A lot of weird stuff went on with the gold stocks just after the 4 pm close. Look at this statement from Northgate Minreals.

Northgate Issues Statement on its American Stock Exchange Closing Price
Friday September 19, 10:05 pm ET

VANCOUVER, Sept. 19 /PRNewswire-FirstCall/ - (All figures in US dollars except where noted) - Northgate Minerals Corporation (TSX: NGX, AMEX: NXG) has noted that a large volume of the Company's shares were traded on the American Stock Exchange shortly after 4:00 pm ET on September 19, 2008 at a price of $1.01. This share price was considerably outside the intraday trading range and inconsistent with the Cdn$1.57 closing price recorded on the Toronto Stock Exchange. Northgate wishes to assure the market that it is unaware of any recent change or adverse development with respect to the Company's assets, financial position, or any other factor, that could have accounted for the unusual trading activity that took place after 4:00 pm ET today on the American Stock Exchange.

After hours it ended up 27 cents to $1.28