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Central Andean Coastal IOCG Belt, Chilean Coastal Range Manto deposits, Chilean Iron Belt |
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Chile |
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Cu Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The significant IOCG sensu stricto and other iron oxide-alkali altered deposits of the Central Andean Coastal Belt of Chile and Perú, extend over an interval of ~2600 km from just south of Lima in Peru to El Soldado in central Chile (Figs. 1 and 2). It includes the major IOCG sensu stricto deposits at
Candelaria (Marschik et al., 2000; Marschik and Fontboté, 2001) and the surrounding Punta del Cobre District,
Productora,
Mantoverde District (Rieger et al., 2010; Benevides et al., 2007),
Santo Domingo District, (Daroch and Barton, 2011),
Raúl- Condestable (de Haller et al., 2006),
Marcona and
Mina Justa (Chen et al., 2010), which fall within a Late Jurassic to Early Cretaceous volcano-plutonic belt (Sillitoe, 2003). This belt, which is characterised by voluminous tholeiitic to calc-alkaline volcanic piles and plutonic complexes of primitive mantle origin gabbro to granodiorite, is associated with an extensional to transtensional event when the underlying crust was attenuated and subjected to high heat flow. All of the intrusive rocks are oxidised and belong to the magnetite series (Charrier et al., 2007; Sillitoe, 2003 and sources cited therein).
The IOCG sensu stricto ores have a close temporal and spatial association with the plutonic complexes of the volcanic belt and with major, broadly coeval, longitudinal fault systems. They share the belt with massive iron oxide-apatite, vein-type and manto copper-silver (with or without accompanying iron oxides), and small to moderate porphyry copper-gold deposits (Sillitoe, 2003; Chen, 2010).
The Chilean Coastal Range manto deposits comprise a series of grossly stratabound copper with minor silver deposits are the basis of significant mines in the Coastal Ranges of Chile. These include the
El Soldado,
Mantos Blancos,
Mantos de la Luna, Buena Esperanza, Mantos del Pacifico and Lo Aguirre deposits and those of the
Michilla District. Mineralisation is confined to two specific periods of extensional tectonics, namely the Jurassic and the Lower Cretaceous. These deposits are discussed in a paper in the monograph: "Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective" volume 2, published by PGC Publishing, Adelaide, Australia. Read the Abstract.
The massive iron oxide-apatite deposits of what is known as the Chilean Iron Belt, include the
El Algarrobo, Los Colorados and
El Romeral deposits. The Chilean Iron Belt is around 30 km wide and extends over a north-south interval of approximately 700 km, from 25 to 31°S. It embraces a large number of magnetite-apatite accumulations, ~40 of which are of economic significance and a more limited number (~5) that are mined for iron on a large scale (Bookstrom, 1977). K-Ar ages of alteration minerals and post-ore dykes from a number of these deposits are between 128 and 102 Ma (Zentilli, 1974; Pichon,1981).
Crustal Setting
The tectonic and geological history contributing to, culminating in, and then overprinting mineralising episodes, can be sumarised as follows.
The Central Andean segment of western South America has been an active margin for much of the time from the Mesoproterozoic, although it has experienced periods as a passive margin, particularly in southern Perú. It is underlain by a series of accreted autochthonous terranes, and Proterozoic to Tertiary sedimentary and volcanosedimentary sequences. The main elements of the continent are the large Mesoarchaean to late Mesoproterozoic Amazonian craton to the north, and the contiguous Rio de la Plata craton and Pampean cratonic terrane to the south (Fig. 1). The Pampean terrane is interpreted to have docked with both the Amazonian craton to the north, and the Rio de La Plata craton to the east during the Mesoproterozoic to form the original proto-South America (Ramos, 2008). The youngest rocks on the western Amazonian craton are deformed 1.28 to 0.95 Ga passive margin sedimentary rocks and syn- to late-tectonic 1.0 Ga granitic suites of the Sunsás province, outboard of the 1.55 to 1.3 Ga Rondonian-San Ignacio province (Fig. 1; Chew et al., 2010). To the west of this, extending from 200 km south of Lima (Perú) to the Chilean border, is the first of the accreted terranes, the 800 x 100 km Arequipa Massif, the partially exposed section of the broader Arequipa Terrane (Fig. 1), composed of granulites with dioritic gneisses, basic meta-igneous rocks and migmatites dated at 1.9 Ga in the north, with juvenile magmatism further south of 1.5 to 1.4 Ga and rejuvenated metamorphic ages of around 1.0 Ga. This terrane was accreted to the Amazonian craton as part of the assembly of Rodinia at around 1.0 Ga, sandwiched by the advancing Laurentia (North America) and coincident with the Sunsás province orogenesis. The massif was subsequently intruded by substantial Ordovician (~470 Ma) granitoids of the Coastal Batholith in Perú (Ramos, 2008). A second block, the Antofalla Terrane, is contiguous with the Arequipa Massif on its southern margin, extending to around 100 km south of Antofagasta.
