Dyke detection as the main target of groundwater exploration using Magnetometry and Electromagnetic data

Abstract

Dolerite structures such as dykes and sills are the main target for groundwater exploration in Karoo Supergroup area which is the main stratigraphy unit in South Africa. Morgenzon Farm is one of the sites in Karoo Supergroup, including a dolerite dyke, which is interested here. Magnetization/susceptibility and resistivity of dolerite dyke are significantly larger than those of encompassing sedimentary materials. Therefore, low induction number electromagnetic (EM-LIN) and magnetometry approaches may be useful to its detection. EM-LIN is composed of three techniques: EM38, EM31 and EM34, with the latter being manipulated. Since both EM34 and magnetometry inverse problems are linear, regularized weighted minimum length solution algorithm is utilized for their inverse modeling, but with one main discrepancy: model weighting function for magnetometry method is attained from multiplication of depth weighting and compactness constraints, while model weighting function is only equal to depth weighting for EM34 approach. Recovered susceptibility and conductivity sections derived respectively from magnetic and EM34 data sets show high consistency. Inverted models represent a dolerite dyke in the middle of the profile with depth range of 4 to 15m.

Keywords

• dyke
• em-lin
• groundwater
• magnetometry