Andean Cu-Au-base metals province - Southern Andes and Patagonia
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The Southern Andean or Patagonian Cordillera (the 'Southern Andes') represents a Jurassic to Recent orogen developed on the western margin of the Patagonia Terrane. The Patagonia Terrane occupies most of Chile and Argentina south of ~39°S, and is a Lower to Late Palaeozoic allochthonous to peri-autochthonous terrane that collided with the south to southwestern margin of Gondwana in the Lower Permian. It is part of the Terra Australis Orogen that had developed along the Pacific margin of Gondwana, and extended over a continuous pre-dispersal length of ~18 000 km and up to 1600 km width, from eastern Australia and New Zealand, the periphery of Antarctica, and along the western fringe of the South American plate. The Pacific margin was the result of rifting associated with the Neoproterozoic break-up of Rodinia. Despite a long history of plate convergence, reorganisation and terrane accretion, the Pacific ocean has never subsequently closed, and the Terra Australia Orogen has been both a passive and active margin at different times and localities since the Lower Palaeozoic (Cawood, 2005).
This record details the tectonic and geological setting of the Southern Andes and Patagonia Terrane as a context to other records covering individual ore deposits within the terrane. For details of the adjoning Central Andes to the north see the Central Andes and Bolivian Orocline record.
Basement to this terrane is predominantly composed of crystalline, amphibolite facies metamorphic rocks, mainly gneisses, containing peak metamorphic zircons dated at 468.7±4.3 Ma (U-Pb; Pankhurst et al., 2001), and lesser biotite schists, marbles, amphibolites and foliated granitoids. The lower grade schists within this sequence contain ichnofauna that constrain the age of deposition to between Cambrian and Early Ordovician (González et al., 2002). Geochemical data indicate the lower grade metamorphic rocks are derived from marine facies protoliths associated with a magmatic arc, over an attenuated continental crust setting (Cagnoni et al., 1993), and provenance from a Neoproterozoic, possibly Gondwana, source (Ramos, 2008; Ramos and Ghiglione, 2008).
Gravity and magnetic transects demonstrated an asymmetry and linear discontinuity between the thinner Patagonia Terrane and the older, thicker Transamazonian ~2 Ga Río de la Plata craton to the north (Ramos, 1996). The position of the interpreted craton margin and possible suture between the two terranes, is obscured in Chile by younger intrusions and volcanic cover ~200 km south of Concepción and may be related to one of two sets of east-west lineaments north and south of Temuca respectively. In Argentina, it is masked by the Tertiary Neuquen and Colorado basins. It crosses the Atlantic coast ~150 km south of Bahia Blanca (Ramos, 2010), and coincides with the Huincul fault, a regional trans-continental strike-slip fault defined in this segment by Ploszkiewicz et al. (1984). It is also seen to truncate the north-south magnetic fabric of the Gondwana margin, including the sutures between the Chilenia and Cuyania, as well as between Cuyania and Pampia terranes on the southwestern margin of the Río de La Plata craton (Dalla Salda and Francese, 1989; Ramos, 2008).
To the north of this craton margin, in Argentina, the Río de la Plata craton is unconformably overlain by a passive margin sequence bracketed between Middle-Late Cambrian and Devonian times. Palaeocurrent analyses of mature orthoquartzites in this sequence indicate a NE to SW transport direction and NE provenance. These are unconformably overlain by arkoses and wackes with Late Carboniferous to Early Permian fauna and a 274±10 Ma upper tuff layer (U-Pb; Tohver et al., 2007), with a SW provenance. This sedimentary source reversal indicates uplift to the SW, culminating in syntectonic sedimentation and a major episode of deformation in the uppermost part of the Lower Permian sequence (López Gamundi et al., 1995) along the Gondwana margin. Deformation lasted at least until Middle Permian, as the complete Early Permian sequence is folded (Ramos, 2008).
An Early Cambrian granodiorite (529±7.5 Ma; Söllner et al., 2000; Charrier et al., 2007), emplaced into what was thought to be a Precambrian gneissic basement has been encountered in deep drilling below the Austral Basin in southern Patagonia, between the western metamorphic-magmatic belt (see below) and the Patagonian Andes. This basement has been shown to be lowest Cambrian (536.8±3.3 to 527.2±5.2 Ma; U-Pb SHRIMP zircon; Hervé et al., 2008). In the same tectonic setting of southern Argentina, the basement Punta Dúngenes Gneiss (649±62 Ma) has been encountered in drilling and in outcrop (Ramos, 2008).
