Last Thursday (September 22) the prices of gold and silver suddenly crashed: over the weekend silver dropped by 34% (from 39.7 to 26.1 USD /ounce) and gold by 16% (from 1817 to 1533 USD / ounce).
There are a number of assumptions that are rumored to have caused this crash. I personally find most likely that the sudden increase of margin requirements on silver and gold contracts has caused this crash: these new rules were only announced on Friday and were already effective on Monday. Due to this sudden change in the rules traders were forced to liquidate their silver and gold positions. The subsequent drop in price triggered more selling, thereby causing an accelerated downward movement. (A detailed article in German can be found here.)
There is some indication that this crash was politically intended in order to prevent a greater flight from paper currencies – in particular the US dollar: already earlier this year gold and silver were caused to crash in the very same manner when during the Easter holidays the margin requirements had suddenly been raised several times in a row.