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Quellaveco |
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Peru |
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Cu Mo
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Super Porphyry Cu and Au
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The Quellaveco porphyry copper deposit is ~15 km north of Toquepala, ~11 km SE of Cuajone and 115 km SE of Arequipa, in southern Peru (#Location: 17° 6' 16"S, 70° 37' 16"W).
Geological Setting
The deposit is located near the northern end of the Paleocene to early Eocene porphyry copper belt of the central Andes (Sillitoe, 1988; Clark et al., 1990). It is elongated in a northwesterly direction, and is exposed on both flanks of the deep westerly trending valley of the Rio Asana, which is incised into a modified Altos de Camilaca surface, represented by a gently rolling high plain ~3800 to 4100 metres above sea level (masl). The valley floor of the Rio Asana where it cuts the Quellaveco deposit is 3500 to 3600 masl.
The deposit is centred on a multiphase early Eocene (57-52 Ma) quartz monzonite porphyry stock emplaced into an equigranular granodiorite pluton, which in turn, cuts rhyolitic volcanic rocks assigned to the Late Cretaceous to early Paleocene subaerial Toquepala Group (Estrada, 1975; Guerrero and Candiotti, 1979; Candiotti, 1995). The Toquepala Group comprises an Upper Cretaceous to Paleogene suite of calc-alkaline to shoshonitic subaerial volcanics, which is regionally underlain by Upper Triassic to Jurassic marine volcanic and sedimentary sequences and then by Precambrian metamorphic rocks of the Arequipa terrane which are cut by Palaeozoic granites.
The emplacement of the mineralised stock is interpreted to represent the terminal stage in the development of the Toquepala Group. The pluton, which crops out over >3 km2 in the vicinity of the Quellaveco stock, as well as extending northward beneath post-mineral ignimbrite and gravel cover, is part of the granodioritic to monzogranitic Yarabamba superunit of the 1500 x >100 km, composite Peruvian Coastal Batholith (Pitcher, 1985; Bellido, 1979; Beckinsale et al., 1985).
Subsequent to the emplacement of the hypogene mineralised stock, a prolonged period of mid-Tertiary erosion ensued, with the gradual reduction of the topography to a more subdued relief which, in the vicinity of the deposits, may have been <500 to 1000 masl. This eroded surface was overlain by predominantly continental clastic strata of the Oligocene to earliest Miocene Moquegua Formation (Barua, 1961; Bellido and Landa, 1965; Bellido, 1979; Marocco and Noblet, 1990), forming an aggradational facies of the erosional system. From the late Oligocene, into the early Miocene, a succession of more abrupt uplift events at ~25 Ma produced a regionally extensive, generally subplanar, largely degradational landscape, now preserved in the Precordillera surrounding the deposit and at the summits of the Coastal Cordillera to the west. These uplifts events generated conglomerate horizons in the uppermost Moquegua Formation to the southwest. The erosional surface attained its final form between 25 and 19 Ma, and was complete by 18 Ma and is referred to as the Altos de Camilaca surface (Tosdal et al., 1984).
In the early Neogene, the mineralised area was situated in the same physiographic framework as it is today, in the Precordillera zone at the oceanward front of the volcanic arc. The four major physiographic terrains of the topography are as follows, from the Pacific Ocean, inland:
i). the Cordillera de la Costa (Coastal Range), a discontinuous belt of mountains attaining elevations of ~1000 to 1800 masl;
ii). the Llanuras Costaneras (Coastal Plain), a sloping faceted terrain rising northeastward from ~350 masl at the inner foot of the Coastal Range to ~3000 masl;
iii). the Precordillera, a subplanar ~4000 masl bench with a steep southwestern interface with the Coastal Plain; and
iv). the Cordillera Occidental, which at this latitude is dominated by stratovolcanoes, in part glaciated, and reaching a maximum elevation of 5815 masl. at Volcan Tutupaca.
