Copper is on a remarkable run and companies mining it are doing even better. The metal’s price reached a decade high this week and has more than doubled since hitting a low in mid-March of last year as the pandemic shuttered businesses and curtailed demand. During that span, an index of 30 producers’ stocks tracked by Bloomberg Intelligence has jumped 400%, helped by low energy and credit costs that have fueled profit gains, and bets that a cautious approach toward spending will leave more money for shareholders in the form of dividends and buybacks.