Investors have grown immune to the economic and geopolitical risks that typically drive haven demand for gold. That’s how Richard Hayes, the chief executive officer of Australia’s Perth Mint, summed up the reason behind bullion’s slump to a 19-month low even at the height of tensions between the U.S. and China and the collapse of the Turkish lira that roiled markets. The World Gold Council said this month that demand for the metal in the first half of the year was the weakest in almost a decade.