Sales of American Eagle silver coins by the U.S. Mint jumped 40 percent in October to the highest in 21 months, defying a slump in New York futures to the lowest in more than four years.

Sales surged to 5.79 million ounces, the most since January 2013, the month that set an all-time high at 7.5 million. Today, sales jumped 33 percent in one of the busiest times this year, Tom Jurkowsky, a spokesman at the Washington-based mint, said in an interview. Last month’s total was 4.14 million.

Silver and gold futures plunged today to the lowest since 2010 as the dollar rose to a four-year high against a basket of 10 currencies and equities climbed to a record close. The Federal Reserve is weighing the timing of interest-rate increases as other central banks add to stimulus to bolster their economies.

“We saw demand surge over the past two days,” Michael Kramer, the president of New York-based MTB Inc., a dealer authorized to purchase coins directly from the mint, said in a telephone interview. “Business was almost triple than what it has been over the past few months.”

Silver futures for December delivery dropped 1.9 percent to close at $16.106 an ounce on the Comex in New York. Earlier, the price touched $15.635, the lowest for a most-active contract since Feb. 25, 2010.

Gold futures for December delivery fell 2.3 percent to $1,171.60 an ounce. The price touched $1,160.50, the lowest since July 28, 2010.

Sales of American Eagle gold coins in October rose 16 percent to 67,500 ounces from a month earlier. The amount was the highest since January.

To contact the reporter on this story: Debarati Roy in New York at droy5@bloomberg.net

To contact the editors responsible for this story: Millie Munshi at mmunshi@bloomberg.net Patrick McKiernan, Joe Richter