Precambrian basement has also apparently been encountered over a large north-south elongated area offshore of much of the Argentine coast, where it has a north-south structural grain. These occurrences most likely mark the eastern margin of Lower Palaeozoic deposition and were possibly rifted from the Kalahari Craton of Southern Africa during the opening of the Atlantic Ocean (Ramos, 2008).
Two mid to late Palaeozoic metamorphic-magmatic belts have been superimposed on the basement rocks of the Patagonia Terrane to the south of the southern margin of the Río de la Plata craton.
The northern metamorphic-magmatic belt, which is >100 km wide, trends generally east-west in the northern Patagonian Andes in Chile, to WNW-ESE in eastern Argentina, and is sub-parallel to, and up to 100 km inboard of the northern margin of the Patagonia Terrane. It is characterised by a NW aligned metamorphic fabric and amphibolite facies orthogneisses. These gneisses have Late Carboniferous to early Permian metamorphic ages of 304 and 281 Ma (Basei et al., 2002), and are hosted within probable early Palaeozoic amphibolite, marble and phyllite, and are unconformably overlain by Silurian to Early Devonian orthoquartzites deposited in a passive margin setting (Ramos, 2008). These rocks are cut by undeformed, 244±9 Ma Late Permian granitoids, lacking the metamorphic fabric of the orthogneisses (Ramos, 2008; Ramos and Ghiglione, 2008).
These observations would be consistent with the northern metamorphic-magmatic belt being the result of a south dipping oceanic plate, attached to the passive Río de la Plata craton margin, being subducted below the approaching Palaeozoic Patagonian Terrane, with deformation of a thick accretionary wedge, imbrication, metamorphism, magmatism and subsequent relaxation, uplift and exhumation of rocks from deeper crustal levels during Mesozoic extension.
The western metamorphic-magmatic belt is also 100 to >150 km wide. It intersects the northern belt near the Chile-Argentina border north of Bariloche, and trends generally SSE to the east of the Patagonian Cordillera of the Andean chain, obliquely crossing the Atlantic coast south of Comodoro Rivadavia, ~1000 km to the south. This belt coincides with the Río Chico structural high dividing the post Mesozoic San Jorge Basin. This high continues
southwards for a further 500 km as the offshore Punta Dúngenes structural palaeo-high that separates the the post Mesozoic Austral and Malvinas basins (Galeazzi, 1996).
Within the western metamorphic-magmatic belt, redschist to amphibolite facies metamorphic rocks, including muscovite-chlorite schists, metaquartzites,
and tourmalinite strata-bound schists, are associated with foliated tonalites, granodiorites and two-mica granites, mylonites and granitic cataclasites. The main metamorphic episode is syntectonic, accompanied by significant anatexis, with a 310 to 325° trending main foliation. The protoliths of some of these metamorphic rocks can be demonstrated to be shales, sandstones and greywackes. These rocks have been shown to be no older than ~473 Ma, whilst granitoids to the south are mainly early Palaeozoic, ranging in age between 472 and 454 Ma (Loske et al., 1999). However, the majority of the metamorphic and igneous rocks are dated in the range 375 to 310 Ma in the Upper Devonian to Mid-Carboniferous, with interspersed Early Permian 290±3 Ma two-mica granite (U-Pb zircon; Varela et al., 2005) and deformed leucogranite associated with migmatite, dated at 289±2 Ma (U-Pb; Pankhurst et al., 2006).
To the west of the northern to central section of the western metamorphic-magmatic belt, an up to 5000 m thick sequences of greywackes, shales and diamictites are encountered (Page et al., 1984), containing brachiopod fauna indicating an Early Carboniferous to Early Permian age (Andreis et al., 1987). The rocks are mildly deformed, generally postdate an early Palaeozoic deformation, and are intruded by 243 to 211 Ma tholeiitic gabbros (K-Ar; Page, 1984; Poma, 1986). Sedimentary structures in these Early Carboniferous to Early Permian sequences indicate dominant palaeo-currents from NE to SW, suggesting derivation from an uplifted highland in the vicinity of the western metamorphic-magmatic belt during and after the period it was undergoing metamorphism and magmatism from the Devonian to mid Carboniferous.