This terrane is composed of gneisses, amphibolites and migmatites dated at ~1.2 to 1.0 Ga in the north, while further south high-grade metamorphic rocks and granitoids are dated at ~520 to 390 Ma. Ramos (2008) considers the Antofalla terrane to have been accreted to the Pampean cratonic block at ~1.0 Ga, in the same event that resulted in docking of the Arequipa Massif with the Amazonian and Rio de La Plata cratons, although earlier sources favoured a late Neoproterozoic (e.g., Ramos, 2004), or Ordovician docking (e.g., Charrier et al., 2007).
The breakup of Rodinia at the end of the Neoproterozoic, referred to as the Pampean Tectonic Cycle, resulted in extension and the development of a broad shallow extensional basin filled with intracratonic platformal clastic sediments lapping onto the Amazonian craton and Arequipa Massif, without the development of intervening oceanic crust. The suture between the Antofalla Massif and Pampean cratonic block to the south however, opened in a ‘scissor-like' fashion, to form a southward opening gulf as much as 1000 km wide, with an oceanic crustal floor (the Puncoviscana Basin). This basin was fi lled with several thousand metres of Neoproterozoic to Early Ordovician siliciclastic sediments, minor carbonate and mafic volcanic rocks cut by early Cambrian granitoids that form a narrow magmatic arc. To the south, this basin was open to the sea where an extensive carbonate shelf was developed grading westwards into fine siliciclastic sediments deposited on a basement of oceanic crust. Similar siliciclastic sequences were deposited to the west of the Antofalla Massif (Ramos, 2008).
The Famatinian Tectonic Cycle, a period from the late Cambrian to Early Devonian involved contraction, amalgamation and orogenesis, and included the development of a number of corresponding significant magmatic arcs of lower to middle Palaeozoic age. During the Ordovician, a compressive regime had been re-established and the Antofalla Massif was again accreted to the Pampean cratonic block by eastward subduction of the intervening oceanic crust before the beginning of the Silurian. During this period, and after the accretion, eastward subduction of the oceanic plate to the west had proceeded below both the Arequipa and Antofalla massifs, and below the Pampean cratonic block to the south of the latter. An additional exotic micro-continent, the Cuyania (Precordillera) terrane, believed to be derived from Laurentia after the Rodinia breakup, docked with the Pampean cratonic block in the Mid- to Late Ordovician, immediately to the south of the Antofalla Massif (Ramos, 2008). The Cuyania terrane comprises Grenville age (~1 Ga) basement and an exotic Cambrian to Ordovician cover succession (Cawood, 2005). A carbonate platform sequence was developed on this shallowly submerged microcontinent (Ramos, 2004). Following collision, marked by an ophiolitic suture zone, subduction stepped back and continued below the Cuyania terrane until at least the Mid- to Late-Devonian, when the exotic Chilenia terrane collided with the amalgamated Cuyania-Pampean cratonic block over the same interval of the continental margin. The Chilenia terrane is also masked by a Lower Palaeozoic passive margin foreland wedge, although minor erosional windows reveal schists and gneisses with metamorphic(?) ages as old as 1.0 Ga (Ramos and Basei, 1997). A further sliver of Laurentia, the Mejillonia terrane, largely masked by younger rocks, but outcropping sporadically along the coast from Antofagasta to Iquique, is interpreted to have accreted to the immediate west of the Antofalla Massif between 500 and 439 Ma, as indicated by subduction-obduction of ophiolites, and thrusting and folding of sedimentary rocks.
