Uranium deposits, types

Abstract strong commodity prices in the last few years have led to a remarkable renaissance of uranium exploration in Labrador, focused in a complex and geologically diverse region known as the Central Mineral Belt (CMB). Potentially economic epigenetic U deposits are mostly hosted by supracrustal rocks of Paleoproterozoic and Mesoproterozoic age, and are difficult to place in the traditional pantheon of uranium deposit types. Recent exploration work implies that structural controls are important in some examples, but the relationships between mineralization and deformation remain far from clear. Geochronological data imply at least three periods of uranium mineralization between 1900 and 1650 Ma. It seems likely that the Labrador CMB represents a region in which U (and other lithophile elements) were repeatedly and sequentially concentrated by hydrothermal processes. The current exploration boom lends impetus for systematic research studies that may ultimately lead to refined genetic models that may be applicable elsewhere. 

Unconformity-related deposits are found near principal unconformities. Examples include the ore bodies at Quff Lake, Key Lake, and Rabbit Lake in northern Saskatchewan, Canada, and in the Alligator Rivers area in northern Australia. Sandstone deposits are contained in rocks that were deposited under fluvial or marginal marine conditions. The host rocks nearly always contain pyrite and organic plant matter. The sediments are commonly associated with tuffs. Unoxidized deposits of this type consist of pitchblende and coffinite in arkasoic and quartzitic sandstones. Upon weathering, secondary minerals such as camotite, tuyamunite, and uranophane are formed. More information on these and other uranium deposit types is available (1). 

Table 2 Comparison of Proterozoic and Phanerozoic uranium deposit types...

Geochemical Nature and Types of Deposits. The cmst of the earth contains approximately 2—3 ppm uranium. AlkaHc igneous rock tends to be more uraniferous than basic and ferromagnesian igneous rocks (10). Elemental uranium oxidizes readily. The solubiHty and distribution of uranium in rocks and ore deposits depend primarily on valence state. The hexavalent uranium ion is highly soluble, the tetravalent ion relatively insoluble. Uraninite, the most common mineral in uranium deposits, contains the tetravalent ion (II). 

Intrusive Deposits. Deposits included in the intmsive deposit type are those associated with intmsive or anatectic rocks of different chemical composition, eg, alaskite, granite, monzonite, peralkaline syenite, carbonatite, and pegmatite. Examples include the uranium occurrences in the porphyry copper deposits such as Bingham Canyon and Twin Butte in the United States, the Rossing Deposit in Namibia, and Ilimaussaq deposit in Greenland, Palabora in South Africa, and the deposits in the Bancroft area, Canada (15). 

Phosphorite Deposits. Sedimentary phosphorites contain low concentrations of uranium in fine-grained apatite. Uranium of this type is considered an unconventional resource. Significant examples of these uranium ore types include the U.S. deposits in Elorida, where uranium is recovered as a by-product, and the large deposits in North African and Middle Eastern countries (16). 

Volcanic Deposits. Uranium deposits of volcanic deposits type are strata-bound and stmcture-bound concentrations in acid volcanic rocks. Uranium is commonly associated with molybdenum, fluorine, etc. Examples are the uranium deposits in Michelin, Canada Nopal I in Chihualiua, Mexico Macusani in Pern and numerous deposits in China and the CIS (16). 

Sur cia.1 Deposits. Uraniferous surficial deposits maybe broadly defined as uraniferous sediments, usually of Tertiary to recent age which have not been subjected to deep burial and may or may not have been calcified to some degree. The uranium deposits associated with calcrete, which occur in Australia, Namibia, and Somaha in semiarid areas where water movement is chiefly subterranean, are included in this type. Additional environments for uranium deposition include peat and bog, karst caverns, as well as pedogenic and stmctural fills (15). 

