ASSOCIATED MINERALS AND GEOCHEMICAL ANOMALIES

Several minerals are often associated with uranium-bearing minerals in valley-fill and lacustrine/playa deposits.

Amongst the most common accessory minerals are celestite, fluorite, and barite. Celestite (SrS04) is often present as it has been observed in Yeelirrie [42], Mauritania [43], Somalia [44], and calcrete horizons in Texas [30]. Its distribution is largely erratic and confined to specific parts of the deposit. This is reflected geochemically by very high strontium contents up to 6 %[12, 30]. Fluorite (CaF2) has been observed in the Lake Austin prospect [43] and in Somalia [44]. Barite (BaSO4) is thought to occur in the Yeelirrie deposit [24].

Molybdenum is sometimes present in supergene chemical precipitates [36]. In young uranium deposits [1 3, 30]

molybdenum anomalies are systematic but their mineralogical associations are unknown at present. Some selenium anomalies are also possible. In recent bogs, marshes, and closed basin environments, there are positive correlations between uranium and copper, selenium, rare earths, arsenic, vanadium, and molybdenum, all of which show local enrichments [36].

Studies of clay minerals would be of great benefit for the understanding of and prospecting for surficial uranium deposits, but there are too little data to fully assess their potential use. For example, there are no maps and only a few profiles representing their distribution. Moreover, it seems that some clays are unimportant with respect to the distribution of uranium. In the case of Yeelirrie, a profile published by Western Mining Corp. [42] indicates that montmorillonite is important, whereas more recent studies have shown that sepiolite is a major clay mineral [1].

In valley-fill and lacustrine/playa deposits it appears that in mineralized samples, sepiolite is often present but occasionally attapulgite occurs. In the Mudugh deposit in Somalia, Barbier et al [44] have estimated that between 5 and 20 % of mineralized samples contain attapulgite and sepiolite. This is also the case of the Hammadasfrom Mauritania. In the Ain Ben Tili area [45] the clay mineral associations change within the sedimentary profile and from the bottom to the top are as follows: in the basal conglomerate, montmorillonite + illite; in the mid section, montmorillonite + attapulgite; and in the top calcareous cap, montmorillonite decreases and sepiolite appears.

The association of sepiolite and attapulgite is in fact very common in all the calcrete deposits of the world [46].

Smectite has been found in several deposits (Table 1). Briot[43] described an interlayered illite/smectite clay and suggested that smectite resulted from the transformation of illite. Smectite and illite are also present in the Tumas

River deposit of Namibia [43]. Kaolinite and illite are also often present in uranium occurrences, but their relationships to mineralized zones are not clear in some cases but in others they are the only clays present.

Table 3

A Proposed Classification of Uranium-Bearing Minerals in Surficial Uranium Deposits

A short distance away from the deposits otherclay mineral assemblages may exist, and Briot [43] noted that along the margins of Yeelirrie, the clay is composed of chlorites with traces of illite and talc.

In altered phosphorites, the clay mineral assemblage can be quite unique. For example, in the Bakouma uraniferous phosphate deposit in the Central African Republic, illite, kaolinite, montmorillonite, and chlorite are present. In the reduced zones, however, illite predominates whereas in the oxidized (possibly leached) zones, kaolinite is the major clay mineral.

6. CONCLUSION

Economically, carnotite is the most important uranium mineral in surficial uranium deposits. This is because of its very low solubility. The other uranium minerals in the surficial environments occur largely in uneconomic occurrences. Unfortunately, there is insufficient data available on the interactions between uranium in solution and host rock minerals (in particular clays) in order to fully understand the paragenesis of the ores.

REFERENCES

[I] BRIOT, P., FUCHS, Y., Processus de minéralisation uranifère des calcretés: une hypothèse non-pédologique, this Volume.

[2] KOVALEV, A.A., Les occurrences uranifères par evaporation dans les régions arides, Vestrik. Akad. Nauk., 3, 204(1962) 23-34.

[3] BUTT, C.R.M., MANN, A.W., HORWITZ, R.C., Régional setting, distribution and genesis of surficial uranium deposits in calcretés and associated sediments in Western Australia, this Volume.

[4] HAMBLETON-JONES, B.B., Surficial uranium deposits in South Africa, this Volume.

