Abstract The Chuquicamata district of northern Chile contains > 130 million metric tons (Mt) Cu in resources and past production. The mineralization occurs in various types of Eocene to early Oligocene porphyry Cu systems hosted by Paleozoic and Triassic volcanic and Triassic granodiorite rocks. Emplacement of the deposits occurred during E-W-directed contraction, crustal shortening, and uplift related to the Incaic orogeny between 38 and 31 Ma. The N-S-oriented West Fissure is the most important structural feature of the district, with significant postmineral, left-lateral displacement of 30 to 35 km estimated by regional mapping, although it remains to be confirmed by displaced alteration-mineralization features at the individual deposit scale. The West Fissure, across which both the geology and mineralization differ at any given point, divides the district into two domains. The Eastern Block comprises Paleozoic metamorphic and intrusive complexes overlain by Permian and Triassic volcanic and sedimentary rocks and intruded by Triassic granodiorite. These are overlain in the north by Cretaceous continental sedimentary and volcanic rocks and in the south by Eocene to Miocene sedimentary rocks of the Calama Basin, the lowermost units of which show evidence of syntectonic deposition. The Eastern Block contains the Chuquicamata and Radomiro Tomic deposits, both hosted by the Chuqui Porphyry Complex, a N-NE-oriented, 14- × 1.5-km megadike intruded into Triassic volcanic and intrusive rocks, and with a SHRIMP U-Pb age of ∼ 36 Ma. Hypogene mineralization at Chuquicamata occurs mainly in the East porphyry, the dominant phase of the porphyry complex and does not show a close relationship to smaller, later porphyry bodies with SHRIMP U-Pb ages of ∼ 34 Ma. Much of the Cu was introduced early (∼ 34–35 Ma; 40 Ar/ 39 Ar) during potassic alteration, which comprises a large low-grade body containing biotitized hornblende. Within this large low-grade body higher Cu grades occur as bornite and other Cu-bear-ing sulfides, without pyrite, in intense potassic alteration halos (K-feldspar-sericite) along early fractures. This was followed by introduction of quartz-molybdenite veins, with an Re-Os age of ∼ 35 Ma. Sericite-quartz-pyrite alteration, with advanced argillic alteration near veins, is later, as shown by crosscutting relationships, and returns 32 to 31 Ma 40 Ar/ 39 Ar ages. Veins with high sulfidation Cu-bearing sulfide-pyrite assemblages are part of this later stage, which overprinted and sulfidized the earlier Cu-bearing sulfides. Similar early and late mineralization occurs at Radomiro Tomic, but there the late-stage veins are of lesser importance. The Western Block comprises Paleozoic metamorphic complexes, Permian and Triassic volcanic and sedimentary rocks, and Triassic granodiorite in the south, overlain by Jurassic carbonates and continental sedimentary rocks. In the north, Cretaceous and Lower Tertiary volcanic and continental sedimentary rocks overlie the Jurassic unit. Jurassic to Eocene strata in the central to northern parts of the Western Block hosts the Eocene Los Picos and Fortuna batholiths. The Mina Ministro Hales deposit, at the eastern edge of the Western Block, is associated with Eocene porphyries (∼ 39–35 Ma SHRIMP and LA-ICP-MS U-Pb ages) that intrude wall rocks similar to those at Chuquicamata. Mina Ministro Hales is characterized by mineralization similar to that at Chuquicamata, but late-stage sericitic and advanced argillic alteration (∼ 32 Ma 40 Ar/ 39 Ar ages) are of greater importance, especially at the shallower levels. The Toki Cluster deposits, farther to the west, are associated with swarms of small porphyries thought to be late-stage phases of the ∼ 38 Ma Fortuna granodiorite batholith. The mineralization consists of bornite and/or chalcopyrite, commonly with magnetite but little or no pyrite, in A-type veins accompanying potassic alteration. The strongest mineralization is in and near the earliest porphyries and is truncated by the next younger porphyries, which in turn are cut by similar but less intense mineralization and still younger, less-mineralized porphyries. Late pyrite-sericite alteration occurs mostly on the peripheries of these deposits and carries little Cu. A favorable combination of desert climate and morphotectonic evolution resulted in the formation and preservation of significant supergene enrichment and/or oxidation. The potassic zones at Chuquicamata, Radomiro Tomic, and the Toki Cluster underwent in situ oxidation. Supergene enrichment blankets formed in quartz-sericite-pyrite alteration at Chuquicamata and Mina Ministro Hales. Supergene processes also resulted in lateral migration of Cu and formation of the Mina Sur exotic deposit. From an exploration perspective, the history of the district demonstrates how geologic observations and interpretation have played a key role in development of the resource base. Only the Chuquicamata oxide Cu mineralization cropped out, and original open-pit development in 1912 was followed by exploration and evaluation of the giant, high-grade enrichment blanket from the 1930s onward. District-scale exploration resulted in discovery of Radomiro Tomic in the 1950s, Mina Sur in the 1960s, Mina Ministro Hales in the 1990s and the Toki Cluster at the beginning of this century, none of which were exposed at surface. The Chuquicamata district, now producing ∼ 900,000 t Cu/yr, has been operating for 100 years and retains a substantial resource base that will enable it to continue for many years to come.

