and Camargo. In 1631 Juan Rangel de Biezma discovered a rich vein of silver, and subsequently established San Jose del Parral near the site. Parral remained an important economic and cultural center for the next 300 years. On December 8, 1659 Fray Garcia de San Francisco founded the mission of Nuestra Senora de Guadalupe de Mansos del Paso del Rio del Norte and founded the town El Paso Del Norte (present day Ciudad Juarez) in 1667. The Spanish society that developed in the region replaced the sparse population of indigenous peoples. The absence of servants and workers forged the spirit of northern people as self-dependent, creative people that defended their European heritage. In 1680 settlers from Santa Fe, New Mexico sought refuge in El Paso Del Norte for twelve years after fleeing the attacks from Pueblo tribes, but returned to Santa Fe in 1692 after Diego de Vargas recaptured the city and vicinity. In 1709, Antonio de Deza y Ulloa founded the state capital Chihuahua City; shortly after, the city became the headquarters for the regional mining offices of the Spanish crown known as Real de Minas de San Francisco de Cuellar in honor of the Viceroy of New Spain, Francisco Fernandez de la Cueva Enriquez, Duke of Alburquerque and the Marquee of Cuellar..

Answer this question, if possible (if impossible, reply "unanswerable"): Which precious metal did Biezma discover?
silver