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Pampa de Pongo

Peru

Main commodities: Cu Fe Au
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The Pampa de Pongo iron ± copper ± gold deposit is located approximately 450 km south of Lima, Peru and around 30 km to the south-east of the large Marcona magnetite deposit (#Location: 15° 22' 30"S, 74° 49' 30"W).

The potential resources based on limited wide spaced drilling include more than 1000 Mt of magnetite mineralisation which is concealed below 20 m or more of sand. Pampa de Pongo contains 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.

The Pampa de Pongo Fe (-Cu-Au) deposit, which is covered by at least 20 m of sand, was discovered in 1994 by drilling a large magnetic anomaly. Host rocks to the mineralisation are dolostones and andesitic volcanics of the Oxfordian-Tithonian Jahuay Formation, which are higher in the sequence than the Marcona iron deposits and is composed of coarse volcaniclastics and conglomerate, and banded siltstone, shale, sandstones and carbonate rich sediments. Clastic and carbonate sediments and plagioclase phyric andesites outcrop to the NW and SE (where the andesites are predominantly sills and dykes) of the mineralised zone. Overall the andesitic bedded flows, tuffaceous rocks, sills and dykes account for 400 to 450 m of the sequence. These are underlain by 600 m of white, predominantly dolomitic marbles that outside of the mineralised zone are characterised by tremolite porphyroblasts and networks of talc veinlets. The hosts at Marcona are absent, the interval they occupy corresponding to an angular unconformity with the basement. Some 800 m to the east of the deposit, the dioritic Acari pluton is exposed, considered to be part of the possible 96 to 80 Ma Coastal Batholith. The age of the Pampa de Pongo mineralisation is uncertain, although the preferred genetic model for the district involves a large metal flux coeval with deep-seated Jurassic, and probably Cretaceous igneous intrusive activity (related to the Acari pluton).

Bedding dips shallowly at 15 to 20° across the deposit area.

The iron mineralisation exhibits both replacement and breccia-fill facies within a steeply northwest-dipping fault corridor. There are sharp cut-offs to the iron mineralisation to the east and west, with higher Cu and Au (up to 0.42% Cu, 0.68 g/t Au) in the hangingwall and the SW footwall, although grades are significantly lower in the bulk of the iron bodies. Alteration includes widespread albitisation, serpentinisation and replacement of all rock-types, but particularly dolomitic units, by magnetite. Magnetite mineralisation in the andesites is associated with Fe-chlorite, talc and clinochrysotile, whereas replacement of the underlying dolostone includes magnetite-amphibole-serpentine associations.

The mineralisation at Pampa de Pongo proceeded through the following stages:

i). Early "skarn" phase - characterised by andraditic garnet intergrown with diopsidic clinopyroxene believed on textural evidence to be the result of Ca metasomatism of earlier albitised igneous protoliths,
ii). Main magnetite (-pyrrhotite) stage - which occurs as veins, replacement of altered andesite of cementation of hydrothermal breccias. The veins are the initial or peripheral stages of the hydrothermal breccia. Fine magnetite is also present as a network of thin veinlets coalescing to form irregular patches. Coarse magnetite is almost everywhere intergrown with pyrrhotite, pyrite and locally marcasite. Coarse pyrrhotite is replaced by pyrite and then by magnetite, with an infilling of calcite as an interstitial matrix veining. This stage has associated biotite, Fe-rich chlorite, talc and clinochrysotile alteration.
iii). Sulphide-calcite stage - the coarse magnetite crystals are widely intergrown with coarse and vughy white carbonate and fine chlorite and is widely intergrown with late pyrite and locally grains of sphalerite, galena, tennantite and arsenopyrite.

At a local scale, iron oxide-associated mineralisation at Pampa de Pongo 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).

The most recent source geological information used to prepare this summary 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.


  References & Additional Information
   Selected References:
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


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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