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Cerro Colorado (Pampa Norte Division) |
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Chile |
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Cu Mo
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Super Porphyry Cu and Au
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The Cerro Colorado mine, which exploits supergene copper ore developed over hypogene porphyry style mineralisation, is located 120 km east of Iquique in northern Chile. This deposit, with the Spence mine, ~300 km to the south, that is just south of Calama, is managed as part of the Pampa Norte Division.
(#Location: 20° 2' 55"S, 69° 15' 6"W).
Cerro Colorado is one of the chain of major lower Eocene to earliest middle Eocene porphyry copper deposits, extending from Cerro Verde in Peru to Spence in Chile and paralleling the plate boundary, which are associated with a volcano-plutonic arc that was initiated in the Late Cretaceous. It outcrops on an upper extension of the low relief Pampa del Tamarugál at an elevation of around 2600 m asl. The Pampa del Tamarugál is a gently west dipping surface between the Coastal Cordillera and the Precordilleran foothills to the Cordillera Occidental.
The hypogene ore deposit at Cerro Colorado is dated at 51.8 Ma. The principal host for mineralisation is a succession of porphyritic to aphanitic andesites of the Upper Cretaceous to, possibly, Paleocene Cerro Empexa Formation which are present as a gently dipping sequence of subaerial volcanics and volcano-sediments that are widespread in northern Chile. These are intruded in the Cerro Colorado district by Upper Cretaceous and Paleogene porphyritic hypabyssal stocks, while in the mine area several such stocks are emplaced within two major, late stage, breccia complexes. The intensely altered breccias comprise clasts of various porphyries within a fine-grained matrix of quartz, sericite, pyrite and clay with small masses of barren tourmaline-cemented breccia. These breccias however are generally less mineralised than the andesites they cut. Both the breccias and the andesites are intruded by biotite-quartz-plagioclase porphyry stocks which are in turn intruded by quartz porphyry stocks and late plagioclase porphyry dykes.
Early stage middle Eocene (51.8 ± 0.5 Ma) biotite-albite alteration had no accompanying copper mineralisation. The second or main stage, upwardly zoned from sericite-chlorite-clay, to quartz-sericitic-clay and capped by advanced argillic alteration assemblages, was associated with the majority of the chalcopyrite and pyrite, while a subsequent true phyllic quartz-sericite-pyrite alteration phase accompanied the breccia formation and only brought moderate chalcopyrite and pyrite, but much of the molybdenite of the deposit.
A weathered profile extends to a depth of 450 m below the present surface and incorporates the supergene orebody. The supergene profile has been subdivided into four facies as follows: 1). A leached cap (with generally around 0.1% Cu, but locally up to 0.3%) that underlies the Choja pediplain, a regionally extensive mid-Tertiary erosion surface, 2). Upper Supergene Ore, 3). Lower Leached zone; and 4). Lower Supergene ore.
Both leached zones, namely the the Leached cap and Lower Leached zone are predominantly hematitic, implying chalcocite-rich precursors. The Upper Supergene ore is predominantly oxides with dominant brochantite, atacamite and lesser malachite, and only relics of chalcocite, although it includes a superimposed zone of abundant chrysocolla veining, which is more abundant in it's upper sections. The Lower Supergene ore which overlies the hypogene mineralisation is composed mainly of chalcocite, usually accompanied by supergene kaolinite and smectite.
The almost horizontal east-west elongated, approximately 2.8 x 1 km Cerro Colorado Supergene orebody is from 100 to 180 m thick and concealed below a 50 to 200 m thick leached cap. Within this area, the Main (or East) Zone is separated from the West Zone by a lower grade section.
Supergene ore reserves in 2001 were - 228 Mt at 1.0% Cu
Hypogene protore below the supergene enrichment averages 0.4 to 0.5% Cu.
SX-EW recovery in 2000 amounted to 117 000 tonnes of copper.
Published JORC compliant ore reserves and minerals resources at 30 June 2012 (BHP Billiton, 2012) and 30 June 2015 (BHP Billiton, 2015) include:
Total measured + indicated + inferred resources, for,
Oxide (2012) - 286 Mt @ 0.63% Cu (2015) - 237 Mt @ 0.58% CuTotal 0.42% CuSoluble;
Sulphides (2012) - 209 Mt @ 0.64% Cu (2015) - 168 Mt @ 0.57% CuTotal 0.11% CuSoluble.
Total proved + probable reserves, (included in resources) for,
Oxide (2012) - 131 Mt @ 0.61% Cu (2015) - 99 Mt @ 0.56% CuTotal 0.40% CuSoluble;
Sulphides (2012) - 71 Mt @ 0.65% Cu (2015) - 54 Mt @ 0.65% CuTotal 0.12% CuSoluble.
The source of this summary was Bouzari & Clark, 2002.
The most recent source geological information used to prepare this decription was dated: 2002.
Record last updated: 2/12/2012
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 Colorado
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Selected References:
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Bouzari F and Clark A H, 2006 - Prograde Evolution and Geothermal Affinities of a Major Porphyry Copper Deposit: The Cerro Colorado Hypogene Protore, I Region, Northern Chile : in Econ. Geol. v 101 pp 95-134
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Bouzari F, Clark A H 2002 - Anatomy, evolution, and metallogenic significance of the supergene orebody of the Cerro Colorado Porphyry Copper deposit, I region, northern Chile: in Econ. Geol. v97 pp 1701-1740
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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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