A bar of silver bullion stamped with a &#39;Made in Mexico&#39; label sit in the precious metals vault at Grupo Mexico SAB&#39;s La Caridad smelter facility in Sonora, Mexico, on Tuesday, May 7, 2013. Silver prices declined 2.1 percent in New York trading over the week ending May 10. Photographer: Susana Gonzalez/Bloomberg via Getty Images