The Search for the “Missing Half” of a World-Class Copper Resource in the Chuquicamata District, Chile

Orebodies may be dismembered by post-ore faulting, and partial burial by more recent cover can complicate the acquisition of structural data. This poses a significant challenge to tectonic reconstructions and the discovery of displaced mineralized blocks. A prime example is the behemothian Chuquicamata porphyry copper district in northern Chile. This district exhibits major postmineralization strike-slip faulting that translated a potentially sizable portion of the original deposit to a yet unknown location, likely hidden by thick, postmineralization, post-tectonic sedimentary cover. Since the 1990s, the Ministro Hales deposit, located ~10 km south of Chuquicamata, has been proposed by some investigators as being that piece. Here, we use new high-precision zircon and molybdenite geochronology results to show that although both deposits are derived from the same multimillion-year Chuquicamata Intrusive Complex, they formed 1.5 to 2 Ma apart, ruling out their twinship. However, a consistent southward-younging trend in magmatic and hydrothermal activities across the Chuquicamata Intrusive Complex suggests correlation of the Ministro Hales deposit with the oldest and northernmost part of the Chuquicamata Intrusive Complex, ~10 km north of the Chuquicamata mine. A compilation of available exploration data from beneath the Oligocene to Quaternary sedimentary cover in the Calama basin enabled the construction of a basement geologic map, which independently supports the fault offset inferred from the geochronological correlations. The geologic and geochronological data suggest the “missing half” of Chuquicamata may be located ~20 km south of the Chuquicamata mine, below the City of Calama.