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Toquepala |
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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 Toquepala porphyry copper deposit is located 120 km SE of Arequipa, in southern Peru.
(#Location: 17° 14' 46"S, 70° 36' 48"W)
Toquepala lies in the belt of Paleocene to early Eocene porphyry copper deposits in the Main Arc Domain of Andean magmatism and is believed to have been emplaced at between 52 and 56 Ma. It is within an area occuppied by the Upper Cretaceous to Paleogene calc-alkaline to shoshonitic subaerial volcanics of the Toquepala Group. Regionally these rocks are underlain by Upper Triassic to Jurassic marine volcanic and sedimentary suites and then by Precambrian metamorphics which are cut by Palaeozoic granites. All of these rocks are intruded by the composite, polyphase Cretaceous to Paleogene Andean Batholith ranging in age over a 150 m.y. period and in composition from gabbro to alkali feldspar granite, although quartz-diorite, quartz-monzodiorite and granodiorite predominate.
Porphyry copper-molybdenum mineralisation at Toquepala developed as the terminal stage in the evolution of the volcano-plutonic arc represented by the Toquepala Group. Mineralisation is closely associated with a complex, 1500 m diameter intrusive centre dominated by four phases of porphyritic dacite plugs ("T", "Main", "L/M" & "Late") , a dacite diatreme and agglomerates, extensive hydrothermal breccias and latite porphyry stocks and dykes.
Mineralisation and alteration were related to four hydrothermal events, known as the "Early", "Tourmaline", "Main" and "Late" stages. The Early stage (characterised by potassic and sodic alteration and by chalcopyrite-pyrite stockwork mineralisation), representing about 5% of the deposit's copper, and largely followed the first (T) dacite porphyry intrusions event, but came before the Main and L/R (which are essentially barren, but the most extensively exposed of the dacite porphyries in the pit). A voluminous sulphide barren tourmaline breccia pipe with scarce tourmaline-quartz veins represented the tourmaline stage, and was emplaced after the Main and L/R dacite porphyries. The tourmaline breccias comprise quartz-sericite altered clasts in a tourmaline-quartz matrix.
The tourmaline breccias were subsequently re-opened and the wall rocks fractured by the Main stage hydrothermal fluids to essentially emplace all of the molybdenite and most of the chalcopyrite. This resulted in the development of typically 3 mm wide quartz-rich veins with important amounts of molybdenite and chalcopyrite which followed continuous fractures and had no well defined alteration envelopes. Chalcopyrite-pyrite veins, fracture coatings and fracture controlled disseminations were also formed.
The dacite agglomerate and latite porphyry, which are not cut by the Main stage ore veining, were emplaced following the formation of the main hypogene orebody as described above, but were coeval with the extensive Late stage, copper poor, quartz-sericite-pyrite-andalusite alteration and more localised advanced argillic development. This intrusive phase was also responsible for large scale phreato-magmatic eruptions producing a 300 m diameter pebble breccia pipe and a swarm of pebble dykes.
Supergene enrichment was more extensive at Toquepala than at either Quellaveco or at Cuajone, commencing in the Oligocene and continuing into the Miocene when the deposit may have been capped by thick tuffs. Secondary chalcocite after chalcopyrite and bornite was developed over a total vertical interval of around 425 m and represents multiple chalcocite blankets, with "hanging" blankets within leached rock above the main enrichment layer, which has a variable, thickness of up to 150 m or more. The upper surface of this zone of enrichment is broadly planar, but has a marked slope, dropping around 100 m in a distance of 700 m from east to west across the pit. The base in contrast is very irregular with deep roots of supergene enrichment into the transitional and hypogene zone. The chalcocite blanket ore is accompanied by a pale bluish grey supergene argillic alteration.
The deposit has been quoted as comprising: 800 Mt @ 0.95% Cu, 0.01% Mo.
Supergene production, 1960 to 1994: 465 Mt @ 1.07% Cu, 0.034% MoS2
Mostly Hypogene production, 1988 to 1994: 0.83% Cu, 0.030% MoS2.
For detail see the reference(s) listed below which were the source of the information summarised above.
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.
Toquepala
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Selected References:
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Clark A H 1990 - The slump breccias of the Toquepala Porphyry Cu(-Mo) deposit, Peru: implications for fragment rounding in hydrothermal breccias: in Econ. Geol. v85 pp 1677-1685
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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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Mattos R, Valle J 1999 - Exploracion, geologia y desarrollo del yacimiento Toquepala (Language: Spanish): in ProExplo 1999 Proceedings pp 101-116
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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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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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