Figure 1. The location of the Chilean Coastal Belt IOCG Province and the IOCG sensu stricto and other iron oxide-alkali altered ore deposits within the tectonic framework of South America and West Africa. Those of the West African and Amazonian cratons are located towards the margin of Archaean nucleii of the Reguibat Shield (Guelb Moghrein) and the Xingu-Iricoumé block of the Central Amazonian Province of the Amazonian craton in Brazil (Carajás Mineral Province - Sossego, Salobo, Igarapé Bahia, Cristalino and a number of smaller deposits). Note the outline of the ~1.8 Ga large igneous province, a vast sheet of largely felsic volcanic rocks and comagmatic granitoids that may influence the second generation, but smaller deposits of the Carajás Mineral Province. The deposits of the Central Andean Belt in northern Chile and southern Perú, while hosted dominantly by Mesozoic (but also some Palaeozoic) rocks, overlie a thick basement composed largely of exotic terranes of Palaeo-, Meso and possibly Neoproterozoic metamorphics, specifically of the Arequipa (Perú) and Chilenia (Chile) terranes. These older basement blocks are only very locally exposed, being separated and overlain by Neoproterozoic to Tertiary ophiolites, sedimentary sequences and magmatic arcs. However, they influence the controlling structures (e.g., the northern Atacama Fault) and the chemical and physical nature of the crust through which ore related fluids are introduced and circulated, as well as the thickness of underlying subcrustal lithospheric mantle. Details plotted are largely after Cordani and Teixeira (2007), Chew et al. (2010); Ramos (2008); (2004), Petters (1986).
The succeeding Gondwana Tectonic Cycle commenced in the Mid-Devonian and continued to the Late Permian. At the close of the Famatinian Cycle, subduction retreated to near the current coastline, the subducting plate dipping east below the now amalgamated Arequipa, Antofalla, Mejillonia and Chilenia terranes, accompanied by the development of a growing accretionary prism and a complex sequence of both “I” and “S” type granitoids and associated volcanic rocks which are exposed in various parts of the Cordilleran Frontal and Coast Ranges. An arc is considered to have essentially been centred on the present day high cordillera, flanked progressively to the west by a forearc basin and accretionary complex (Charrier et al., 2007). To the south of Santiago, the pattern of northsouth elongated slivers of exotic terranes is broken by the parautochthonous Patagonian Terrane (Fig. 1), which collided with Gondwana from the south during the Early Permian, across an east-west suture, in the final stages of Pangean assembly (Charrier et al., 2007; Ramos 2008).
The Pre-Andean Tectonic Cycle that followed, persisted from the latest Permian to earliest Jurassic and marks a 55 m.y. hiatus in orogenic magmatism between the amalgamation of Gondwana/Pangea and the commencement of its break-up. Over this period, following the final consolidation of the supercontinent, plate movement and subduction either ceased or was seriously curtailed. During this period, heat accumulated in the upper mantle below western Gondwana, melting of the lower crust, producing of enormous volumes of magma along the northern Chilean coast through to northern Argentina. This in turn resulted in crustal down-warping, extension of the upper, brittle crustal layer, and the development of extensional basins to produce the characteristic silicic magmatic activity and northnorthwest oriented extensional basins of the continental margin. The orientation of these basins has been attributed to structures related to the sutures that bound the exotic terranes of the region (Charrier et al., 2007 and sources cited therein). This magmatic activity includes substantial S- and A-type granitoids in north-western Argentina including the high Andes to the north, while similar aged intrusive rocks in the Coastal Range from north of Copiapó to south of La Serena in Chile may be of similar origin (Fig. 2; Charrier et al., 2007 and sources cited therein). The succeeding Andean Tectonic Cycle lasted from the late Early Jurassic to the present and corresponds to the break-up of Gondwana, with the eventual renewal of subduction activity, largely accommodating the split between South America and Africa, in the process generating Andean arc magmatism. Central and northern Chile (north of ~40°S), is characterised by the development of a magmatic belt parallel to, and on the western edge of the continental margin, bounded to the east by a backarc basin (Fig. 2). There was a gradual eastward migration of the axis of magmatic activity from the Late Cretaceous to Early Palaeogene, and development of foreland basins on the eastern side, to the current architecture from the Late Paleogene to the present (Charrier et al., 2007).
