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Cerro de Pasco

Peru

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The Cerro de Pasco copper-lead-zinc-silver deposit is located ~175 km northeast of Lima, in the Andes of central Peru at an elevation of 4300 m asl (#Location: 10° 40' 38"S, 76° 15' 34"W).

It falls to the east of the continental watershed and west of the Cordillera Oriental in an area of moderately folded and faulted Mesozoic sedimentary rocks, in a zone which contains the majority of the central Peruvian ore deposits.

For details of the regional setting, see the separate Peruvian Andes Cu-Au Province record.

In the Cerro de Pasco district, a major regional north-south oriented longitudinal fault juxtaposes Palaeozoic metamorphic rocks with Mesozoic sedimentary rocks. In the mine area, this fault is interpreted to be represented by a set of high-angle, 345°-striking reverse faults. The oldest rocks exposed at Cerro de Pasco are weakly metamorphosed and belong to the Devonian Excelsior Group, comprising shale, phyllite and quartzite. On the eastern side of the diatreme dome complex that hosts the ore deposit, this Group phyllite occurs as the north-south striking, north-plunging Cerro anticline. The Excelsior Group is overlain above an angular unconformity by sandstone and conglomerate of the Permo-Triassic Mitu Group, containing pebbles of quartz and Excelsior-type argillaceous clasts (McLaughlin, 1924; Jenks, 1951).

The Mitu Group is rarely exposed in the Cerro de Pasco district, but becomes more widespread to the south. North of the eastern half of the district, this Group is covered by an up to 3000 m thickness of the Upper Triassic to Lower Jurassic Pucará Group (Angeles, 1999, Rosas et al., 2007), a carbonate sequence, largely composed of dark, thick-bedded, limestone and dolomite with local interbeds of shale and siliceous concretions (Jenks, 1951). In the west, the Pucará Group is only 300 m thick and comprises thin-bedded, light-colored limestone (Jenks, 1951).

Multiple NE-SW trending folding episodes from the Eocene to lower Miocene, brought the Excelsior, Pucará and the Mitu Group rocks to shallower levels. During the Middle Miocene, magmatic activity affected the region (Silberman and Noble, 1977; Bendezú et al., 2003; Baumgartner, 2007; Bendezú, 2007). At Cerro de Pasco and in the nearby Colquijirca district, magmatism comprised of an early phase of explosive volcanism, represented mainly by a dacitic diatreme breccia (the Rumiallana Agglomerate), and minor external volcanic deposits, followed by multiple 15.4 Ma dacitic porphyritic domes (Baumgartner, 2007) and 15.4 to 15.1 Ma quartz-monzonite porphyry dykes (Baumgartner, 2007). These vertical diatreme breccia bodies contain angular clasts of of Pucará carbonate rocks that are several cm diameter in size, set in a matrix of carbonate rock-flour (Baumgartner et al., 2008).

The orebody at Cerro de Pasco is located on the eastern margin of a middle Miocene diatreme-dome complex, associated with a 2.5 km diameter Tertiary volcanic vent filled with pyroclastic breccia and intruded by Miocene plugs and dykes of quartz-monzonite porphyry. This vent is located in the core of an anticline of Devonian shales, phyllites and quartzites which are overlain by Triassic to Jurassic limestones, the hosts to ore.

The ore is present as massive to semi-massive sulphide replacement and fissure vein sulphides within the carbonates, defining large interconnected pipe like bodies. The main massive sulphide replacement body is principally hosted by carbonate rocks east of the main Cerro de Pasco volcanic neck. It contains an early association of pyrrhotite and FeS-rich sphalerite, altered by late fluids to pyrite-marcasite and FeS-poor sphalerite.

The first stage of ore deposition comprises an initial large pyrite-quartz body replacing Lower Mesozoic Pucará carbonate rocks and, to a lesser extent, diatreme breccia. This body is comprises pyrite with pyrrhotite inclusions, quartz, and black and red chalcedony which contains hypogene hematite. The diatreme breccia is altered to pyrite-quartz-sericite-pyrite at the contact with the pyrite-quartz body. This body is partially replaced by pipelike pyrrhotite bodies zoned outward to Fe-rich sphalerite bearing carbonate-replacement Zn-Pb ores (with up to 24 mol.% FeS; Baumgartner et al., 2008).

