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A news report from Tsodilo Resources (TSX:TSD) on July 22nd 2013 caught my eye:

A total of 63.70 line kilometers [of ground magnetics] was covered during the month of June as area totaling 2.53 km2. The expected monthly target is 360 line kilometers for the month and the shortfall is largely attributed to machine malfunction of all units. All magnetometer machines were sent back to the manufacturer for repair and software upgrades.

Mike de Wit, the COO of this company used to work for De Beers in South Africa at the same time I did. I know he is using American Cesium Magnetometers. Hence I am not surprised to read that they have failed in the terrain and vegetation Tsodilo is working in. These ground magnetometers have too many external cables that can be damaged on rocks and vegetation. They also don’t have a high enough gradient tolerance for Iron Ore.
The report went on to say:

The ground magnetic survey was concentrated around the southern tip of the XIF body near the village of Nxamasere. A crew of two was employed to carry out the ground magnetic survey while the directional survey was carried out by the field geophysicist.

Thus the ground magnetometers they where using did not have built in navigation and the geophysicist had to use a handheld GPS and walk ahead of the magnetometer operators to lead the way. This would have HALVED productivity, or worse if you consider the relative pay scales of operators and geophysicist. It is much more efficient to use a magnetometer with built in navigation.
The planned production rates seem extremely low too. 6 l-km per day seems very low for just outside the pan handle in the Okavango Delta. I can only assume that the large heavy backpacks they where using were hooking on trees and weighing them down or they weren’t surveying 7 days a week. In contrast Modern Mag crews median lowest line-km in a day is 16 l-km and has gone up from there using our new backpack design.

The message here is clear. If you are using magnetometers in rough terrain and vegetation you should use the GSM-19 overhauser magnetometers with GPS and navigation. If you are in REALLY rough terrain and vegetation you should use a Modern Mag backpack with either a GSMP-35 (especially for iron ore) or GSM-19 Overhauser. This way, you will get twice as much done, with less effort, more safely and with better quality data to boot.

The full press release can be found here…