The presence of Precambrian and Lower Palaeozoic basement to the west of the western metamorphic-magmatic belt (Ramos, 2008), as detailed above opens the possibility that the belt is the product of Devonian to Carboniferous collision between the main Palaeozoic Patagonian Terrane to the east and an exotic Precambrian terrane in western Patagonia. The latter may be a sliver related to the Rodinia breakup, analogous to the exotic terranes that make up most of the basement of the central Andes in central and northern Chile. The metamorphism, anatexis and magmatism of the western metamorphic-magmatic belt would be consistent with continent-continent collision, intense imbrication, and subsequent relaxation, uplift and exhumation of rocks from lower crustal levels during Mesozoic extension.
Mesozoic Chon Aike Large Igneous Province - All of the rock packages described above are overlain by a >700 000 km2 sheet of Early Jurassic to earliest Cretaceous volcanic rocks, dominated by rhyolitic ignimbrites, which form a bimodal association with minor mafic and intermediate lavas (Poblete et al., 2014; Pankhurst et al., 1998). These rocks are broadly coeval with the original regionally contiguous Jurassic Karoo basalts (183.8±2.4 Ma to 176.2±), Ferrar basalts (~177 to ~184 Ma) and successor Early Cretaceous (138 to 128 Ma) Parana-Etendeka basalt provinces of southern Africa, Antarctica-Tasmania and Brazil-Namibia respectively. All of these large igneous provinces are coincident with pulses of extension during the early stages of Gondwana break-up (Storey et al., 1996), prior to the final separation of Africa and South America at ~100 Ma.
The Chon Aike sequence includes volcanic and volcaniclastic rocks, cut by dykes and overlain by rhyolitic domes. Pyroclastic rocks predominate, with ~85% ignimbrites, subordinate lacustrine epiclastic deposits, laminated tuffs, air-fall tuffs and intercalated lavas. The sequence varies from 300 to >1100 m in thickness. East to west diachronism is recognised, with an Early to Middle Jurassic 188 to 178 Ma pulse in eastern Patagonia, interpreted to represent widespread crustal anatexis related to extensive mafic underplating shortly after the Karoo and Ferrar mafic magmatism (Pankhurst et al., 1998). This was followed by Middle Jurassic to earliest Cretaceous volcanism from 172 to 162 Ma and further west, 157 to 152 Ma in the eastern Andean foothills. The latter, which constitute the Ibáñez and Tobífera formations to the north and south respectively, overlie a Palaeozoic metamorphic basement (Parada et al., 1997) and were locally faulted, tilted and thrust during Cretaceous-Tertiary Andean deformation (Suárez and De la Cruz, 2000) along the Patagonian Cordillera.
This transition from east to west is accompanied by a change in geochemical characteristics, from relatively high-Zr and -Nb types in the east to subalkaline arc-related rocks in the west. However, the dominance of rhyolites remains as a characteristic. All of the mafic rocks are well fractionated in contrast to direct mantle derivatives. Petrogenetic studies favour partial melting of immature lower crust due to the intrusion of basaltic magmas, with subsequent fractionation by crystal settling or solidification and remelting. The formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas, which are thus rare in the province (Pankhursta et al., 1998).
While extension took place to the east, the westward moving Patagonia Terrane was overriding and subducting the Phoenix oceanic plate to the west, forming a magmatic arc in what was to become the Andean Orogen. The Chon Aike and Andean magmatic arc sequences coalesced within the Ibáñez and Tobífera formations that straddle the transition between the two regimes (Pankhurst et al., 1998).
Within the Deseado Massif, the Middle to Late Jurassic Chon Aike Large Igneous Province is represented by the Bahía Laura Volcanic Complex which is dated at between 187 and 151 Ma (Haller, 1997). This complex is inferred to overlie a basement of sandstone and pelites of the Mid- to Upper-Triassic El Tranquilo Formation, as evidenced by clasts in veins and intrusions within the exposed overlying sequence. It is subdivided into the following formations after Sharpe et al. (2002); Guido and Jovic (2014) and others:
• Roca Blanca Formation, the lowest exposed unit, comprising ~990 m of Lower Jurassic sandstones and sandy tuffs;
• El Piche Formation, composed of amygdaloid basalts and andesites(?) assigned to the Lower Jurassic (Jovic 2010). Previously equated with the Bajo Pobre Formation (e.g., Páez et al., 2010), which Guido and Jovic (2014), interpret to be higher in the sequence (see below), with the El Piche Formation being a separate and older unit.
