The geology of uranium mineralization at Mika, N.E. Nigeria

International Nuclear Information System (INIS)

Funtua, I.I.; Okujeni, C.P.; Elegba, S.B.

1995-01-01

The Uranium mineralization at Mike is located near Zing in Taraba State, N.E., Nigeria. The host rock consist of a sheared Pan-African medium-grained granite which is in places intruded by rhyolite and siliceous veins. Numerous joints, faults and fractures criss-cut the area. Some of the fractures are filled with secondary quartz. The ore occurs in two parallel N-S trending shear Zones with the western limb hosting a rhyolite body. Drill section reveals a subsurface extension of the mineralization. In the upper limb, mineralization consisting of metal autunite and coffinite occurs associated with the rhyolite body. In lower ore limb meta-autunite, coffinite and pitchblende occur along a set of two parallel shear surface. The pitchblende occurs massive and as vein lets in association with sulphides. The ore body is marked by distinct hydrothermal alteration zones which feature sericitization, silicification, hematization and kaolination. Reactivated regional structures of NE-SW and the N140oE and N170E played an important role in the formation of Mika mineralization. These acted as channel and as mechanical barrier for the mineralization fluid. The bimodal magmatism of the Burashika group is postulated to be related to the process of mineralization in view of the ubiquitous rhyolite in the mineralized bodies

Dissolution and alteration of uraninite under reducing conditions

International Nuclear Information System (INIS)

Janeczek, J.; Ewing, R.C.

1992-01-01

The behavior of uraninite under hydrothermal, reducung conditions is discussed on the basis of data in the literature and the authors' investigation of samples from two natural analogue sites: Oklo, Gabon and Cigar Lake, Canada. Uraninite under reducing conditions, in the presence of saline hydrothermal solutions may be altered through dissolution, preferential loss of lead and/or Y + HREE, and coffinitization. Textural features indicative of dissolution or uraninite include embayed grain boundaries, corroded relicts of uraninite embedded in a clay matrix, and replacement of uraninite by clays and sulfides. The alteration textures and phase chemistries at Oklo and Cigar Lake are remarkably similar. Dissolution of uraninite at Cigar Lake and Oklo was associated with the precipitation or illite and was probably caused by saline, uraninite moderately acidic solutions at approximately 200deg C. Increased oxygen fugacity may have occured locally due to release of excess oxygen from uraninite during dissolution or by α-radiolysis of the solution. The formation of Pb-rich (up to 18 wt% Pb, uraninite-I) and Pb-depleted (approximately 7-8 wt% Pb, uraninite-II) uraninites at both Oklo and Cigar Lake resulted from the loss of Pb due to predominantly episodic volume diffusion related to regional geologic events. Lead loss was not associated with U mobilization. In addition to uraninite dissolution, coffinitization resulted in U, Pb and REE release. (orig.)

Uranium mineralization in the Lower Mahadek Sandstones of Laitduh Area, East Khasi Hills District, Meghalaya

International Nuclear Information System (INIS)

Mahendra Kumar, K.; Bhattacharjee, P.; Ranganath, N.

2008-01-01

Significant uranium mineralization hosted in feldspathic sandstone of Upper Cretaceous Lower Mahadek Formation has been located at Laitduh, East Khasi Hills district, Meghalaya. Two mineralized horizons have been identified within Lower Mahadek Formation with vertical separation of 30 m. Samples from upper horizon have assayed upto 0.17% U 3 O 8 , whereas samples from lower mineralized horizon have assayed upto 0.50% U 3 O 8 . The radioactive minerals identified are coffinite and pitchblende occurring in association with carbonaceous matter. (author)

The geology of the Cluff Lake uranium deposits

International Nuclear Information System (INIS)

Harper, C.T.

1978-01-01

The uranium deposits discovered by Amok (Canada) Ltd. in the Cluff Lake area of northwestern Saskatchewan occur at or near the southern edge of the uplifted basement core of the Carswell circular structure. Two types of mineralization, distinguishable by their geological and structural setting and mineral paragenesis, have been recognized. The N-Claude type is characterized by a relatively simple mineral assemblage, consisting of uraninite or pitchblende with coffinite, and is accompanied by variable amounts of graphite and organic matter, and Fe, Cu, Pb and Mo sulphides. Both N and Claude orebodies occur within quartzofeldpathic gneisses of the basement core. On the other hand, the D-type ore has a complex mineral assemblage consisting of: uraninite, pitchblende, tucholite and coffinite, along with native gold and selenium; gold tellurides, and selenides of Pb, Bi, Ni and Co; sulphides of Fe, Cu and Pb; and organic matter. The D orebody occurs within carbonaceous shales at the base of the Athabasca Formation as well as in fault zones in regolithic quartzofeldspathic gneisses above the inverted unconformity. An age of 1050 m.y., which is consistent with a period (circa 1200-1000 m.y.) of widespread hydrothermal activity and uranium mineralization or reworking within and adjacent to the Athabasca Basin, has been obtained from uranium mineralization from the D orebody. Later reworking (circa 470 m.y.) of the mineralization occurred at the intersection of older mineralized shear zones with radial faults produced during meteorite impact. (auth)

Geology and ore deposits of the Section 23 mine, Ambrosia Lake District, New Mexico

International Nuclear Information System (INIS)

Granger, H.C.; Santos, E.S.

1986-01-01

The Section 23 mine is one of about 18 large uranium mines opened in sandstones of the fluvial Westwater Canyon Member of the Jurassic Morrison Formation, in the Ambrosia Lake uranium district, during the early 1960s. Two distinct types of unoxidized ore occur in the mine. One type consists of uranium-rich authigenic organic matter that impregnates parts of the reduced sandstone host rocks. This type of ore occurs as peneconcordant layers which are typically elongate east-southeast, subparallel both to the sedimentary trends and to the regional strike of the host rock. A second type of ore is essentially devoid of organic matter and occurs in thick zones which conform to interfaces that separate oxidized from reduced parts of the host rocks. Genesis of the second type of ore is similar to that of roll-type deposits in Tertiary rocks of Wyoming and Texas. Organic matter in the primary ores was probably introduced into the host rock as humic acids that precipitated in the pores of the sandstone. This material is inferred first to have fixed uranium as urano-organic compounds but with further diagenesis, to have released some of the uranium to form coffinite. Vanadium, molybdenum, and selenium are associated with primary ore and may also have been fixed by the organic matter. The secondary or roll-type ores contain uranium mostly in the form of coffinite and only rarely as uraninite. They also contain vanadium and selenium but are virtually devoid of molybdenum

Rare earth silicate (Ce, La, Nd, Ca, Th) SiO4 and cheralite (Th, Ca, Ce, La) (Psi)O4 are the responsible minerals for the anomalies of Morro de Ferro

International Nuclear Information System (INIS)

Fujimori, K.

1982-01-01

The Rare Earth silicate (La, Ce, Nd, Ca, Th)SiO 4 and cheralite (identified by Prof. Freeborn on a sample prepared from drilling core) were recognized as the most probable radioactive minerals that gave origin to high radioactive anomaly at Morro do Ferro hill together with coffinite, thorite, pyrochlore, apatite, etc., that are found in small quantity. The acids produced by decomposition of pyrite and fluorite have etched these radioactive minerals giving the high radioactive anomaly caracterized by high grade desiquilibrium of 232 Th serie. (Author) [pt

Oxidation-reduction phenomena in tabular uranium-vanadium bearing sandstone from the Salt Wash deposits (Upper Jurassic) of the Cottonwood Wash district (Utah, USA)

International Nuclear Information System (INIS)

Meunier, J.D.

1984-02-01

A braided to meandering fluvial environment has been postulated for this area after a sedimentological study. The mineralization is spatially related with conifer derived organic matter and wood is preserved in these sediments because of the reducing environment of deposition. The degree of maturation of the organic matter has been estimated from chemical analyses. Results show the presence of variable diagenetic oxidation depending on the environment. The organic matter which was least affected by this oxidation have attained a thermal maturation characteristic of the end stage of diagenesis. The high grade ore is situated at the edges of or within the trunks of trees (which remained permeable during diagenesis) and at the boundaries of the carbonaceous beds. Geochemical study shows there to be good correlation between uranium and vanadium. Uranium occurs as pitchblende, coffinite or as impregnations in the vanadiferous clay cement. A detailed study of clays shows an association of chlorite and roscoelite which most probably contain V 3+ . Fluid inclusion study suggests burying temperatures of >= 100 0 C and shows the existance of brines before the mineralization. The following genetical model is proposed. Low Eh uraniferous solutions move through a reduced pyritised environment. The low degree of oxidation of the pyrites propagates the destabilization of the clastic iron-titanium oxides which release vanadium and the dissociation of uranylcarbonates. Then, the deposit of pitchblende, coffinite, montroseite and vanadiferous clays took place in association with a secondary pyrite. When the rocks were uplifted to the subsurface, uranium (IV) and vanadium (III) were remobilised in an oxidising environment to form a secondary mineralization essentially represented by tyuyamunite [fr

A study on mineralization U,REE and related processes in anomaly No.6 Khoshomy area central Iran

International Nuclear Information System (INIS)

Heidaryan, F.

2005-01-01

Uranium mineralization in Khoshomy prospect, located in central. part of Iran, with 303-15000 (cps) and 14 to 4000 (ppm) released, The main rock types include: gneiss, granite, pegmatite and migmatite, that influenced by pegmatite-albitic vines (quartz-heldespatic). Acidic and basic dykes, granodioritic, units and dolomite and marble have been seen. The alteration associated with the mineralization is potassic, argillic, propylitic, carbonization, silisificaition and hematitizaition. Uranium mineralization occurred in a hydrothermal phase with Cu, Mo, Ni and Au elements. Uranium primary minerals include pitchblende, coffinite, uraninite; and uranium secondary minerals include uranophane and . boltwoodite. REE mineralization occurred by the potassic phase in peginatitization process

Mineralización de uranio en la Sierra de Velasco, La Rioja

International Nuclear Information System (INIS)

Morello, O.; Aparicio González, P.

2013-01-01

This contribution describes an uranium mineralization found in the Sierra de Velasco, La Rioja Province, Northwest of Ar¬gentina. In the study area crop out granites, pegmatites and metamorphic rocks. The host rocks of the mineralization are the La Chinchilla Granite (Carboniferous) and the La Cébila metamorphic Complex (Precambrian-Ordovician). The mine¬ralization is perigranitic and occurs disseminated, in fractures and in the contact between the granite and the metamorphic rocks. In the La Chinchilla Granite was identified a U-Nb-Ta oxide, and in the metamorphic rocks U-silicates (uranophane, uranophane-beta), U-phosphates (phurcalite and meta-autunite) and uranium oxides (pitchblende and coffinite) were found. (authors) [es

Primary uranium mineralization in paleochannels of the Um Bogma formation at Allouga Southwestern Sinai

International Nuclear Information System (INIS)

Bisher, A. H.

2012-12-01

The Um Bogama formation in the Allouga area is within a major Graben trending NNW-SSE. The formation is composed mainly of sandy dolostone. Lactomicin marl, siltstone and carbonaceous shale with a high content of organic matter. The black carbonaceous shale represents the redox-front (reduced facies) at which hexavalent uranium can reduce to the presence state, resulting in the redeposition of uranium mineral. The presence of uranium minerals are increased with an increasing amount of carbonaceous matter in the paleochannels of the Allouga area. Small-scale fault planes also show an increase in the uranium content. The present study reveals the presence of the primary uranium contents, uranium, pitch blends and coffinite, which are recorded for the first time in the area. (Author)

Petrography and geochemistry of granitoids from the Samphire Pluton, South Australia: Implications for uranium mineralisation in overlying sediments

Science.gov (United States)

Domnick, Urs; Cook, Nigel J.; Bluck, Russel; Brown, Callan; Ciobanu, Cristiana L.

2018-02-01

The Blackbush uranium deposit (JORC Inferred Resource: 12,580 tonnes U), located on the north-eastern Eyre Peninsula, is currently the only sediment-hosted U deposit investigated in detail in the Gawler Craton. Uranium is hosted within Eocene sandstone of the Kanaka Beds, overlying Mesoproterozoic granites of the Samphire pluton, affiliated with the Hiltaba Intrusive Suite ( 1.6 Ga). These are considered the most probable source rocks for uranium mineralisation. By constraining the petrography and mineralogy of the granites, insights into the post-emplacement evolution can be gained, which may provide an exploration indicator for other sediment-hosted uranium systems. Three geochemically distinct granite types were identified in the Samphire Pluton and correspond to domains interpreted from geophysical data. All granites show complex alteration overprints and textures with increasing intensity closer to the deposit, as well as crosscutting veining. Alkali feldspar has been replaced by porous K-feldspar and albite, and plagioclase is overprinted by an assemblage of porous albite + sericite ± calc-silicates (prehnite, pumpellyite and epidote). This style of feldspar alteration is regionally widespread and known from Hiltaba-aged granites associated with iron-oxide copper-gold mineralisation at Olympic Dam and in the Moonta-Wallaroo region. In two granite types biotite is replaced by calcic garnet. Calc-silicates are indicative of Ca-metasomatism, sourced from the anorthite component of altered plagioclase. Minor clay alteration of feldspars is present in all samples. Mineral assemblages in veins include quartz + hematite, hematite + coffinite, fluorite + quartz, and clay minerals. Minor chlorite and sericite are found in all vein types. All granite types are anomalously rich in U (concentrations between 10 and 81 ppm). Highly variable Th/U ratios, as well as hydrothermal U minerals (mostly coffinite) in granites and veins, are clear evidence for U mobility. Uranium

Radioactive ores from Agostinho field, Pocos de Caldas (MG), Brazil

International Nuclear Information System (INIS)

Fujimori, K.

1974-01-01

Aiming to characterize the radioactive minerals of Campo Agostinho, Pocos de Caldas - Brazil, the survey of all natural radiactive elements and their geochemical behaviors, decays and radioactive equilibrium was done. Several models of radioactive instability of the minerals or the radioactive samples were proposed to characterize the geochemistry and the mineralization of radioactive elements. The complete isotopic analysis of the elements was done by high resolution gamma spectrometry, using a Ge(Li) detector, at the temperature of liquid nitrogen, coupled to a multichannel analyser. The sample in radioactive equilibrium of Atomic Energy Comission of United States - A.S. n.6, NBL - New Brunswick Laboratory, was considered as standard sample. Fluorite, zircons, pirite, molibinite, rutile, anatase, niobophyllite, and in small ratio (bellow 0.1%) uranothorianite, coffinite, pyrochlore, monazite and apatite. (M.C.K.) [pt

Uranium in the Bunter sediments of the Polish area

International Nuclear Information System (INIS)

Saldan, M.; Strzelecki, R.

1980-01-01

Uranium mineralization occurring in the Triassic sediments in the Polish area is discussed. Systematic work conducted for over ten years revealed the presence of uranium mineralization in the following geological units: Peribaltic syneclize, Fore-Sudetic monocline, Zary pericline and Pomerania trough. Out of three uranium-bearing horizons which can be correlated with each other two (the lower and the middle) are connected with the Middle Bunter, while the upper horizon is related to the Upper Bunter. Mineralization was found in sandstones, conglomerates, mudstones and claystones and, in the Fore-Sudetic monocline, also in carbonates. Among uranium minerals uranium black and coffinite were identified. In addition to uranium, increased vanadium, selenium and molybdenum contents were found in the sandstones. Some of the uranium-bearing horizons are of economic value. (author)

Evaluation of the Cerro Solo nuclear ore, province of Chubut. Geological characteristics of the deposit and of the basin. Pt. 2

International Nuclear Information System (INIS)

Benitez, A.F.; Fuente, A.; Maloberti, A.; Landi, V.A.; Bianchi, R.E.; Marveggio de Bianchi, N.; Gayone, M.R.