Rhyodacitic ash-flow tuffs were apparently erupted locally from ~29 Ma, prior to the main peneplanation, and became more intense over the period 26 to 25 Ma during the initial phases of late Oligocene rapid uplift, with several tuff units being intercalated within the coarse clastic sediments of the uppermost Moquegua Formation (Bellido, 1979; Tosdal et al., 1981). Subsequent felsic pyroclastic eruptions accompanied the development of both the Altos de Camilaca surface, and mantle wide areas of the Precordilleran slope of the Cordillera Occidental (Tosdal et al., 1981, 1984). These widespread tuffs that rest on the Altos de Camilaca surface are assigned to the 18.4±0.6 Ma (K-Ar; Tosdal et al., 1981) Huaylillas Formation, whilst ignimbrites and lahars that are contemporaneous with the subsequent incision are predominantly restricted to valleys, and are grouped as the 13.1±0.7 Ma Chuntacala Formation (Tosdal et al., 1981, 1984). Clark et al. (1990) suggest there is evidence that the ash-flow tuffs emplaced in the vicinity of the ore deposit possessed low permeabilities and were thus likely to act as aquicludes affecting supergene processes.
From ~15 to 8 Ma, in the middle and earliest late Miocene, the Altos de Camilaca surface was uplifted, variably tilted and eroded. Broad open valleys were developed across the Precordillera in the northeast and fluvial conglomerates with a 9.5±0.5 Ma ignimbrite, assigned to the uppermost Chuntacala Formation, were deposited (Tosdal et al., 1981). Pedimentation in the Cordillera Occidental to the east, and elsewhere ceased in the late Miocene. This corresponds to eruption of the upper Miocene and Pliocene Sencca Formation ignimbrites, now preserved only above ~3800 masl. Since then, steep-walled valleys and gorges/quebradas have been incised into the Pacific slope due to continued episodic uplift during the still active Valley and Terrace stage of landform development, causing considerable degradation of the earlier planate or gently incised landforms.
Deposit Geology
The Quellaveco deposit was buried at different times by volcanic rocks of the early Miocene Huaylillas Formation, middle and upper Miocene Chuntacala and uppermost Miocene and Pliocene Sencca Formations.
The bulk of the ore at Quellaveco occurs as a single supergene sulphide enrichment blanket, in which two zones are distinguished:
i). an upper, irregular 50 to 60 m thick chalcocite bearing zone of moderate to strong enrichment, reaching depths of 250 to 300 m below the present surface. The enriched blanket generally underlies a zone of leaching and/or oxidation, extending from the surface to a maximum depth of 80 m. The northern part of the enrichment blanket is offset ~75 m downward by an east-west trending fault close to the present axis of the Asana Valley (Estrada, 1975). Restoration of this offset shows the enrichment blanket has a trough like shape, subparallel to the surface on the opposing sides of the Asana Valley. However, the enriched zone is truncated by the lower slopes of the present Asana Valley. On the northern flank of the valley, the unconformity beneath the 9.5±0.5 Ma ignimbrite and the underlying conglomerate Chuntacala Formation intersects the sulphide enrichment zone as well as the overlying leached-oxidised zone. The highest occurrences of the enriched zone is towards its southern extremity, where it lies at altitudes of ~375O masl, ~250 m below the extrapolated position of the Altos de Camilaca surface. It is possible that enrichment at Quellaveco occurred beneath the lower Miocene surface, prior to its mantling by the 18.4 Ma Huaylillas Formation volcanic rocks. The open valley inferred to have subsequently developed at Quellaveco would have been incised to within 75 to 100 m of the preserved enrichment zone. Given suitable hydrologic conditions for supergene processes, it is likely that a second phase of enrichment would have then taken place, upgrading and deepening the earlier formed blanket. This is supported by the trough like form of the enriched zone, broadly reflecting the valley. However, enrichment would again have been interrupted by deposition of the thick Chuntacala Formation succession from ~13.1 Ma and terminated before 9.5 Ma. Oxidation, but little sulphide enrichment, accompanied the more recent stages during deepening of the Asana Valley. The major fault following the valley did not focus significant sulphide enrichment or oxidation of the ores.
ii). a 15 to 20 m thick lower grade underlying zone, representing a downward transition to unaltered hypogene mineralisation.