• Chon Aike Formation, predominantly Middle to Upper Jurassic rhyolites which have calc-alkaline, peraluminous and high potassium signatures, accompanied by minor dacites and trachydacites. These extrusives built an extensive rhyolitic plateau, dominated by large volumes of pyroclastic material (~90% ignimbrites with subordinate intercalated lavas) erupted as high fluidity ash flow tuffs (Pankhurst et al., 1998; Panza and Haller, 2002; Guido, 2004);
• Cerro León Formation, typically porphyritic subvolcanic laccoliths, sills and dykes, which de Barrio et al., (1999) and Jovic et al. (2008) regarded as representing feeders and intrusive equivalents of the Bajo Pobre Formation that Sharpe et al. (2002) interpreted to be equated with the El Piche Formation of Guido and Jovic (2014). However, dactic and rhyolitic dykes attributed to the Cerro León Formation cut through into the highest volcanic unit of the Chon Aike Formation (Guido and Jovic, 2014);
• Bajo Pobre Formation, composed of intermediate to basic calc-alkaline, mostly andesitic, volcanic rocks, dominated by lavas, with subordinated ash flow tuffs and agglomerates which interfinger with the upper Chon Aike Formation and/or the tuffs of the lower La Matilde Formation, representing the extrusive equivalent of the Cerro León Formation (Panza and Haller, 2002);
• La Matilde Formation, a homogeneous Upper Jurassic sequence of ash fall tuffs and reworked volcaniclastic sediments deposited in low energy fluvial and lacustrine settings, with minor ash flow and air fall tuff intercalations. It is intercalated with and partially a lateral equivalent of the upper ignimbrites of the Chon Aike Formation (de Barrio et al., 1999).
The sequence described above is unconformably overlain by sandstone and course clastic sedimentary rocks of the Lower Cretaceous Bajo Grande Formation
Cover and exposed massifs - Much of the Patagonia Terrane to the east of the main Andean Cordillera is masked by Late Mesozoic and Cenozoic cover, framing the 60 000 km2 Deseado Massif and ~100 000 km2 Somún Cura (or North Patagonian) Massif in the central to southern and northern part of the terrane respectively. These two massifs expose Chon Aike igneous province volcanic piles and windows of older rocks.
Below the Chon Aike igneous province, the Late Devonian to Permian western metamorphic-magmatic belt divides the Deseado Massif into two halves.
The cover sequences include a number of thick, areally extensive Cretaceous to Quaternary basins, Miocene foreland basins and two broad volcanic plateaux comprising Late Oligocene to Early Miocene and Late Pliocene to Quaternary with 'in-plate' mafic lavas and subordinate ignimbrites (Bermúdez et al., 1993; Kay and Copeland, 2006).
Southern or Patagonian Andes
The Southern or Patagonian Andes, which occupy the western margin of this terrane, have been uplifted, and largely comprise the 100 to 150 km wide, composite, Patagonian Batholith that extends for ~2000 km, from 39 to 55°S. In the north, three pulses of intrusion are recognised, although remnants of Carboniferous (335 to 320 Ma, U/Pb in zircons; Pankhurst et al., 2005) basement granitoids are also found within its confines. The main pulses are i). Jurassic to Cretaceous (170 to 90 Ma, K/Ar; Lizuaín, 1981; González et al., 1984); ii). Paleogene (55 to 37 Ma, K/Ar); and iii). Middle Miocene (13 to 15 Ma, K/Ar; González et al., 1984). To the south, the central segment of the batholith, between 43°30' to 46°30' S, comprises pulses of Early Cretaceous (140 to 124 Ma, Rb/Sr), younging eastward to Middle Cretaceous (117 to 98 Ma; Pankhurst et al., 1999), with a series of minor 110 to 87 Ma (K/Ar and U-SHRIMP) stocks east of the batholith (Ramos, 1981; Ramos et al., 1982; Rolando et al., 2002). The southern section of the batholith commences with Late Jurassic 157 Ma bimodal leucogranites and gabbros along the Magellan Strait, passing northwards into 145 to 137 Ma Cretaceous varieties, and late 136 to 111 Ma Early Cretaceous granitoids along the western margin, and then Late Cretaceous 99 and 78 Ma plutons at about 52° 45'S. Cenozoic plutons in this part of the batholith, are confined to the axial zone, emplaced in two pulses, i). Paleogene, between 65 and 40 Ma; and ii). Neogene leucogranites, from 22 and 16 Ma (U-SHRIMP in zircons; Hervé et al., 2004).