1993-01-01

The Cerro Solo uranium ore deposit, is located 420 km west from Trelew city, Chubut province, in the extra-andean. The geologic environment belongs to the northwest edge portion of the intracratonic San Jorge Gulf Basin. The uraniferous district is named Pichinanes Ridge district. The mineralization lies 25 to 130 m depth, and is hosted by Los Adobes formation aged Aptian-Albian, made up by conglomerates, sandstones, coarse-sandstones and less abundant siltstones and claystones. The Cerro Solo ore deposit that belongs to the sandstone type-uranium occurrences are lenticular or tabular shaped, associated with organic material and pyrite, generally roughly parallel to the bedding (Trend-Type). The uranium minerals are uraninite and coffinite associated with organic material and pyrite, and frequently hematite, goethite, calcite, siderite and barite are observed. (Author)

Uranium and thorium deposits of Northern Ontario

International Nuclear Information System (INIS)

Robertson, J.A.; Gould, K.L.

1983-01-01

This, the second edition of the uranium-thorium deposit inventory, describes briefly the deposits of uranium and/or thorium in northern Ontario, which for the purposes of this circular is defined as that part of Ontario lying north and west of the Grenville Front. The most significant of the deposits described are fossil placers lying at or near the base of the Middle Precambrian Huronian Supergroup. These include the producing and past-producing mines of the Elliot Lake - Agnew Lake area. Also included are the pitchblende veins spatially associated with Late Precambrian (Keweenawan) diabase dikes of the Theano Point - Montreal River area. Miscellaneous Early Precambrian pegmatite, pitchblende-coffinite-sulphide occurrences near the Middle-Early Precambrian unconformity fringing the Lake Superior basin, and disseminations in diabase, granitic rocks, alkalic complexes and breccias scattered throughout northern Ontario make up the rest of the occurrences

Mode of distribution of uranium mineralization and sequence of the formation of minerals in albitites

International Nuclear Information System (INIS)

Grechishnikov, N.P.; Kramar, O.A.; Rapovich, F.I.

1985-01-01

On the basis of analysis and generalization of factural material data on the distribution nature of accessory uranium mineralization in albitites permitting to judge of the role and textural-structural peculiarities of enclosing rocks in mineralization localization are given. It is shown that the uranium mineral formation is closely related with the albitite formation and proceeded during two stages. A main mass of primary uranium minerals (brannerites and uraninites) in the form of impregnated mineralization was formed during the first uraninite-brannerite-albitite stage. Uranium oxides, silicates and titanates in the shape of veines formed. During the second coffinite-pitchblende-chloritic stage the formation of uranium oxides, silicates and titanates occured. Uranium mineralization in albitites developes in zones of cataclasm, small jointing, mylonitization localizing in fine-grained aggregates. A main mass of primary uranium minerals in albitites (brannerite, uraninite relates to neogenic during metasomatosis dark-coloured minerals (riebenite, aegirine, chlorite)

Evaluation and design of the uranium project “Tigre I – La Terraza”, Sierra Pintada, Mendoza, Argentina

International Nuclear Information System (INIS)

Mansilla, M.; Dieguez, S.

2014-01-01

The Sierra Pintada uranium district in Mendoza Province, Argentina, was discovered by airborne survey. This deposit is associated with a volcanic caldera and occurs in the Lower Permian volcaniclastic sediments of the Cochico Group, in which aeolian and fluvial sandstones, inter-bedded with ignimbrites, were reworked by pyroclastic flows. The origin of the mineralization is interpreted as a product of the leaching of the inter-bedded rhyolitic tuff. The mineralization is lenticular and nearly concordant with the bedding. The deposit has been affected by a complex fault system, which is responsible for mineralization and disposition via spatial displacement. The primary uranium minerals are uraninite, brannerite and coffinite. Uranophane and low liebigite uranium are the products of the oxidative alteration of primary minerals. This study involves the technical and economical evaluation of the open pit uranium mining project Tigre I – La Terraza in Mendoza, Argentina, at prefeasibility level. Its development includes geological modeling through economic evaluation, and the incorporation of different mining-specific software.

Uranium-bearing zeolite-analcime concretions with authi genous loellingite

International Nuclear Information System (INIS)

Kudryavtsev, V.E.; Kashenova, A.G.; Gundrenko, E.I.

1978-01-01

Zeolite-analcime concrections, mounted in green-coloured molasses of middle Palaeozoic, were studied by X-ray radiometric method. It is established that concrection formator is heliogenious carbonated pellitemorphic material arisen at the cost of aluminium-silicon gels in the process of their dehydration into the sediment diagenesis stage. Uranium, molybdenum, arsenic, zirconium and other metals are scattered in a dispersed way in the pellitemorphic material. They are present in the aqueous solution of liquid inclusions. They can also form smallest extractions of nasturane, uranium black (coffinite), loellingites, pyrite, chalcopyrite, arseno-pyrite, molybdenite and others in the substrate. Loellingite forms tetra and hexabeam triplets. There are xenomorphic extractions and seldom crystals with extended rectangular or hexagonal cross sections in big grains. Its main constituents are arsenic and ferrum. The loellingite presence in the concrections studied testifies to the possibility of its formation not only under the conditions of hydrothermal and metasomatic deposits, but in a wider range of thermodynamic conditions

Apatite-brannerite-pitchblende association in hydrothermal quartz veins

International Nuclear Information System (INIS)

Brodin, B.V.; Mel'nikova, A.M.; Osipov, B.S.; Pavlov, E.G.

1976-01-01

A study into the vein quartz mineralization confined to the tectonic zones of crush and silicification in sedimentary-igneous rocks of the lower Paleozoic has been made. The physicochemical characteristics of minerals were studied by way of optical and electron microscopy, chemical, laser-microspectral and X-ray structural analyses, microprobing and alpha-microradiography. 3 mineral associations have been discriminated, representative of the sequence of hydrothermal mineralization. An unusual parogenesis of pitchblende and brannerite with apatite, xenotime and more recent goethite has been revealed. The results are indicative of a medium-low-temperature hydrothermal process occurring at the final stages of formation of uraniferrous quartz veins. By composition and mineralization sequence, the latters are close to low- and medium-temperature uranium-quartz-chlorite-hydromica formations with apatite, coffinite, brannerite and pitchblende. The weak initial metamictization of goethite in veins 80 to 100 million years old is due to the radioactive effect of the submicroscopic radioactive mineral impurity on the crystalline lattice

Uranium occurence in California near Bucaramanga (Columbia)

International Nuclear Information System (INIS)

Heider Polania, J.

1980-01-01

The mining district of California, Bucaramanga, is on the west side of the Cordillera Oriental in the Santander massif region. The oldest rocks of the area form a complex of metamorphites and migmatites of the predevonic age. Amphibolite various types of paragneiss and orthogneiss are represented. Several stages of metamorphism can be documented in some rocks, as well as double anatexis. Triassic to jurassic quarz diorites and leukogranites show wide distribution. Porphyric rocks of granodioritic to granitic composition, to which the uranium mineralization is mainly bonded, intruded into the sediments of the lower cretaceous. Atomic absorption spectral analyses were carried out for the elements Cu, Zn and Li, as well as the uranium contents of some samples using fluorimetry. Uranium is primarily bonded to pitch blende and coffinite. The latter mostly occur in fine distribution grown in quarz and belong to the most recent mineralization phase. Autunite, meta-autunite, torbernite, meta-torbernite, zeunerite, meta-zeunerite and meta uranocircite detected as secondary uranium minerals. (orig./HP) [de

Uraninite and its alternation at Palmottu - A possible natural analogue for spent fuel under reducing conditions

International Nuclear Information System (INIS)

Ruskeeniemi, T.; Blomqvist, R.; Ahonen, L.

1994-01-01

Uraninite is the major uraniferous mineral in the Precambrian U-Th rich pegmatites at Palmottu. Most euhedral uraninite grains were partially altered by silica-rich hydrothermal solutions during the late stage pegmatitic crystallization. The dominant secondary mineral is uranium silicate, with a chemical composition similar to that of coffinite (USiO 4 * Nh 2 O). The simultaneous formation of galena and other sulfides with the uranium silicate indicates that the alteration took place under reducing conditions. Hence, uranium occurs predominantly in the uranous (U 4+ ) state. Preliminary mass balance calculations imply that significant amounts of U, Th, and Pb were released during the replacement process. As the Palmottu U-Th deposit extends from ground level to distinctly reduced parts of the bedrock, it affords the opportinity of studying the stability and alteration of uraninite as an analogue for spent nuclear fuel under various redox conditions. (orig.) (28 refs., 5 figs., 1 tab.)

VEIN-TYPE URANIUM MINERALIZATION IN THE EASTERN DESERT OF EGYPT

Directory of Open Access Journals (Sweden)

M. M. Ghoneim

2018-03-01

Full Text Available Vein type uranium deposits where uranium minerals fill cavities veins, fractures, fissures, pore spaces, shear zone, breccia and stockworks in igneous, meta-sediments and metamorphic rocks are common source of uranium mineralization all over the wold. In Egypt, El-Erediya, El-Missikat and El Sela uranium mineralization occur in younger granite plutons in the Eastern Desert of Egypt. These plutons are considered as good examples of intra-granitic vein-type uranium mineralization. The goal of this review article is to study the characteristics of granites and Th-U vein mineralization El Sela area. Main tasks are characteristics of vein type uranium mineralization in the world and Egypt, characteristics of ore-bearing intrusive rocks in the El Sela area, mineralogy of Th-U vein-type mineralization in El Sela area and secondary U and Th minerals in granites. Results. The article revealed that El Sela granite is a peraluminous, high-K Calc-Alkaline (HKCA granite. Two-mica leucogranitic pluton is considered the source rock of U-mineralization at El-Sela area, while the altered microgranite and dolerite dikes are good traps for these mineralizations. The reactivated faults system trending ENE-WSW and NNW-SSE make favorable condition to form uranium mineralization associated with polymetallic mineralization that are redeposited in the two mica granite, microgranite and dolerite dikes. The metallic mineral assemblages in the veins mainly consist of pyrite, chalcopyrite, galena, sphalerite and fluorite that are associated with primary (uraninite, coffinite and secondary U-mineralization (uranophane and autunite that occur either as disseminated clusters or as microfracture filling and coating joint surface. Five types of thorite-group minerals can be distinguished: thorite, Zr-rich thorite, phosphothorite, uranothorite and Zr-rich uranothorite. ThO2 content of uraninite vary from (1.1 to 3 wt.%, for PbO contents from 1.16 to 2.35 wt.%, P2O5 contents from

Geology and ore deposits of the Section 23 Mine, Ambrosia Lake District, New Mexico

Science.gov (United States)

Granger, H.C.; Santos, E.S.

1982-01-01

The section 23 mine is one of about 18 large uranium mines opened in sandstones of the fluvial Westwater Canyon Member of the Jurassic Morrison Formation in the Ambrosia Lake mining district during the early 1960s. The Ambrosia Lake district is one of several mining districts within the Grants mineral belt, an elongate zone containing many uranium deposits along the southern flank of the San Juan basin. Two distinct types of ore occur in the mine. Primary ore occurs as peneconcordant layers of uranium-rich authigenic organic matter that impregnates parts of the reduced sandstone host rocks and which are typically elongate in an east-southeast direction subparallel both to the sedimentary trends and to the present-day regional strike of the strata. These are called prefault or trend ores because of their early genesis and their elongation and alinement. A second type of ore in the mine is referred to as postfault, stacked, or redistributed ore. Its genesis was similar to that of the roll-type deposits in Tertiary rocks of Wyoming and Texas. Oxidation, related to the development of a large tongue of oxidized rock extending from Gallup to Ambrosia Lake, destroyed much of the primary ore and redistributed it as massive accumulations of lower grade ores bordering the redox interface at the edge of the tongue. Host rocks in the southern half of sec. 23 (T. 14 N., R. 10 W.) are oxidized and contain only remnants of the original, tabular, organic-rich ore. Thick bodies of roll-type ore are distributed along the leading edge of the oxidized zone, and pristine primary ore is found only near the north edge of the section. Organic matter in the primary ore was derived from humic acids that precipitated in the pores of the sandstones and fixed uranium as both coffinite and urano-organic compounds. Vanadium, molybdenum, and selenium are also associated with the ore. The secondary or roll-type ores are essentially free of organic carbon and contain uranium both as coffinite and

Simulation of uranium transport with variable temperature and oxidation potential: The computer program THCC [Thermo-Hydro-Chemical Coupling

International Nuclear Information System (INIS)

Carnahan, C.L.

1986-12-01

A simulator of reactive chemical transport has been constructed with the capabilities of treating variable temperatures and variable oxidation potentials within a single simulation. Homogeneous and heterogeneous chemical reactions are simulated at temperature-dependent equilibrium, and changes of oxidation states of multivalent elements can be simulated during transport. Chemical mass action relations for formation of complexes in the fluid phase are included explicitly within the partial differential equations of transport, and a special algorithm greatly simplifies treatment of reversible precipitation of solid phases. This approach allows direct solution of the complete set of governing equations for concentrations of all aqueous species and solids affected simultaneously by chemical and physical processes. Results of example simulations of transport, along a temperature gradient, of uranium solution species under conditions of varying pH and oxidation potential and with reversible precipitation of uraninite and coffinite are presented. The examples illustrate how inclusion of variable temperature and oxidation potential in numerical simulators can enhance understanding of the chemical mechanisms affecting migration of multivalent waste elements

Organic matter in uranium concentration during ancient bed oxidation of carboniferons sediments

International Nuclear Information System (INIS)

Kruglova, V.G.; Uspenskij, V.A.; Dement'ev, P.K.; Kochenov, A.V.

1984-01-01

Changes in the organic matter accompanying the process of epigenetic ore formation are studied using the example of a deposit localized in carboniferous molasse strata of the Cretaceous period. Peculiarities of the organic matter as the main mineralization agent are studied by a complex of physical and themical methods. A distinct relationship between the uranium concentration and the degree of organic matter oxigenation is a most characteristic feature of the ore localization, however, there is no direct correlation between the contents of uranium and organic matter in ores. Uranium minerallzation was accumulated during infiltration of acid uraniferous.waters into grey stratum in the process of the bed oxidation zone formation oxidizing. Brown coal matter possessing a maximum adsorbability, as compared to other sedimentary rocks, apprared to be the uranium precipitator. The adsorption was accompanie by the formation of proper uranium minerals (coffinite, pitchblende) due to uranium reduction by oxidizing organic matter. Thus, the oxidative epigenesis was an are-forming process with the uranium concentration on organic matter proportionally to oxidation of the latter

Geochemistry of vanadium in an epigenetic, sandstone-hosted vanadium- uranium deposit, Henry Basin, Utah

Science.gov (United States)

Wanty, R.B.; Goldhaber, M.B.; Northrop, H.R.

1990-01-01

The epigenetic Tony M vanadium-uranium orebody in south-central Utah is hosted in fluvial sandstones of the Morrison Formation (Upper Jurassic). Measurements of the relative amounts of V+3 and V +4 in ore minerals show that V+3 is more abundant. Thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as V+4. The ore formed as V+4 was reduced by hydrogen sulfide, followed by hydrolysis and precipitation of V+3 in oxide minerals or chlorite. Uranium was transported as uranyl ion (U+6), or some complex thereof, and reduced by hydrogen sulfide, forming coffinite. Detrital organic matter in the rocks served as the carbon source for sulfate-reducing bacteria. Vanadium most likely was derived from the dissolution of iron-titanium oxides. Uranium probably was derived from the overlying Brushy Basin Member of the Morrison Formation. Previous studies have shown that the ore formed at the density-stratified interface between a basinal brine and dilute meteoric water. The mineralization processes described above occurred within the mixing zone between these two fluids. -from Authors

U-Pb age for some base-metal sulfide deposits in Ireland: genetic implications for Mississippi Valley-type mineralization

International Nuclear Information System (INIS)

Duane, M.J.; Welke, H.J.; Allsopp, H.L.

