That is an interesting theory Peter, and am certainly not a metallurgist.
However, last winter detecting, the one and only 0.75gm. nugget I found was at around 15cm., well compacted gravel, 14x9 NF coil on the 4500.
In light of the Eric Foster theory, this nug. was found at Western Creek, FN Qld. where the gold is approx. 20% diluted with silver (19K) and found ~3 times deeper than in his experiment.
He does not say what size/weight of sample was used, but as we have previously discussed, I believe that detected depth is often increased by a "halo" effect around the nugget.
I also find most interesting the theory of actual nugget formation (bacterial?) and "why" and "where" it was located.