The Oil Drum

As a student, I once worked in White Pine. A most unusual copper mine. Its use of the room-and-pillar underground mining technique resembled that in a coal mine. They were considering moving to longwall mining (continuous), also typical of coal mines (more difficult and expensive, but doesn't waste the 40% of the ore in the pillars). Although some native copper (and native silver) was present in the ore, most of the copper values were in Cu-sulfide, enriched in silver, within the shale. Native copper was far more typical of the so-called amygaloidal copper mines further up the Peninsula, in an older basalt horizon. These also were highly atypical deposits.