spaces in the source rocks picks up uranium and carries it away in solution. Later the uranium is redeposited in porous sandstone layers where mining can occur.

Wyoming is the leading U.S. producer of uranium at 1.75 million pounds of yellowcake per year (Smith Ranch-Highland and Willow Creek). Wyoming's uranium energy resource is exported to other markets and used for electrical generation.

The Shirley Basin Mine and the Development of the Roll-Front Model of Uranium Ore Deposits: A Historical Perspective is $15 and available to order via the WSGS Online Store at http://sales.wsgs.wyo.gov/catalog/product_info.php?products_id=3399, or by calling (307) 766-2286 ext. 228.


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