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The epigenetic uranium deposits in the eastern part of the Athabasca Basin are classified as unconformity-related ore deposits. Their explicit spatial association to reactivated basement faults is observed within the regional structural NNE trend Wollaston-Mudjatik transition zone, marked by elongated dravite, illite, and chlorite alteration zones. Accordingly, geochemical studies have advocated a circulation and focalization of large amount of one or more fluids to carry and precipitate aqueous chemical materials. At the deposit-scale, the uranium deposits are found mainly at the intersection between two or more fault sets, and described as elongated-like bodies varying in orientation from E-W to NNE direction along the regional transitional zone. Furthermore, some orebodies show a change of orientation and dip of their structures. Thus, what is the hydro-mechanical response of reactivated and inherited fault architecture (e.g., intersection zone) under different stress states (e.g., reverse, strike-slip, and normal faulting regime), and its potential contribution to the shape and orientation of orebodies at deposit scale?Using hydro-mechanical numerical modeling, this project demonstrates the role that fault intersections play in controlling mineralized fluids by examining the various fluid flow patterns observed when reactivated intersected faults are under various stress states. Numerical modeling is performed using 3-Dimensional Distinct Element Code (3DEC). The numerical models are subdivided into two categories: 1) simplified 3-D models of two intersecting faults, 2) 3-D complex models of fault network at different deposits sites (e.g., the Cigar Lake deposit). While the first simple models attempt to evaluate the effects of intersection angle, burial depth, fluid pressure, basin permeability and stress states on the fluid flow patterns; the second models investigate the stress state under which certain orebodies may have formed.Our preliminary results from simplified models show that at defined intersection angles, the fluid flow deviates from the main fault toward the secondary fault at their intersection point. The deviation in fluid flow is referred to the value of intersection angle at which the shear stress varies along the secondary fault, leading to the opening of secondary fault. Additionally, the burial depth does not affect the flow along the basement faults, whereas, the overlying highly permeable basin reduces the horizontal flow along the basement faults toward the intersection zone, and reorients a part of the flow toward the basin. In the complex models (the Cigar Lake model), considering a compressional regime, the E-W fault set is reactivated once the maximum stress is oriented N40W to N65W, which is in agreement with field observations.

International audience; The global water demand for industrial, agricultural, and drinking water needs increases but so is the number of soil and groundwater contaminations. Light Non-Aqueous Phase Liquids (LNAPLs) which come from the accidental release of refined petroleum products (diesel or fuel…) represent 40% of these contaminations. After their infiltration in the unsaturated zone, part of LNAPLs reaches and accumulates above the top of the water table as a mobile liquid phase able to be displaced by water table level variations. Hence, pump-induced, or seasonal variations in the groundwater level led to the significant vertical spreading of these light petroleum hydrocarbon contaminants at the capillary fringe that can temporarily favor their release into the air and groundwater. In the coming decades, an intensification of these groundwater level variations is expected in response to extreme climatic events and variations in precipitations patterns and water needs. This context may strongly impact the mobilization of these organic contaminants, impacting their release in the air and water and their attenuation rates. It is, therefore, essential to better understand the impact of the groundwater level fluctuation patterns on the fate of LNAPLs. To this end, an innovative system was developed this year at the GISFI station (Homécourt, France - http://gisfi.univ-lorraine.fr). This device is composed of two lysimetric columns of soil equipped with in-situ sensors that combine indirect geophysical (complex electrical conductivity, permittivity), physical-chemical (pH, Eh, temperature), and geochemical measurements. This device allows to assess and compare the evolution of the LNAPL saturation distribution in soil, the nature and the amount of LNAPLs release into the air and groundwater during two groundwater level fluctuations and precipitation scenarios of 14 months: one based on the current rainfall and groundwater fluctuation patterns calculated after the last ten years regional climate records; the other based on the most extreme predictions of IPCC climatic models. The remobilized hydrocarbons will be collected from lysimeters via suction cups (dissolved phase) and gas collection chambers (vapor phase) and regularly analyzed (µGC, GC-MS, FTIR) using the analysis protocol established in the laboratory for these pollutants. To prepare these experiments, laboratory tests are also conducted on laboratory decametric columns and 2D tanks of soil under controlled soil saturation of air/LNAPL, water/LNAPL, and air/water to calibrate the signals of in-situ sensors. The complementarity of these monitoring techniques should provide a better understanding of the current and future behavior of these organic pollutants and the evolution of the associated environmental risks (water/air quality) at contaminated sites under various climatic conditions. Preliminary results concerning the migration of the pollution through the unsaturated zone of the columns after their release will be presented to illustrate the capability of this new instrumental system.

International audience; Light Non-Aqueous Phase Liquids (LNAPLs) are an important source of soil contamination. When they infiltrate through the unsaturated zone, part of the LNAPLs remains trapped by capillary forces. The others accumulate above the top of the water table, forming a floating ‘free’ phase able to generate a long-term dissolved LNAPL plume. Seasonal variations in the groundwater level lead to significant vertical dispersion of these contaminants at the capillary fringe, favoring their release into the air and water. The IPCC predicts an intensification of these groundwater level variations over the next century in response to variations in rainfall intensity and frequency (related to climate change) and the increasing use of water resources. This context may strongly impact the LNAPL remobilization. It is, therefore, essential to better understand the impact of these groundwater level fluctuations on the remobilization processes of these hydrocarbon contaminants. To this end, an original experimental system combining indirect geophysical (electrical conductivity), in situ physical-chemical (pH, Eh, temperature), and geochemical measurements was developed at the GISFI station (Homécourt, France). This device allows the assessment and the comparison of nature and the amount of LNAPLs release into the atmosphere and water from a contaminated soil during two groundwater level fluctuations scenarios: one corresponding to the ‘actual’ rainfall pattern based on regional climate records; the other based on the most extreme IPCC scenario. This study will be conducted at different scales (laboratory decametric columns and 2 m3 lysimeters) and on soils of different geological complexity. The remobilized hydrocarbons will be collected via porous candles and gas collection chambers and regularly analyzed (GC-MS, FTIR). The complementarity of the monitoring methods will be evaluated and numerical simulations of the LNAPL flow and transport through the contaminated soil will be carried out to identify the processes responsible for the pollutant remobilization. This work is partly funded by the DEEPSURF project ”Lorraine Université d’Excellence”, ANR-15-IDEX-04-LUE”.

International audience

International audience; A fully coupled HM –XFEM method with cohesive zone model: application to fluid-driven fracture network