my usual technique is starting at Y5 and go in a straight 1x2 line for however far I can (usually a few hundred blocks until I hit gravel and get annoyed) and then on my way back I make holes in the walls usually 5 blocks in, place torch, see if there's anything, then move on about 2-5 blocks down and do it again on ...

KUC's Bingham Canyon mine is one of the largest and most efficient mines in the world. It has produced more copper than any other district in the U.S., accounting for over 16% of total U.S. copper production. In addition to copper, the mine produces gold, molybdenum, and silver.