Experts say the mine could yield more than $300 billion in metals and hundreds of jobs.

This mine employed over 3,000 people and became the most productive in Cornwall, yielding almost 450,000 tons of copper ore.

By the turn of the century, the copper boom was in full swing but the mines only yielded for a few years.

Besides graphite, the mine yielded modest amounts of lead and iron.

Production began in 2007, and in 2010 the mine yielded 322,700 tonnes of copper.

These mines yielded many large and fine stones in the sixteenth and the seventeenth centuries.

The town's mines yielded rich gold which was easily extracted at first.

Candente estimates that the mine will yield 75,000 tonnes per day with a minimum life of nineteen years.

(The mine also yielded smaller but, nevertheless, financially significant amounts of copper.)

The successful mine had yielded $55m in gold and $10m in dividends for investors.