The batholith largely comprises a series of plutons of granodioritic, tonalitic and dioritic composition, with Late Miocene to early Pliocene leucogranites (Pankhurst et al., 1999), whilst to the south of 47°, gabbroic to granitic plutons predominate (Moreno and Gibbons, 2007).
Along its western margin, the batholith intrudes 256 to 195 Ma Middle Triassic to Early Jurassic fore-arc accretionary complex rocks, comprising variable limestones, turbidites, pelagic cherts and variable MORB basalts, with fault controlled slivers of blue- and red-schist rocks (Thomson and Hervé, 2002). In contrast the rocks intruded along its eastern margin are of 364 to 250 Ma, Late Devonian to Permo-Triassic age, characterised by a thick sequence of clastic turbidites and isolated recrystallised limestones with large scale folding and low grade metamorphism (Thomson and Hervé, 2002), and by Jurassic felsic volcanic rocks that correspond to the largely rhyolitic succession of the Mesozoic Chon Aike large igneous province. The batholith intrudes along and obliterates the boundary between the predominantly Palaeozoic cratonic basement of the Patagonia Terrane and the western Late Palaeozoic to Late Triassic accretionary prism (Hervé et al., 2008).
Most of the foothills on either side of the northern Patagonian Andes are composed by thick Paleogene andesitic volcanic sequences and associated volcaniclastic rocks, with some intercalated marine deposits (González Bonorino, 1973). Late Oligocene to Early Miocene marine deposits on both slopes of the cordillera suggest that Pacific transgressions were able to go across the Andes, prior to uplift and erosion (Ramos, 1982). The Central Depression persists south from the Central Andes into the northern section of this interval, filled by Miocene to Pliocene and Recent unconsolidated pyroclastic and sedimentary rocks, before pinching out to the south.
In the central section of the batholith, Paleogene volcanic and plutonic rocks are absent from both slopes of the Patagonian Cordillera, which are characterised by thick sequences of Middle to Late Jurassic to Early Cretaceous andesitic volcanic and volcaniclastic rocks overlying deformed Late Palaeozoic sedimentary rocks (Ramos, 1979; Haller and Lapido, 1980; López Gamundi, 1980; Suárez and de la Cruz, 1997). Marine volcano-sedimentary sequences are found on the western margin, and continental suites to the east, suggesting the range formed an emergent barrier. In the south part of the ranges, overlying synorogenic Paleogene and Miocene sequences are again evident over and flanking the batholith (Ramos and Ghiglione, 2008).
A chain of at least, 60 historically and potentially active Late Cenozoic stratovolcanoes in Chile and Argentina commences in the northern part of the terrane, south of the volcanic gap associated with flat slab subduction on the southern section of the Central Andes. These volcanoes were emplaced over exhumed rocks of the Patagonian Batholith, and are predominantly found along the western slope of the Southern Andes. There is a <50 km long gap at ~46 to 49°S, adjacent to the Chile Rise-Trench triple junction, where the ~east-west oceanic volcanic ridge separating the Nazca and Antarctic oceanic plates is being subducted below the South American plate (Stern, 2004). The volcanoes are predominantly Late Oligocene to Late Miocene north of 38°S, and Late Cretaceous and Late Miocene south of that latitude (Folguera and Ramos, 2011).
Crustal thickness decreases southwards from >50 km on the southern end of the Central Andes, to ~30 to 35 km below the Patagonian Andes where Pre-Andean basement ranges from Palaeozoic to early Mesozoic (Munizaga et al., 1988; Nelson et al., 1999). Over most of this interval, the up to 45 Ma Nazca plate is being subducted below the continent at 7 to 9 cm/yr at an angle of 22 to 30° NE of orthogonal with the trench. In the central and southern Patagonian Andes, where the crust is relatively thin, tholeiitic and high-Al basalts and basaltic andesites are the dominant rocks type erupted from the stratovolcanoes and many minor eruptive centres, although andesites, dacites and rhyolites also occur (Stern, 2004 and references cited therein).
