REGIONAL ALTERATION IN THE EL ESPINO IRON OXIDE COPPER GOLD DISTRICT, COASTAL CORDILLERA OF NORTHERN CHILE

The El Espino prospect is located within the Mesozoic Iron Belt in the Coastal Cordillera of Northern Chile. The Espino area contains a series of intermediate stocks of granodioritic to dioritic composition which intruded a mixed submarine volcanic-sedimentary succession of Cretaceous age. The prospect occurs within a larger hydrothermally altered zone affecting the intrusive complex and the volcanic-sedimentary rocks. The hydrothermal system and the spatially associated intrusive complex are within a left stepping dilatational jog that connects two major north-striking fault segments. Sodic alteration characterized by albite is extensively developed in the greater Espino area at low to medium structural levels. Sodic alteration is overprinted by a spatially more restricted sodic-calcic alteration assemblage at low to medium structural levels. This style of alteration is characterized by actinolite-epidote-albite and forms alteration fairways which include the El Espino prospect. Potassic alteration has been recognized in limited exposures at the structurally lowest portions of the hydrothermal system. High-level hydrolytic alteration is focused along chlorite-sericite-quartz and quartz-sericite veins that contain anomalous Au and copper. Iron oxides and copper sulfides are concentrated in N- to NE-striking veins in sodic-calcic and chlorite-sericite alteration zones. Disseminated copper sulfides are found in the limited exposures of potassic alteration.