In the hypogene zone, the host quartz monzonite porphyry stock has abundant phenocrysts of plagioclase, quartz and biotite, with scattered K feldspar and hornblende, all surrounded by aplitic groundmass. The porphyry and immediately surrounding granodiorite have been subjected to extensive potassic (biotite-K feldspar) and sericitic (quartz-sericite) alteration, the former generally overprinted and partly obliterated by the latter. Both host rocks contain veinlet and disseminated chalcopyrite. The potassic alteration is transitional outward into the precursor granodiorite to a pyrite-bearing propylitic assemblage, which defines the periphery of the system (Estrada, 1975; Candiotti, 1995; Kihien, 1995). Fluid inclusion studies showed that the main potassic and sericitic alteration and associated copper mineralisation took place at temperatures of 590 to 340°C (Kihien, 1995).
Mineralisation at the Quellaveco spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late-mineral porphyry body that postdates essentially all copper introduction. The U-Pb ages of zircons from these intrusive rocks show an interval of 1.08±0.58 m.y. between the precursor pluton and initiation of stock emplacement. The porphyry system was subsequently intermittently active for at least 3.25 m.y. (i.e., 4.07±0.82 m.y.), with at least 75% of the contained copper being deposited in <3.12 m.y. (i.e., 2.51±0.61 m.y.) (after Sillitoe and Mortensen, 2010).
Reserves and Resources
JORC compliant ore reserves and mineral resources at 31 December 2011 (Anglo American plc, 2012) were:
Proved + probable reserves - 916.4 Mt @ 0.65% Cu, 0.019% Mo, plus,
Measured + indicated resources - 823.8 Mt @ 0.44% Cu, 0.016% Mo,
Inferred resources - 183.0 Mt @ 0.45% Cu.
JORC compliant ore reserves and mineral resources at 31 December 2015 (Anglo American plc, 2016) were:
Proved + probable reserves - 1.332 Gt @ 0.58% Cu, 0.019% Mo, plus,
Measured + indicated resources - 776.1 Mt @ 0.38% Cu, 0.013% Mo,
Inferred resources - 747.2 Mt @ 0.33% Cu, 0.010% Mo.
This summary is largely drawn from, and in part paraphrased from Clark et al., 1990 and Sillitoe and Mortensen, 2010.
The most recent source geological information used to prepare this decription was dated: 1989.
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.
Quellaveco
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Selected References:
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Clark A H, Farrar E, Kontak D J, Langridge R J, Arenas M J, France L J, McBride S L, Woodman P L, Wasteneys H A, Sandeman H A, Archibald D A 1990 - Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru: in Econ. Geol. v85 pp 1520-1583
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Clark A H, Tosdal R M, Farrar E, Plazolles A 1990 - Geomorphologic environment and age of supergene enrichment of the Cuajone, Quellaveco, Toquepala Porphyry Copper deposits, southeastern Peru: in Econ. Geol. v85 pp 1604-1628
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Quang, C.X., Clark, A.H., Lee, J.K.W. and Hawkes, N., 2005 - Response of Supergene Processes to Episodic Cenozoic Uplift, Pediment Erosion, and Ignimbrite Eruption in the Porphyry Copper Province of Southern Peru: in Econ. Geol. v.100, pp. 87-114.
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Sillitoe R H and Mortensen J K, 2010 - Longevity of porphyry copper formation at Quellaveco, Peru: in Econ. Geol. v.105 pp. 1157-1162
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Simmons A T, Tosdal R M, Wooden J L, Mattos R, Concha O, McCracken S and Beale T, 2013 - Punctuated Magmatism Associated with Porphyry Cu-Mo Formation in the Paleocene to Eocene of Southern Peru: in Econ. Geol. v.108 pp. 625-639
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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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