1986-01-01

Evidence is presented that links the timing of vein-type (Cu-Ag(U)) to stratiform Mississippi Valley-type (MVT, Pb-Zn) ore events in Ireland. The rare occurrence of pitchblende, coffinite(?), and brannerite mineralization, which is regarded as a precursor component to the sulfide mineralization in the Gortdrum deposit (Ireland), provides the first direct radiometric dating tool for these carbonate-hosted deposits. The U-Pb (340 +25/-20 Ma) and Pb-Pb (359 +/- 26 Ma) whole-rock ages constrain the uranium and base-metal mineralizing events to the Early Carboniferous. The data support a model according to which MVT and earlier uranium mineralization stages of some major ore bodies resulted from fracturing coincident with large basin-dewatering events. The Pb-Pb and concordia data are consistent with an Early Carboniferous age for the mineralization at Gortdrum and agree closely with a previously published Rb-Sr age of 359 +/- 22 Ma, obtained for Missouri glauconites. Furthermore, other comparative geologic data from Ireland and from North American MVT mineral provinces support a model of Pb-Zn-Cu(U) mobilization on a regional scale that implicates the later closing stages of the proto-Atlantic. 40 references, 3 figures, 1 table

Proterozoic stratabound dolostone-hosted uranium mineralisation in the Komantula - Reddypalle area, Cuddapah basin, Anantpur district, Andhra Pradesh, India

International Nuclear Information System (INIS)

Sharma, U.P.; Pandit, S.A.; Gangadharan, G.R.; Panda, Arjuna; Roy, Minati

1998-01-01

The Komantula-Reddypalle area constitutes the northern sector of the 160 km long, uranium mineralised belt along the western and southern margins of the Cuddapah basin. The mineralisation is hosted by impure dolostone of the Vempalle Formation of Cuddapah Supergroup and occurs in the form of pitchblende, coffinite and U-Ti complexes. Uranium minerals occur along the bedding plane, carbonate-phosphate mineral contact, suture boundaries of microstylolites, and grain boundaries of clasts. The ore bearing horizon has been traced for about 65 kms and samples have assayed from 0.01% to 0.67% U 3 O 8 with negligible thorium. The source of uranium for this mineralisation appears to be the nearby fertile basement granitic rocks present in the western margins of Cuddapah basin. This mineralisation as compared with those found in the Tummallapalle-Rachkuntapalle area in the southern sector, contains high Cu (65-8100 ppm) and low P 2 O 5 (0.07-0.59 wt%) and significant but varying Mo (20-292 ppm). Stratigraphically, this area differs from that of Tummalapalle-Rachkuntapalle area to its south in two respects, viz., absence of intraformational conglomerate below and presence of a non-radioactive limestone above the radioactive dolostone. (author)

Persistent U(IV) and U(VI) following in-situ recovery (ISR) mining of a sandstone uranium deposit, Wyoming, USA

Science.gov (United States)

Gallegos, Tanya J.; Campbell, Kate M.; Zielinski, Robert A.; Reimus, P.W.; J.T. Clay,; N. Janot,; J. J. Bargar,; Benzel, William M.

2015-01-01

Drill-core samples from a sandstone-hosted uranium (U) deposit in Wyoming were characterized to determine the abundance and distribution of uranium following in-situ recovery (ISR) mining with oxygen- and carbon dioxide-enriched water. Concentrations of uranium, collected from ten depth intervals, ranged from 5 to 1920 ppm. A composite sample contained 750 ppm uranium with an average oxidation state of 54% U(VI) and 46% U(IV). Scanning electron microscopy (SEM) indicated rare high uranium (∼1000 ppm U) in spatial association with P/Ca and Si/O attributed to relict uranium minerals, possibly coffinite, uraninite, and autunite, trapped within low permeability layers bypassed during ISR mining. Fission track analysis revealed lower but still elevated concentrations of U in the clay/silica matrix and organic matter (several 10 s ppm) and yet higher concentrations associated with Fe-rich/S-poor sites, likely iron oxides, on altered chlorite or euhedral pyrite surfaces (but not on framboidal pyrite). Organic C (mining, the likely sequestration of uranium within labile iron oxides following mining and sensitivity to changes in redox conditions requires careful attention during groundwater restoration.

Uranium fixation by mineralization at the redox front

International Nuclear Information System (INIS)

Isobe, Hiroshi

1998-01-01

The behavior of actinide elements including uranium in geomedia is controlled by redox conditions. Under the oxidized conditions, uranium forms uranyl ion (UO 2 2+ ) and its complexes, and dissolves in ground water. Under the reduced conditions, U(IV) has much lower solubility than uranyl ion. In the Koongarra uranium deposit, Australia, lead-bearing uraninite, uranyl lead oxide and uranyl silicate minerals occur in the unweathered, primary ore zone, and uranyl phosphate minerals occur in the weathered, secondary ore zone. Between unweathered and weathered zones, the transition zone exists as a redox front. In the transition zone, graphite and sulfide minerals react as reducing agents for species dissolved in ground water. By SEM, spherical grains of uraninite were observed in veins with graphite. Pyrite had coffinite rim with crystals of uraninite. Calculation based on the ground water chemistry and hydrology at Koongarra shows that the uranium in the transition zone may be fixed from the ground water. In the Koongarra transition zone, recent mineralization of uranium by reduction takes place. Mineralization is much stronger fixation mechanism than adsorption on clay minerals. Pyrite in the buffer materials of possible radioactive waste repositories can fix radionuclides in oxidized ground water by mineralization with reducing reactions. (author)

Geological and geochronological evidence for the effect of Paleogene and Miocene uplift of the Northern Ordos Basin on the formation of the Dongsheng uranium district, China

Science.gov (United States)

Zhang, Chuang; Yi, Chao; Dong, Qian; Cai, Yu-Qi; Liu, Hong-Xu

2018-02-01

The Dongsheng uranium district, located in the northern part of the Ordos Basin, contains the largest known sandstone-hosted uranium deposit in China. This district contains (from west to east) the Daying, Nalinggou, and Dongsheng uranium deposits that host tens of thousands of metric tonnes of estimated recoverable uranium resources at an average grade of 0.05% U. These uranium orebodies are generally hosted by the lower member of the Zhiluo Formation and are dominantly roll or tabular in shape. The uranium deposits in this district formed during two stages of mineralization (as evidenced by U-Pb dating) that occurred at 65-60 and 25 Ma. Both stages generated coffinite, pitchblende, anatase, pyrite, and quartz, with or without sericite, chlorite, calcite, fluorite, and hematite. The post-Late Cretaceous uplift of the Northern Ordos Basin exposed the northern margins of the Zhiluo Formation within the Hetao depression at 65-60 Ma, introducing groundwater into the formation and generating the first stage of uranium mineralization. The Oligocene (∼25 Ma) uplift of this northern margin exposed either the entirety of the southern flank of the Hetao depression or only the clastic sedimentary part of this region, causing a second gravitational influx of groundwater into the Zhiluo Formation and forming the second stage of uranium mineralization.

Rare-earth, yttrium and zirconium mobility associated with the uranium mineralisation at Okrouhla Radoun, Bohemian Massif, Czech Republic

Energy Technology Data Exchange (ETDEWEB)

Milos, Rene [Academy of Sciences of the Czech Republic, Prague (Czech Republic). Inst. of Rock Structure and Mechanics

2015-01-15

The mobility of rare-earth elements (REE), Y and Zr during the Late-Variscan and post-Variscan mineralisation event in the Okrouhla Radoun. uranium deposit has been investigated to elucidate their behaviour during the hydrothermal alteration of leucogranites and high-grade metamorphic rocks in the Moldanubian Zone (Bohemian Massif). The alteration of leucogranites has caused enrichment in Na, Ca, Fe{sup 3+}, Zr and the bulk of REE while depleting K, Fe{sup 2+}, Si, Th, Rb and Ba. The alteration of high-grade metasediments has also led to an enrichment in Na and Ca while depleting K, Si, Rb and Ba. However, this change is connected to the depletion of REE, as well as the enrichment of P and Th in the bulk. The high mobility of Y and Zr during formation of the uranium mineralisation is supported by the occurrence of Y- and Zr-rich coffinite (up to 3.4 wt.% Y{sub 2}O{sub 3} and 13.8 wt.% ZrO{sub 2}). The massive hydrothermal alteration of host rocks, as well as the high mobility of REE, Y and Zr indicate an influx of oxidised basinal fluids in the Permian to the crystalline rocks of the Moldanubian Zone.

Studies on radioactivity distribution and radioactive mineral identification in uranium ores from Espinharas (PB), Brazil

International Nuclear Information System (INIS)

Oliveira, G.N.M. de.

1979-01-01

Studies about the identification of radioactive minerals in uranium bearing rocks from Espinharas (PB), Brazil are presented. Autoradiography with α-sensitive nuclear emulsions was utilized for determining radioctivity distributions and for localizing radioactive minerals, in combination with microscopy, X-ray diffractometry, PIXE and eletron microprobe analysis for its identification. Mineralized gneisse and feldspatic rock, the two principal samples studied, show distinct differences in radioactive distribution patterns, however the main carriers for U and Th seem to be the same. Microanalysis shows that elements are associated with Si, Ca, Fe and Al an some trace elements like Y, Zr, Ti, etc. U and Th are distributed uniformly in feldspatic rock and inhomogeneously in mineralized gneisse, indicating that the zonary structure of the radioactive cristals, frequently observed in gneisse, could be due to variable U:Th ratios. Chemical analysis, X-ray diffraction datas and microscopic studies indicates that the principal carrier for radioactivity in the rocks of Espinharas is a silicate mineral of U and Th, probably situaded in the series of transition: Coffinite -> uraninite, thorogummite -> thorianite. Some additional experiments about leachability of uranium with diluted sulfuric acid are reported, which confirm the different nature of radioactivity distribution in feldspatic and gneissic rocks. (author) [pt

Preliminary report on the geology of uranium deposits in the Browns Park Formation in Moffat County, Colorado, and Carbon County, Wyoming

International Nuclear Information System (INIS)

Ormond, A.

1957-06-01

Uranium was first discovered in the Browns Park Formation in 1951 in the Miller Hill area of south-central Wyoming. Since that time economically important deposits in this formation have been discovered and developed in the Poison Basin of south-central Wyoming and in the Maybell area of northwest Colorado. The Browns Park is the youngest formation (Miocene) in the region and overlies older rocks with angular unconformity. The formation consists of a basal conglomerate, fluviatile, lacustrine, and eolian sandstones, and locally a few thin beds of clay, tuff, and algal limestone. The sandstones are predominantly fine- to medium-grained and consist of quartz grains, scattered black chert grains, and interstitial clay. The uranium deposits are of the sandstone-impregnation type and are not confined to specific stratigraphic horizons. The important ore minerals are autunite and uranophane in oxidized sandstones, and uraninite and coffinite in unoxidized sandstones. Uranium is often associated with limonite and calcium carbonate in concretionary forms. Woody material, thought to play an important part in the deposition of uranium in many sandstone-type deposits, is not present in the deposits of the Browns Park Formation. However, organic carbon in the form of petroleum and petroleum residues has been observed in association with uranium in both the Poison Basin and the Maybell areas

Petrography and mineralogy of alteration halos around the Cigar Lake deposit and their relation to the mineralization

International Nuclear Information System (INIS)

Pacquet, A.; Weber, F.

1993-01-01

Around the Cigar Lake orebody, the present zoneography of alteration halos reflects several alteration episodes, some of which are anterior to and others coeval with the mineralizing events and have a regional extension. In the main pod, the uraninite mineralization was dated 1341 ± 12 Ma. In the sandstones, it is surrounded by ferromagnesian chlorites with a variable sudoitic character. This proximal alteration halo grades into a more distal envelope, visible in the sandstone and in the basement, that is composed of magnesium sudoite and 3T hydromuscovite. During this mineralizing event, dravite crystallized in the form of urchin-like clusters in the basement and xenotime overgrowth, around altered zircon, and apatite formed in the sandstones. Around the main pod and in some perched orebodies, an alteration zone of vanadium-bearing ferrikaolinite and iron-bearing 3T hydromuscovite, crosscut by a later siderite, surrounds the pitchblende dated 323 ± 4 Ma. Coffinite and an aluminous hydromuscovite crystallized during a later fracture event. The aluminous hydromuscovite also appears, with a silica-carbon-uranium complex, in perched mineralizations. Kaolinization and iron-sulfide oxidation into iron hydroxides occurred in perched orebodies that were more exposed to meteoric alteration. 19 refs., 12 figs., 11 tabs [fr

Summary of the mineralogy of the Colorado Plateau uranium ores

Science.gov (United States)

Weeks, Alice D.; Coleman, Robert Griffin; Thompson, Mary E.

1956-01-01

In the Colorado Plateau uranium has been produced chiefly from very shallow mines in carnotite ores (oxidized vanadiferous uranium ores) until recent deeper mining penetrated black unoxidized ores in water-saturated rocks and extensive exploration has discovered many deposits of low to nonvanadiferous ores. The uranium ores include a wide range from highly vanadiferous and from as much as one percent to a trace of copper, and contain a small amount of iron and traces of lead, zinc, molybdenum, cobalt, nickel, silver, manganese, and other metals. Recent investigation indicates that the carnotite ores have been derived by progressive oxidation of primary (unoxidized) black ores that contain low-valent uranium and vanadium oxides and silicates. The uranium minerals, uraninite and coffinite, are associated with coalified wood or other carbonaceous material. The vanadium minerals, chiefly montroseite, roscoelite, and other vanadium silicates, occur in the interstices of the sandstone and in siltstone and clay pellets as well as associated with fossil wood. Calcite, dolomite, barite and minor amounts of sulfides, arsenides, and selenides occur in the unoxidized ore. Partially oxidized vanadiferous ore is blue black, purplish brown, or greenish black in contrast to the black or dark gray unoxidized ore. Vanadium combines with uranium to form rauvite. The excess vanadium is present in corvusite, fernandinite, melanovanadite and many other quadrivalent and quinquevalent vanadium minerals as well as in vanadium silicates. Pyrite and part or all of the calcite are replaced by iron oxides and gypsum. In oxidized vanadiferous uranium ores the uranium is fixed in the relatively insoluble minerals carnotite and tyuyamunite, and the excess vanadium commonly combines with one or more of the following: calcium, sodium, potassium, magnesium, aluminum, iron, copper, manganese, or barium, or rarely it forms the hydrated pentoxide. The relatively stable vanadium silicates are little

Simulation of effects of redox and precipitation on diffusion of uranium solution species in backfill

International Nuclear Information System (INIS)

Carnahan, C.L.

1987-12-01

This investigation addresses the problem of prediction of the rate of migration of redox-sensitive solution species within packing and backfill materials under conditions of variable oxidation potential. Effects of changes of oxidation potential and precipitation of stable uranium compounds during diffusion of uranium from a region of high oxidation potential into a region of low oxidation potential were simulated numerically. Questions of particular interest addressed in the investigation were the existence of a moving ''redox front'' and the influence of precipitation-dissolution processes on uranium migration. The simulations showed that no expanding redox fronts existed at any simulated time up to 3.2 x 10 5 years (10 13 s). In simulations where precipitation of stable solids was not allowed, variations of oxidation potential did not affect total uranium concentrations in solution. Concentration profiles could be predicted simply by diffusion of the (constant) source concentrations. In simulations where precipitation of stable solids was allowed, uraninite and calcium uranate accumulated at the source-transport domain interface, while coffinite penetrated further into the transport domain. Total uranium concentrations in regions of precipitation were determined by solubilities of the precipitated solids, and were six to seven orders of magnitude lower than those in the simulations without precipitation, throughout the domain of transport. 14 refs., 7 figs., 2 tabs

Evaluation of Uranium depositional system in sedimentary rocks of Sibolga formation, Tapanuli Tengah

International Nuclear Information System (INIS)

I Gde Sukadana; Heri Syaeful

2016-01-01

Uranium in nature formed in various deposit type, depends on its sources, process, and depositional environments. Uranium occurrence in Sibolga, hosted in sedimentary rocks of Sibolga Formation, is properly potential to develop; nevertheless, the depositional pattern and uranium mineralization process so far had not been recognized. The research aim is to determine the rock distribution patterns and the existence of uranium grade anomalies based on surface geology and borehole log data. Mineralization occurrences from borehole log data distributed from basalt conglomerate unit (Kgl 1), sandstone 1 unit (Bp 1), conglomerate 2 unit (Kgl 2), and sandstone 2 unit (Bp 2) with their distribution and thickness are thinning to the top. Mineralization distribution in the eastern area, mainly on Kgl 1 unit, dominated by detritus materials from epi-genetic depositional in the form of monazite which is formed along with the formation of granite as its source rock. Meanwhile, mineralization on the upper rocks units formed a channel pattern trending northeast-southwest, which formed in syn-genetic process consist of uraninite, carnotite, and coffinite. Sibolga Formation deposition originated from east to west and uranium deposit formed because of the differences of depositional environment from oxidation in the east to the more reductive in the southwest. The increasing of organic materials in southwest basin caused the reduction condition of depositional environment. (author)

Behavior of Colorado Plateau uranium minerals during oxidation

Science.gov (United States)

Garrels, Robert Minard; Christ, C.L.

