Characterization Of The Uranium Occurrence In Pre- And Post-Leach Ore Samples From Sandstone Deposits In Texas And Wyoming
Authors: Wood Susan 
Published: December 2007

Uranium ore samples from open-pit mines in the Shirley Basin of Wyoming and in Texas are currently being utilized to simulate in situ leaching conditions in laboratory column-leach tests at the W R and D Center. Evaluation of their uranium mineralogies was achieved through analysis of mounted and polished specimens with the electron beam microanalyzer and scanning electron microscope, after first delineating alpha-active regions by radioluxography. The two ores exhibited both different uranium distributions and mineralogies, but these characteristics were similar for as-received and processed material from each site. No uranium was detected in acid-leached Wyoming ore.

In-situ leaching has become a very attractive method for recovering uranium from secondary arkosic sandstone deposits because of both the relatively low capital costs involved and the amenability of such ore bodies co this leaching technique. To improve and further the understanding of the leaching of uranium by this method, laboratory simulation, utilizing column-leaching apparatus, is currently being exploited at the W R and D Center. Although the ores used in these experiments originated in sandstone deposits in Texas and Wyoming, they were obtained from open-pit sites rather than the deeper mineralized roll-fronts normally subjected to insitu mining. Furthermore, the ore was processed through drying, blending and column-packing operations before being leached. Hence, it is not known, for example, if the uranium distribution in the column truly represents that in the original ore body or if the mineralogies of the open-pit ores are typical of those observed in deposits located at greater depths.

This paper describes the results of a characterization study designed to answer these types of questions. in addition to delineating the uranium mineralogy of both the virgin Texas and Wyoming ores, the uranium distributions in as-received and processed ores were evaluated using a radioluxograph processed ores were evaluated using a radioluxograph technique. The alpha-maps thus obtained were also utilized to identify U-rich zones for subsequent examination by use of electron beam microanalysis (EBMA) and scanning electron (SEM) for the delineation of uranium mineralogy. Wyoming ore subjected a sulfuric acid leach was also examined. The low uranium content of the ores prohibits evaluation of uranium mineralogies by petrography and necessitates the use of more sophisticated analytical techniques.

EXPERIMENTAL PROCEDURES

A. Selection and Packaging of Ore

Ore samples were obtained from the Lucky Mc mine in the Shirley Basin of Wyoming and the Conquista Project near Falls City, Texas. Material for the Project near Falls City, Texas. Material for the pre-leach characterization study was selected from pre-leach characterization study was selected from currently-mined arms in the open-pit to be within a grade of 0.05–0.12 Wt% U O (as determined by on-site y-logging techniques). Some of the ore, used only for characterization purposes, was sealed under nitrogen at the mine site, while a larger, bulk sample was merely packaged in a polyethylene bag. This latter material was subsequently dried and processed for column-leach studies.

B. Preparation of Mounted Specimens

In general, both the Texas and Wyoming ores are poorly consolidated, which necessitated packing he poorly consolidated, which necessitated packing he as-received material in small cardboard boxes for mounting purposes. Because the Lucks Mc (Wyoming) ore also contained pieces (with a maximum dimension of 4 cm) which retained their competency, several of these were also selected for mounting. Samples were oven-dried for 24 hrs. at 50 deg. C before vacuum impregnating with Spurr, a low viscosity resin cured by baking at 50 deg. C for approximately 16 hrs. Specimens were subsequently ground through 600 grit SiC and polished to 0.5 pm diamond using water as the vehicle. polished to 0.5 pm diamond using water as the vehicle.