The lead- zinc veins of the Chilete mining district in Northern Peru

Abstract

Lead-zinc-silver veins in the Chilete mining district in the Department of Cajamarca in northern Peru have been worked sporadically since the 17th century, but the greatest activity dates only from 1951. The ore deposits are in a thick section of andesitic volcanic rocks that overlie with marked unconformity a sequence of Cretaceous limestone, shale, and quartzite. The volcanic rocks form a gently north-dipping block of apparently simple structure. The Chilete deposits are quartz-sulfide veins consisting essentially of sphalerite, pyrite, and galena in a gangue of quartz and silicified and pyritized and sericitized. Wall rocks are calcitized chloritized, pyritized, and sericitized. The veins were formed by fissure filling, breccia filling, and replacement. Veins strike either northwest or east-northeast and dip steeply. They range from a few centimeters to 4 m. in width and the longest has a strike length of about 1700 m. The veins are cut by a number of post-mineral strike-slip faults of small displacement. Thicker sections of the principal northwest-striking vein, Murcielago, tend to occur where the strike swings slightly to the north. Vein intersections are not favorable loci for ore deposition, and several intersections seem to be distinctly unfavorable. All the veins have roughly the same combined content of lead and zinc at all levels, but the proportion of zinc to lead increases notably at the lowest levels of exploration 200-250 m. below the outcrops.