1956-01-01

Uranium occurs as U(VI) and U(IV) in minerals of the Colorado Plateau ores. The number of species containing U(VI) is large, but only two U(IV) minerals are known from the Plateau: uraninite, and oxide, and coffinite, a hydroxy-silicate. These oxidize to yield U(VI) before reacting significantly with other mineral constituents. Crystal-structure analysis has shown that U(VI) invariable occurs as uranyl ion, UO2+2. Uranyl ion may form complex carbonate or sulfate ions with resulting soluble compounds, but only in the absence of quinquevalent vanadium, arsenic, or phosphorous. In the presence of these elements in the +5 valence state, the uranyl ion is fixed in insoluble layer compounds formed by union of uranyl ion with orthovanadate, orthophosphate, or orthoarsenate. Under favorable conditions UO2+2 may react to form the relatively insoluble rutherfordine, UO2CO3, or hydrated uranyl hydroxides. These are rarely found on the Colorado Plateau as opposed to their excellent development in other uraniferous areas, a condition which is apparently related to the semiarid climate and low water table of the Plateau. Uranium may also be fixed as uranyl silicate, but little is known about minerals of this kind. In the present study emphasis has been placed on a detailing of the chemical and crystal structural changes which occur in the oxidation paragenetic sequence.

Redistributed orebodies of Poison Canyon, Sec. 18 and 19, T. 13 N., R. 9 W., McKinley County

International Nuclear Information System (INIS)

Tessendorf, T.N.

1980-01-01

Since the early 1950's, the Poison Canyon mine has been considered a classic example of uranium geology. Owing to present economic condtions, a close examination of the redistributed mineralization is taking place. Because of the evolution of the structure and geomorphology of Poison Canyon, the primary mineralization went through further oxidation and reduction. Enriched solutions of uranium migrated downdip through permeable sands. These solutions were controlled by north-trending fracture patterns, with some vertical movement along major faults. The uranium collected in structural and lithological traps, forming amoeba-like orebodies with the higher grade mineralization located in the fractures. First-generation redistributed ore is primarily coffinite. Forming later is second-generation redistributed ore, which is mainly tyuyamunite. The latter formed from further oxidation and redistribution of the primary and first-generation mineralization, combined with an increasing nearness to surface. The authigenic minerals in the redistributed mineralization are found in carbon-deficient sands. The redistributed minerals are locally associated with pascoite, although this mineral is rare. The radiometric equilibrium of the primary minerals differs from that of the redistributed minerals. The uranium has been leached from the primary minerals making chemical values less than radiometric values. The redistributed minerals are chemically greater than radiometric, producing a favorable equilibrium. The percent extraction in the mill process is greater for the redistributed ore than for the primary ore. The paragenetic position of the different minerals has a direct bearing on these observations

Factor analysis of geochemical data from ore and host rocks of the uranium mineralization at Mika, N. E. Nigeria

International Nuclear Information System (INIS)

Funtua, I. I.

1997-01-01

The Mika uranium occurrence is located in one of a series of NW-NE trending shear zones which host uraniferous Jurassic rhyolitic dykes located in Pan-African brecciated granites within peraluminous granite complex of NE Nigeria. The bodies of mineralization are about 100 metres long and up to 4 metres thick. The U mineralization associated with the rhyolite dykes contains predominantly meta-autunite and apatite, while that of the brecciated granites displays variable mineralogy with meta-autunite, one or two generations of coffinite and colloformic, pitch blend in open veins. The mineralization is thought to be related to bimodel magmatism of the Burashika group and the reactivation of regional structures. Multivariate statistical evaluation of geochemical data of 28 elements/oxides in 296 host rock and mineralized samples from the surface and drill cores display a coherent association of [(U, Pb, Zn, Cu, P 2 O 5 , Fe 2 O 3 ) + Mo], [(CaO, Zr, Sr) +(Y, Mo, V, As)] and [(MgO, K 2 O) + (TiO 2 , Rb)] in the mineralized rocks; reflecting the presence of hamatized phosphate bearing ores in association with sulphide minerals and apatite in the granite rhyolites. A link of the mineralizing fluids with the emplacement of the rhyolites is implied from the striking resemblance between the above element association in mineralized rocks to those of the unmineralized rhyolites. A source of ore fluids over saturated in uranium and silica emanating from crystallizing rhyolitic melts which were expelled into faults and/or shear zones in the surrounding country rock is inferred

Evolution of uranium distribution and speciation in mill tailings, COMINAK Mine, Niger.

Science.gov (United States)

Déjeant, Adrien; Galoisy, Laurence; Roy, Régis; Calas, Georges; Boekhout, Flora; Phrommavanh, Vannapha; Descostes, Michael

2016-03-01

This study investigated the evolution of uranium distribution and speciation in mill tailings from the COMINAK mine (Niger), in production since 1978. A multi-scale approach was used, which combined high resolution remote sensing imagery, ICP-MS bulk rock analyses, powder X-ray diffraction, Scanning Electron Microscopy, Focused Ion Beam--Transmission Electron Microscopy and X-ray Absorption Near Edge Spectroscopy. Mineralogical analyses showed that some ore minerals, including residual uraninite and coffinite, undergo alteration and dissolution during tailings storage. The migration of uranium and other contaminants depends on (i) the chemical stability of secondary phases and sorbed species (dissolution and desorption processes), and (ii) the mechanical transport of fine particles bearing these elements. Uranium is stabilized after formation of secondary uranyl sulfates and phosphates, and adsorbed complexes on mineral surfaces (e.g. clay minerals). In particular, the stock of insoluble uranyl phosphates increases with time, thus contributing to the long-term stabilization of uranium. At the surface, a sulfate-cemented duricrust is formed after evaporation of pore water. This duricrust limits water infiltration and dust aerial dispersion, though it is enriched in uranium and many other elements, because of pore water rising from underlying levels by capillary action. Satellite images provided a detailed description of the tailings pile over time and allow monitoring of the chronology of successive tailings deposits. Satellite images suggest that uranium anomalies that occur at deep levels in the pile are most likely former surface duricrusts that have been buried under more recent tailings. Copyright © 2015 Elsevier B.V. All rights reserved.

Hydrothermal uranium vein deposits in Marysvale volcanic field, Utah

International Nuclear Information System (INIS)

Rasmussen, J.D.; Cunningham, C.G.; Steven, T.A.; Rye, R.O.; Romberger, S.B.

1984-01-01

Hydrothermal uranium veins are exposed over a 300 m (980 ft) vertical range in mines of the Central Mining area, near Marysvale, Utah. They cut 23 Ma quartz monzonite, 21 Ma granite, and 19 Ma rhyolite ash-flow tuff. The veins formed 18-19 Ma, in an area 1 km (0.6 mi) across, above the center of a composite magma chamber at least 12 x 6 km across that fed a sequence of 21-14 Ma hypabyssal granitic stocks, and rhyolitic lava flows, ash-flow tuffs, and volcanic domes. Intrusive pressure uplifted and fractured the roof; molybdenite-bearing, uranium-rich glassy dikes were intruded; and a breccia pipe and uranium-bearing veins were formed. The veins appear to have been deposited near the surface above a concealed rhyolite stock, where they filled high-angle fault zones and flat-lying to concave-downward pull-apart fractures. Low pH and fO 2 hydrothermal fluids at temperatures near 200 0 C (392 0 F) permeated the fractured rocks; these fluids were rich in fluorine and potassium, and contained uranium as uranous-fluoride complexes. Fluid-wall rock interaction increased fluid pH, causing precipitation of uranium minerals. At the deepest exposed levels, wall rocks were altered to kaolinite and sericite, and uraninite, coffinite, jordisite, fluorite, molybdenite, quartz, and pyrite (with delta 34 S near zero per mil) were deposited. The fluids were progressively oxidized higher in the system; iron in the wall rocks was oxidized to hematite, and sooty uraninite and umohoite were deposited

Origin of the Okrouhlá Radouň episyenite-hosted uranium deposit, Bohemian Massif, Czech Republic: fluid inclusion and stable isotope constraints

Science.gov (United States)

Dolníček, Zdeněk; René, Miloš; Hermannová, Sylvie; Prochaska, Walter

2014-04-01

The Okrouhlá Radouň shear zone hosted uranium deposit is developed along the contact of Variscan granites and high-grade metasedimentary rocks of the Moldanubian Zone of the Bohemian Massif. The pre-ore pervasive alteration of wall rocks is characterized by chloritization of mafic minerals, followed by albitization of feldspars and dissolution of quartz giving rise to episyenites. The subsequent fluid circulation led to precipitation of disseminated uraninite and coffinite, and later on, post-ore quartz and carbonate mineralization containing base metal sulfides. The fluid inclusion and stable isotope data suggest low homogenization temperatures (˜50-140 °C during pre-ore albitization and post-ore carbonatization, up to 230 °C during pre-ore chloritization), variable fluid salinities (0-25 wt.% NaCl eq.), low fluid δ18O values (-10 to +2 ‰ V-SMOW), low fluid δ13C values (-9 to -15 ‰ V-PDB), and highly variable ionic composition of the aqueous fluids (especially Na/Ca, Br/Cl, I/Cl, SO4/Cl, NO3/Cl ratios). The available data suggest participation of three fluid endmembers of primarily surficial origin during alteration and mineralization at the deposit: (1) local meteoric water, (2) Na-Ca-Cl basinal brines or shield brines, (3) SO4-NO3-Cl-(H)CO3 playa-like fluids. Pre-ore albitization was caused by circulation of alkaline, oxidized, and Na-rich playa fluids, whereas basinal/shield brines and meteoric water were more important during the post-ore stage of alteration.

Diagenesis of amorphous organic matter as an essential aspect of genesis and alteration of tabular-type uranium-vanadium deposits, Colorado Plateau

International Nuclear Information System (INIS)

Spirakis, C.S.; Hansley, P.L.

1987-01-01

Organic matter was the key to the initial concentration of uranium and vanadium (during the sulfate reduction stage of early diagenesis) in all sandstone-hosted, tabular deposits in the Morrison Formation, Colorado Plateau. In deposits rich in amorphous organic matter, as are many in the Grants uranium region (GUR), diagenesis did not proceed beyond sulfate reduction. In contrast, in organic-poor, chlorite deposits of the Henry Mountains district, 13 C- and 18 O-enriched dolomites preserve evidence of a subsequent methanogenic stage. In these and similar organic-poor deposits in the Slick Rock district and in parts of the GUR, aluminosilicate dissolution (including a distinctive, organic-acid-induced etching of garnets) and growth of coarse-grained coffinite, albite, ankerite, and chlorite suggest diagenesis reached the organic acid stage. Temperature and thermal maturation indicators (vitrinite reflectance, type IIb chlorite, ordered illite/smectite, and fluid inclusion data) are consistent with temperatures of organic-acid stage diagenesis (∼ 100 0 C). The localization of these alterations in and around organic-poor, clay-rich ore; the similarities in type and sequence of these alterations to the normal alteration of organic-bearing sediments; the alteration of iron-titanium oxides (attributed to the action of soluble organic complexes) around both organic-rich and organic-poor deposits; and the gradation from organic-rich to organic-poor, chlorite-rich deposits (in GUR) suggest that (1) amorphous organic matter was involved in the genesis of all of these deposits and (2) differences among deposits may reflect varying degrees of diagenesis of the organic matter

Alteration of rhyolitic (volcanic) glasses in natural Bolivian salt lakes. - Natural analogue for the behavior of radioactive waste glasses in rock salt repositories

International Nuclear Information System (INIS)

Abdelouas, A.

1996-06-01

Alteration experiments with the R7T7 glass in three salt brines, saturated respectively in MgCl 2 , MgCl 2 -CaCl 2 and NaCl, showed that the solubilities of most radionuclides are controlled by the secondary phases. Nd, La, and Pr are trapped in powellite, Ce in cerianite, U in coffinite, and Sr is partially immobilized in barite. There is a good similarity between the secondary phases formed experimentally on volcanic glasses and the R7T7 glass altered in MgCl 2 CaCl 2 -saturated brine (formation of hydrotalcite and chlorite-serpentine at short-term and saponite at long-term). These results support the use of volcanic glasses alteration patterns in Mg-rich solutions (seawater, brines) to understand the long-term behavior of nuclear waste glasses and to evaluate the stability of the secondary phases. The study of the sediments of Uyuni (Bolivia) showed that the corrosion rate of the rhyolitic glass in brines at 10 C is 12 to 30 time lower than those of rhyolitic glasses altered in high dilute conditions. The neoformed phases in the sediments are: Smectite, alunite, pyrite, barite, celestite and cerianite. The low alteration rate of rhyolitic glasses in brines and the formation of secondary phases such as smectite, barite and cerianite (also formed during the experimental alteration of the R7T7 glass), permit us to expect the low alteration of nuclear waste glasses at long-term in brines and the trapping of certain radionuclides in secondary phases. (orig.) [de

Bhima Basin, Karnataka, India uranium mineralisation in the Neoproterozoic

International Nuclear Information System (INIS)

Achar, K.K.; Pandit, S.A.; Natarajan, V.; Kumar, M.K.; Dwivedy, K.K.

2001-01-01

Based on the geological analogy of known uranium mineralisation in other Proterozoic basins of India, the Bhima basin in northern Karnataka, covering an area of 5200 sq km, was taken up for uranium exploration. An integrated approach involving exploration techniques such as terrain analysis using satellite imageries, jeep-borne radiation survey, regional hydrogeochemical sampling and ground radiometric surveys were used. In addition gamma-ray logging of borewells drilled for water have enabled delineation of subsurface mineralisation at Gogi. Uranium mineralisation is associated with: (1) altered phosphatic limestone along the cherty limestone-shale boundary as at Ukinal, (2) brecciated non-phosphatic limestone as at Gogi, and (3) basic enclaves in the basement granites, as at Gogi East. Uranium occurs essentially as adsorbed phase on limonite and absorbed in collophane in the phosphatic limestone as at Ukinal. Mineralisation at Gogi is characterised by intense fracturing and brecciation apparently related to E-W trending Kurlagere-Gogi fault and is essentially low temperature (c.200 deg. C) hydrothermal nature represented by coffinite (thin veins and globular aggregates) along with pitchblende, pyrite (both framboidal and euhedral), pyrrhotite, haematite and anatase. Mineralisation is both syngenetic - remobilised as in the phosphatic limestones (Ukinal) and epigenetic hydrothermal (Gogi). The spatial relation of the unconformity, basement faults, and uranium - bearing basic enclaves within the basement points to the importance of the unconformity as a surface for fluid transport and fixation in conducive hosts. Presence of labile uranium in the basement granites with significant groundwater anomalies (up to 309 ppb U) enhances such possibilities. (author)

Sandstone uranium deposits: analogues for surf disposal in some sedimentary rocks

International Nuclear Information System (INIS)

Brookins, D.G.

1987-01-01

Sandstone uranium deposits are well suited as analogs for SURF. These deposits typically occur as tabular or lensoid masses of uraniferous sandstone, commonly where the argillaceous mineral and organic content is high. Primary minerals consist of pitchblende and/or coffinite, with possibly some urano-organic phases as well. The ore is usually associated with authigenic ferromagnesian clay minerals, such as chlorite and/or authigenic illite and/or mixed layer smectite-illite; and with pyrite ± jordisite ± seleniferrous species ± calcite. Organic matter is usually associated with the ore. The clay minerals in the ore zones are commonly vanadiferrous. The genesis of the sandstone uranium deposits is now fairly well understood and allows semi-quantitative estimates to be placed on behaviour of analog-elements for many constituents of SURF (or HLW). Prior to mineralization, oxidized species of U, V, Se, Mo, As are carried together as oxyanions; these species precipitate in a restricted range of Eh-pH when reducing conditions are met. Concomitant with removal of these species, due to formation of reduced, insoluble species, several other elements of interest are concentrated in the ore zones as well. Chalcophile elements, such as Cu, Co, Mn, Zn, Cd, Sb, and others are fixed in authigenic sulfide phases, and the alkalis Rb, K, and Cs are fixed in the authigenic illite and illitic mixed layer clays. The alkaline earth elements Sr and Ba are commonly fixed in sulfate-rich rock. The rare earth elements (REE) are incorporated into authigenic clay minerals or into oxy-hydroxide phases. (author)

Genesis of uranium deposits of the Tono Mine, Japan

International Nuclear Information System (INIS)

Katayama, N.; Kubo, K.; Hirono, S.

