Marine self-potential gradient exploration of the continental margin
Date
2005
Authors
Heinson, G.
White, A.
Robinson, D.
Fathianpour, N.
Editors
Advisors
Journal Title
Journal ISSN
Volume Title
Type:
Journal article
Citation
Geophysics, 2005; 70(5):G109-G118
Statement of Responsibility
Graham Heinson, Antony White, David Robinson, and Nader Fathianpour
Conference Name
Abstract
The self-potential (SP) method for mineral exploration is seldom used on land, primarily because of electrode noise problems and nonunique interpretations. Marine measurements of the horizontal gradient of the SP field, on the other hand, are relatively simple to make with an array of electrodes towed behind a ship. With low ship speeds of 5 to 10 km/hour, dense spatial sampling (∼1 m) can be obtained with resolution of better than 1 μV/m. In this paper we report on gradient SP data recorded on the continental shelf of South Australia by a horizontal array of towed electrodes approximately 20 m above the seafloor. Ocean waves and swells with periods of 5 to 15 s yielded large amplitude signals ±20 μV/m, but subseafloor mineralization produced SP gradient anomalies of ±50 μV/m and widths of 2 km or more in a number of parallel traverses. Integrating the observed SP gradients along each line delineated SP anomalies of amplitude up to −100 mV. Self-potential and magnetic anomaly data show limited spatial correlation and have different wavelengths, suggesting that SP sources are probably nonferrous minerals, such as graphite, and are deeper than the magnetic sources. The source of the SP signal is probably reduction-oxidation (redox) potential (Eh) variations across a conducting body below the seafloor. We approximate the source as being two dimensional and find the most probable locations of line sources by an image reconstruction method. Numerical finite-element modeling of more realistic source regions suggests shallow, easterly dipping (∼15◦) conductors of 1 Ω.m in the uppermost 2 km.
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Geophysics, Volume 70, Issue 5, pp. G109-G118 (September-October 2005) Copyright © 2005 Society of Exploration Geophysicists