This is so true in the area I and my wife prospect for gold specimens on tailing piles here in Colorado. We have tried many different types of PI detectors in the past on none will detect the gold specimens we find with a VLF detector. We were hoping the Garrett Axiom would be able to detect this type of gold and this last spring met with Rusty Curry with Garrett to see if the Axiom offered some promise. Unfortunately the Axiom wasn't able to detect the gold specimens, even using the different types of coils they had to offer. We are hoping someday a PI detector will be produced by somebody that can detect these type of gold specimens, as there are certain areas where we are plagued with hot rocks and minerialzation and a VLF detector is basically useless.
Here is a .67 Gram wiregold specimen that a PI detector will not detect: