Uranium deposits, types vein-type

The world s largest and highest-grade uranium deposits occur in metamorphic rocks. An extensive review of the classification of uranium deposits was given by Ruzicka. His classification of uranium vein deposits was subdivided into five types, based mainly on mineralogy. 

Coffinite was first described as a new mineral by Stieff and co-workers from several localities in the sandstones of the Colorado Plateau deposits often intimately associated with asphaltic material. It was also found in vein-type deposits in Spain by Arribas and has since been found in almost all types of deposits. The composition has been reported as U(SiOi4)i AOrganic matter was always present and organometallic complexes of uranium may have accounted for the excess uranium rather than requiring excess (OH) to account for the U Si ratio deviating from unity. USi04 has been prepared by Fuchs and Gebert with no evidence of OH substitution. 

Ferguson J. and Rowntree J. C. Vein-type uranium deposits in Proterozoic rocks. Reference 22, 485-96. 

Tremblay L. P. Geologic setting of the Beaverlodge-type of vein-uranium deposit and its comparison to that of the unconformity-type. Reference 4, 431-56. 

Fisher J. C. Remote sensing applied to exploration for vein-type uranium deposits. Front Range, Colorado. Ph.D. thesis, Colorado School of Mines, 1976. 

Much of the world s currently minable uranium is found in vein-like deposits of uncertain origin. They consist of three general types of unequal importance. Most important are unconformity-related deposits and vein-like deposits in meta-morphic rocks. Least important and probably of different origin are vein-like deposits in sedimentary rocks. The origin of all three types is a matter of much conjecture. Major unsolved genetic questions are the source of the uranium and its mode of transport, the source of the mineralizing solutions, the nature and role o f reductants and the control exerted on uranium deposition by structural and lithologic features of the host rocks. Unconformity-related deposits and vein-like deposits in metamorphics commonly occur in brecciated and foliated metamorphic rocks in stable Precambrian Shield areas. They contain about 24.4% of the Western world s reasonably assured 30 uranium resources. 

Langford F. F. A supergene origin for vein-type uranium ores in the light of the Western Austrahan calcrete-carnotite deposits. Econ. Geol, 69, 1974, 516-26. 

The Precambrian European province proper contains limited resources in vein-type deposits in northern Sweden and, again, a huge low-grade uranium natural stock in Cambrian black shales. Grades, under present market conditions, are not economic. 

Uranium deposits in this unit are of numerous geological types, but three are typical of the Hercynian orogen (1) intra-granitic deposits related to leucogranites, (2) deposits bound to the contact-metamorphic haloes of granite intrusives in Lower Palaeozoic shales (the so-called Iberian type ) and (3) deposits bound to Permian cover rocks or Permian acid volcanics. Other types are veins in less differentiated granites, veins in metamorphic environments, sandstone-type deposits in Mesozoic or Caenozoic cover rocks in basin structures of the Hercynian space included in or adjacent to the Moldanubian zone (or its Iberian equivalent). 

Uranium vein-type deposits in metamorphic environment without apparent connexion with granites... 

Barbier M. J. Continental weathering as a possible origin of vein-type uranium deposits. Mineral. Deposita, 9, 1974, 271-88. 

In conclusion, uranium deposition is clearly related to two main structural events, both distinguished by widely spaced tension faults with wide vertical displacement.-Two major controls on mineralization have been identified to date— structural (N and N60 E-trending faults) and lithogeochemical (contact between the basement and the Collio formation or its immediate surroundings). The deposit can tentatively be stated to be of the hydrothermal vein type, though some aspects are typical of the vein-like type. ... 

Chen Zhaobo. Double mixing genetic model of uranium deposits in volcanic rocks and the relationship between China s Mesozoic vein type uranium deposits and Pacific plate tectonics. Paper presented at 26th International Geological Congress, Paris, 1980. 

Figure 19. Typical example of how uranium is released to the environment (redrawn and completed after Pfeifer et al. (1994)). By weathering and erosion U-rich ore quality material (pitchblende veins in granitic gneiss) is deposited on the slope beneath a cliff. The soil and plants devel-opping on it are enriched in uranium (up to 2500 ppm in the soils vs. 3 ppm in the reference soil outside the touched area, 50 m to the south-east, marked with r 100 mg/kg U in contaminated plants, - see Appendix A.8). The waters from this type of environment contain between 10 and 30 jxg/l U (cf. Fig. 18, Section 2.2 and Appendix A. 1).

Pitchblende is the dominant uranium mineral in all these vein-like deposits in sedimentary rocks. It occurs as small veinlets along fractures within and surrounding the structures and as finely disseminated crystals in porous breccia fragments within the structures. Pitchblende concentrations may be distributed zonally within the ore, and in some deposits may be concentrated in the upper levels of the structure. Associated minerals may include sulphides and sulpharsenides. Calcite and quartz are the most common gangue. Types of alteration include bleaching of red sediments, silicification, carbonatization and argillization. 

Uranium orebodies present two main morphological types. The classical vein-like linear bodies result in the association of east-west directions with the northwestern. The resulting trends vary from WNW to northwest (Fig. 6). Only the east-west sections present mica-episyenite alteration. The same is observed in vertical sections (Fig. 7). When intersecting or partly following lamprophyre dykes, veins often present conspicuous uranium enrichment. This was the case of the famous Henriette orebody, which was the first economic deposit in France. It... 

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