I've never heard anything about any magnetometer that can find noble metals. a magnetometer reads the earths magnetism and senses anomalies in it due to ferrous metals being in the area. I have heard some fired earthenware may cause a very slight anomaly. with all the iron in the rocks around here it would just go bonkers.
I had heard something about a so called mag that could find non-ferrous metals on a recent TV/History Channel program, but dismissed it and figured they were referring to a towable metal detector of some sorts like a Pulse 12 and confused the two.
The basic principles behind a magnetometer really prohibit it from even detecting non-ferrous metals since they have no magnetic susceptibility.
DinkyDick or anyone else feel free to step in and share your thoughts.