Exploration in Australia.
In spring time 2008, exploration works were conducted in Australia. We investigated the occurrence of the ore chute in the region of the Wooldlawn gwag on request of the Tri Origin Minerals Ltd. The desired area of about 6 km2 (rectangle with sides two and three km) has been pointed out to us, but no geological data were present except some deplorable information (bad conditions for current line grounding and outcrops of basalts).
The CED radius was 450 m. The total current was 19.2 A. Receivers with the effective area of 800 m2 were used. Measurements of the dBz/dt component of a transient process were taken at 223 points. These transient processes reflected the heterogeneity effect on a medium conductivity.
The Figure presents the normalized areal VECS signal at time 0.34 ms. How it may be interpreted? It is the electromagnetic image of a medium reflecting the real conductivity distribution, and therefore the real structure of the geological medium. In this case we clearly see and the medium heterogeneity, and a geologist, who also has other data, will get help just from the geological model.
At every time we can image such a “picture” and that will be compatible with a certain depth. Shown in Fig.6 is the areal signal at time 1 ms. The areal representation is also interesting in that the ring-type structure is seen in the western part of the area in the region of negative signals.
Areal (normalized) VECS signal of the dBz/dt component a) at time 0.34 ms; b) at time 1.0 ms.
Below the three-dimensional visualization of our data is present. To construct it, we created a data cube based on measurements of the dBz/dt component. The time was transformed with respect to depths making use of the well-known formula for the skin-layer. This data representation is well displayable. In practice, we recognize a three-dimensional structure characterizing the area surveyed by us directly in a field. We appreciate that the apparent three-dimensional target is present in the Figures whereas the real ore target is somewhat displaced and it differs from this electromagnetic image. Therefore, in later works we began to study additional electromagnetic field components and to apply 3D interpretation.
The 3D display of isosurface of the signal value
Booklets
Electrical prospecting by the method of vertical electric current sounding (VECS) as applied to ore targets. 3.0 Мb, pdf-file