If rumors are correct, it seems like a very big player, such as a bank or hedge fund, dumped more than 33,000,000 shares of GDXJ on the market yesterday near the close of business, causing the ETF to crater way below its NAV. The value of such a dump was around $820,000,000. They must have needed cash quickly due to a margin call or something because this dump had the hallmarks of a large player in panic mode.