1974-01-01

The uranium deposits of the Tono mine, Gifu Prefecture, Japan, occur in the basal part of the Toki group of Miocene age, and are distributed in the tributaries or at the head of channels on the plane of unconformity under the formation. These features characterize the basal ground-water type of uranium deposit, and they are unique in that their typical ore mineral is a zeolite of the heulandite-clinoptilolite group, uranium being adsorbed in it. The paper presents the history of formation of the Tsukiyoshi deposits, the most intensely explored in the Tono mine. The matrices of conglomerates and sandstones of the Toki group usually contain tuffaceous material, which has been montmorillonitized or zeolitized diagenetically. The conduit of uranium-bearing ground waters that migrated from the basement granites into the Tertiary sediments was controlled by the impermeable barriers, which are rocks in which montmorillonite predominated, or by the Tsukiyoshi fault, as well as by channel structures. Where the waters became rather stagnant, uranium was adsorbed in zeolite from them. Enrichment of uranium further proceeded locally as follows. Pyrite was oxidized to produce sulphuric acid solution which leached the uranium that had been adsorbed in zeolite. The pH of the uranium-rich solution became higher and higher in the course of migration and, as soon as it reached about 4, the uranium in the solution was again adsorbed in zeolite, the uranium content of which may have been enriched up to 0.9%. Coffinites have been formed where uranium was accumulated over the adsorption capacity of zeolite or where strongly reducing conditions were maintained by carbonaceous matter. (author)

Discussion on geological features and genesis of Chulute uranium metallogenetic region of North Hanggay Province in Mongolia

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Zhao Fengmin

2005-01-01

Chulute uranium metallogenetic region is situated in the northern part of North Hanggay Province in Mongolia. Geotectonically, it is located at the very western end of Mongolia-Transbaikal fold system. The granite with elevated uranium content is widely developed in this region, where the uranium content in the granite aged from Later Triassic to Early Jurassic ranges from 5 x 10 -6 to 6 x 10 -6 . Due to the neotectonic activation, quaternary palaeo-valleys that incised the basement were formed on the basement granite and were filled with organic matter-rich clastic sediments and basalt crusts. The palaeo-valley type uranium mineralization (Dajinhe, Bayaer and Shuer uranium occurrences) is discovered in the two palaeo-valleys which incised the granitoids. Of them, Shuer uranium occurrence has been studied more in detail. An ore-body with the thickness from 9.1 m to 19.75 m has been found in an area with the width of 500 m, and the uranium grade ranging from 0.01% to 0.05%. The uranium mineralization occurs in the bleached and limonitized grey loam and clayey soil and sand which bear rich calliferous plant debris and lamella of black mudstones. Coffinite is the uranium mineral. The uranium resources in Shuer deposit has been proven as 2500 t. The total predictive resources in above mentioned two palaeo-valleys reach as much as 15000-16000 t (P 2 ). The uranium mineralization in this region is characterized by young mineralization age and adjacent sources. The ore formation is possibly related to the surface thermal field which is originated from the eruption of the basaltic magmas. (authors)

National Uranium Resource Evaluation. Groundwater prospecting for sandstone-type uranium deposits: the merits of mineral-solution equilibria versus single element tracer methods. Final report

International Nuclear Information System (INIS)

Chatham, J.R.; Wanty, R.B.; Langmuir, D.

1981-02-01

Groundwaters from aquifers in two different sandstone-type uranium mining districts in Texas and Wyoming were collected and chemically analyzed. The data were used to compare the merits of using the computed saturation state of the groundwater with respect to uranium minerals, to that of single-element tracers in the groundwater for geochemical prospecting. Chemical properties of the Texas waters were influenced locally by preferred groundwater flow within buried fluvial channel deposits; upward leakage of brines along growth faults into the aquifer; and the establishment of a redox interface (Eh = 0 volts) within the aquifer. Chemical characteristics of aquifer waters in Wyoming changed gradually downdip, reflecting regional homogeneity in groundwater flow and a more gradual downdip reduction of Eh values than in Texas. The most reliable indicator of reduced uranium ore in both study sites was the saturation state of groundwater with respect to uraninite or coffinite. For both minerals, this saturation state increased from 15 to 20 log units as reduced ore deposits were approached over distances of 3 to 4.5 km in both sites. Tyuyamunite and carnotite approached or exceeded saturation in some oxidized waters of the Texas site reflecting possible occurrences of these minerals. The radiogenic elements Ta and Rn were excellent indicators of ore directly within the deposits, where anomalous values were 2 to 3 orders of magnitude above background. Helium also increased near the ore, although anomalies were generally displaced in the direction of groundwater flow. Uranium and uranium isotope values did not individually pinpoint ore, but may be used together to classify groundwater samples in terms of their position relative to uranium mineralization

Geochemical behavior of uranium mill tailings leachate in the subsurface

International Nuclear Information System (INIS)

Brookins, D.G.

1993-01-01

Leachate generated from surface disposal of acidic uranium mill tailings at Maybell, CO has impacted groundwater quality within the underlying mineralized Browns Park Formation. The extent of groundwater contamination, however, is located directly beneath the tailings impoundment. The milling process consisted of sulfuric acid extraction of uranium from the feed ore by a complex chemical leaching and precipitation process. Tailings leachate at the site contains elevated concentrations of Al, As, Cd, Mo, Ni, NO 3 , Se, U, and other solutes. From column leach tests, the concentrations of contaminants within tailings pore fluid are SO 4 >NH 4 >NO 3 >U>Se>Ni>As>Cd at pH 4.0. The carbonate buffering capacity of the tailings subsoil has decreased because of calcite dissolution in the presence of acidic leachate. Groundwater quality data, mineralogical and microbiological studies, and geochemical modeling suggest that As, NO 3 , Se, U and other solutes are being removed from solution through precipitation, adsorption, and denitrification processes under reducing conditions. Presence of hydrogen sulfide, liquid and gaseous hydrocarbons, dissolved organic, and abundant pyrite within the Browns Park Formations have maintained reducing conditions subjacent to the tailings impoundment. Groundwater is in close equilibrium with coffinite and uraninite, the primary U(IV) minerals extracted from the Browns Parks Formation. Denitrifying bacteria identified in this study catalyze redox reactions involving NO 3 . Subsequently, contaminant distributions of NO 3 decrease 1000 times beneath the tailings impoundment. Applying geochemical and biochemical processes occurring at Maybell provides an excellent model for in situ aquifer restoration programs considered at other uranium tailings and heavy-metal-mixed waste contaminated sites. (author) 4 figs., 4 tabs., 27 refs

Uraninite alteration in an oxidizing environment and its relevance to the disposal of spent nuclear fuel

International Nuclear Information System (INIS)

Finch, R.; Ewing, R.

1990-12-01

Uraninite is a natural analogue for spent nuclear fuel because of similarities in structure and chemistry. Effective assessment of the long-term behavior of spent fuel in a geologic repository requires a knowledge of the corrosion products produced in that environment. Several important natural analogue sites are reviewed, illustrating a wide variety of environments from oxidizing to reducing, including, among others: Cigar Lake, Canada, a uraninite-bearing ore body at depth within a strictly reducing environment; the ore body has 'seen' extensive groundwater interaction with virtually no significant oxidation or mobilization of U apperent. Koongara, Australia is a highly altered uraninite-bearing ore body partially exposed to meteoric water; alteration at depth has resulted from interaction with groundwater having a somewhat reduced Eh compared to the surface. Uraninite, Pb-uranyl oxide hydrates and uranyl silicates control U solubility at depth; uranyl phosphates and U adsorption onto clays and FeMn-oxides control U solubility near the surface. Pocos de Caldas, Brazil displays a redox from moving through uraninite-bearing rocks near the surface and shows local remobilization of U. Oklo, Gabon, a uraninite- and coffinite-bearing ore body, locally affected by intense hydrothermal alteration during fission reactions, demonstrates restricted radionuclide and fission product transport within a reducing environment. A current study being conducted by the authors at Shinkolbwe, Zaire, a uraninite-bearing ore body exposed to highly oxidizing conditions at the surface, provides over 50 species of uranyl phases for detailed study, and illustrates a complex uranyl phase paragenesis over several million years, from earliest-formed uranyl oxide hydrates and uranyl silicates to later-formed uranyl phosphate. (au) (268 refs.)

A rapid in situ method for determining the ages of uranium oxide minerals: Evolution of the Cigar Lake deposit, Athabasca Basin

International Nuclear Information System (INIS)

Fayek, M.; Harrison, T.M.; Grove, M.; Coath, C.D.

2000-01-01

The authors present a rapid and accurate technique for making in situ U-Pb isotopic measurements of uranium oxide minerals that utilizes both electron and ion microprobes. U and Pb concentrations are determined using an electron microprobe, whereas the isotopic composition of Pb for the same area is measured using a high-resolution ion microprobe. The advantages of this approach are: mineral separation and chemical digestion are unnecessary; homogeneous uranium oxide standards, which are difficult to obtain, are not required; and precise and accurate U-Pb ages on ∼10 microm spots can be obtained in a matter of hours. The authors have applied their method to study the distribution of U-Pb ages in complexly intergrown uranium oxides from the unconformity-type Cigar Lake uranium deposit, Saskatchewan, Canada. In situ U-Pb results from early formed uraninite define a well-correlated array on concordia with upper and lower intercepts of 1,467 ± 63 Ma and 443 ± 96 Ma (±1σ), respectively. The 1,467 Ma age is interpreted as the minimum age of mineralization and is consistent with the age of clay-mineral alteration (approximately1477 Ma) and magnetization of diagenetic hematite (1,650 to 1,450 Ma) that is associated with these unconformity-type uranium deposits and early diagenesis of the Athabasca Basin sediments. In situ U-Pb isotopic analysis of uraninite and coffinite can document the Pb*/U heterogeneities that can occur on a scale of 15 to 30 microm, thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits

Contribution to the study of uranium dioxide aqueous corrosion mechanisms

International Nuclear Information System (INIS)

Gallien, J.-P.

1994-01-01

The corrosion of uranium dioxide by a synthetical ground water has been studied in order to understand the behaviour of nuclear fuels in the hypothesis of a direct storage. An original leaching unit has been carried out in order to control the parameters occurring in the oxidation-dissolution of the uranium dioxide and to condition the leachate (in particular the temperature and the partial pressure of the carbon dioxide). A ground water in equilibrium with the geological enveloping site has been reconstituted from data acquired on the site. The influence of two parameters has been followed: the carbon dioxide carbon pressure and the redox potential. Each experiment has been carried out at 96 C during one month and the time-history of the solutions and of the solids has been studied. In oxidizing conditions, the uranium concentration in solution has been controlled by an U(VI) complex (one oxide, one hydroxide or a carbonate). The possibility of a control by an U(IV) complex (as coffinite, uraninite or uraninite B) has been confirmed in the case of reducing leaching. An original interpretation of the Rutherford backscattering spectra has allowed to describe the decomposition of the samples in a succession of layers of different densities. A very good agreement between the analyses of the solids and those of the solutions has been obtained in the experiments occurring in reducing conditions. Complementary leaching involving solutions containing stable isotopes (deuterium, O 18 ) have revealed the formation of an hydrated layer and the contribution of grain boundaries to the corrosion phenomenon of uranium dioxide. The results of the current hydro-geochemistry study on the uranium Oklo deposit prove the realism of the experiments that have been carried out in the laboratory. (O.M.)

The latest study on development of metallogenic mechanism of Baimianshi uranium field, Jiangxi Province, China

International Nuclear Information System (INIS)

Fan, H.; He, D.; Wang, F.

2009-01-01

It has been considered that deposits in Baimianshi uranium field have similar features and ore-forming type, it is the syngenetic sedimentation that caused some U-bearing minerals to concentrate, and as a result of the enrichment in the late lithogenetic stage the deposit formed which is separate genesis to sandstone type and volcanic hydrothermal sub-type. This paper takes Huangnihu deposit in Baimianshi field as an example, and regards Baimianshi field as hydrothermal type according to research on intergrowth assemblage, fluid inclusions, U-Pb isotopic dating and Nd-Sr isotopic tracing. Ore minerals are mainly uraninite, brannerite, coffinite, etc, while the assistant gangue minerals are mainly galena, hematite, marcasite, blende, etc. The materials for uranium mineralization are mainly crust-derived rocks. Continuous extraction of uranium from the upper crust and basement granite by mantle-derived fluids with little of ore-forming elements may be responsible for the remobilization and transformation of uranium. Mixing of ore-enriched fluid with groundwater in some enclosed places overlain by basalt leads to the precipitation of ore-forming materials from the mixed fluid. There are three episodes of uranium mineralization: The first one is 160.4±0.5Ma, related to double-peak type volcanism, with basalt lithogenetic age of 172.8±7.7Ma and rhyolite lithogenetic age of 164.8±0.57Ma (from Chen Peirong, etc., 1999). The second one is 128±0.8Ma, related to Yanshanian Magmatic activities, for example, Danguanzhang rock mass and several phases of complements. The third one is about 100Ma, related to sub-volcanic rocks and dykes, namely quartz porphyry (99Ma) and diabase (105Ma). The above achievements will play an important part in the guidance of future prospecting in the deeper in that area. (author)

Geology and uranium favorability of the Sonora Pass region, Alpine and Tuolumne Counties, California

Energy Technology Data Exchange (ETDEWEB)

Rapp, J.S.; Short, W.O.

1981-06-01

Uranium mineralization at the Juniper Mine is restricted to host rocks of the Relief Peak Formation and is most common in coarse-grained lithic sandstone, conglomerate, and lithic wacke. The richest beds contain as much as 0.5% U/sub 3/O/sub 8/. Uranium is present as coffinite, uraninite, and unidentified minerals. Thorium/uranium ratios are generally low and erratic. Equivalent uranium determinations are low in comparison with chemical uranium values, indicating that uranium mineralization of the Juniper Mine is geologically young. Core drilling at 16 localities shows that widely separated exposures of the Relief Peak Formation have very similar lithology, geochemistry, and stratigraphy. Some sections are similar to the Juniper Mine section. Core from the bottom of drill hole SP-1 contains 83 ppM uranium, the greatest known concentration outside the mine area. Significant uranium deposits may be concealed beneath the thick Tertiary volcanic cover of the region. The quartz latitic Eureka Valley Tuff is fairly widespread in east-central California and western Nevada. It contains 12 to 14 ppM uranium and stratigraphically overlies the Relief Peak Formation. It is permeable and contains abundant alkali metals and volcanic glass. Because of its petrology, geochemistry, and position, this formation is the most likely source for uranium mineralization of the Sonora Pass region. It should be examined as a potential source rock in other areas with special regard to its relationship to carbonaceous sedimentary formations. The uraniferous granite pegmatitite dike that crops out in the Niagara Creek area appears too small to be a significant source rock. The most favorable rocks in the Sonora Pass region occur near the Juniper Mine and west of it, in the Dardanelles, the Whittakers Dardanelles, and the area of the Big Meadow Quadrangle. Potential uranium host rocks crop out in areas along the crest of the Sierra Nevada from Lake Tahoe to Yosemite.

Geology and uranium favorability of the Sonora Pass region, Alpine and Tuolumne Counties, California

International Nuclear Information System (INIS)

Rapp, J.S.; Short, W.O.