During the first stage of the Andean Tectonic Cycle in northern Chile, magmatic activity commenced with a pile of as much as 5 to 10 km in thickness of subaerial to locally shallow submarine basaltic-andesitic, to andesitic to dacitic volcanic rocks, the Mid to Late Jurassic La Negra Formation and equivalents. This arc extended from near the Peruvian border in the north, to La Serena in the south. It is mostly conformable with the Pre-Andean anorogenic volcanic sequences and is host to IOCG-like vein mineralisation north of Antofagasta and the Mantoverde deposit further to the south. South of 26°S (Chanaral) to near 29°S (La Serena), succeeding Late Jurassic to Early Cretaceous arc volcanism is represented by up to 3 km of basaltic-andesitic, to andesitic to dacitic volcanic rocks of the Punta del Cobre Group that host the Candelaria-Punta del Cobre IOCG deposits (Marschik and Fontboté, 2001; Sillitoe, 2003). These volcanic and pyroclastic rocks extend eastward into the back-arc Tarapacá basin and interfinger in the east with carbonate rocks of the stable continental margin (Mpodozis and Ramos, 1990).
North of 27°S (Copiapó) the Tarapacá basin is dominated by marine carbonate and continental terrigenous clastic sedimentary rocks, with some interbedded volcanic rocks. South of La Serena, the Central Chile back-arc basin contains Jurassic marine carbonates, which includes a thick gypsum unit, overlain by Late Jurassic red beds and then by Early Cretaceous marine carbonate rocks. The arc to the west in this region is represented by an intra-arc volcanic and volcaniclastic rocks of high-K calc-alkaline to shoshonitic basalt to andesite (Sillitoe, 2003; Ramos, 2000; Mpodozis and Ramos, 1990). During the Late Jurassic, the changing tectonic pattern resulted in the back-arc basins in northern Chile being uplifted and progressing from marine to well developed evaporitic facies (Oyarzun et al., 2003). The Mid Jurassic to Early Cretaceous volcanic pile in Northern Chile is accompanied by voluminous, broadly contemporaneous, plutonic tholeiitic to calc-alkaline complexes of noritic and gabbroic, to quartz diorite and leucocratic tonalite and granodiorite in composition. These rocks are of primitive, mantle derived parentage in a series of batholiths, typically >50 km long. They are known to have been emplaced as a series of short pulses of between 3 and 15 m.y. where extensive dating has been undertaken between 25°30' and 27°30'S (Dallmeyer et al., 1996; Lara and Godoy, 1998; Grocott and Taylor, 2002; Sillitoe, 2003). At least some of these batholithic masses (e.g., in the Candelaria mine area) are demonstrated to be gently dipping, tabular bodies, emplaced by roof uplift-floor depression mechanisms during regional extensional deformation (Arévalo et al., 2006), although others from the Late Jurassic, may be steeply dipping slabs, localised by ductile shear zones (Grocott and Wilson, 1997).
