You might be right! However, in the first two pics, there are no support timbers or shimming up of the walls to be seen. Also, the O.P. stated the following: "My friend took his small army surplus folding shovel and started poking around and a hole appeared. He was able to move enough dirt that he exposed a small tunnel leading to an old mine shaft.", so that led me to believe it was an air shaft but of course, it could have been an escape tunnel. While I would never advocate anyone going into the mine to check but the bluish, blue-green and purplish appearing rocks in the first pic have the appearance of Peacock Ore and other ores which may be valuable by themselves or point toward a decent Gold deposit. I wonder if they are that color or if it was a lighting effect when the pic was taken!!??