The big story Wednesday was a "bear raid". It began with what some initially referred to as either a mistake ("fat fingered") with unusually large selling of Treasury futures contracts (over 100K contracts in one trade). The trade, later described as legitimate (see WSJ story) was based on the idea Bernanke would take QE3 off the table sending interest rates higher. The size of these trades created a domino effect triggering heavy selling in commodity markets, especially with precious metals which are also on an options expiration cycle.
Much of the related selling was triggered by HFT algos piling headlines with selling. It's also been common the past couple of years now to see some deliberate manipulation of prices by a handful of institutions in precious metals markets at the futures and options exchanges. Gold prices fell over 5% and silver almost 7% as trailing stops were triggered. These have been termed "bear raids" by most participants. It makes being involved in these markets like swimming with sharks.