Geophysical and Hydrogeological Groundwater Prospectivity Mapping in the Kraaipan Granite-Greenstone Terrain, Southeast Botswana

Abstract

Application of regional geophysical methods for hydrogeological purposes has increased over the last two decades especially in arid and semi-arid areas. A project to map the Kraaipan granite-greenstone terrain in southeast Botswana has recently been undertaken using regional aeromagnetic and gravity data with the aim to map the rocks at depth to understand the geology while the secondary objective was to subsequently assess the mineralization and groundwater potential in the area. An integrated analysis of the aeromagnetic and gravity data and their derived/processed products is hereby investigated for groundwater for drinking and agricultural purposes. The studies include: subsurface characterisation and delineation of structural framework suitable for groundwater exploration and determination of petrophysical relationships used to link the geophysical properties (e.g., density) to hydrological properties (e.g., porosity). The results of interpretation indicate that the rocks are under ~50 m of Kalahari cover and the study area is composed of three aquifers: the extensive hard rock aquifer (granitic and volcanic), the important (fractured) karst aquifer and the minor sedimentary aquifer. The area is dissected by an ENE-to-EW-trending dyke swarm visible on the regional aeromagnetic data and much clearer on high resolution aeromagnetic data. Minor fault and/or dyke elements of NW-SE and NE-SW trend are observed. Spectral analysis reveals three main average ensample interfaces at depths of 0.7 km, 1.99 km and 4.8 km. The linear Euler solutions maps reveal that the majority depths to top of magnetic bodies range from 40 m to 400 m throughout the survey area. The shallowest depths are the most significant one in this case as they probably relate to depth of bedrock and thickness of regolith or thickest sediments. For 2695 existing boreholes analysed, maximum borehole depth is 482 m (mean 108 m), and almost half (1263) /hr) and an average water strike of 64 m. There is very little correlation between interpreted hydrogeological features and the existing borehole locations. The study shows the importance of preliminary geophysical investigations before ground borehole siting and drilling in order to improve borehole success rates and/or reduce costs inherent in groundwater projects.

Uso de dados aeromagnéticos e eletromagnéticos na avaliação de estruturas condicionadoras de aquíferos fraturados e produtividade dos poços, no Sistema Aquífero Embasamento Cristalino, na região de Bagé (RS)

“…Nesse contexto, a análise e interpretação de dados aeromagnéticos em estudos hidrogeológicos, tem se mostrado eficiente, principalmente, na identificação de estruturas geológicas. Diversos autores realizaram estudos semelhantes utilizando dados de aeromagnetometria, como por exemplo, Hewaidy et al (2015), Ranganai et al (2017) e Bongiolo et al (2014). Neste último, os autores utilizaram mapas aeromagnéticos no estudo da conectividade e compartimentação magnético-estrutural dos Sistemas Aquífe-ros Serra Geral e Guarani no centro do estado do Paraná.…”

Análise da compartimentação estrutural do sistema aquífero embasamento cristalino no município de Bagé (RS) com base no uso de lineamentos (SRTM e magnéticos) e de dados hidrogeológicos

“…Nesse contexto, a análise e interpretação de dados aeromagnéticos em estudos hidrogeológicos, tem se mostrado eficiente, principalmente, na identificação de estruturas geológicas. Diversos autores realizaram estudos semelhantes utilizando estes dados, como por exemplo, Hewaidy et al (2015), Ranganai et al (2017) e Bongiolo et al (2014). Neste último, os autores utilizaram mapas aeromagnéticos no estudo da conectividade e compartimentação magnético-estrutural no centro do estado do Paraná.…”

The hydrogeological mapping of the southwestern part of Serang Regency, Banten, Indonesia

“…The study area included four districts, namely Baros, Ciomas, Paburuan, and Padarincang. The requisite for implementing groundwater management is the hydrogeological characteristics of a region [4][5][6][7]. These data include aquifer characteristics that are observable from drill data, geophysical measurement results, pumping test data, hydrogeological features (e.g., rock structure, rock type, and the presence of springs, lakes, ponds, and rivers), and underground caves and rivers (i.e., the typical features of areas dominated with dissolution process) [8][9][10].…”