1981-06-01

Uranium mineralization at the Juniper Mine is restricted to host rocks of the Relief Peak Formation and is most common in coarse-grained lithic sandstone, conglomerate, and lithic wacke. The richest beds contain as much as 0.5% U 3 O 8 . Uranium is present as coffinite, uraninite, and unidentified minerals. Thorium/uranium ratios are generally low and erratic. Equivalent uranium determinations are low in comparison with chemical uranium values, indicating that uranium mineralization of the Juniper Mine is geologically young. Core drilling at 16 localities shows that widely separated exposures of the Relief Peak Formation have very similar lithology, geochemistry, and stratigraphy. Some sections are similar to the Juniper Mine section. Core from the bottom of drill hole SP-1 contains 83 ppM uranium, the greatest known concentration outside the mine area. Significant uranium deposits may be concealed beneath the thick Tertiary volcanic cover of the region. The quartz latitic Eureka Valley Tuff is fairly widespread in east-central California and western Nevada. It contains 12 to 14 ppM uranium and stratigraphically overlies the Relief Peak Formation. It is permeable and contains abundant alkali metals and volcanic glass. Because of its petrology, geochemistry, and position, this formation is the most likely source for uranium mineralization of the Sonora Pass region. It should be examined as a potential source rock in other areas with special regard to its relationship to carbonaceous sedimentary formations. The uraniferous granite pegmatitite dike that crops out in the Niagara Creek area appears too small to be a significant source rock. The most favorable rocks in the Sonora Pass region occur near the Juniper Mine and west of it, in the Dardanelles, the Whittakers Dardanelles, and the area of the Big Meadow Quadrangle. Potential uranium host rocks crop out in areas along the crest of the Sierra Nevada from Lake Tahoe to Yosemite

Purification of uranothorite solid solutions from polyphase systems

Energy Technology Data Exchange (ETDEWEB)

Clavier, Nicolas, E-mail: nicolas.clavier@icsm.fr [ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule – Bât. 426, BP 17171, 30207 Bagnols/Cèze cedex (France); Szenknect, Stéphanie; Costin, Dan Tiberiu; Mesbah, Adel; Ravaux, Johann [ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule – Bât. 426, BP 17171, 30207 Bagnols/Cèze cedex (France); Poinssot, Christophe [CEA/DEN/DRCP/DIR, Site de Marcoule – Bât. 400, BP 17171, 30207 Bagnols/Cèze cedex (France); Dacheux, Nicolas [ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule – Bât. 426, BP 17171, 30207 Bagnols/Cèze cedex (France)

2013-10-15

Graphical abstract: Display Omitted -- Highlights: •Purification of Th{sub 1−x}U{sub x}SiO{sub 4} uranothorites from oxide mixture was investigated. •Repetition of centrifugation steps was discarded due to poor recovery yields. •Successive washings in acid and basic media allowed the elimination of oxide secondary phases. •Structural and microstructural characterization of the purified samples was provided. -- Abstract: The mineral coffinite, nominally USiO{sub 4}, and associated Th{sub 1−x}U{sub x}SiO{sub 4} uranothorite solid solutions are of great interest from a geochemical point of view and in the case of the direct storage of spent nuclear fuels. Nevertheless, they clearly exhibit a lack in the evaluation of their thermodynamic data, mainly because of the difficulties linked with their preparation as pure phases. This paper thus presents physical and chemical methods aiming to separate uranothorite solid solutions from oxide additional phases such as amorphous SiO{sub 2} and nanometric crystallized Th{sub 1−y}U{sub y}O{sub 2}. The repetition of centrifugation steps envisaged in first place was rapidly dropped due to poor recovery yields, to the benefit of successive washings in acid then basic media. Under both static and dynamic flow rates (i.e. low or high rate of leachate renewal), ICP-AES (Inductively Coupled Plasma – Atomic Emission Spectroscopy) analyses revealed the systematic elimination of Th{sub 1−y}U{sub y}O{sub 2} in acid media and of SiO{sub 2} in basic media. Nevertheless, two successive steps were always needed to reach pure samples. On this basis, a first cycle performed in static conditions was chosen to eliminate the major part of the accessory phases while a second one, in dynamic conditions, allowed the elimination of the residual impurities. The complete purification of the samples was finally evidenced through the characterization of the samples by the means of PXRD (Powder X-Ray Diffraction), SEM (Scanning Electron

The South Greenland regional uranium exploration programme

International Nuclear Information System (INIS)

Armour-Brown, A.; Tukiainen, T.; Nyegaard, P.; Wallin, B.

1984-02-01

This report describes the work and results of the last two field seasons (1080 and 1982) of the Syduran Project. The field work was concentrated in the Motzfeldt Centre and the Granite zone with a short reconnaissance of five uranium anomalies in the Migmatite Complex. The results from the Motzfeldt Centre show that it is composed of at least 6 syenite units which can be divided into two major phases of igneous activity. The radioactive mineralisation has been mapped by gamma-spectrometer and has proved to be very extensive. Uranium mineral occurrences found in the Granite Zone occur in the many faults and fractures, which dissect the area. A study of the fractures and fault movements in the zone makes it possible to suggest an overall structural framework in which to place the uranium occurrences in the zone. Field work on the Igaliko peninsula was confined to a small area known as Puissagtag where four pitchblende veins have been discovered. Numerous uraniferous showings, associated with fractures, have been located in the Vatnaverfi peninsula south of the Igaliko Fjord. Mineralogical studies have shown that 12 of these showings contain pitchblende, that 7 of them contain coffinite and that most of them contain brannerite. The most interesting find during the 1982 field season was in the Migmatite Complex. Five anomalously high uranium areas in the complex were explored briefly with the helicopter-borne scintillometer. Near a place called Igdlorssuit, where a particlarly high gamma-spectrometer anomaly was found during the reconnaissance gamma-spectrometer survey, a large raft of meta-sediments in rapakivi granite was found, in which radioactive mineralisation occurred. This proved to be due to fine disseminated uraninite which occurs over some 150 m of strike length with a width of 1-2 m. The results confirm that there is a good possibility of finding exploitable uranium mineral occurrences in South Greenland. (author)

Discovery of the Sierra Pintada uranium district, Mendoza Province, Argentina

International Nuclear Information System (INIS)

Rodrigo, F.; Belluco, A.E.

1981-01-01

Since 1956, uranium-bearing minerals have been known to exist in Sierra Pintada, Mendoza Province, Argentina. Based on paragenetic considerations, a first radiometric prospection was carried out, leading to the discovery of two groups of anomalies (Puesto Agua del Toro and Cuesta de los Terneros), such as vein-type deposits, with uraninite and 'yellow minerals' and one sandstone-type deposit (Puesto La Josefa), related to sediments with carbon trash. Some recent geological research and surveys in the area, and a reduced drilling programme carried out on selected anomalies, led to reinterpretation of the potential of the area. Furthermore, and as a result of an airborne radiometric prospection performed in mid-1968, numerous anomalies have been discovered. The main constellation of anomalies, along the flanks of the El Tigre Brachyanticline, occurs in sandstones of Permian age. Explored by 80 000 m of drilling, they have shown the existence of several peneconcordant lens-shaped ore bodies of economic size, with uranophane on the surface and prevailing uraninite and some brannerite, coffinite and davidite below the water table. Reserves exceed 20 000 tonnes of U 3 O 8 . A new regional programme with a 4-km drill-grid initiated in 1978 led to the discovery of new ore bodies which are at present being evaluated. The alternatives and discontinuities during the development of the district, the prospecting and exploration techniques employed, and the results achieved in the different stages of the operation are discussed in detail. This case history attempts to illustrate the developing philosophy which was successfully applied in Sierra Pintada, with emphasis on the following points: (a) the need for adequate geological knowledge of the area; (b) the advantage of a massive survey (in this case, air survey); (c) the necessity for exploration (drilling) in order to define the anomalies and make their evaluation possible; and (d) the convenience of extending exploration

Evolution of uranium distribution and speciation in mill tailings, COMINAK Mine, Niger

International Nuclear Information System (INIS)

Déjeant, Adrien; Galoisy, Laurence; Roy, Régis; Calas, Georges; Boekhout, Flora; Phrommavanh, Vannapha; Descostes, Michael

2016-01-01

This study investigated the evolution of uranium distribution and speciation in mill tailings from the COMINAK mine (Niger), in production since 1978. A multi-scale approach was used, which combined high resolution remote sensing imagery, ICP-MS bulk rock analyses, powder X-ray diffraction, Scanning Electron Microscopy, Focused Ion Beam — Transmission Electron Microscopy and X-ray Absorption Near Edge Spectroscopy. Mineralogical analyses showed that some ore minerals, including residual uraninite and coffinite, undergo alteration and dissolution during tailings storage. The migration of uranium and other contaminants depends on (i) the chemical stability of secondary phases and sorbed species (dissolution and desorption processes), and (ii) the mechanical transport of fine particles bearing these elements. Uranium is stabilized after formation of secondary uranyl sulfates and phosphates, and adsorbed complexes on mineral surfaces (e.g. clay minerals). In particular, the stock of insoluble uranyl phosphates increases with time, thus contributing to the long-term stabilization of uranium. At the surface, a sulfate-cemented duricrust is formed after evaporation of pore water. This duricrust limits water infiltration and dust aerial dispersion, though it is enriched in uranium and many other elements, because of pore water rising from underlying levels by capillary action. Satellite images provided a detailed description of the tailings pile over time and allow monitoring of the chronology of successive tailings deposits. Satellite images suggest that uranium anomalies that occur at deep levels in the pile are most likely former surface duricrusts that have been buried under more recent tailings. - Highlights: • The evolution of U distribution and speciation in mill tailings is investigated. • High resolution satellite images provide useful information on tailings evolution. • U and many other elements are enriched in a sulfate-rich duricrust. • Formation of

Evolution of uranium distribution and speciation in mill tailings, COMINAK Mine, Niger

Energy Technology Data Exchange (ETDEWEB)

Déjeant, Adrien, E-mail: adrien.dejeant@normalesup.org [Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris (France); Université Paris Diderot — Paris VII, 5 rue Thomas Mann, 75013 Paris (France); Galoisy, Laurence [Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris (France); Université Pierre et Marie Curie — Paris VI, 4 place Jussieu, 75005 Paris (France); Roy, Régis [AREVA Mines — Geoscience Department, Tour AREVA, 1 place Jean Millier, 92084 Paris, La Défense (France); Calas, Georges; Boekhout, Flora [Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris (France); Université Pierre et Marie Curie — Paris VI, 4 place Jussieu, 75005 Paris (France); Phrommavanh, Vannapha; Descostes, Michael [AREVA Mines — R& D Department, BAL 0414C-2, Tour AREVA, 1 place Jean Millier, 92084 Paris, La Défense (France)

2016-03-01

This study investigated the evolution of uranium distribution and speciation in mill tailings from the COMINAK mine (Niger), in production since 1978. A multi-scale approach was used, which combined high resolution remote sensing imagery, ICP-MS bulk rock analyses, powder X-ray diffraction, Scanning Electron Microscopy, Focused Ion Beam — Transmission Electron Microscopy and X-ray Absorption Near Edge Spectroscopy. Mineralogical analyses showed that some ore minerals, including residual uraninite and coffinite, undergo alteration and dissolution during tailings storage. The migration of uranium and other contaminants depends on (i) the chemical stability of secondary phases and sorbed species (dissolution and desorption processes), and (ii) the mechanical transport of fine particles bearing these elements. Uranium is stabilized after formation of secondary uranyl sulfates and phosphates, and adsorbed complexes on mineral surfaces (e.g. clay minerals). In particular, the stock of insoluble uranyl phosphates increases with time, thus contributing to the long-term stabilization of uranium. At the surface, a sulfate-cemented duricrust is formed after evaporation of pore water. This duricrust limits water infiltration and dust aerial dispersion, though it is enriched in uranium and many other elements, because of pore water rising from underlying levels by capillary action. Satellite images provided a detailed description of the tailings pile over time and allow monitoring of the chronology of successive tailings deposits. Satellite images suggest that uranium anomalies that occur at deep levels in the pile are most likely former surface duricrusts that have been buried under more recent tailings. - Highlights: • The evolution of U distribution and speciation in mill tailings is investigated. • High resolution satellite images provide useful information on tailings evolution. • U and many other elements are enriched in a sulfate-rich duricrust. • Formation of

The influence of biofilms on the migration of uranium in acid mine drainage (AMD) waters

International Nuclear Information System (INIS)

Krawczyk-Baersch, E.; Luensdorf, H.; Arnold, T.; Brendler, V.; Eisbein, E.; Jenk, U.; Zimmermann, U.

2011-01-01

The uranium mine in Koenigstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO 2 SO 4 ) and UO 2 ++ speciation as well as of the solid uranium species Uranophane [Ca(UO 2 ) 2 (SiO 3 OH) 2 ·5H 2 O] and Coffinite [U(SiO 4 ) 1-x (OH) 4x ], which are defined in the stability field of pH > 4.8 and Eh 0 and Eh 4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be inhibited. - Highlights: → Redox potential and pH of the biofilm differ significantly compared to the AMD water. → Formation of an aqueous uranium(VI) sulfate complex in the biofilm and in the AMD water. → Experiments revealed that the F. myxofaciens dominated biofilms have a substantial impact on the migration of uranium. → Due to homeostatic mechanisms the microbes maintain their intracellular pH even when the pH of the water increases.

Contribution of U-Pb geochronology to characterizing the Cadomian magmatism of the southeastern French Massif Central and of the related uranium-ore at Bertholene

International Nuclear Information System (INIS)

Leveque, Marie-Helene

1990-01-01

U-Pb geochronology and whole-rock geochemistry (major, trace and rare earth elements) were applied to various ortho- and paragneiss formations of the southeastern part of the French Massif Central. The Mendic granite and the Les Palanges granite were dated at 603 ± 9 Ma and 540 ± 18 Ma, respectively. Their micaschist host-rocks show a multi-episodic evolution that matches the U-Pb data obtained on metasediments and leucogranites of the Variscan Orogen. An old zircon source was detected at 1.87 Ga in the Les Palanges micaschist, while, seemingly, this heritage was wiped out of the Mendic micaschist during the Cadomian events. In the Decazeville gneiss, where a crustal component of unknown age has been detected, the major event is the Variscan migmatization. At Bertholene, the geochronology of uranium ores associated to the Les Palanges orthogneiss evidenced two periods of emplacement: -the relicts of the first phase, of Liassic age at 173 ± 9 Ma, are restricted to an uranium oxide; -the second phase, related to coffinites, represents the economical ore emplaced from Oligocene until Recent times, generated through remobilization of the Liassic stock. A comparison between the geochronological data from the ore, and of those from its granite host, suggests a genetic relationship between the Cadomian magmatism and the U-concentrations, spatially linked to the unconformity between the Les Palanges basement and its Permo-Carboniferous cover series. Metamictization of the source minerals combined with tectonic processes would be responsible for the release of uranium. Uranium-rich minerals from Bertholene, from Lodeve and from Les Pierres-Plantees have been subjected to trial dating by the isotopic Xe-Xe method, which confirms the evolution admitted for those occurrences. This technique is demonstrably expeditious and faithful. Various phenomena were investigated, at the scale of the crystalline structure, related to the xenon energy states and to the problem of rare

Geochemical modelling of the weathering zone of the 'Mina Fe' U deposit (Spain): A natural analogue for nuclear spent fuel alteration and stability processes in radwaste disposal

International Nuclear Information System (INIS)

Arcos, D.; Perez del Villar, L.; Bruno, J.; Domenech, C.

