As I write this, gold continues to trade above $2,500 an ounce after surging past the psychologically important level for the first time ever in mid-August. For seasoned gold-mining investors, this should be a moment of validation. After all, the yellow metal has long been seen as the ultimate hedge against economic uncertainty. And yet, despite the bull run, gold stocks — those companies that mine, process and sell the metal — are trading at historically low valuations relative to the market.