Abstract The Farallon Resources, Ltd., Campo Morado precious metal-rich, massive sulfide deposits occur in a Lower Cretaceous, bimodal, calc-alkaline volcanic sequence that forms a major, north-trending belt in the Guerrero terrane in northeastern Guerrero state, Mexico. During Upper Cretaceous to lower Tertiary greenschist facies regional metamorphism, the rocks were deformed strongly into a northeast-verging fold and thrust belt. Three stages of later, weak deformation were dominated by kink folds, broad warps, and extensional faults, respectively. Most deposits occur at the stratigraphic contact of a sequence of felsic flows and het-erolithic volcaniclastic rocks with overlying chert and argillite-sandstone. The Reforma and El Rey deposits are on the overturned limb of a major thrusted anticline, and the Naranjo, South Naranjo, and El Largo deposits are on the upright limb of the same fold to the south. The La Lucha and San Rafael showings are in a thrust plate west-southwest of South Naranjo. In the Reforma and South Naranjo massive sulfide deposits, gold, silver, lead, and zinc are concentrated near the stratigraphic top, and copper is concentrated near the stratigraphic base. Major minerals are pyrite, quartz, ankerite, sphalerite, galena, and chalcopyrite. Gold and silver occur in gold-electrum, ten-nantite, and freibergite. The underlying pyrite-quartz stockworks contain chalcopyrite, sphalerite, and chlorite. In the stratigraphic footwall, hydrothermal alteration minerals are pyrite, quartz, chlorite, and ferroan dolomite/ankerite. In the stratigraphic hanging wall, hydrothermal alteration minerals are sericite, calcite-dolomite, and lesser clays and quartz. The deposits belong to a low-sulfidation, volcanogenic massive sulfide system formed in a subaqueous environment, and are of the bimodal, siliciclastic, massive sulfide type.