The second stage of mineralisation is partially superimposed on the first and comprises zoned east-west trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins in the western part of the deposit, hosted by the diatreme breccia, and well-zoned Zn-Pb-(Bi-Ag-Cu) carbonate-replacement orebodies. Both contain sphalerite that is Fe poor, with the inner parts of the orebodies typically having associated advanced argillic alteration assemblages, including aluminum phosphate sulphate minerals. The zoned enargite-pyrite veins have a mineral zonation, from a core of enargite-pyrite ± alunite with traces of gold, to an intermediate zone of tennantite, chalcopyrite and Bi minerals, to a poorly developed outer shell containing sphalerite-galena ± kaolinite (Baumgartner et al., 2008).

The carbonate-hosted replacement ores are developed along 35, 90, 120 and 170° trending faults, and form well-zoned upward-flaring pipelike bodies that have a core of famatinite-pyrite and alunite, an intermediate shell with tetrahedrite-pyrite, chalcopyrite, matildite, cuprobismutite, emplectite and other Bi minerals accompanied by aluminum phosphate sulphate minerals, kaolinite and dickite, and an outer zone composed of Fe-poor sphalerite (with 0.05 to 3.5 mol.% FeS) and galena. The outermost halo contains hematite, magnetite and Fe-Mn-Zn-Ca-Mg carbonates. Most of the second-stage carbonate-replacement orebodies plunge between 25 and 60°W (Baumgartner et al., 2008).

The orebody contained 100 Mt of pyrite, 4 Mt of Zn, 2 Mt of Pb, >1 Mt of Cu and 10 000 t of Ag.

The deposit is quoted (Cheney, 1991) as having comprised:
    27 Mt @ 9.2% Zn, 3.6% Pb, 85 g/t Ag (Production, 1955-76), plus
    43.7 Mt @ 8.5% Zn, 3.2% Pb, 76 g/t Ag (Reserves, 1991).

Baumgartner et al. (2008) quote post-1950 production plus known resources (from Einaudi, 1977; Geological staff of Cerro de Pasco, 1950, pers. commun., 2001) to total:
    >175 Mt @ 7 wt.% Zn, 2 wt.% Pb, 93 g/t Ag.

The most recent source geological information used to prepare this summary was dated: 2009.     Record last updated: 12/12/2012
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.


Cerro de Pasco

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Baumgartner R, Fontbote L and and Vennemann T,  2008 - Mineral Zoning and Geochemistry of Epithermal Polymetallic Zn-Pb-Ag-Cu-Bi Mineralization at Cerro de Pasco, Peru: in    Econ. Geol.   v.103 pp. 493-537
Baumgartner, R., Fontbote, L., Spikings, R., Ovtcharova, M., Schaltegger, U., Schneider, J., Page, L. and Gutjahr, M.,  2009 - Bracketing the Age of Magmatic-Hydrothermal Activity at the Cerro de Pasco Epithermal Polymetallic Deposit, Central Peru: A U-Pb and 40Ar/39Ar Study : in    Econ. Geol.   v.104, pp. 479-504.
Cheney E S,  1991 - Structure and age of the Cerro de Pasco Cu-Zn-Pb-Ag deposit, Peru: in    Mineralium Deposita   v26 pp 2-10
Einaudi M T,  1977 - Environment of ore deposition at Cerro de Pasco, Peru: in    Econ. Geol.   v72 pp 893-924
Rottier, B., Kouzmanov, K., Walle, M., Bendezu, R. and Fontbote, L.,  2016 - Sulfide Replacement Processes Revealed by Textural and LA-ICP-MS Trace Element Analyses: Example from the Early Mineralization Stages at Cerro de Pasco, Peru: in    Econ. Geol.   v.111, pp. 1347-1367.
Silberman M L and Noble D C,  1977 - Age of igneous activity and mineralization, Cerro de Pasco, Central Peru: in    Econ. Geol.   v72 pp 925-930


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