In southern Perú, thick accumulations of mostly basaltic-andesitic volcanic arc rocks are found, similar to those in northern Chile, e.g., the Río Grande-Chala Formations, extending into the analogous back-arc basins which are filled with Early Jurassic basaltic volcanic (~1500 m) and several kilometres of Mid to Late Jurassic terrigenous sedimentary rocks in the Arequipa basin to the south, and high-K calc-alkalic and shoshonitic basalt and basaltic andesite with subordinate dacite and rhyolite in the contiguous Cañete basin to the north. These volcanic successions are underlain by clastic-carbonate rocks with very minor evaporites (Caldas, 1978; Romeuf et al., 1993; Palacios et al., 1992). The Middle to Upper Jurassic units in this succession, which host significant Early Cretaceous IOCG deposits, e.g., Mina Justa (Perú), were intruded by gabbroic plutons and dykes (Atherton and Webb, 1989; Pichowiak et al., 1990), and then, from the Early Cretaceous, by the enormous dioritic to tonalitic Coastal Batholith (Pitcher and Cobbing, 1985; Grocott and Taylor 2002; de Haller et al., 2006), which probably formed through wrench tectonics along crustal lineaments (Polliand et al., 2005).
Sillitoe (2003) notes that the Jurassic and Early Cretaceous arc and intra-arc successions of the Coastal Cordillera are predominantly basaltic-andesite to andesite in composition, with subordinate dacite and rhyolite, which impart a bimodal signature. They range from tholeiitic to calc-alkaline in composition, but may be locally high-K calc-alkaline and shoshonitic. They apparently have a greater proportion of lava than pyroclastics, and lack volumetrically significant felsic volcanic rocks. There is also little evidence of major volcanic edifices typical of subduction related arcs, and the regime may well be more akin to a flood basalt province (Sillitoe, 2003). All of the intrusive rocks are oxidised and belong to the magnetiteseries (Sillitoe, 2003). Sillitoe (2003) outlines isotope signatures and trace element characteristics of the Mid Jurassic to Early Cretaceous volcanic and intrusive rocks, consistent with maximal extension and crustal thinning, indicating that during the Early Cretaceous they were derived from a subduction fluid modified mantle source without significant crustal contamination (e.g., Williams et al., 2005).
In both Chile and Perú, these rocks are underlain by a basement of Palaeozoic sedimentary, volcanic and felsic intrusive rocks, which in turn overlie and separate Mesoproterozoic metamorphic rocks of the Arequipa, Antofalla and Mejillonia terranes (as described previously). The homoclinal dip of the La Negra volcanic succession, the total absence of tight folds and the observation that the volcanic rocks generally only exhibit low-grade, non-deformational hydrothermal-burial metamorphism (Aguirre, 1988; Atherton and Aguirre, 1992), has been taken to imply deposition under extensional conditions (Charrier et al., 2007 and sources quoted therein). A regional extensional regime is also evidenced by geochemical data and the enormous thickness of volcanic rocks and backarc sediments. This extension was accompanied by uplift of the asthenospheric wedge beneath the arc and back-arc basin, and is interpreted to reflect slab-steepening and rollback of the subducting Phoenix plate slab over a period of ~90 m.y., from the late Early Jurassic to late Early Cretaceous, following the prolonged pause in subduction during the Pre-Andean cycle (Charrier et al., 2007) and consequent cooling (and probable detachment) of the cold, dense, brittle slab.
It is suggested here that during the Pre-Andean tectonic cycle the prolonged break in subduction eventually resulted in the detachment of the cooled slab, triggering delamination and detachment of SCLM below the thickened leading edge of the adjacent continental crust. This led to upwelling of asthenospheric mantle and decompression melting to form an under-/intraplate magma chamber below the thinned lithosphere, anatectic melting of the lower crust, and production of anorogenic magmatism during the Pre-Andean cycle. At the beginning of the Andean cycle, the commencement of the advance of the now cooled, heavy Phoenix plate resulted in roll-back, and extension in the crust. By then the under-/intraplate had been fractionating for some time, and could release less dense fractions to exploit transcrustal fractures consequent upon the extension/transtensional regime (e.g., the Atacama fault and related systems), to release large quantities of magma. The Phoenix plate, while rolling-back, was still sinking steeply and undergoing partial melting to fertilise the asthenospheric wedge and promote melting to recharge the under-/intraplate magma chamber and feed the magmatism within the crust.
This extensional phase was closed by a pulse of compressive deformation in the Late Cretaceous, which inverted the former back-arc basins and created a major regional unconformity (Charrier et al., 2007).