Other Deposits. Those deposits which cannot be classified as one of the previous 14 deposit types are called other. These include the uranium deposits in the Jurassic Todilto Limestone in the Grants district in New Mexico (17). 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Unconformity-type uranium deposits, as well as sandstone-hosted deposits, should be zoned in their 238y 5y pg jgg gg g result of two processes. In the first process, the 238y 235y... 

Fig. 2. Geological framework of the basement to the eastern Athabasca Basin, including the location of the major unconformity-type uranium deposits, from Annesley et al. (2005).

Nash, J.T., Granger, H.C., Adams, S.S. 1981 Geology and concepts of genesis of important types of uranium deposits. Economic Geology, 75 Anniversary Volume, 63-116. 

Geochemical detection of uranium deposits in sandstone-type deposits depends on the geochemical behavior of U and pathfinder elements (Rose Wright 1980). Uranium is dispersed under oxidizing conditions but is immobile under reducing conditions. Adsorption on freshly precipitated Fe-oxides and certain types of organic matter also limits dispersion unless high concentrations of or... 

SopucK, V.J., Carla, A. de, Wray, E.M., Cooper, B. 1983. The application of lithogeochemistry in the search for unconformity-type uranium deposits. Northern Saskatchewan, Canada. Journal of Geochemical Exploration, 19, 77-99. 

Unconformity-type uranium deposits from the Athabasca Basin (Saskatchewan, Canada) represent the worid-richest uranium ores with the McArthur River deposit as a prime exampie. They are mainiy iocated ciose to the unconformity between a Paieo- to Meso-Proterozoic sedimentary basin, the Athabasca Basin, and an Archean to Paieoproterozoic metamorphic to piutonic basement. For severai years, a new type of uraniferous mineraiization, entireiy iocated in the basement, has been driiied in the South-Eastern part of the basin. Few data are avaiiabie for this type of deposit, iimiting the comparison of their characteristics and possibie genetic iinks with deposits iocated at the unconformity. 

Fig. 1. Location of the Millennium, Eagle Point, P-Patch, and some of the main unconformity-type uranium deposits in Athabasca Basin (modified from Card ef al. 2007)...

The chondrite-normalized REE patterns for basement-hosted uranium oxides are similar, except for a small variation of LREE abundances, indicating identical physico-chemical deposition conditions (T, pH, fluid composition) for the Eastern part of the Athabasca Basin basement. The previous REE distinction made between Ingress and Egress deposits (Fayek Kyser 1997) is not confirmed by the present study, because both types have similar REE abundance and fractionations, indicating the similarity of the sources and the processes for both deposit types. Thus, these results suggest... 

Fayek, M. Kyser, T.K. 1997. Characterization of multiple fluid-flow events and rare-earth-element mobility associated with formation of unconformity-type uranium deposits in the Athabasca Basin, Saskatchewan. Canadian Mineralogist, 35, 627-658. 

This report concerns the application of Pb isotope geochemistry in the exploration for unconformity-type uranium deposits in the Athabasca Basin of northern Saskatchewan (Fig. 1). 2006 Pb isotope data from a number of current projects, several with U mineralization, will be discussed (Cigar Lake East, Close Lake, Midwest A, Wolly/McClean Lake, Cree-Zimmer project, and Shea Creek). 

CuNEY, M., Chabiron, a., Kister, P., Golubev, V., Deloule, E. 2002. Chemical versus ion microprobe isotopic dating (Cameca IMS 3f) of the Shea Creek unconformity type uranium deposit (West Athabasca, Saskatchewan, Canada). Program and Abstracts, 27,... 

Hoeve, J. SiBBALD, T.I.I. 1978. On the genesis of Rabbit Lake and other unconformity-type uranium deposits northern Saskatchewan, Canada. Economic Geology, 73, 1451-1473. 

Depending on type, uranium deposits exhibit characteristic primary alteration and trace element zoning patterns, the latter commonly including, but are not limited to, elements exhibiting changes in oxidation state such as vanadium, selenium, molybdenum, arsenic, cobalt, and nickel (Fig. 3). It can be shown that... 

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