IRON OXIDE-COPPER-GOLD (IOCG) MINERALIZATION ASSOCIATED WITH CALCIC ALTERATION, EL ESPINO PROSPECT, CENTRAL CHILE

The El Espino IOCG prospect is located in the Chilean Coastal Range to the south of other known Chilean IOCG deposits. The prospect has been identified and explored as an IOCG since the late 1990’s. The prospect area contains a mixed sequence of Lower Cretaceous sedimentary and volcanic rocks. Alteration and mineralization occur mainly in the sedimentary rocks along a regional north-striking fault system. The sedimentary rocks include volcaniclastic siltstones, sandstones, and conglomerates in addition to limestones and gypsum beds. The sedimentary rocks appear to have been deposited in a relatively small (7 km long) marine basin within a major volcanic pile. Contact metamorphism effects are recognized locally in the sedimentary and volcanic rocks. The prospect displays a complex structural history, several alteration events and diverse styles of mineralization. Alteration and mineralization are concentrated mainly in thin-bedded siltstone units, though late epidote-dominated calcic alteration also affects other units. Sodic alteration characterized by albitization accompanies silica replacement. Potassic alteration characterized by K-feldspar appears to be weak and overprints sodic alteration assemblages. Sodic and potassic alteration are overprinted by a complex calcic alteration event consisting of early actinolite-chlorite-(epidote) alteration and later epidote-calcite-(chlorite) alteration. Calcic alteration contains an iron oxide assemblage dominated by specular hematite with lesser mushketovite and magnetite. Chalcopyrite and lesser pyrite are locally intergrown with iron oxides. Iron oxide and sulfide mineralization occurs along NNE to NE-striking faults and NW-striking quartz-calcite veins. Significant strike changes along the fault system correspond to better developed alteration and mineralization.