I've had similar Dowsing experiences. On one homestead I was dowsing with L-rods using Silver to signal with. I signaled one target and dug a terribly rusted knife. There was no Silver visable. It was either Silver plated at one time, or the Iron used to make the knife wasn't pure. Another example, I was out Dowsing by the Manistee river near me, using Gold to signal with. I had a target that didnt signal being a Meteorite, so I followed the signal line to the Gold.. Within a mile from where I signaled from was my target. It was the old Iron bridge, called Harvey bridge, built in 1906. When Dowsing with Elements, all targets with that Element react. Even if it's only Trace. The Iron used to make the bridge wasn't totally pure. Gold in trace amounts are in the Iron matrix. If I was to check, other Elements are probably in the matrix in trace amounts. Like Silver, Telleride, Copper. Just because it's not visable, doesn't mean it's not there.