Deformation in central and northern Chile during the late-Early Jurassic to late-Early Cretaceous was principally concentrated along the major, Atacama Fault Zone which developed during this stage as a deeply penetrating, continental-scale, strike-slip fault that can be traced for >1000 km, from Iquique in the north, to south of La Serena in the south, and runs through the plutonic rocks of this period, suggesting a reduction of crustal strength caused by the high heat flow. Both ductile and brittle deformation, and dextral (transtensional) and sinistral (transpressional), as well as late vertical displacement is recognised. Two other structures, the ductile to brittle Tigrillo and Chivato fault systems are found to the west and east respectively of the Atacama fault. These three fault zones, which together mark progressive younging to the east, had a marked control on the development of the associated Tarapacá and Central Chile basins in Chile, while comparable structures e.g., the deeply penetrating Treinta Libras fault system, are associated with the Arequipa-Cañete basin in southern Perú (Caldas, 1978; Atherton and Aguirre 1992; Sillitoe, 2003).
During the roll-back period, the advancing Phoenix plate behind the steepening slab approached the South American continent obliquely from the northnorthwest, from a generally northeast-southwest oriented spreading centre (Arévalo et al., 2006). This produced direct strikeslip movement on the Treinta Libras fault system in Perú, parallel to the direction of approach, while the oblique advance towards the Chilean Coastal Belt would have caused transtensional-dextral and transpressional-sinistral displacement on the Atacama Fault respectively during extension and compression.
Both the axis of Mid Jurassic to Early Cretaceous magmatism and associated IOCG sensu stricto and iron oxide-apatite and other iron oxide-alkali altered deposits are diachronous, gradually migrating eastward with time (Sillitoe, 2003). This mineralisation, which occurs as either veins, hydrothermal breccias, replacement mantos, calcic "skarns" or a composite of more than one of these forms (which includes most of the larger examples), appears to have a close relationship with both plutonic complexes and broadly coeval fault systems. Mineralisation was introduced in two main periods, including from ~175 to 156 Ma (e.g., Marcona magnetite, Perú and the smaller vein system Cu deposits, north of Antofagasta in Chile, such as those near Tocapilla), and 120 to 112 Ma (e.g., Raúl- Condestable in Perú; Mantoverde and Candelaria near Copiapó in Chile). Other significant mineralisation includes the 140 Ma hematitic mantos at Mantos Blancos which lie to the south and east of the vein deposits north of Antofagasta; Chilean Iron Belt deposits, south of Copiapó and closer to the coast, which were emplaced between 130 and 116 Ma (e.g., El Romeral and El Algarrobo); and the El Soldado manto, further to south at 108 Ma. The Mina Justa copper deposit 3 to 4 km east of Marcona in Perú is dated at 109 to 95 Ma (all of these dates and sources are quoted in Chen, 2010 and Chen et al., 2010).
A major change in plate interaction along the continental margin in the early-Late Cretaceous, was caused by the commencement of very rapid oceanic crust production at the mid-ocean ridges in both the Pacific and Atlantic oceans, and reduction of the slab-subducting angle below South America. This led to a period of intense contraction, emergence of the continental margin, inversion and consequent uplift and erosion of the Jurassic to Early Cretaceous backarc basins, the eastward migration of the axis of magmatism (several tens to a 100 km inland from the present coast), the formation of a continental foreland basin to the east and a wide forearc basin to the west. This activity produced more intense magmatic activity resulting in major plutons and abundant andesitic to rhyolitic-dacitic volcanic rocks, frequently associated with large calderas in a dominant extensional/transtensional regime, due to a very oblique convergence rate between the northward approaching Farallon (beneath the Pacific Ocean) and the South American plates (Charrier et al., 2007 and sources quoted therein). By the early Miocene, the Nazca plate was being subducted below South America, with an increasing convergence rate from 49.5 to 42 Ma, until by 26 Ma the approach direction was almost orthogonal east-west directed.