2008-01-01

The 'Mina Fe' U deposit (Salamanca, Spain) has been studied in the context of Enresa's programme for U-mine sites restoration and also as a natural analogue for processes in high-level nuclear waste (HLNW) geological disposal. The investigations encompassed an array of geoscience disciplines, such as structural geology, mineralogy, hydrogeology and elemental and isotopic geochemistry and hydrogeochemistry of the site. Based on the obtained results, a conceptual mineralogical and geochemical model was performed integrating the main geochemical processes occurring at the site: the interaction between oxidised and slightly acidic water with pyrite, pitchblende, calcite and dolomite, as essential minerals of the U fracture-filling mineralisation, and hydroxyapatite from the host rock, as the main source of P. This conceptual model has been tested in a systematic numerical model, which includes the main kinetic (pyrite and pitchblende dissolution) and equilibrium processes (carbonate mineral dissolution, and goethite, schoepite and autunite secondary precipitation). The results obtained from the reactive-transport model satisfactorily agree with the conceptual model previously established. The assumption of the precipitation of coffinite as a secondary mineral in the system cannot be correctly evaluated due to the lack of hydrochemical data from the reducing zone of the site and valid thermodynamic and kinetic data for this hydrated U(IV)-silicate. This precipitation can also be hampered by the probable existence of dissolved U(IV)-organic matter and/or uranyl carbonate complexes, which are thermodynamically stable under the alkaline and reducing conditions that prevail in the reducing zone of the system. Finally, the intense downwards oxic and acidic alteration in the upper part of the system is of no relevance for the performance assessment of a HLNW disposal. However, the acidic and oxidised conditions are quickly buffered to neutral-alkaline and reducing at very

Geochemical modelling of the weathering zone of the 'Mina Fe' U deposit (Spain): A natural analogue for nuclear spent fuel alteration and stability processes in radwaste disposal

Energy Technology Data Exchange (ETDEWEB)

Arcos, D. [AMPHOS XXI Consulting S.L., Passeig de Rubi, 29-31, 08197 Valldoreix, Barcelona (Spain)], E-mail: david.arcos@amphos21.com; Perez del Villar, L. [CIEMAT, Dpto.de Medio Ambiente, Avda, Complutense 22, 28040 Madrid (Spain); Bruno, J.; Domenech, C. [AMPHOS XXI Consulting S.L., Passeig de Rubi, 29-31, 08197 Valldoreix, Barcelona (Spain)

2008-04-15

The 'Mina Fe' U deposit (Salamanca, Spain) has been studied in the context of Enresa's programme for U-mine sites restoration and also as a natural analogue for processes in high-level nuclear waste (HLNW) geological disposal. The investigations encompassed an array of geoscience disciplines, such as structural geology, mineralogy, hydrogeology and elemental and isotopic geochemistry and hydrogeochemistry of the site. Based on the obtained results, a conceptual mineralogical and geochemical model was performed integrating the main geochemical processes occurring at the site: the interaction between oxidised and slightly acidic water with pyrite, pitchblende, calcite and dolomite, as essential minerals of the U fracture-filling mineralisation, and hydroxyapatite from the host rock, as the main source of P. This conceptual model has been tested in a systematic numerical model, which includes the main kinetic (pyrite and pitchblende dissolution) and equilibrium processes (carbonate mineral dissolution, and goethite, schoepite and autunite secondary precipitation). The results obtained from the reactive-transport model satisfactorily agree with the conceptual model previously established. The assumption of the precipitation of coffinite as a secondary mineral in the system cannot be correctly evaluated due to the lack of hydrochemical data from the reducing zone of the site and valid thermodynamic and kinetic data for this hydrated U(IV)-silicate. This precipitation can also be hampered by the probable existence of dissolved U(IV)-organic matter and/or uranyl carbonate complexes, which are thermodynamically stable under the alkaline and reducing conditions that prevail in the reducing zone of the system. Finally, the intense downwards oxic and acidic alteration in the upper part of the system is of no relevance for the performance assessment of a HLNW disposal. However, the acidic and oxidised conditions are quickly buffered to neutral-alkaline and

Exploration for sandstone- type uranium mineralisation in the Siwaliks of northwestern Himalaya, India

International Nuclear Information System (INIS)

Swarnkar, B.M.; Kothari, P.K.; Umamaheswar, K.; Srinivasan, S.

2002-01-01

The Siwalik Group with a thickness of about 6000m of fluvial sediments of middle Miocene to Pleistocene age has been explored extensively over two decades for U, using various types of exploration techniques involving air-borne gamma-ray spectrometry, radiation jeep survey, hydrogeochemical survey, ground radiometric survey, radon survey, exploratory drilling and mining, Exploration effort by the Atomic Minerals Directorate for Exploration and Research (AMD) has helped in identifying numerous uranium occurrences spread over the entire Siwalik belt between Poonch (Jammu and Kashmir) in the west and Tanakpur (Uttar Pradesh) in the east, in the northwest Himalaya. Eight significant zones were delineated, mostly confining to distinct stratigraphic horizons of the transition zone between Middle and Upper Siwaliks, and occasionally the transition zone between Lower and Middle Siwaliks. These mineralised zones have a considerable lateral extent of up to 12 km and are associated with sandstones and rarely conglomerates. Uranium mineralisation occurs in the form of peneconcordant lensoidal bodies with individual lenses traceable from a few tens of metres to 700m, sub-parallel to strike or dip, with average grades varying from 0.020 - 0.060% U 3 O 8 and thickness less than a metre to 4m. The host rock of uranium mineralisation is predominantly sandstone containing carbonaceous matter, pyrite and clay pellets. The sandstone is often arkosic and micaceous, and termed as lithic wacke and arkosic wacke. The uranium minerals present are uraninite, pitchblende, coffinite and secondary minerals such as tyuyamunite, metatyuyamunite, uranophane, bayleyite, andersonite, schoepite, liebegite, swartzite, schroekingerite, wulfenite, billictite, betauranophane, autunite and torbernite. Relatively higher concentrations or Se, Mo, Cu, Co, V and Au have been noted in a few uranirerous zones. Concentration or uranium in the Siwalik clastic sediments is controlled by the redox interface

The origin of the Avram Iancu U-Ni-Co-Bi-As mineralization, Băiţa (Bihor) metallogenic district, Bihor Mts., Romania

Science.gov (United States)

Zajzon, Norbert; Szentpéteri, Krisztián; Szakáll, Sándor; Kristály, Ferenc

2015-10-01

The Băiţa metallogenic district in the Bihor Mountains is a historically important mining area in Romania. Uranium mining took place between 1952 and 1998 from various deposits, but very little is known about the geology and mineralogy of these deposits. In this paper, we describe geology and mineralogy of uranium mineralization of the Avram Iancu uranium mine from waste dump samples collected before complete remediation of the site. Texturally and mineralogically complex assemblages of nickeline, cobaltite-gersdorffite solid solution, native Bi, Bi-sulfosalts, molybdenite, and pyrite-chalcopyrite-sphalerite occur with uraninite, "pitchblende," and brannerite in most of the ore samples. The association of nickel, cobalt, and arsenic with uranium is reminiscent of five-element association of vein type U-Ni-Co-Bi-As deposits; however, the Avram Iancu ores appear to be more replacement-type stratiform/stratabound. Avram Iancu ore samples contain multistage complex, skarn, uranium sulfide, arsenide assemblages that can be interpreted to have been formed in the retrograde cooling stages of the skarn hydrothermal system. This mineralizing system may have built-up along Upper Cretaceous-Paleogene "Banatite" intrusions of diorite-to-granite composition. The intrusions crosscut the underlying uraniferous Permian formations in the stacked NW-verging Biharia Nappe System. The mineralization forms stacked, multilayer replacement horizons, along carbonate-rich lithologies within the metavolcanic (tuffaceous) Muncel Series. Mineral paragenesis and some mineral chemistry suggest moderate-to-high <450, i.e., 350-310 °C, formation temperatures for the uranium sulfide stage along stratigraphically controlled replacement zones and minor veins. Uranium minerals formed abundantly in this early stage and include botryoidal, sooty and euhedral uraninite, brannerite, and coffinite. Later and/or lower-temperature mineral assemblages include heterogeneous, complexly zoned arsenide

Study of rhyolitic glasses alteration in contact with natural brines (Bolivia). Application to the study of the long-term behaviour of the R7T7 nuclear glass

International Nuclear Information System (INIS)

Abdelouas, A.

1996-01-01

The purpose of this work is to complement an experimental program on the R7T7 nuclear waste glass alteration in brines at 190 deg C in Germany by the analysis of the structure and the chemical composition of the alteration layers, and to study the alteration of rhyolitic glasses in natural brines from Bolivia as analogue for nuclear waste glasses disposed in salt formations. Alteration experiments with the R7T7 and basaltic glasses and obsidian in MgCl 2 -CaCl 2 -saturated brine at 190 deg. C were also conducted in order to study the influence of the glass composition on the nature of the secondary phases. The experiments with the R7T7 glass in three salt brines, saturated respectively in MgCl 2 , MgCl 2 -CaCl 2 and NaCl, showed that the solubilities of most radionuclides are controlled by the secondary phases. Nd, La, and Pr are trapped in powellite, Ce in cerianite, U in coffinite, and Sr is partially immobilized in barite. These phases are stable for more than one year. There is a good similarity between the secondary phases formed experimentally on volcanic glasses and the R7T7 glass altered in MgCl 2 -CaCl 2 -saturated brine. The abundance of Mg in solution permits the formation of similar magnesian clays on the glass samples independently of the nature of the initial glasses. These results support the use of volcanic glasses alteration patterns in Mg-rich solutions to understand the long-term behavior of nuclear waste glasses and to evaluate the stability of the secondary phases. The study of the sediments of Uyuni (Bolivia) showed that the corrosion rate of the rhyolitic glass in brines at 10 deg. C is 12 to 30 time lower than those of rhyolitic glasses altered in high dilute conditions. The low alteration rate of rhyolitic glasses in brines and the formation of secondary phases such as smectite, barite and cerianite (also formed during the experimental alteration of the R7T7 glass), permit us to expect the low alteration of nuclear waste glasses at long

Uranium speciation in 30-year old Freital mine tailings: an EXAFS, {mu}-XRD, and {mu}-XRF study

Energy Technology Data Exchange (ETDEWEB)

Scheinost, A.C.; Hennig, C. [Institute of Radiochemistry, FZR, D-01314 Dresden (Germany); Somogyi, A. [Synchrotron Soleil, F-91192 Gif-sur-Yvette (France); Martinez-Criado, G. [ESRF, ID-22, F-38043 Grenoble (France); Knappik, R. [VKTA Rossendorf, D-01314 Dresden (Germany)

2005-07-01

Full text of publication follows: Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques ({mu}-XRF, {mu}-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions. In sample F1 (5 m depth, oxic, pH 8, U = 440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U = 430 mg/kg), the combination of {mu}-XRF and {mu}-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy. At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical

Uranium speciation in 30-year old Freital mine tailings: an EXAFS, μ-XRD, and μ-XRF study

International Nuclear Information System (INIS)

Scheinost, A.C.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.

2005-01-01

Full text of publication follows: Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques (μ-XRF, μ-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions. In sample F1 (5 m depth, oxic, pH 8, U = 440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U = 430 mg/kg), the combination of μ-XRF and μ-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy. At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical extractions

IAEA coordinated research project (CRP). The use of selected safety indicators (concentrations, fluxes) in the assessment of radioactive waste disposal. Report 6: Site-specific natural geochemical concentrations and fluxes at the Palmottu U-Th mineralisation (Finland) for use as indicators of nuclear waste repository safety

International Nuclear Information System (INIS)

Kaija, J.; Blomqvist, R.; Rasilainen, K.

2003-01-01

high concentrations of dissolved uranium in bicarbonate groundwater, 4) The secondary uranium deposits may reflect significant mass accumulation of uranium and could constitute important sources to groundwater, 5) The dominant part of the uranium has remained in the ancient U(IV) phases, uraninite and coffinite, throughout its geological history for 1700-1800 Ma, demonstrating that reducing conditions have prevailed in the bedrock for most of its existence, 6) Although the mineralisation has been subject to supergene processes for millions of years, the dispersion of uranium has been very limited. This indicates that the bedrock itself has a very effective reducing capacity. (orig.)

The influence of biofilms on the migration of uranium in acid mine drainage (AMD) waters

Energy Technology Data Exchange (ETDEWEB)

Krawczyk-Baersch, E., E-mail: E.Krawczyk-Baersch@hzdr.de [Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiochemistry, P.O. Box 51 01 19, D-01314 Dresden (Germany); Luensdorf, H. [Helmholtz Centre for Infection Research, Department of Vaccinology and Applied Microbiology, Inhoffenstr. 7, D-38124 Braunschweig (Germany); Arnold, T.; Brendler, V. [Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiochemistry, P.O. Box 51 01 19, D-01314 Dresden (Germany); Eisbein, E. [TU Bergakademie Freiberg, Institute of Physical Chemistry, Akademiestrasse 6, D-09596 Freiberg (Germany); Jenk, U.; Zimmermann, U. [Wismut GmbH, Jagdschaenkenstr. 29, D-09117 Chemnitz (Germany)

2011-07-15

The uranium mine in Koenigstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO{sub 2}SO{sub 4}) and UO{sub 2}{sup ++} speciation as well as of the solid uranium species Uranophane [Ca(UO{sub 2}){sub 2}(SiO{sub 3}OH){sub 2}{center_dot}5H{sub 2}O] and Coffinite [U(SiO{sub 4}){sub 1-x}(OH){sub 4x}], which are defined in the stability field of pH > 4.8 and Eh < 960 mV and pH > 0 and Eh < 300 mV, respectively. The plotting of the measured redox potential and pH of the AMD water and the biofilm into the calculated pH-Eh diagram showed that an aqueous uranium(VI) sulfate complex exists under the ambient conditions. According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to > 4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be

Hydrothermal uranium deposits containing molybdenum and fluorite in the Marysvale volcanic field, west-central Utah

Science.gov (United States)

Cunningham, C.G.; Rasmussen, J.D.; Steven, T.A.; Rye, R.O.; Rowley, P.D.; Romberger, S.B.; Selverstone, J.

1998-01-01

precipitation of uranium minerals. At the deepest exposed levels, wall-rocks were altered to sericite; and uraninite, coffinite, jordisite, fluorite, molybdenite, quartz, and pyrite were deposited in the veins. The fluids were progressively oxidized and cooled at higher levels in the system by boiling and degassing; iron-bearing minerals in wall rocks were oxidized to hematite, and quartz, fluorite, minor siderite, and uraninite were deposited in the veins. Near the ground surface, the fluids were acidified by condensation of volatiles and oxidation of hydrogen sulfide in near-surface, steam-heated, ground waters; wall rocks were altered to kaolinite, and quartz fluorite, and uraninite were deposited in veins. Secondary uranium minerals, hematite, and gypsum formed during supergene alteration later in the Cenozoic when the upper part of the mineralized system was exposed by erosion.

Exploration and uranium mining in Niger

International Nuclear Information System (INIS)

Moussa, M.

2014-01-01

features are important in trapping the mineralisation which is often of roll front type, either reduced consisting in pitchblende and coffinite (Akouta, Arlit, Afasto, Madaouela) or oxidized (Imouraren). The main exploration companies of Uranium in the basin of Tim Mersoï (Northern Iullemenden) are: • AREVA-Niger for the uranium-bearing prospecting permits of Imouraren, Afouday, Agebout; • Cominak for the uranium-bearing prospecting permit Western Afasto; • NorthWestern Mineral Ventures Inc for the uranium-bearing prospecting permits Irhazer and Ingal; • North Atlantic Resources Ltd. for the uranium-bearing prospecting permit Abélajouad; • CNUC for the uranium-bearing permit of Tiguida • Goviex for uranium permit of Madaouéla; • International Uranium Ltd for the uranium-bearing prospecting permits of Agelal I, II, III, IV and Aserka I, II, III, IV; • Total Uranium Corporation for the licences of Chock Negouran I, II, III and IV; • Trend Field Holding SA for the uranium-bearing prospecting permits Tagaza II and IV. (author)

Exploration for uranium in the Bhima basin in parts of Karnataka, India

International Nuclear Information System (INIS)

Pandit, S.A.; Natarajan, V.; Dhana Raju, R.

