April gold (GC=F) futures opened at $4,724 per troy ounce on Friday, down 3.4$4,889.50. The price of gold rose above $4,900 in early trading. Citing high volatility, CME Group raised margin requirements on gold and silver contracts for the third time since Jan. 13. CME Group operates futures and options markets around the world. Margins are deposits that act as collateral for leveraged transactions. CME increased initial and maintenance margins, which are the minimum a ...