The third try is the charm, with grandkids and my son, and a bit of new information, we scoured the western slope of Mine Hill in Auburn NH and finally identified a deep depression in the ground in the area where the new location information had pointed to.
This spot was significantly father down from the top of the hill where previous information had proved to reveal nothing of interest. The depression was about 10-12 feet deep and somewhat circular about 15 feet across on the side of the hill, the bottom was covered in a thick layer of organic matter, leaves and sticks. on the upward hill side of the depression it was easy to tell that the opening had in fact been filled in with back fill and rocks.
The material on the upward slope side of the depression did not look like it was there naturally and the ruts from heavy equipment father up and west on the slope added information that material had been brought in from elsewhere to close the mines Adit to prevent access to the tunnel.
The grandchildren worked on some of the stones in the backfilled area to collect some interesting samples. It was possible to poke a stick between the rocks in quite far in several places indicating that the finer material between the larger rocks is slowly eroding away, but not into the depression area, possibly inward and downward into the mine tunnel.