2002-01-01

Bhima basin, the smallest and youngest Purana (Meso-/Neo-proterozoic) basin of India, is known for huge reserves of quality-limestone that supports a large-scale cement industry in it. But for this, it remained for long as a 'terra incognita' for mineral exploration including radioactive minerals till the discovery of notable uranium mineralisation, first in a phosphatic limestone/calcitic phosphorite near Ukinal in 1995 and later a better-grade in a non-phosphatic, brecciated limestone at Gogi in 1996. Though the former was recorded intermittently for nearly 700m near Ukinal, detailed (sub-surface) exploration was not done, since U is mostly in the adsorbed form with collophane. On the contrary, the latter is promising, since ore microscopic study on a uraniferous sample from Gogi has pointed to hydrothermal vein-type mineralisation in the form of easily leachable coffinite and pitchblende that are intimately associated with reductants of organic matter and pyrite-dominant sulphides. Semi-detailed survey at Gogi was not of much help to prove the extension of mineralisation due to constraints like very few outcrops, soil-cover, vegetation, a big village and a large lake close by. At this juncture, resort was made to a novel technique of gamma-ray logging of nearly 30 drinking water borewells in the village, Gogi, and this proved highly rewarding as the data documented the presence of U-mineralisation of medium-grade and notable thickness. Subsequent multi disciplined and multifaceted exploration, including subsurface, mostly by core-drilling since May, 1997 with an aggregate of nearly 24,000m at Gogi, has established that (a) the rocks hosting hydrothermal vein type U-mineralisation are brecciated limestone (Shahabad formation) and deformed basement granitoid within a post-sedimentary tectonised zone, (b) the mineralisation in limestone (i) occurs as hangwall and footwall bands, (ii) has a strike extension of nearly 2 km with both ends still open, (iii) extends

Geological analysis and petrographic training Tarata in careers (Upper Paleozoic)-test paleoclimatic interpretation in the light of the glacial episode devono-carboniferous (Arlit region, northern Niger)

International Nuclear Information System (INIS)

El Hamet, Mai Ousmane

1983-01-01

anomalies observed in geochemistry will in the same direction. 4-redox phenomena. The study of the diagenetic evolution of double oxides of iron and titanium indicates that tarat sediments were deposited in a reducing environment (the importance of organic matter pyritized) before being oxidized by the late circulation of groundwater acids and oxidizing leaching especially in training Permian reddened.5-Tectonics. The synsedimentary tectonic replays and slow both the regional and the scope of mining have controlled a crucial sedimentation, and consequently the uranium mineralization.6-Impact on uranium mineralization.The analysis of the geological past and new ones made by this study helps identify the problem of setting up large concentrations of uranium Arlit. These seem to be controlled by the combined action of several factors, most of them are themselves controlled by the synsedimentary tectonic replays and slow. Uranium is largely due to leaching of volcanic materials belonging to indigenous or overlying formations. Indeed, originally, uranium appears to be related to volcanic phenomena of soil in tundra environments. Then its concentration is dependent upon the phenomena of oxidation-reduction in conjunction with circulations of water acidic oxidizing water in reducing sediment initially. It is present in the sandy sediment mainly as uraninite pec sphalerite, coffinite and vanadate; in facies for silty clay, it is mainly as complexes organophylliteux and seems to be syn sedimentary. A geochemical study summary shows that the uranium in the deposit Arlit, in addition to its u sual escorts (Pb, Mo, V, Cu) associated with zirconium and titanium. The new stratigraphy proposed for careers in Tarat SOMAIR shows that the mineralized sediments belong to the Lower Carboniferous, but also to Permian [fr

Uranium geology and chemistry, programme and book of abstracts

International Nuclear Information System (INIS)

Patrice Bruneton; Cathelineau, Michel; Richard, Antonin; Mercadier, Julien; Boiron, Marie-Christine; Cuney, Michel; Beaufort, D.; Patrier, P.; Goncalves, Philippe; Trap, Pierre; Van Lichtervelde, Marieke; Jeanneret, Pauline; Marquer, Didier; Feybesse, Jean-Louis; Paquette, Jean-Louis; Mercadier, Julien; Annesley, Irvine R.; Austmann, Christine L.; Creighton, Steve; Eglinger, Aurelien; Vanderhaeghe, Olivier; Andre-Mayer, Anne-Sylvie; Cuney, Michel; Goncalves, Philippe; Durand, Cyril; Feybesse, Jean-Louis; Zeyen, Hermann; Beres, Jan; Pessel, Marc; Gaffet, Stephane; Rousset, Dominique; Senechal, Guy; Dargent, Maxime; Dubessy, Jean; Caumon, Marie-Camille; Trung, Chinh-Nguyen; Richard, Antonin; Montel, Jean-Marc; Peiffert, Chantal; Leborgne, Romain; Seydoux-Guillaume, Anne-Magali; Montel, J.M.; Bingen, B.; Bosse, V.; De Parseval, Ph.; Janots, Emilie; Wirth, Richard; Reiller, Pascal E.; Marang, Laura; Jouvin, Delphine; Benedetti, Marc F.; Clavier, N.; Costin, D.T.; Mesbah, A.; Dacheux, N.; Poinssot, C.; Raimbault, Louis; Mercadier, Julien; Cuney, Michel; Moncoffre, Nathalie; Marchand, Benoit; Perrat-Mabillon, Angela; Gine, A.; Saint-Bezar, B.; Benedicto, A.; Wattinne, A.; Andre, G.; Bonnetti, Christophe; Bourlange, Sylvain; Malartre, Fabrice; Benedicto, Antonio; Liu, Xiaodong; Cretaz, F.; Szenknect, S.; Descostes, M.; Dacheux, N.; Othmane, Guillaume; Allard, Thierry; Menguy, Nicolas; Vercouter, Thomas; Morin, Guillaume; Esteve, Imene; Calas, Georges; Fayek, Mostafa; Barbarand, Jocelyn; Drot, Romuald; Grare, Alexis; Reyx, Jean; Pagel, Maurice; Brouand, Marc; Zakari, Aziz; Bidaud, Adrien; Toe, Wilfried; Milesi, Jean-Pierre; Carrouee, Simon; Moyen, Jean-Francois; Schmitt, Jean-Michel; Brouand, Marc; Bouzid, Majda; Langlais, Valerie; Hocquet, Sebastien; Munara, A.; Boulvais, P.; Carpentier, C.; Ajjabou, Leila; Ledru, Patrick; Fiet, Nicolas; Hocquet, Sebastien; Royer, Jean-Jacques; Fiet, N.; Oppeneau, T.; Berestnev, N.; Merembayev, T.; Parize, Olivier; Aouami, I.; Nedjari, A.; Mahaman, T.; Sanguinetti, H.; Uri, Freddy; Beaufort, Daniel; Riegler, Thomas; Lescuyer, Jean-Luc; Wollenberg, Peter; Dardel, Jacques; Bourgeois, Damien; Maynadie, Jerome; Meyer, Daniel; Courtaud, B.; Auger, F.; Thiry, J.; Fakhi, S.; Fait, E.; Outayad, R.; Mouflih, M.; Voque Romero, I.; Manjon, Guillermo; Ben Mansour, M.; Bouih, A.; Nourreddine, A.; El Hadi, H.; Mokhtari, Hamid; Gourgiotis, Alkiviadis; Bassot, Sylvain; Simonucci, Caroline; Diez, Olivier; Mifsud, Aurelie; Martin-Garin, Arnaud; Coppin, Frederic; Dejeant, Adrien; Galoisy, Laurence; Calas, Georges; Phrommavanh, Vannapha; Descostes, Michael; Wattine-Morice, Aurelia; Belieres, Michel; Ben Simon, Rose; Schmitt, Jean-Michel; Thiry, Medard; Megneng, Melissa; Orberger, Beate; Hofmann, Axel; Wirth, Richard; Dumas, Paule; Sandt, Christophe; Hicks, Nigel; Tudryn, Alina; Tartese, Romain; Boulvais, Philippe; Poujol, Marc

2011-11-01

This meeting of the French Geological Society (SGF) was organized with the joint contribution of Areva, CNRS-INSU, PACEN, GUTEC, IDES, and Paris-Sud University. This document gathers the abstracts of the following 40 presentations: 1 - Uranium deposits of 'Intrusive'-type; 2 - U deposits beneath discordance: analogy with F-Ba-Pb-Zn(Ag) 'Basin Hosted'-type deposits?; 3 - Clays and related minerals as guides for uranium deposits prospecting: status of recent advances; 4 - Hudsonian Uranium mineralizations in the Western part of the Trans-Hudsonian orogen (Saskatchewan, Canada): a source for the formation of discordance-type deposits?; 5 - U-Th elements mobilization during the Panafrican metamorphism: implication on the formation of Cu-Co-(U) deposits, Solwezi dome, NW Zambia; 6 - Fractures network characterization by seismic and electrical anisotropy; 7 - study of uranyl speciation by Raman spectroscopy in chlorinated solutions (LiCl = 0.5 to 15 M) up to 350 deg. C. Metallogenic consequences and perspectives; 8 - Experimental weathering of natural monazite in the conditions of formation of Oklo and discordance-type uranium deposits; 9 - Disturbance of the U-Th-Pb chronometers during the low temperature weathering of monazite: synergy between irradiation damages and dissolution-precipitation; 10 - U(VI) interaction with humic substances: speciation and application to independent data; 11 - Preparation and characterization of Th 1-x U x SiO 4 solid solutions: towards the understanding of coffinite formation?; 12 - A new geochemical tool for the study of U deposits: the anions in uraninite; 13 - Tectonics in the Unegt basin (E-Gobi, Mongolia): deformation stripes, hydrocarbons migration and U mineralizations; 14 - Study of U sources in the Erlian Basin (China); 15 Thermodynamic data acquisition for uranyl phosphates and vanadates: from synthetic analogues to natural samples; 16 - U speciation in Nopal I opals: geochemical consequences for the end of the deposit genesis

Formation of colloids of the tetravalent uranium under influence of silicate in neutral and low alkaline aqueous systems; Bildung von Kolloiden des tetravalenten Urans unter Einfluss von Silikat in neutralen und schwachalkalischen waessrigen Systemen

Energy Technology Data Exchange (ETDEWEB)

Ulbricht, Isabell

2016-03-30

silicate to uranium(IV) content ratio and the higher the pH of the solution are, the smaller and more stable (in terms of pH-changes) are the particles. It should be noted that no colloids were formed in absence of uranium(IV). The mechanism of the colloidal stabilization can be regarded as ''sequestration'' by silicate, a phenomenon well known from heavy metal ions of high ion potential such as iron(III) or manganese(III,IV), but never reported for uranium(IV) so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentration, make up the internal structure of the colloids. The next-neighbor coordination of uranium(IV) in the uranium(IV)-silica colloids is comparable with that of coffinite, USiO{sub 4}. The assessment of uranium behavior in the aquatic environment should take the possible existence of uranium(IV)-silica colloids into consideration. Their occurrence might influence uranium migration in anoxic waters. The silicate-stabilized colloids have been generated in laboratory experiments under controlled conditions; i.e., it is not known yet whether these phases can occur in natural water. The qualitative composition of the matrix of the experimental solutions (H{sup +}, OH{sup -}, Na{sup +}, HCO{sub 3}{sup -}/CO{sub 3}{sup 2-}, silicate) was chosen similar to the geochemical nature of groundwater. Thereby, it can be assumed that such colloids are present in natural waters. The existence of such particles would provide an ex-planation for the occurrence of uranium(IV) colloids in anoxic pore waters or groundwaters. However, it should be noted that these results were observed by the reduction of uranium(VI) carbonate and dilution in the presence of silicate. Studies on the mobility and stability of these colloids in aquatic systems were not subject of this work and an environmental assessment of

Geology of the Honeymoon Uranium Project

International Nuclear Information System (INIS)

Bampton, K.F.; Haines, J.B.; Randell, M.H.

2001-01-01

The Honeymoon Uranium Project comprises the Honeymoon Deposit, Goulds Dam Deposit and Yarramba Prospect in the Southern Lake Frome region, South Australia. Both the Yarramba Prospect and Honeymoon Deposit (which includes Honeymoon and East Kalkaroo orebodies) are located in the Yarramba Palaeovalley. The Goulds Dam Deposit is about 75 km north west of Honeymoon, in the Billeroo Palaeovalley. Exploration for sediment-hosted uranium began in the area in the late 1960s, culminating in the discovery of Honeymoon and Goulds Dam in the early 1970s. In 1982, a 25 L/s demonstration plant was built at Honeymoon to confirm suitability for in situ leaching. The project was put on hold in 1983 due to changes in government policy. Southern Cross Resources Australia Pty Ltd acquired the project in mid 1997. Roll-front deposits form from a migrating geochemical cell, an advancing reduction-oxidation interface between oxygenated uranium-bearing groundwater and its reduced aquifer host. The source of metal is uranium-anomalous granites, which were eroded from surrounding ranges. The weathered granites and resultant sediments are stripped of uranium by oxidised groundwaters, to form solutions carrying uranyl carbonate complexes. The solutions percolate down-slope through permeable sand zones until contacting a reduced environment where uranium precipitates. Uranium mineralisation occurs interstitially between and as thin coatings on sand grains, usually in the form of uraninite or coffinite. The palaeovalleys (previously termed palaeochannels) are incised into underlying Cambrian/Precambrian basement rocks and filled with semi-consolidated, largely un-cemented, Tertiary sediments of the Eyre Formation. The late Palaeocene to middle Eocene Eyre Formation is the basal unit of the Tertiary succession in the Callabonna Sub-basin of the Lake Eyre Basin. Further to the north, the Lake Eyre Basin overlies the Jurassic-Cretaceous Eromanga Basin, which comprises much of the Great Australian

Investigation into formation of nanoparticles of tetravalent neptunium in slightly alkaline aqueous solution

International Nuclear Information System (INIS)

Husar, Richard

2015-01-01

(fcc) nanocrystals under ambient environmental conditions is prevented by admixing silicic acid: amorphous Np(IV) silica colloids are formed when silicate is present in carbonate solution. Herein, the initial molar ratio of Si to Np in solution lead to the formation of Np(IV) silica particles of different composition and size where Si content determines the structure and stability of resulting colloids. Implications for different electronic structures of Np(IV) in dependence on Si content in the solid phase are given by the shift of the absorption maximum at 742 nm characteristic for Np(IV) colloids, silica excess of 5 times the magnitude of Si to Np reveal a redshift up to 6 nm in the colloidal UV-vis spectrum. Precipitation of Np(IV) particles in the ternary system results in a different coordination sphere of Np(IV) compared to the binary system, and the incorporation of Si into internal structure of Np(IV) silica colloids in coffinite-like structure is confirmed by EXAFS. TEM confirms different kinds of particle morphologies in dependence on the silica content. Silica-poor systems reveal porous particles in the micron-range which consist of irregular cross-linked hydrolyzed Np(IV) silica compartments with pores <15 nm. In contrast, long-term stabilized and silica-enriched systems are characterized by isolated particles with an average particle size of 45 nm. Agglomerates of such isolated Np(IV) silica particles appear as consolidated amorphous solids with a densely closed surface and exhibit no internal fractures. The latter mentioned morphology of Np(IV) silica particles might facilitate the migration behavior of Np(IV) in a stabilized colloidal form under environmental conditions. The silica-enriched particles with densely closed surface are long-term stabilized as colloidal dispersion (>1 year) due to repulsion effects caused by significant surface charge. Particles synthesized from Si/Np = 9/1 carry exclusively negative surface charge in nearly the whole p

Origen, transporte y deposición del uranio en los yacimientos en pizarras de la provincia de Salamanca

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Arribas, A.

1985-12-01

Full Text Available The numerous U deposits occurring in the schist-graywacke complex (CEG of the Iberian Peninsula, characterized by the mineral association carbonates, pitchblende (coffinite, adularia and Fe sulphides, have both a considerable economic importance and a high metallogenic interest as their origin has not been convincingly explained yet. In fact, since 1959,these mineralizations have been successively attributed lo the concentration of U in fractured and brecciated zones of the schists due to one of these processes : magmatic, by transportation of U in hydrotermal fluids related to the evolution and emplacement of the Hercynian granites; supergenic , by the release of U from the Hercynian granites during the weathering and erosion processes which gave place to the Pliocene peneplain; segregation, by leachin, g of U from plutonic rocks under the effects of late- and /or post-Hercynian tectonic movements; and diffusion, by concentration of U from fertile metasediments by thermal diffusion or hydrothermal flow.
In this paper, taking into account field and laboratory studies carried out recently in the FE mine, so far the most important Spanish U deposit of this kind, the above mentioned hypothesis are discussed and the main metallogenic features of the orebody are given, Among these, the most significant are: the high geochemica1 U content, 30 to 200 ppm, of the CEG carbonaceous slates prevalent in the area; the nature and alteration processes, chloritization and hematitization, of the host rocks; the radiometrie age of the pitchblende 37 to 57 m. y.; the low temperature mineral association; the peculiar gravitational textures of the ore minerals; the temperature and salinity of the fluid inc1usions of the carbonates, ranging from 230º to less than 70º C, and from 0 to 25% NaCl equiv , respectively; and the shallow tectonic activity giving place to the hydraulic fracturing and fault breccias controlling the ore deposition. Finally, he FE