149 Economic Geology

Tuesday, 24 October 2006
1:30 PM - 5:30 PM

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

Paper number: 149-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

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.