Another Myth Debunked -- What Magnetometers Detect

[GB_Amateur]

I've been wondering about this for quite a while and finally got around to looking into it.  Let's start with the answer before proceding to the rant.  😏  From Wikipedia:

Magnetometers can be used as metal detectors: they can detect only magnetic (ferrous) metals,...

Note in particular "only magnetic (ferrous) metals".  I can't remember the number of times I've seen people (particularly on TV shows) say that magnetometers detect gold.  Well, maybe if it's in an iron/steel box.  Most shipwrecks, even the old (16th-18th Century) ones contain iron/steel in moderately large quantities so getting an anomalous signal on a magnetometer could indicate a shipwreck.  It doesn't indicate precious metals.  Similarly for mineral exploration -- if a ferromagnetic mineral is associated with a desired metal/mineral then a magnetometer can give an indication of a spot that more investigation is warranted.

[Aureous]

Many years ago, an Aussie elec engineer made an add-on device that attached to your metal detector which was a mini magnetometer for determining if those deep targets were actually worth digging.  90% of deep targets tend to be iron of course and the mag would enable the user to 'yes or no' the target. I think the concept failed due to the weight which was added.

[Steve Herschbach]

18 hours ago, Aureous said:

Many years ago, an Aussie elec engineer made an add-on device that attached to your metal detector which was a mini magnetometer for determining if those deep targets were actually worth digging.  90% of deep targets tend to be iron of course and the mag would enable the user to 'yes or no' the target. I think the concept failed due to the weight which was added.

No, the real problem is a Minelab PI will hit a nail way deeper than a magnetometer, so it does not solve the problem on the targets where you most need it - the deepest. I know because I tried using a portable mag in conjunction with a Minelab many moons ago. Once you got the hole half dug you would get the mag start saying you were zooming in on a ferrous target, but by that point it was kind of a “might as well finish this hole” sort of thing. For the shallower stuff you could use a VLF as much as a magnetometer, but lots of people including myself have tried toting two machines around to do that, and in the end again it’s just easier to go ahead and dig them. Now, if it was all built efficiently into one light detector with an easy way to switch modes and check, that would be another matter. It’s technically feasible, one of those things no real company has yet tackled for some reason.

[Aureous]

7 minutes ago, Steve Herschbach said:

No, the real problem is a Minelab PI will hit a nail way deeper than a magnetometer, so it does not solve the problem on the targets where you most need it - the deepest. I know because I tried using a portable mag in conjunction with a Minelab many moons ago. Once you got the hole half dug you would get the mag start saying you were zooming in on a ferrous target,  it by that point it was kind of a “might as well finish this hole” sort of thing.

Yeah I agree. The guy I saw that tested the thing said his main issue was that it added a kilo to the overall weight. But it only gave a proper Fe response once the soil was open....it sorta stopped you from finishing the hole, rather than stopping it being dug in the 1st place. But, it was a very neat contraption, a small addition and easy to use. Ive used Dipole magnetometers in the mining industry but this thing was cleverly miniaturized. The Decane-filled sensor added most of the weight I reckon.

[bklein]

I’ve had a few different types of magnetic locators, like the Schonstedt GA-52CX. It utilizes magnetometer technology. They are cool in that they are very sensitive and work like a magic wand - pointing to the target. Might be great for meteorites. It picked up concentrated areas at the beach but not concentrated enough to have good targets. I would think the gold mode on the EQ800 would be just about as good, or better.