[5] AVITAL, Y., STARINSKY, A., KOLODNY, Y.,. Uranium geochemistry and fission-track mapping of phosphorites, Zefa Field, Israel,' Econ. Geol. 78 (1983) 121-131.

[6] KOLODNY, Y., KAPLAN, I.R., Uranium isotopes in seafloor phosphorites, Geochim. etCosmochim. Acta,34 (1970) 3-24.

[7] BURNETT, W.C., VEEH, H.H., Uranium series disequilibrium studies in phosphorite nodules from the west coast to South America, Geochim. et Gosmochim. Acta, 41 (1977) 755-764.

[8] BURNETT, W.C., GOMBERG, D.N., Uranium oxidation and probable subaerial weathering of phosphatized limestone from the Pourtales terrace, Sedimentology, 24 (1977) 291-302,

[9] GLAGOLEV, N.A., Development features of a supergene zone on a uranium-phosphorous deposit. Inter.

Geol. Rev. 22. 9 (1980) 1070-1076.

[10] CARRE, J.L, Les minéralisations uranifères des dépôts oligocènes de Saint Pierre (Cantal, France) dans leur cadre géologique régional et local. Thèse INP Nancy, unpubl. (1979).

[II] CUNEY, M., Geologic environment, mineralogy and fluid inclusions of the Bois Noirs Limouzat vein, Forez, France, Econ. Geol. 73 (1978) 1567-1610.

[12] CARLISLE, D., MERIFIELD, P.M., ORME, R.R., KOHL, M.S., KOLKER, 0., The distribution of calcretés and gypcretes in southwestern United States and their uranium favourability based on a study of deposits in Western Australia and South West Africa (Namibia), US Dept. of Energy, Open-File Report GJBX-29(78) (1978)274.

[13] CULBERT, R.R., BOYLE, D.R., LEVINSON, A.A., Surficial uranium deposits in Canada, this Volume.

[14] BACH, A., Evolution dans les conditions d'affleurement de shales uranifères à matière organique (Bassin Permien de l'Aumance France), Thèse I.N.P. Nancy, unpubl. (1980) 100.

[15] ROUZAUD,J.N., Etude structurale de matières carbonées associées à des minéralisations uranifères, Thèse Orléans, unpubl. (1979) 109.

[16] NAKASHIMA, S., DISNAR, J.R., PERRUCHOT, A., Etude expérimentale des mécanismes de concentration de l'uranium par une matière organique sédimentaire dans des conditions de diagenèse croissante, premiers résultats, C.R. Acad. Se. Paris t 296, Série II, 1425-1428.

[17] BOROVEC, K., The adsorption of uranyl species by fine clay, Chem. Geol. 32 (1981) 45-58.

[18] GIBLIN, A.M., The role of clay adsorption in genesis of uranium ores. In: Uranium in the Pine Creek Geosyncline/IAEA Vienna (1980) 521-529.

[19] MICHEL, D., Modalités des liaisons fer-uranium: le cas des concentrations ferrifères de Saint Pierre du Cantal (Cantal, France), C.R. Acad. Se. Paris, t. 293 Série II (1981) 209-214.

[20] MICHEL, D., N'GANZI, C., SAMAMA, J.C., L'adsorption: implications sur la prospection géochimique de l'uranium en milieu tropical, In: Symposium on Geochemical Prospecting, IAEA, Vienna (1982), in press.

[21] SAMAMA, J.C., Uranium in lateritic terranes, this Volume.

[22] GUENIOT, B., GUILLET, B., SOUCHIER, B., Fixations de l'uranium sur les surfaces d'oxyhydroxydes de fer (lepidocrocite) des horizons placiques de sols hydromorphes: exemple des stagnoglays des Vosges cristallines, C.R. Acad. Se. Paris, t. 295, II (1982) 31-36.

[23] BUTT, C.R.M., HORWITZ, R.C., MANN, A.W., Uranium occurrences in calcrete and associated sediments in Western Australia, Australia, CSIRO, Division of Mineralogy Report No. FP 16 (1977) 67.

[24] MANN, A. W., DEUTSCHER, R. L Genesis principles for the precipitation of carnotite in calcrete drainages in Western Australia, Econ. Geol. 73, 8 (1978) 1724-1737.

