Magmatic and hydrothermal behavior of uranium in syntectonic leucogranites: The uranium mineralization associated with the Hercynian Guérande granite (Armorican Massif, France)

Most of the hydrothermal uranium (U) deposits from the European Hercynian belt (EHB) are spatially associated with Carboniferous peraluminous leucogranites. In the southern part of the Armorican Massif (French part of the EHB), the Guérande peraluminous leucogranite was emplaced in an extensional deformation zone at ca. 310 Ma and is spatially associated with several U deposits and occurrences. The apical zone of the intrusion is structurally located below the Pen Ar Ran U deposit, a perigranitic vein-type deposit where mineralization occurs at the contact between black shales and Ordovician acid metavolcanics. In the Métairie-Neuve intragranitic deposit, uranium oxide-quartz veins crosscut the granite and a metasedimentary enclave. Airborne radiometric data and published trace element analyses on the Guérande leucogranite suggest significant uranium leaching at the apical zone of the intrusion. The primary U enrichment in the apical zone of the granite likely occurred during both fractional crystallization and the interaction with magmatic fluids. The low Th/U values (18Owhole rock = 9.7–11.6‰ for deformed samples and δ18Owhole rock = 12.2–13.6‰ for other samples) indicate that the deformed facies of the apical zone underwent sub-solidus alteration at depth with oxidizing meteoric fluids. Fluid inclusion analyses on a quartz comb from a uranium oxide-quartz vein of the Pen Ar Ran deposit show evidence of low-salinity fluids (1–6 wt.% NaCl eq.), in good agreement with the contribution of meteoric fluids. Fluid trapping temperatures in the range of 250–350 °C suggest an elevated geothermal gradient, probably related to regional extension and the occurrence of magmatic activity in the environment close to the deposit at the time of its formation. U-Pb dating on uranium oxides from the Pen Ar Ran and Métairie-Neuve deposits reveals three different mineralizing events. The first event at 296.6 ± 2.6 Ma (Pen Ar Ran) is sub-synchronous with hydrothermal circulations and the emplacement of late leucogranitic dykes in the Guérande leucogranite. The two last mineralizing events occur at 286.6 ± 1.0 Ma (Métairie-Neuve) and 274.6 ± 0.9 Ma (Pen Ar Ran), respectively. Backscattered uranium oxide imaging combined with major elements and REE geochemistry suggest similar conditions of mineralization during the two Pen Ar Ran mineralizing events at ca. 300 Ma and ca. 275 Ma, arguing for different hydrothermal circulation phases in the granite and deposits. Apatite fission track dating reveals that the Guérande granite was still at depth and above 120 °C when these mineralizing events occurred, in agreement with the results obtained on fluid inclusions at Pen Ar Ran. Based on this comprehensive data set, we propose that the Guérande leucogranite is the main source for uranium in the Pen Ar Ran and Métairie-Neuve deposits. Sub-solidus alteration via surface-derived low-salinity oxidizing fluids likely promoted uranium leaching from magmatic uranium oxides within the leucogranite. The leached out uranium may then have been precipitated in the reducing environment represented by the surrounding black shales or graphitic quartzites. As similar mineralizing events occurred subsequently until ca. 275 Ma, meteoric oxidizing fluids likely percolated during the time when the Guérande leucogranite was still at depth. The age of the U mineralizing events in the Guérande region (300–275 Ma) is consistent with that obtained on other U deposits in the EHB and could suggest a similar mineralization condition, with long-term upper to middle crustal infiltration of meteoric fluids likely to have mobilized U from fertile peraluminous leucogranites during the Late Carboniferous to Permian crustal extension events

Uranium resources, scenarios, nuclear and energy dynamics

ISBN 978-1-49-51-6286-2International audienceA dynamic simulation of coupled supply and demand of energy, resources and nuclear reactors is done with the global model Prospective Outlook for Long Term Energy Supply (POLES) over this century. In this model, both electricity demand and uranium supply are not independent of the cost of all base load electricity suppliers. Uranium consuming Thermal Neutron Reactors and future generation, free from the uranium market once started, breeder reactors are only one part of the market and are in a global competition, not limited to the other nuclear generation. In this paper we present a new model of the impact of uranium scarcity on the development of nuclear reactors. Many scenarios rely on the subjective definition of ultimate uranium resources. We suggest that when uranium will mainly be extracted together with other resources, its cost should not be simply a function of cumulated uranium mined but also of mine yearly outputs. We describe the sensitivities of our model to breeder reactor physical performance indicators. Used fuels can be seen as a liability or as a source of usable material and a scarce resource limiting fast reactor startups in fast development in India or China. We present the impact of synergetic strategies where countries with opposite strategies share used fuels

Petrological and Geochronological Peculiarities of Novoukrainka Massif Rocks and Age Problem of Uranium Mineralization of the Kirovograd Megablock of the Ukrainian Shield

