David:
I don't know of any skin conditions you get in mines, at any rate, any that persist in specific areas as yours does. Since your examination and workup ruled out
commonCommon cold and contagious diseases, I'm going to go out on a limb and suggest that what happened is this: you were in a dusty, dirty, and unfamilar environment and left with the conviction that you "picked up something." Thinking this made you itch and scratch. which in turn perpetuated the itch and reinforced the conviction that you indeed picked up something.
You didn't pick up anything. Apply Sarna lotion (OTC) every time it itches and put the matter out of your mind. Out of mines, out of mind.
Good luck.
Dr. Rockoff