Abstract The Esperanza porphyry copper-gold deposit is located approximately 60 km south of Calama, in the porphyry copper province of northern Chile. Although partly exposed, historically mined from small-scale pits, and intermittently explored over many years, its true size and potential were appreciated only in 1999. Discovery was the direct result of detailed geologic mapping of key rock types and hydrothermal alteration assemblages and zoning and was partly underpinned by a property-wide ground-magnetic survey. The geology of the region is typical of the Cordillera de Domeyko and includes several fault-controlled basement blocks of late Paleozoic age and a number of sedimentary and volcano-sedimentary sequences of Mesozoic and Cenozoic age. Of these, the Late Cretaceous Quebrada Mala Formation and the middle Eocene domes of the Estratos de Cerro Casado are widely distributed in the area. Much of the region is mantled by moderately consolidated gravels of middle Eocene to middle Miocene age, collectively grouped as the Calama and Tambores Formations. The regional structure is dominated by several north-northeast-trending splays of the Domeyko fault system, which display evidence for both strike-slip and reverse movements and exert a strong control on the location of Esperanza. The deposit is part of a northeast-trending corridor of middle Eocene porphyry deposits that includes Telégrafo, Centinela, and Polo Sur. At Esperanza, a series of structurally controlled, medium-grained granodiorite porphyry dikes intrude a sequence of massive andesite flows and interbedded pyroclastic and calcareous volcano-sedimentary horizons of the Quebrada Mala Formation. Hydrothermal alteration consists of a core of potassic alteration partly overprinted, but mainly surrounded by, intermediate argillic, quartz-sericitic, and propylitic assemblages. Early biotite-bearing alteration from the central potassic zone yields a 40 Ar- 39 Ar age of 41.3 ± 0.3 Ma. Hypogene copper-gold mineralization occurs dominantly as chalcopyrite and bornite in multiple stockworks of pyrite-poor, A- and B-type veinlets with quartz, K-feldspar, biotite, magnetite, apatite, and anhydrite, which are spatially and genetically associated with the potassic assemblages. Primary fluid inclusions in these veinlets possess homogenization temperatures (T h ) of between 435° and 592°C and salinities in the 41 to 60 wt percent NaCl equiv range. Minor molybdenite accompanying these veinlets yields an Re-Os age of 41.80 ± 0.13 Ma. Overprinted intermediate argillic alteration is characterized by chlorite, illite, smectite, and greenish sericite, with chalcopyrite and pyrite, whereas quartz-sericitic assemblages are barren of copper and dominated by disseminated and veinlet pyrite in classic D-type veinlets. Primary fluid inclusions in quartz veinlets from these assemblages show lower T h (217°–330°C), although still retaining a magmatic component to generate salinities of 40 to 53 wt percent NaCl equiv. Within the potassic core, anhydrite becomes increasingly abundant with depth and, locally, forms a large structurally controlled massive body with interbedded proximal skarn rich in garnet and diopside. Supergene copper mineralization is developed in the upper 150 m of the deposit where it is characterized by atacamite and chrysocolla with subordinate brochantite, copper wad, and copper-rich clays. Minor amounts of chalcocite, covellite, native copper, and cuprite occur near the redox interface. From a regional standpoint, Esperanza confirms that copper-gold and copper-molybdenum deposits coexist in continental arcs within the same metallogenic belt, and porphyry copper and copper-gold mineralization in the northern Chile porphyry copper province was, at least in part, intimately associated with contractional deformation during the middle to late Eocene Incaic orogeny.