BY JOHN W. MILLER
BINGHAM CANYON, Utah—Miners have drilled, blasted and dug 19 million tons of copper out of this valley—enough for all the nickels, dimes and quarters ever minted—in what is the world’s deepest surface mine.
There is plenty more in an untapped region far below the mine, and owner Rio Tinto, the global mining behemoth, is investing $165 million to explore the area, which may hold some $5 billion worth of copper.
Some mining companies that have relied mostly on surface mining—the removal of ground over minerals near the Earth’s surface—are going deeper. Mineral deposits are often concentrated in the same region. …