Hi Brad,
I have been a fairly avid reader on some of the remarkable cave art discovered in Europe which has been attributed to Cro-Magnon man and I've even read about much simpler swirls and waves etched into a cave ceiling in South Africa by earlier Homo Sapiens (or possible an earlier species of man). I seem to recall reading somewhere that in certain cases ancients sometimes went to a great deal of trouble to navigate far into caves in order to create cave art--the description of the distance you have travelled has reminded me of this, but I can't cite a reference at the moment. I've even personally visitted Lasceaux in France and been in the full-scale reproduction--the original is closed now in order to protect the fragile cave art that was starting to be affected by the modern human traffic. I don't believe they are 100% sure why the cave art was created, but I think that one of the leading theories is that it was done for religious and/or ceremonial purposes.
The fact that you have discovered several etched and squared off mounds in front of other tunnels is interesting for sure. It starts to get a bit tricky now, however, with the potential destruction of an etched mound. I think it's highly unlikely that there will be metal in that mound or even in the tunnel behind it, however there may be an ancient burial chamber, cave art, or something else in there. The problem is that the etched mound itself may be and likely is historically significant. I don't know what the answer is as it's a real dilemma and I urge you restraint in considering destroying the etched mound. Perhaps molds can be made of the etchings or there is some non-destructive alternative. This is where a professional would be helpful and I know the University you contacted has not been terribly forthcoming. But it might be important to contact the right University or the right museum/historian in order to get the information you are seeking. The Institute of Human Origins (created by Donald Johanson the discoverer of "Lucy") at Arizona State University (?) may be of some help or at least be able to put you in touch with the right folks. You should be able to Google them to get contact info. Please don't take my post in any sort of bad light as I'm only trying to help you out and I know how hard you have been working to do things in an historically responsible way. I very much look forward to seeing the long video that you've just taken!