Below the streets of Lower Manhattan, in the vault of the Federal Reserve Bank of New York, the world’s largest trove of gold — half a million bars — has lost about $75 billion of its value. In Fort Knox, Ky., at the United States Bullion Depository, the damage totals $50 billion. And in Pocatello, Idaho, the tiny golden treasure of Jon Norstog has dwindled, too. A $29,000 investment that Mr. Norstog made in 2011 is now worth about $17,000, a loss of 42 percent. “I thought if worst came to worst and the government brought down the world economy, I would still have something that was worth something,” Mr. Norstog, 67, ... (full story)