Geophysical model of geological discontinuities in a granitic aquifer: Analyzing small scale variability of electrical resistivity for groundwater occurrences
Résumé
Geological discontinuities such as quartz reef, a common geological feature in hard rock terrain occurring as an intrusive body, has been investigated using geophysical methods in order to explore and map the potential aquifer. Electrical resistivity response of quartz reef intrusive in granite host rock has been studied using synthetic simulation for different physical conditions such as: (1) fresh intrusive body with no alteration at contacts, (2) fresh intrusive body with weathered-fissured contacts, and (3) also fissured intrusive body with weathered-fissured contacts. Electrical Resistivity Tomography (ERT) was carried out traversing across and along the quartz reef at Kothur village, Hyderabad, India. Based on the ERT results 11 bore wells have been drilled followed by yield measurement. litholog collection, and electrical resistivity logging. Geomorphology, ERT images, lithologs, resistivity logs and yield of the wells are found corroborating with each other. Deepening of the weathering fronts are confirmed along the contacts of the quartz reef and granite, which may qualify suitable sites for groundwater occurrence. This has been finally validated from the drilling results, where high yielding (18 m(3)/h) bore well found at low resistive zones within the quartz reef. The study has helped in preparing a 2D section of the structural set up of the quartz reef in granite host medium and finally revealed that the quartz reefs may provide potential groundwater zone. The distribution of electrical resistivity of the geological discontinuity is useful providing promising input to the groundwater flow model particularly in three dimensional.