Climate, Erosion and Uplift
The transition from the Central to Southern Andes coincides with both the northern margin of the Patagonia Terrane, and the dividing line between the influence of the moist westerly wind weather pattern to the south and the dominant tropical atmospheric circulation cell between the equator and the sub-tropics that produces the 'SE Trade Winds'. The latter results in much of the high central Andes being in a rain shadow, producing a very arid landscape with low weathering and erosion rates. In contrast, the westerly weather pattern that affects the Patagonian Andes results in a high rainfall on the western slopes of the uplifted range and greater erosion rates, delivering much larger volumes of sediment fill to the trench, which, in turn, lubricates the subduction channel. This reduces the coupling between the continental upper plate and the subducted slab, producing a narrower mountain range (Ramos and Ghiglione, 2008). However, the Central Depression separating a Mesozoic Coastal and eastern Main Cordillera in the Central Andes persists south into the northern Patagonian Andes for several hundred kilometres, before the two ranges merge to become a single narrower cordillera.
Tectonic uplift of the Patagonian Cordillera was initiated during the Miocene, with most of the western slope of this part of the cordillera being subjected to an extreme erosional gradient, that, in turn, induced a yet higher rate of isostatic uplift. This enhanced uplift and erosion resulting in the stripping of the capping volcanic sequences of the magmatic arc to expose the root batholith. Volcanic facies of the magmatic arc are only preserved on the eastern margins of the batholith. This enhanced uplift and erosion removed much of the porphyry and porphyry-epithermal environment, except in the north in the transition to the more arid central Andes.
The Patagonia Terrane is terminated to the south by a major east-west trending, sinistral transform fault, separating it from the oceanic Scotia Plate. This transform splays eastward from the southern Chilean Trench, passing through Tierra del Fuego, to the south of the Malvinas/Falkland Islands and south Georgia. The Scotia Plate is ~600 to 700 km wide, north-south, and ~2000 km long. It is, in turn, separated from the Antarctic Plate to the south by another sinistral east-west transform fault passing to the north of the Antarctic Peninsular tip and the South Orkney Islands.
To the east, these two transforms both curve around the eastern extremity of the Scotia plate to join and form a rounded nose that overrides subducting oceanic crust with an east vergence, defining the eastern limit of the Scotia Plate. The subduction zone is overlain by the South Sandwich arc of small volcanic islands. This eastern nose forms a rounded wedge 'penetrating' the east-west boundary between the oceanic sections of the South American and Antarctic plates.
To the west, the southern Chilean Trench curves eastward to form the western margin of the Scotia Plate, separating it from the Antarctic Plate. Over this interval, the north-south subduction zone below the trench becomes a NW-SE sinistral transform that is truncated by the transform that forms the southern margin of the Scotia Plate. Both incipient and established spreading centres divide the Scotia Plate into a number of microplates (after Ramos, 2010).
The two 'finger-like' Scotia and Caribbean plates, which define the southern and northern margins of the South American Plate respectively, are somewhat similar in character, other than that the Caribbean Plate represents thick oceanic plateau crust.
Hervé et al. (2008) suggest that prior to the Early Jurassic extensional event, the Antarctic Peninsula, which comprises a Mesozoic 'Chon Aike-like' igneous province overlying Lower Palaeozoic gneisses, formed part of the continental margin to the SW of the southern Patagonia Terrane. As it was rifted and drifted south the intervening Scotia Plate was formed.
A number of relatively small and/or low grade porphyry Cu deposits and prospects are known within the northern Patagonian Andes. These are largely restricted to the northern transition between the Central and Southern Andes, where erosion has been shallower, and to the remnant Paleogene arc fringing the Patagonian Batholith. A small number of uneconomic prospects persist as far south as the central Patagonian Batholith (Zappettini et al., 2008).
The most significant of the small number of porphyry deposits and prospects on the northern extremity of the Patagonian Andes is the Paleogene, ~61 Ma Campana Mahuida deposit, with a resource of 20 Mt @ 0.8% Cu (or 194 Mt @ 0.49% Cu, 0.1 g/t Au), located in the main cordillera in Neuquén, close to the Chilean border (USGS MRDS database). None of the other prospects appear to have estimated resources.
In addition, the pre-Andean, Late Carboniferous, 316 to 312 Ma La Voluntad occurrence (Garrido et al., 2008) containing 250 Mt @ 0.15% Cu is located in Neuquén Province of western Argentina, most likely hosted within the western metamorphic-magmatic belt of the Patagonia terrane, located on the eastern margin of the cordillera.
