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Electrical Resistivity Modeling of Quartz Reef and Dolerite Dyke in Granite Hard Rocks

Author(s): Electrical resistivity tomography of lineament
Congress: 2008
Author(s): Benoit Dewandel(2), Dewashish Kumar (1),Shakeel Ahmed(1), Subash Chandra(1)
1IFCGR, National Geophysical Research Institute, Hyderabad-500007, A.P., India 2BRGM, Water Division, Hard Rock Aquifers Unit, 1039, Rue Pinville 34000 Montpellier, France Email: schandra75@gmail.com, chandra_s75@ngri.res.in, b.dewandel@brgm.fr, dew_

Keyword(s): Electrical Resistivity, Modeling, Quartz Reef, dolerite dyke, Granite, India
Poster:
AbstractHard rocks are well known to be complex for groundwater occurrences because of inherent anisotropy, heterogeneities, differential weathering-fracturing, etc. In India, groundwater over-exploitation towards the need of increasing population for their domestic, irrigation and industrial purposes has led to a severe decline in the groundwater level and results in failure number of wells. The bore wells are being deepened in order to tap the water from deeper horizon. The present situation has made the earth scientists to explore the deep potential aquifers for sustenance of mankind. The lineaments may play an important role in the groundwater dynamics and act as indicator for bore well siting. Lineaments can be either potential or non-potential in term of groundwater resources. Various attempts have been made by several researchers to characterize the lineaments for their groundwater potentiality. Work has been carried out here to investigate the quartz reef intrusive for its groundwater potentiality through geophysical method. Such intrusive bodies obviously have thick weathered zone that are favourable for groundwater, and it is of interest to characterize their 2D and 3D geometry. For this purpose, seven ERT field surveys have been carried across and along the quartz reefs in granite rock in Andhra Pradesh (India). Resistivity parameters were confirmed with the drilling and logging results. To understand the geoelectrical signature of quartz reef intrusive body embedded in granite, synthetic simulation has been carried out using RES2DMOD (2D Model) for different physical conditions such as: fresh intrusive body with unweathered at contacts, fresh intrusive body with weathered contacts, and also fissured intrusive body with weathered contacts. Results reveal that the quartz reef usually at contacts is characterized by a significant deepening of the weathering front with highly weathered materials, which is potential for groundwater occurrences. However, sometimes the center of the quartz reef body itself could also be potential for groundwater occurrences because of local deep fissuring due to weathering. Although quartz reef and dolerite dykes both are intrusive, they have different characteristics. Geoelectrical signature of quartz reef has been compared to the one of dolerite dyke. Weathering is found quite deeper in the quartz reef body compared to surrounding granite, which is not in dolerite.
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