Gradiometers and alluvial gold finding

[Caterpillar]

Hi,

I live and prospect in Western Australia. I've used VLF and Minelab PI machines for close on 30 years. I'm no electronics expert but I am familiar with the basic theories involved in metal detectors. I'm interested in how a gradiometer could be used to locate alluvial gold nuggets. I'm a bit puzzled by the fact that a gradiometer is basically a magnetometer but gold isn't magnetic. So how does a gradiometer assist in finding nuggets? Is it the case where the gradiometer is set up such that the area to be searched is used as the "null matrix" as far as magnetism goes and a gold nugget becomes a "void" or "bubble" in the matrix background and thus registers a signal somehow? A "negative" signal maybe?

Gradiometers are sucessful in locating unexploded ordanance. This is understandable as such a large "iron" object would generate a "positive" magnetic signal. But how does gold figure in all this?

Also, what kind of sensitivity can be expected in locating deeper alluvial nuggets over that produced by the current Minelab GPX detector?


Thanks,

[Davor]

Alluvial gold can't be detected by a magnetometer directly, but the black sands that accompany it can.