**4. Current gathering**

Current gathering in long conductors is one of the main advantages with the Turam energizing techniques. This makes deep exploration possible. If it is possible to obtain galvanic contact with a conductor in the ground, one should use this as one of the grounding electrodes of the energizing cable. Lile et al. [6] investigated how gathered currents could be modeled by a two-dimensional computer model. **Figure 3** shows how the anomalous magnetic field lines in the ground are influenced by gathered current in a nearby conductor.

In field measurements, we usually want as much gathered current as possible. Therefore, it is preferable to connect one of the electrodes to the mineralization. However, in some cases, the field from gathered currents can mask anomalies, which may be more interesting. By using grounded electrodes, it is possible to have full control of the current distribution in the half-space and in the mineralization.

In **Figure 4**, the amount of current in the conductive body is 5% of the total current in the half-space. In this case, the edges of the body are outlined. With shallow flat conductors, it is important to have strong induced current at the edges of

### **Figure 3.**

*This figure shows the magnetic field from the induced currents in the half-space and in the long conductor situated in the half-space. The model is the same as shown in Figure 1. The good conductor gathers current from the half-space resulting in moving the vortex to the conductor. In this case, the amount of current in the conducting body is 30% of the total amount of current in the half-space [6].*

### **Figure 4.**

*The amount of gathered current in the conductor is dependent on the conductivity of the body relative to the half-space and the length of the conducting body. In this case, the amount of current in the conducting body is 5% of the total current in the half-space [6].*

the body to be able to outline the conductor. The gathered current in the conductor should in such cases be weaker. A cable loop on the ground surface can serve as the transmitter of the primary field.