Basing on the new and published data of isotopic dating, the ages of the rock complexes of the Novoukrainka granite massif (the Ukrainian Shield) and uranium mineralization in albitites with the complexes of the host rocks were compared. A sequence of the geologic events in the Ingul megablock of the Ukrainian Shield is marked: formation of the Kirovograd (2025–2060 mln. y. ago) and Novoukrainka (2025–2040 mln. y. ago) magmatic complexes — formation of the uranium deposits (~ 1800 mln. y. ago, but the age should be precised) — Korsun-Novomyrgorod magmatic complex (1730–1760 mln. y. ago). The Novoukrainka massif is presented by differentiated magma of the magmatic melt originated from the upper crust material.На основі нових та узагальнених літературних даних про ізотопне датування проведено вікові порівняння породних комплексів Новоукраїнського гранітного масиву та уранового зруденіння в альбітитах з комплексами вмісних порід. Визначено таку послідовність геологічних подій в Інгульському мегаблоці Українського щита: становлення кіровоградського (2025–2060 млн рр. тому) та новоукраїнського (2025–2040 млн рр. тому) магматичних комплексів — формування уранових родовищ (~ 1800 млн рр. тому, вік потребує уточнення) — корсунь-новомиргородський магматичний комплекс (1730–1760 млн рр. тому). Зроблено припущення, що Новоукраїнський масив представлений диференціатами єдиного магматичного розплаву, що утворився за рахунок плавлення верхньокорового матеріалу.На основании новых и обобщенных литературных данных по изотопному датированию осуществлено возрастное сравнение породных комплексов Новоукраинского гранитного массива и уранового оруденения в альбититах с комплексами вмещающих пород. Установлена такая последовательность геологических событий в Ингульском мегаблоке Украинского щита: становление кировоградского (2025–2060 млн лет назад) и новоукраинского (2025–2040 млн лет назад) магматических комплексов — формирование урановых месторождений (~ 1800 млн лет назад, возраст должен быть уточнен) — корсунь-новомиргородский магматический комплекс (1730–1760 млн лет назад). Высказано предположение, что Новоукраинский массив представлен дифференциатами единого магматического расплава, образовавшегося вследствие плавления верхнекорового материала

Le magmatisme de la région de Kwyjibo, Province\ud du Grenville (Canada) : intérêt pour les\ud minéralisations de type fer-oxydes associées

The granitic plutons located north of the Kwyjibo property in Quebec’s Grenville Province are of\ud Mesoproterozoic age and belong to the granitic Canatiche Complex . The rocks in these plutons are calc-alkalic, K-rich,\ud and meta- to peraluminous. They belong to the magnetite series and their trace element characteristics link them to\ud intraplate granites. They were emplaced in an anorogenic, subvolcanic environment, but they subsequently underwent\ud significant ductile deformation. The magnetite, copper, and fluorite showings on the Kwyjibo property are polyphased\ud and premetamorphic; their formation began with the emplacement of hydraulic, magnetite-bearing breccias, followed by\ud impregnations and veins of chalcopyrite, pyrite, and fluorite, and ended with a late phase of mineralization, during\ud which uraninite, rare earths, and hematite were emplaced along brittle structures. The plutons belong to two families:\ud biotite-amphibole granites and leucogranites. The biotite-amphibole granites are rich in iron and represent a potential\ud heat and metal source for the first, iron oxide phase of mineralization. The leucogranites show a primary enrichment in\ud REE (rare-earth elements), F, and U, carried mainly in Y-, U-, and REE-bearing niobotitanates. They are metamict and\ud underwent a postmagmatic alteration that remobilized the uranium and the rare earths. The leucogranites could also be\ud a source of rare earths and uranium for the latest mineralizing events

Role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium deposits: insights from reactive-flow modeling

The role of hydrodynamic factors in controlling the formation and location of unconformity-related uranium (URU) deposits in sedimentary basins during tectonically quiet periods is investigated. A number of reactive-flow modeling experiments at the deposit scale were carried out by assigning different dip angles and directions to a fault and various permeabilities to hydrostratigraphic units). The results show that the fault dip angle and direction, and permeability of the hydrostratigraphic units govern the convection pattern, temperature distribution, and uranium mineralization. Avertical fault results in uranium mineralization at the bottom of the fault within the basement, while a dipping fault leads to precipitation of uraninite below the unconformity either away from or along the plane of the fault, depending on the fault permeability. A more permeable fault causes uraninite precipitates along the fault plane,whereas a less permeable one gives rise to the precipitation of uraninite away from it. No economic ore mineralization can form when either very low or very high permeabilities are assigned to the sandstone or basement suggesting that these units seem to have an optimal window of permeability for the formation of uranium deposits. Physicochemical parameters also exert an additional control in both the location and grade of URU deposits. These results indicate that the difference in size and grade of different URU deposits may result from variation in fluid flow pattern and physicochemical conditions, caused by the change in structural features and hydraulic properties of the stratigraphic units involved

Cartographie prédictive du potentiel d'exhalation du radon-222 à la surface des sols: Exemple d'application dans le Massif Armoricain

International audienceRadon-222 is a radioactive natural gas produced by the decay of radium-226, itself produced by the decay of uranium-238 naturally present in rocks and soil. It can accumulate in buildings, and inhalation of this gas and its decay products is a potential human health risk. Effective risk management needs to determine in advance the areas in which the density of buildings with high radon levels is likely to be highest. Research programs over the past several years have successfully developed a methodology for predicting and mapping the radon exhalation potential at the soil surface. This approach, based on quantification of the radon flux at the surface, starts from a precise characterization of the main local geological and pedological variables that influence the radon source and its transport to the soil/atmosphere interface. The methodology crosses the cartographic analysis into a Geographic Information System (GIS) and a simplified model for vertical transport of radon by diffusion through pores in the soil. This code, called TRACHGEO, calculates the radon flux density as a function of the chemical and physical properties of the rock and the subjacent soil. In this paper, we discuss the results from the application of this approach to an area (3,000 km2) located in Brittany (Western France). We discuss the validity of our forecasts and the use of such predictive maps as guides for radon risk management in existing or future buildings