Exploration in Kamchatka Peninsula.
In November 2008, electrical exploration was performed in the Kamchatka Peninsula. Ore body (nickel) occurring at the shallow depth (the first tens of meter) and possessing an increased conductivity (the first tens of ohm*m) served as a target being explored. The host medium is characterized by increased resistivity (more than 100 ohm*m). The CED radius was 500 m (every current line length). The total current in the CED was 1.6 A. We used induction receivers PDI-100 (effective area was 10000 m*m). The exploration area was about 0.5 km*km (rectangle with sides 600 m and 900 m). It has been conducted 207 measurements of the dBz/dt component. It can be seen that the measurements were conducted on the area that was less than the CED area itself. This cannot be considered as reasonable. An essentially undersized CED could be used. The difficulty was that the current, by conditions of grounding, was only 0.2 A in each current line and that could be compensated (for lesser CED) by closer, due to the lesser radius, arrangement of a source.
The signal of interest to us starts to manifest itself from 50 us. The informative range of times can be determined from 50 uV to 500 uV. The Figure displays areal normalized VECS signals at times 65 us and 145 us. In the northern area part, the anomalous zone is distinguished. Such early times (according to standards of TEM method) are real owing to both significant resistivities of the host rocks and the shallow depth of the target occurrence.
This is clearly apparent from the present time slices that the areal VECS signal free from the host medium background is highly visualisable. The data processing consist in viewing the data, rejection of data of survey stakes and doubles, smoothing, determination of informative time ranges, areal equalization (compensation of remote decay), generation of areal information for single times (time slices), and formation of three-dimensional data cube.
We distinguish the target with increased conductivity situated at shallow depth (nearly the surface). As to the target outlines, this issue is somewhat more complicated. The mathematical simulation for bodies of simple forms, which differ from host rocks only by resistivity, denotes that the local target creates a bi-polar signal of the dBz/dt component and the line of sign change passes through the middle of the local target. Such situation takes place in surveying ore bodies. So that, according to the Figure, the target may be extended into the area of another sign signals.
Areal distribution of normalized e.m.f. ( dBz/dt component) at time 65 us. б)-at time 145 us.
The Figure 2 also shows three-dimensional visualization based on the data cube of the dBz/dt component. It is seen that, aside from our target, the deeper dipping conductive horizon is also observed.
Three-dimensional display of isosurfaces of the dBz/dt signal value.
Booklets
Electrical prospecting by the method of vertical electric current sounding (VECS) as applied to ore targets. 3.0 Мb, pdf-file