U.S. markets closed mixed on light volume Monday. The S&P 500 gained 0.9%, the Dow Jones Industrial lost 0.9% and the Nasdaq ended the day exactly where it started. Crude oil plummeted to its lowest level in five-and-a-half years. Prices for February delivery fell about 2% to settle at $53.61 a barrel. Gold prices also sank on the strengthening U.S. dollar. Gold futures slipped more than 1%, losing more than $13. No big changes in shares of Intercontinental Exchange (ICE) despite the buzz from the New York Post that it may sell the New York Stock Exchange as soon as next year. Burger chain Shake Shack filed for an Initial Public Offering. It hopes to raise $100 million from the IPO. JPMorgan (JPM), Morgan Stanley (MS) and Goldman Sachs (GS) are its major underwriters.