I'd like to install an outlet above my wood burning fireplace so that I can mount a tv. Problem is the entire wall is a 70's era stone wall. I thought I had a slick solution. There is a smaller rock (circled in red) that I could remove and put an outlet in its place. From what I could tell looking up the vent above the fireplace (circled in blue) there seems to be a 2x4 wall and insulation between the chimney and rock wall. So I figured as long as I have the romex between the insulation and rock wall it should be fine.
Problem is I finally chiseled out the rock and was not prepared for what I found. It was rock, like 3 inches of mortar, wire mesh, then drywall which was all expected. Directly behind the drywall is a metal plate or something. I dont know how thick it is. It doesn't seem like it is the chimney. My question is is it ok to drill through it to run the electrical? What is it for? I suspect it might be some kind of radiant barrier, but like I said it seems like there is insulation between the rock wall and the chimney so it seems odd a radiant barrier would be between insulation and drywall. If I do drill through it and dont like what I find is there a way to patch that hole?