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Marcona |
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Peru |
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Fe Cu Au
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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.
Available as Full Text for direct download or on request. |
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The Marcona iron ± copper deposit is located approximately 400 km south of Lima, Peru and less than 20 km from the Pacific Ocean coast and the port of San Nicolas. It is the largest iron accumulation with associated Cu and Au along the western coast of South America (#Location: 15° 12' 17"S, 75° 6' 41"W).
Approximate resources at Marcona are ~1.95 Gt @ 55.4% Fe, 0.12% Cu (Chen et al., 2010). A further 1000 Mt of magnetite mineralisation is known some 30 km to the southeast, at the similar, Pampa de Pongo deposit which is hosted by sedimentary rocks and tuffs at a higher stratigraphic position, and is concealed below 20 m of sand. Both deposits contain some Cu and Au and exhibit numerous features that allow their inclusion as "Iron Oxide-Copper-Gold" style deposits.
The Marcona iron deposits were first identified in 1915 and mining commenced in 1953, while artesenal copper mining had been carried out in the district from the late 19th century. The larger iron bodies are hosted by the Lower Paleozoic Marcona and Middle to Upper Jurassic Río Grande Formations. The Marcona Formation is dominated by arenites and both calcitic and dolomitic carbonates, whereas the Río Grande Formation comprises a thick sequence of basaltic andesites and andesites (sills and flows), volcaniclastics and minor limestones.
Although the iron ore at Marcona includes major carbonate replacement facies, the iron deposits widely exhibit intra-mineralisation hydrothermal breccia textures and multistage iron oxide ±copper sulphide mineralisation. Copper mineralisation is mainly associated with magnetite and lesser specularite. The iron oxide bodies strike northeast and north-northwest and show both fault and lithological controls on ore geometry. Intra- and post-iron mineralisation igneous activity in the Marcona Mine area included dacitic/granodioritic dykes and andesitic 'ocöite' dykes.
At a local scale, iron oxide-associated mineralisation at Marcona and the surrounding district probably formed in an environment characterised by repeated crustal extension over a 20 to 60 m.y. period. The anomalous concentration of thick andesitic volcanics or sills and dykes at Marcona, and evidence for district-scale thermal anomalies preceding and during the main introduction of iron oxide mineralisation, indicate that the area was also an important volcanic centre and the site of a long-lived thermal anomaly (Hawkes, et al., 2002).
Chen et al. (2010) note that deposition of the magnetite orebodies at Marcona was preceded from ~177 to 162 Ma by Mg-Fe metasomatism producing cummingtonite and phlogopite-magnetite assemblages, and widespread sodic albite-marialite alteration. However, they report evidence indicating the actual orebodies, which were emplaced from 162 to 156 Ma, represent massive magnetite intrusions, the product of hydrous iron oxide melts, without obvious
associated micro- or megascopic indications of iron metasomatism. The ores occur as intimately associated, immiscible, amoeboid interfingering, massive magnetite and dacite phases. They interpret the formation of these bimodal ores to reflect co-mingling of oxide and silicate melts, exsolved during the mixing of juvenile andesitic and rhyolitic (or rhyodacitic) parental magmas, enhanced by dissolution of quartz from the intruded host Marcona Formation sedimentary rocks. They conclude that crystallisation of the oxide melts at 800 to 700°C, to form magnetite-actinolite±biotite aggregates, released large volumes of brines responsible for the intense potassic and/or sodic metasomatic halos to the orebodies. Quenching of these magmatic fluids to <400°C resulted in the precipitation of further, but metasomatic magnetite and substantial pyrrhotite and pyrite, and only minor chalcopyrite, accompanied by actinolite/tremolite, the termination of K feldspar alteration, and by phlogopite supplanting biotite. This final low-magnetite, sulphide-dominated stage formed in a relatively reduced and cooler (360 to 160°C) regime.
The most recent source geological information used to prepare this decription was dated: 2002.
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.
Marcona
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Chen H, 2010 - Mesozoic IOCG Mineralisation in the Central Andes: an Updated Review: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.3 pp. 259-272
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Chen H, Clark A H and Kyser T K, 2010 - The Marcona Magnetite Deposit, Ica, South-Central Peru: A Product of Hydrous, Iron Oxide-Rich Melts?: in Econ. Geol. v105 pp 1441-1456
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Chen H, Cooke D R and Baker M J, 2013 - Mesozoic Iron Oxide Copper-Gold Mineralization in the Central Andes and the Gondwana Supercontinent Breakup: in Econ. Geol. v.108 pp. 37-44
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Chen Huayong, Clark A H, Kyser T K, Ullrich T D, Baxter R, Chen Yuming and Moody T C, 2010 - Evolution of the Giant Marcona-Mina Justa Iron Oxide-Copper-Gold District, South-Central Peru: in Econ. Geol. v105 pp 155-185
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Hawkes N, Clark A H and Moody T C, 2002 - Marcona and Pampa de Pongo: Giant Mesozoic Fe-(Cu, Au) Deposits in the Peruvian Coastal Belt: in Porter T M (Ed), 2002 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, PGC Publishing, Adelaide, v2 pp 115-130
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Injoque J, 2002 - Fe Oxide-Cu-Au Deposits in Peru: An Integrated View: in Porter T M (Ed), 2002 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide v.2 pp. 97-113
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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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