I find quite a bit of abandoned drill core when exploring mining areas. I thought it might be fun to slice one to make a preformed round cab. Here is my project:
I had the same problem when swinging a GPX5000. I was getting horribly frustrated with what seemed to be good targets that disappeared when digging. Problem solved when I panned out the dirt I had been digging. Small gold in the pan.
My only complaint is the charging port. I used mine for two weeks in the Aruba salt water. I guess I didn't rise it well enough and it turns green and stops charging until I clean it with vinegar. I have multiple detectors and it is still my go-to for everything but nuggets. For that I still...
One quick response to your example. If the target disappears or diminishes as you dig for gold, put your dirt into a gold pan and you might be surprised how much smaller gold is present. Of course, little bits of oxidized iron can also be the cause.
As for air testing. It isn't useless. It...