[25] HAMBLETON-JONES, B.B., ANDERSEN, N.J.B., Natural and induced disequilibrium in surficial uranium deposits, this Volume.

[26] RYAN, G.R., Uranium in Australia, In: Geology, Mining and Extractive Processing of Uranium (1977).

[27] BIANCONI, F., BORSHOFF, J., Surficial uranium deposits in the United Republic of Tanzania, this Volume.

[28] RODRIGO, F., ÖLS EN, H., BELLUCO, A.E., Surficial uranium deposits in Argentina, this Volume.

[29] BELL, K.G., Uranium in carbonate rocks, US Geol. Surv. Prof. Paper 474-A (1963) 29.

[30] OTTO N, J.K., Surficial uranium deposits in the United States of America, this Volume.

[31] HAMBLETON-JONES, B.B., The geology and geochemistry of calcrete-gypcrete uranium deposits in duricrusts, of the Namib desert. South West Africa, Econ. Geol. 73 8 (1978) 1407-1408.

[32] YEREMENKO, G.K., ILNENOV, Y.S., AZINI, N.A., Finds of weeksite-group minerals in Afghanistan, Doklade Akademii Naule SSR 273, 5 (1977) 1191-1193.

[33] CHERNIKOV, A.A., SIDORENKO, G.A., VALUYEVA, A.A., New data on uranyl minerals in the ursilite-weeksite group. Int. Geol. Rev. 20, 11 (1978) 1347-1356.

[34] MIAUTON, J.D., Bakouma-Genèse et gîtologie d'un gisement néoformé continental phosphate uranifêre, Thèse INP Nancy (1980) 160.

[35] BUTT, C.R.M., GRAHAM, J., Sodian potassian hydroxonian meta-autunite, first occurrence of an intermediate member of a predicted solid solution series. Amer. Mineral. 66 (1981) 1068—1072.

[36] BOYLE, R.W., Geochemical prospecting for thorium and uranium deposits. Developments in Economic Geology, 16 (1982)498.

[37] SHERIDAN, D.M., MAXWELL, C.H., COLLIER, J.T., Geology of the Lost Creek schroeckingerite deposits, Sweetwater County, Wyoming, US Geol. Surv. Bull. 1087-J (1961) 391-478.

[38] MORTIMER, C., Surficial uranium deposits in Botswana, this Volume.

[39] ANIEL B., Les gisements d'uranium associés au volcanisme acide tertiaire de la Sierra de Pena Bianca (Chihuahua, Mexique), Géol. Géochim. Uranium, Mém. Nancy, 2 (1983)291.

[40] LANGMUIR, D., Uranium solution mineral equilibria at low temperatures with applications to sedimentary ore deposits, Géochim. et Cosmochim. Acta, 42 (1978) 547—569.

[41] O'BRIEN, T.J., WILLIAMS, P.A., The aqueous chemistry of uranium minerals— Part 4, Schroeckingerite, grimselite, and related alkali uranyl carbonates. Mineral. Mag. 47 (1981) 69—73.

[42] WESTERN MINING CORP., A general account of the Yeelirrie uranium deposits. Privately published and distributed to 25th Intern. Geol. Cong. tours, Sydney, Australia (1975) 14.

[43] BRIOT, P., Phénomères de concentration de l'uranium dans les environments évaporitiques intercontin-entaux: les calcrétes de l'YIgarn Australien. Essai de comparaison evec les calcrétes de Mauritanie et de Namibie, Thèse Orsay (1978) 167.

[44] BARBIER. J., BAUBRON, U.C., BOSCH, B., BRIOT, P., JACOB, C., Données préliminaires sur les isotopes du soufre dans les calcrétes uranifères, un exemple dans la Province de Mudugh (Somalie), C.R. Acad. Sei.

(Paris), D, 290 (1980) 1047-1050.

[45] BRAUN, R., Etude des hamadas de la dorsale Reguibat Région d'Ain BenTili (Rep.Mauritanie) Rapport DEA Faculté St Jérôme-Marseille (1974) 67.

[46] GOUDIE, A., The chemistry of world calcrete deposits, J. Geol. 80 (1 972) 449-463,

THE GENESIS OF SURFICIAL URANIUM DEPOSITS