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Deep Chargeability Mapping
The figures shown here are a presentation of data and modelling from a single line of dipole-dipole IP (400m TX and 200m RX). The data is measured time domain IP data (TX Frequency ~ 1/20th Hz). It is acquired over an area of thick cover (950m) as depicted in the resistivity section (fig. 1). The measured chargeability pseudo section (fig. 2) is characterised by a consistent increase in chargeability with TX-RX separation (n-level) and high amplitude values. The problem here is that this data contains a significant EM coupling component (generally positive for a dipole- dipole array). Assuming zero coupling can be dangerous in conductive environments as it can result , for dipole-dipole configurations , in false basement anomalies. The chargeability section (fig. 3) is more likely to be a function of coupling than basement chargeability. GRS has undertaken to account for the EM coupling by modelling it using a 1-D earth assumption. This modeled EM coupling component is then used to calculate an ‘EM stripped chargeability ‘. The process is depicted in (fig. 5), where for a single TX-RX pair both chargeability and EM coupling components are modeled. The modeled section below derived from the EM stripped chargeability maps a more localised basement anomaly c.f. ubiquitously high basement chargeabilities in the above section.

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