Gold and silver prices plunged in heavy trading despite the dollar weakening while the stock market rallied Tuesday. Spot gold prices dropped 1.52% to $1,672.20 an ounce to a six-week low and close to its 200-day moving average -- a key technical level that often provides support. A break below this line confirms a strong downtrend. PowerShares DB U.S. Dollar Index Bullish (UUP), measuring the greenback against a basket of major foreign currencies,