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

Contaminación de mercurio de origen volcanico-hidrotermal en el acuífero de la Palma. Islas Canarias, España

Mercury measurements in groundwaters from La Palma, Canary Islands, revealed high Hg levels (up to 1500, pg/L) in some portions of the volcanic aquifer. This Hg pollution does not seem to be related to anthropogenic activities; therefore, a volcanogenic origin might be a potential Hg sourceDeterminaciones de mercurio en las aguas subterráneas de La Palma, Canary Islands, han reflejado niveles altos de mercurio (hasta unos 1500, pg/L) en algunas porciones de este acuífero volcánico. Esta contaminación de Hg no parece estar relacionada con actividades antropogénicas, y por consiguiente puede estar relacionada con un origen volcánic

Facile Synthesis of Perovskite-Structured Powders Using Barite–Celestite Ore under Hydrothermal Alkaline Conditions

Barite–celestite (BC) crystals were treated in highly concentrated alkaline hydrothermal fluid (5 M KOH) coexisting with a Ti(OH)₄·4.5H₂O gel to produce SrTiO₃ particles between 150 and 250 °C for several intervals between 6 h and 96 h. The BC transformation was initiated at a lower temperature (150 °C) and the total precursors consumption was completed at 250 °C for 96 h, resulting only in the crystallization of SrTiO₃ particles. Different temperatures of reaction (≤200 °C) lead to variations in morphology and particle size of the SrTiO₃ . The crystal growth of faceted cubic agglomerates was achieved at 250 °C, and it is provoked by the Oswald ripening mechanism. The release of barium to the hydrothermal fluid from the precursor occurred simultaneously with the transformation process. A low value of activation energy required for the single-step transformation of the BC plates into SrTiO₃ particles was observed (26.33 kJ mol‾¹), under static hydrothermal conditions

Subtle signatures of seeps: Record of groundwater in a Dryland, DK, Olduvai Gorge, Tanzania

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