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 quartz-ite. 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 silici-fied and pyritized andesite. Wall rocks are calcitized, chloritized, pyrit-ized, 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 1,700 m. The veins are eut 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 dis-tinctly unfavorable. Ail the veins have roughly the same combined content of lead and zinc at ail levels, but the proportion of zinc to lead increases notably at the lowest levels of exploration, 200-250 m below the outerops. © 1955 Society of Economic Gelogists, Inc.
