Re: Metal detector & pyrite...and eventually gold
Hello SSR60,
I checked out two iron pyrite (iron sulphide) samples in both true all metal mode, and in zero discriminate mode on my Spectrum XLT (frequency somewhere around 6.6 kHz..I can't remember exactly, but it"s close enough...it's low frequency, coil size nine and one half inches). The auto track was turned off, and the detector was manually ground balanced to about minus 93 VDI (-93) out in my patio....with the samples laid on the frozen ground (that ground balance implies pretty tough mineral background ie close to black sand). Disc Sens @ 64 out of 80, All Metal Sens @ 48 out of 60....modest sensitivities.
(a) the first sample, about two inches long by an inch and a bit in diameter/width gave no reading at all. Nothin'.
(b) the second sample, about two and a half inches by two inches in diameter/width gave a reading that fluctuated between minus two (-2) and plus four (+4) VDI, in both modes (entering the lower foil range).
In either mode the audio response was quite weak, the sample could only be detected approx. two inches from the coil. In discriminate mode, the audio signal was broken (not diggable), while the all metal signal was smooth and clear.
The above VDI range is about what you would expect from low grade silver ore (with bits of native silver showing from low conductive arsenic-cobaltite mix in calcite), but the difference is that same size low grade ore gave off a much more powerful signal and could be detected out to about 10 inches. Thus, a good sized sample of pyrite can be detected with a lower frequency detector, but it's a real low power conductive, implying you must get the coil close to it in order to detect it. Fortunately, some pyrite dumps offer good pickings right on the surface. If you want to hunt this stuff, take Eric's advice above. Hope this helps.
Follow up: A couple of interesting bench test points (a) as the XLT ground balance was decreased from a black sand level to lightly mineralized ground conditions, the pyrite response in all metal gradually diminished to a point where it no longer responded with an audio signal (b) using the Goldstinger, operating @ 15kHz, coil size @ 8 inches, all metal mode @ about 80% sensitivity, both pyrite samples were easily detected, the larger piece out to three and one-half inches easy. It did not matter whether the ground balance was set to black sand, or reduced to light mineralization, the response was pretty much the same throughout the entire span; a slight diminishing of signal strength as salt ground balance was approached (c) the overall signal strength was considerably stronger with the Goldstinger compared to the lower frequency XLT.
That's it I guess, you made me curious too...so long...Jim.
