ROLES DES PHENOMENES DE MICRODEFORMATION ASSOCIEES AUX GRES HOTES DANS LA MISE EN PLACE DES MINERALISATIONS URANIFERESDARLIT AU NORD NIGER

This studyaims to study the micro deformationphenomenaassociatedwith the host sandstones in the emplacement of the Arlit uranium mineralizations in order to evaluatetheirrolesduring the circulation of the mineralizing solutions at the origin of the emplacement of the concentrations.Thin sections and polished sections were made and analyzedusingoptical microscopes and scanning electron microscopes.Thus, the sedimentarymaterial of the Tarat formation isaffected by mechanical, mechanochemical compaction phenomena and sub-parallel to parallelintragranular fractures.The analysis of the microdeformationphenomena shows that the mechanical compaction isillustrated not only by different types of contacts but also by interpenetrations of the grains whichpresent on their surface hollowscorresponding to the imprints of the neighboringparticles and thusgivingconcavo-convex contacts withimpressed quartz grains.As for the phenomena of mechanical-chemical compaction, they are represented by dissolution surfaces materialized by meshed contacts which are irregular joints.The phenomena of pressure-dissolution are illustrated by stylolitization zones and contacts between quartz grains.The systematicstudy of the phenomena of fracture, neoformation and cementationishighlighted by the alteration of potassium feldsparsintoclayminerals (Kaolinite), the alteration of illites in particular at their end to give kaolinite and on the other hand by the alteration of potassium feldspars to give kaolinite, the illiticlining of quartz grains, the crystallization of chlorite at the edge and on quartz grains and cementation of micas at the edge and on detrital quartz grains.