Gold for April delivery dropped $17.60 to $1,578.10 an ounce. The metal fell 4 percent in February, its biggest monthly decline in 10 months.The demand for gold as a defensive investment has waned this year on evidence that the U.S. economy is maintaining its recovery. Platinum for April delivery dropped $16.60 an ounce, or 1 percent, to $1,583.50. Copper for May delivery fell 1.95 cents, or 0.5 percent, to $3.5475 a pound. Benchmark crude for April delivery fell 71 cents to finish at $92.05 a barrel. Wholesale gasoline was up 0.05 cents to $3.11 a gallon. Heating oil fell 2.4 cents to $2.96 a gallon. Natural gas rose 5 cents to finish at $3.48 per 1,000 cubic feet.