More than six, mostly low-sulphidation gold-silver deposits or clusters, and >50 epithermal prospects are distributed over a wide area throughout the Deseado Massif, to the east of the Andes, hosted within the Jurassic Bahía Laura Volcanic Complex (Páez et al., 2010), mostly during the Late Jurassic to Early Cretaceous, from 154 to 130 Ma (Poblete et al., 2014). A number of these deposits are hosted within the Ibáñez Formation at the transition from the Chon Aike igneous province to the Andean magmatic arc, located on the eastern margin of the cordillera, dated between 145 and 124 Ma, whilst other epithermal mineralisation is known nearby in Lower Cretaceous rocks on the eastern flank of the Patagonian Batholith.
The principal deposits/clusters of the Deseado Massif are Cerro Vanguardia, Mina Martha, Manantial Espejo, Cerro Moro, Cerro Negro and San José, with a combined production of >150 t of Au and >3000 t of Ag between 2000 and 2015 (Vidal et al., 2016). The remaining proved reserves in the Cerro Negro district includes 180 t of Au and 1500 t of Ag plus resources of 25 t of Au and 180 t of Ag (Vidal et al., 2016), whilst Cerro Vanguardia had remaining combined open pit + leach + underground resources of 120 t of Au and 2600 t of Ag at an average grade of 2.47 g/t Au and 54.22 g/t Ag (AngloGold Ashanti, 2014).
The Cerro Bayo deposits in eastern Chilean Patagonia are hosted within the Ibáñez Formation.
For more detail, see the individual deposit/district records (when completed).
The most recent source geological information used to prepare this summary was dated: 2016.
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.
References to this deposit in the PGC Literature Collection:
Cawood, P.A., 2005 - Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic: in Earth Science Reviews v.69, pp. 249-279.|
Folguera, A. and Ramos, V.A., 2011 - Repeated eastward shifts of arc magmatism in the Southern Andes: A revision to the long-term pattern of Andean uplift and magmatism: in J. of South American Earth Sciences v.32, pp. 531-546.|
Paez, G.N., Ruiz, R., Guido, D.M., Jovic, S.M. and Schalamuk, I.B., 2010 - The effects of K-metasomatism in the Bahia Laura Volcanic Complex, Deseado Massif, Argentina: Petrologic and metallogenic consequences: in Chemical Geology, v.273, pp. 300-313.|
Pankhurst, R.J., Leat, P.T., Sruoga, P., Rapela, C.W., Marquez, M. , Storey, B.C. and Riley, T.R., 1998 - The Chon Aike province of Patagonia and related rocks in West Antarctica: A silicic large igneous province: in Journal of Volcanology and Geothermal Research v.81, pp. 113–136.|
Poblete, J.A., Bissig, T., Mortensen, J.K., Gabites, J.,Friedman, R. and Rodriguez M., 2014 - The Cerro Bayo District, Chilean Patagonia: Late Jurassic to Cretaceous Magmatism and Protracted History of Epithermal Ag-Au Mineralization: in Econ. Geol. v.109, ppp. 487-502.|
Ramos, V.A. and Ghiglione, M.C., 2008 - Tectonic Evolution of the Patagonian Andes: in Developments in Quaternary Science, v.11, Ch. 4, pp. 57-71.|
Ramos, V.A., 2010 - The Grenville-age basement of the Andes: in J. of South American Earth Sciences v.29, pp. 77-91,|
Ramos, V.A., 2008 - Patagonia: A paleozoic continent adrift?: in J. of South American Earth Sciences v.26, pp. 235-251.|
Stern, C.R., 2004 - Active Andean volcanism: its geologic and tectonic setting: in Revista Geologica de Chile v.31, pp. 161-206.|
Thomson, S.N. and Herve, F., 2002 - New time constraints for the age of metamorphism at the ancestral Pacific Gondwana margin of southern Chile (42-52°S): in Revista Geologica de Chile v.29, pp. 151-165.|
Vidal, C.P., Guido, D.M., Jovic, S.M., Bodnar, R.J., Moncada, D., Melgarejo, J.C., and Hames, W., 2016 - The Marianas-San Marcos vein system: characteristics of a shallow low sulfidation epithermal Au–Ag deposit in the Cerro Negro district, Deseado Massif, Patagonia, Argentina: in Mineralium Deposita v.51, pp. 725-748.|
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