Clay identification! Now there is something you don't see every day! Remote sensing noted that smectite clay alteration was closely associated with gold deposits of the SW states. You can distinguish between montmorillonite, illite, smectite, and kaolinite by their conductivity. (Scientific American, the Amateur Scientist 1970--) A device can cheaply be made. I don't think that is the process Petra is using, but some other sort of reflective thingie. The kimberlite conductivity sensing by TDEM aerially in the NWT is by on-time high frequency electromagnetics which is really just finding the more conductive clay horizons that kimberlite frequently lies beneath.
A method I like which the oldtimers used a lot is the gold pan. You can pan the clays for trace gold. It may be tough as you have to disperse the clay, and some clay does not do that well. A tiny tiny bit of non sudsing Loc detergent (Amway) can help that. Too much and you have an agglomeration problem. Panning requires some surface tension to work well. A 7.5 inch knelson or my patented hand rocker might do the trick here if the clays are too robust otherwise.
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