Geological, structural, and temporal framework of hematite-rich IOCG mineralization at La Farola deposit in the Candelaria-Punta del Cobre district, Chile

Abstract

Iron oxide-copper–gold (IOCG) deposits encompass a diverse set of mineralization styles, leading to outstanding questions about how different alteration facies are related across a single ore-producing system and the overarching mechanisms of ore genesis. This study investigates the age and characteristics of mineralization at the La Farola deposit, a hematite-dominated IOCG deposit located at the southern margin of the Candelaria-Punta del Cobre IOCG district of northern Chile. Two lithologically-controlled ore bodies occur along the WSW-ENE striking, ∼18° NNW-dipping contact between the Lower Cretaceous Chañarcillo Group and Punta del Cobre Formation. Syn-mineralization N-S to NNW-SSE striking sinistral strike-slip faults likely acted as fluid pathways. Distinct mineral assemblages include an early Na-Ca assemblage (albite-scapolite) overprinted by skarnoid garnet with minor pyroxene, Ca-Fe (magnetite-actinolite), and K-Fe (magnetite-k-feldspar-biotite and minor sulfides) assemblages. The main sulfide mineralization (chalcopyrite-pyrite with minor bornite) is associated with specular hematite-white mica-K-feldspar-calcite and overprints all previous assemblages. The presence of hematite as the dominant Fe-oxide phase associated with Cu mineralization is characteristic of lower-temperature IOCG deposits, and may be a result of La Farola’s stratigraphic position <700 m higher than other deposits in the district. New U-Pb ages of 115.7 ± 1.2 Ma for garnet and Re-Os ages of ∼113–114 Ma for sulfides indicate mineralization occurred within a 3-million-year timeframe. These findings confirm hematite-dominant mineralization at La Farola was coeval with IOCG mineralization across the district. This research contributes to understanding IOCG systems and their formation mechanisms, highlighting the control local geological structures and alteration processes has on the diversity of mineralization types associated with a single IOCG system.