EL ESPINO IRON-OXIDE COPPER GOLD DEPOSIT, COASTAL CORDILLERA OF NORTHERN CHILE

Iron-Oxide Copper Gold (IOCG) deposits are magnetite and/or hematite-rich epigenetic systems with Cu and Au mineralization. The El Espino IOCG prospect is located within the Mesozoic Iron Belt in the Coastal Cordillera of Northern Chile to the south of other known IOCG deposits in Chile. The El Espino area contains a mixed sequence of early Cretaceous sedimentary and volcanic rocks intruded by a dioritic to granodioritic complex. The sedimentary rocks appear to have been deposited in a relatively small (10 km long) marine to continental basin within a major volcanic pile during extensinal conditions. Local contact metamorphism effects are recognized in the sedimentary rocks around the intrusive complex.

The El Espino prospect occurs within a large zone of hydrothermal alteration. Alteration and mineralization occur mainly in the sedimentary rocks within blocks controlled by N- and NE-striking fault zones. Mineralization also occurs along NNE- to NE-striking veins either within the volcanic/sedimentary sequence or the intrusive complex. The geometry, kinematics and timing of this fault system are not yet fully understood though it appears that the NNE- to NE-striking faults zones and veins form a left lateral stepping dilatational jog developed in a major north to northwest striking fault system which has also controlled the localization of hydrothermal alteration and intrusions.

Sodic alteration is extensively developed in the greater Espino area. It covers and area of 100km2 and it affects all rocks types. Later sodic-calcic alteration affects a much smaller area (approximately 25 km2) than sodic alteration. Potassic alteration occurs locally. High-level hydrolitic alteration occurs along quartz veins that contain anomalous Au-Ag and trace copper.

Copper-gold mineralization occurs with sodic-calcic, potassic and hydrolitic alteration stages. Sodic-calcic alteration contains an iron oxide assemblage dominated by specular hematite with lesser magnetite. Chalcopyrite and pyrite are locally intergrown with iron oxides in both events.