The convergence rate increased to a maximum at 12 Ma. The main post-Incaic porphyry copper deposits of the Andean belt were formed during the Late Eocene to Oligocene north of La Serena and Late Miocene to Pliocene to the south. This extended description illustrates the setting of the Mid Jurassic to Early Cretaceous rocks of the Central Andean Coastal Range above a complex collage of Palaeozoic to Mesozoic arcs and underlying exotic terranes of varying ages (from Palaeo- to Mesoproterozoic) and diverse compositions, separated by an array of sutures. All of these characteristics influence the composition and emplacement of any anorogenic magmatism, magma contamination, circulated fluids, structural framework or location of intrusions and volcanic conduits.
District- to Deposit-scale Alteration and Mineralisation
The iron oxide-alkali altered mineralised systems and deposits of the Central Andean Coastal Belt have been subdivided into a number of styles, including veins, hydrothermal breccias, tabular replacement bodies (mantos) and calcic-skarns, and composite deposits comprising two or more of the preceding. The veins tend to be hosted by intrusive rocks, particularly gabbrodiorite and diorite, whereas the larger composite bodies (e.g., Candelaria) are within volcanosedimentary sequences up to several kilometres from a pluton contact, intimately associated with major fault structures. All are accompanied by combinations of sodic, calcic, potassic and iron oxide alteration (Sillitoe, 2003). During the period from 176 to 95 Ma, extensive, district-wide alteration events took place in northern Chile. It is recognised that the main IOCG sensu stricto mineralisation in northern Chile (e.g., Candelaria, Mantoverde) commonly postdates albite- and biotite-magnetite alteration, while magnetite-actinolite-albiteplagioclase mineralisation and alteration characterises the magnetite-apatite deposits of the Chilean Iron Belt (e.g., El Romeral), all of which are generally copper and gold (-silver)-barren (Chen, 2010).
Following the district scale alteration assemblages associated with the other main iron oxide-alkali altered mineralised systems of the Coastal Belt in central to northern Chile and southern Perú, each of the mineralised centres where copper±silver±gold were deposited, was accompanied by more restricted envelopes of alteration related to that mineralisation.
For more detail on the district- to deposit-scale alteration and mineralisation in centra to northern Chile see the individual records and attached references for the Candelaria,
Mantoverde,
Santo Domingo District, and the El Algarrobo, Los Colorados and
El Romeral deposits and districts, as well as the other links at the head of this summary
In southern Perú, two cycles of regional alteration are evident over the period from 176 to 95 Ma, i.e., the Late Jurassic to Early Cretaceous, extending over an area of >75 km2, encompassing both the Marcona, Mina Justa and Raúl- Condestable deposits. This part of southern Perú covers section of the Cañete basin, an extensional rift trough filled by tuffs, amygdaloidal and porphyritic andesite flows and medium to fine-grained andesitic volcaniclastic rocks, with minor sandstone, siltstone and limestone of the Late Jurassic Río Grande Formation. This succession overlies a basement of Palaeoproterozoic to Mesozoic plutonic, metasedimentary and volcanic rocks. The alteration and mineralisation related to the Marcona magnetite ores was emplaced during the extensional phase of the basin, hosted mainly by Palaeozoic metasediments and lesser Mesozoic volcanic rocks. In contrast, the Mina Justa copper mineralisation is hosted by Jurassic volcanic rocks and was deposited during the inversion of the basin (Chen et al., 2010).
The most recent source geological information used to prepare this decription was dated: 2010.
Record last updated: 10/11/2022
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Carrillo-Rosua, J., Boyce, A.J., Morales-Ruano, S., Morata, D., Roberts, S., Munizaga, F. and Moreno-Rodriguez, V., 2014 - Extremely negative and inhomogeneous sulfur isotope signatures in Cretaceous Chilean Manto-type Cu-(Ag) deposits, Coastal Range of Central Chile: in Ore Geology Reviews v.56, pp. 13-24.
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Palma, G., Barra, F., Reich, M., Simon, A.C. and Romero, R., 2020 - A review of magnetite geochemistry of Chilean iron oxide-apatite (IOA) deposits and its implications for ore-forming processes: in Ore Geology Reviews v.126, doi.org/10.1016/j.oregeorev.2020.103748.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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