“Dipole” CHIM: concept and application

Abstract

The “halo” version of the CHIM-method is an electrogeochemical sampling technique which was proposed for mineral exploration in the USSR (Ryss and Goldberg, 1973). It allows for detection of buried deposits by surface identification of their secondary epigenetic (superimposed) haloes. The Halo CHIM is based on selective in situ extraction of electromobile forms of pathfinder elements, with direct electric current, into the specially designed element-collectors (ECs). These collectors are embedded in the soil at a number of measurement points along a profile to be explored and are connected to the direct current sources as either anodes or cathodes. A complementary electrode, common to all the ECs, is positioned at “infinity”. Two main disadvantages of the current CHIM reduce its value as an exploration tool. Firstly, in most cases only positively charged mobile forms are collected, while anionic as well as cationic species may provide useful information. Secondly, the measured parameter is represented by the extracted mass of a certain element instead of its concentration at the measurement point. These data do not allow for quantitative geochemical interpretation. In the present paper, the theoretical and applied aspects of the recently proposed “dipole” version of CHIM are discussed. According to the Dipole CHIM procedure, both anode and cathode are represented by the ECs, and spacing between them in each “dipole” is negligible compared with the distance between adjacent measurement points. This technique enables simultaneous extraction of anionic and cationic species of elements. Moreover, it may allow for quantitative evaluation of the concentrations of the mobile forms in the processed volume. Field tests of this technique have enabled identification of distinct multi-element anomalies in the surface sediments at two sites in Southern Israel: above the Ein Yahav Dyke (the Negev area), and over the boundary of the Kokhav Oil Field, near Ashqelon. The extraction cycles were 2–5 times shorter, and the electrical charges expended were about an order of magnitude lower than those that are typical for the Halo CHIM. Presentation of the extraction data as concentrations in the processed media improved the contrast of the revealed anomalies for several elements.