Iron oxide-copper-gold (IOCG) deposits, defined primarily by their elevated magnetite and/or hematite contents, constitute a broad, ill-defined clan related to a variety of tectono-magmatic settings. The youngest and, therefore, most readily understandable IOCG belt is located in the Coastal Cordillera of northern Chile and southern Peru, where it is part of a volcano-plutonic arc of Jurassic through Early Cretaceous age. The arc is characterised by voluminous tholeiitic to calc-alkaline plutonic complexes of gabbro through granodiorite composition and primitive, mantle-derived parentage. Major arc-parallel fault systems developed in response to extension and transtension induced by subduction roll-back at the retreating convergent margin. The arc crust was attenuated and subjected to high heat flow. IOCG deposits share the arc with massive magnetite deposits, the copper-deficient end-members of the IOCG clan, as well as with manto-type copper and small porphyry copper deposits to create a distinctive metallogenic signature. The IOCG deposits display close relations to the plutonic complexes and broadly coeval fault systems. Based on deposit morphology and dictated in part by lithological and structural parameters, they can be separated into several styles: veins, hydrothermal breccias, replacement mantos, calcic skarns and composite deposits that combine all or many of the preceding types. The vein deposits tend to be hosted by intrusive rocks, especially equigranular gabbrodiorite and diorite, whereas the larger, composite deposits (e.g. Candelaria-Punta del Cobre) occur within volcano-sedimentary sequences up to 2 km from pluton contacts and in intimate association with major orogen-parallel fault systems. Structurally localised IOCG deposits normally share faults and fractures with pre-mineral mafic dykes, many of dioritic composition, thereby further emphasising the close connection with mafic magmatism. The deposits formed in association with sodic, calcic and potassic alteration, either alone or in some combination, reveal evidence of an upward and outward zonation from magnetite-actinolite-apatite to specular hematite-chlorite-sericite and possess a Cu-Au-Co-Ni-As-Mo-U-(LREE) (light rare earth element) signature reminiscent of some calcic iron skarns around diorite intrusions. Scant observations suggest that massive calcite veins and, at shallower palaeodepths, extensive zones of barren pyritic feldspar-destructive alteration may be indicators of concealed IOCG deposits. The balance of evidence strongly supports a genetic connection of the central Andean IOCG deposits with gabbrodiorite to diorite magmas from which the ore fluid may have been channelled by major ductile to brittle fault systems for several kilometres vertically or perhaps even laterally. The large, composite IOCG deposits originated by ingress of the ore fluid to relatively permeable volcano-sedimentary sequences. The mafic magma may form entire plutons or, alternatively, may underplate more felsic intrusions, as witnessed by the ore-related diorite dykes, but in either case the origin of the ore fluid at greater, unobserved depths may be inferred. It is concluded that external 'basinal' fluids were not a requirement for IOCG formation in the central Andes, although metamorphic, seawater, evaporitic or meteoric fluids may have fortuitously contaminated the magmatic ore fluid locally. The proposed linkage of central Andean and probably some other IOCG deposits to oxidised dioritic magmas may be compared with the well-documented dependency of several other magmatic-hydrothermal deposit types on igneous petrochemistry. The affiliation of a spectrum of base-metal poor gold-(Bi-W-Mo) deposit styles to relatively reduced monzogranite-granodiorite intrusions may be considered as a closely analogous example.

Iron oxide-copper-gold deposits: an Andean view

Subduction erosion: Rates, mechanisms, and its role in arc magmatism and the evolution of the continental crust and mantle

http://www.quest.nasa.gov/projects/spacewardbound/docs/sdarticle.pdf

Antiquity of aridity in the Chilean Atacama Desert

Sequence stratigraphy of continental Triassic strata of Southernmost Brazil: a contribution to Southwestern Gondwana palaeogeography and palaeoclimate

Tectonic Regimes of the Central and Southern Andes: Responses to Variations in Plate Coupling During Subduction

Triassic rift-related sedimentary basins in northern Chile (24°–29°S)

The Andean orogeny in the Patagonian Cordillera of southern South America reflects the consequences of the Mesozoic and Cenozoic subduction of an oceanic plate beneath the South American continental margin The geological evolution of the region has been influenced by the Eocene collision and subduction of the Farallon–Aluk Ridge and the Miocene–Recent subduction of the Chile Ridge Another aspect of plate interaction during this period was two intervals of rapid plate convergence, one at 50–42 Ma, and the other at 25–10 Ma, between the South American and the oceanic plates It has been proposed that the collision of the Chile Ridge with the trench was responsible for the development, at least in part, of the Patagonian fold and thrust belt This belt extends for more than 1000 km along the eastern foothills of the southern Andes between 46° and 54° S along the southwestern rim of the Austral Basin The interpretation of a link between subduction of the ridge and formation of the fold and thrust belt is based on assumed time coincidences between contractional tectonism and the collision of ridge segments during Middle and Late Miocene times The main Tertiary contractional events in the Patagonian fold and thrust belt took place during latest Cretaceous–Palaeocene–Eocene and during Miocene times Although the timing of deformation is still poorly constrained, the evidence currently available suggests that there is little or no relationship between the timing of the fold and thrust belt and the collision of ridge segments Most if not all of the contractional tectonism pre-dated the latest episodes of ridge collision Collision of a ridge crest with the continental margin has been active for the past 14 to 15 million years Contrary to the suggestion of a relationship between ridge subduction and compression, the main result of this collision has been fast uplift and extensional tectonism The initiation of the Patagonian fold and thrust belt in latest Cretaceous or early Tertiary times coincided with a fundamental change in the tectonic evolution of the Austral Basin Throughout the Cretaceous most of this basin subsided as a broad backarc continental shelf Only in latest Cretaceous times, and coinciding with the initiation of the fold and thrust belt, the basin underwent a transition to a retro-arc foreland basin This change to an asymmetrically subsiding foreland basin, with an associated foreland fold and thrust belt, was related to uplift of the Andean orogenic belt in the west

Timing and origin of deformation along the Patagonian fold and thrust belt

The Rı́o Lácteo Formation of Southern Chile. Late Paleozoic orogeny in the Andes of southernmost South America

Vertebrate fossils and trace fossils in Upper Jurassic-Lower cretaceous red beds in the Atacama region, Chile

A thick succession of continental redbeds was deposited in a 50 km wide intra-arc basin on the Andean active continental margin in the Atacama region of northern Chile during early Cretaceous times. Upper Jurassic to early Cretaceous marine limestones were buried by the seaward progradation of a succession of coastal dunes, saline lakes and sandflats. Aeolian dune fields migrating towards the east across these coastal plains became stabilized by the growth of vegetation. Interdune alluvial areas between the sand dunes and dune fields developed into extensive alluvial braid plains which were in turn superimposed by alluvial fans. These fans were inundated by a regionally extensive saline lake produced by tectonic or volcanic damming of the sedimentary basin. This lake dried up leaving a large area of playa-lake mudflats. The climate was warm and semi-arid with a low and seasonal rainfall. Parts of the area supported a substantial vegetation of woody plants, together with a vertebrate fauna of dinosaurs, pterosaurs and crocodiles. The continental redbeds were derived from a volcanic source and were deposited on continental crust in a deep but narrow, north-south elongated, fault-bounded graben. This extensional basin formed in an intra-arc setting within an active andesitic volcanic chain. Upwards-coarsening sedimentary successions were the product of uplift of the fault-bounded margins of the basin.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800020501

The depositional environments and tectonic development of a Mesozoic intra-arc basin, Atacama Region, Chile

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