VECS for ore investigations.
Electrical prospecting by the method of vertical electric current sounding (VECS) has a number of features and advantages as applied to ore targets:
• Received ( dBz/dt, dBfi/dt, dBr/dt ) signals are controlled only by three-dimensional heterogeneities. The horizontally-layered medium that is a host medium for ore deposits exhibits no action on these signals.
• Resistivity heterogeneity of a medium is pronounced in the CED field much clearer than with use of the horizontal current line or loop. This allows targets to be distinguished when the target resistivity is weakly-contrasting as compared to that of the host medium.
• Received signals ( dBz/dt, dBfi/dt, dBr/dt ) are controlled by heterogeneities near the measurement points since the anomalous field is also a complete one. In the case when a horizontal line or a current loop are applied, signals are often governed by the host medium and by all 3D targets, which are located between the measurement point and the field source. It is difficult to distinguish the local information in this composite signal. Pretty complex processing procedures are needed. When the conventional one-dimensional approach is applied to interpretation at the first stage, local interpretation will be rejected at all. Data on 3D targets in VECS signals is well separated not only in time, but also in space.
• Signals measured from different electromagnetic field components complement each other well and allow one to reject anomalies revealed in measurements of single components, as well as essentially decrease the area of equivalent solutions.
• VECS implements the long-held dream of prospectors in the field of electrical survey: to separate a measured signal into transient and polarization signals. Separation of the signal allows us to study the change in both the medium resistivity and polarization parameters of the medium. We study a medium resistivity not excepting local three-dimensional inclusions via measurement of magnetic components. Based on measurements of electrical components, we study polarization of a medium already visualizing the resistivity distribution in the medium. The resistivity distribution in the medium can be conceived when we study polarization of a medium based on measurements of electrical components.
• When exploration is performed by the VECS method, it is worthwhile to condense the survey network to the required accuracy of determination of target boundaries. When works are carried out with a current loop or horizontal line, survey network condensation seems to be unsuccessful inasmuch as change of a signal is primarily associated with change in the response of one-dimensional medium depending of a distance between measurement point and the field source. In works by the VECS method, the conventional is the technique with a dense survey network in locations where a signal from targets is recorded. Thus target boundaries can be determined more accurately.
• The CED technique allows a dense areal survey system to be efficiently implemented. Such acquisition geometry is very stable to distortion of a signal at some measurement points. As a consequence, such heavy demands on an accuracy of recorded VECS signals and noise level as in the transient EM technique are not imposed in other methods. VECS responses from local targets exhibit strong variations up to sign change. In measurements with the help of a current loop or horizontal current line, geological conclusions are often drawn as a result of change in a signal by several percent, thereby implying that measurements of the transient response are more accurate.
• For the VECS method, conducting screens (water layers, clay, lakes, etc.) are not complicating circumstances.
• The economic viability also takes place. When works are carried out with CED, a fixed source is used that is once established for survey all the studied area. To produce a dense survey network in the transient EM method, it is required to move all the receiving-current circuit.
Booklets
Electrical prospecting by the method of vertical electric current sounding (VECS) as applied to ore targets. 3.0 Мб, pdf-формат