Geologia del yacimiento epitermal de oro y plata Can Can, Franja de Maricunga, precordillera de Copiapo, Chile

Abstract

ABSTRACT. Geology of the Can Can Gold and silver epithermal deposit, Maricunga belt, precordillera de Copiapo, Chile. Can Can is an acid-sulphate-type Au-Ag epithermal deposit located at 26°48'30’'S and 69°16'W, 140 km northeast of Copiapo, at 4,100 m of altitude. Along with La Coipa, Marte, and other recently discovered precious metal deposits, Can Can occurs within the Maricunga Metallogenic Belt. The altered and mineralized host rocks at Can Can are Upper Triassic shales and conglomeratic sandstones, unconformably covered by subhorizontal volcaniclastic Lower Miocene tuffs. The deposit occurs at the intersection of a northeast-southwest fault, with a north-south trending fracture zone. The altered and mineralized body is funnel-shaped, and wider towards the surface. In the shales, it is approximately 70 m wide and steeply south-plunging. At the unconformity, the altered zone broadens, reaching a width of 400 m. Two principal phases of alteration and mineralization were identified: 1. An early pervasive silicification and 'acid leaching' accompanied by intense argillic and advanced-argillic alteration, with deposition of disseminated Au-Ag; and 2. A late fracturing with the formation of stockwork of silica-alunite veins and hydrothermal brecciation, both with high contents of Au-Ag. Oxidation 01 the entire mineralized body, from 4,360 down to at least 3,800 m elevation posdates the mineralization. The ore assemblage at Can Can consists of native gold, and cerargirite, both associated with silica, alunite, kaolinite, jarosite, and hematite. The ore grade and the Au/Ag ratio is high in the shales and decreases towards the surface. The temperature of ore deposition has been estimated between 200° and 300°C. The erosion level of the deposit has been established at about 100 m below the paleosurface. The discovery of high-grade precious metals in Upper Triassic black shales opens new possibilities for explorations in the Maricunga Belt, and other districts in the Chilean Andes.