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Escondida - Escondida Norte, Zaldivar, Pinta Verde, Pampa Escondida, Carmen, Ricardo

Chile

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Escondida is a giant supergene enriched open pit porphyry copper deposit located in northern Chile, some 160 km to the east-south-east of Antofagasta (#Location: 24° 16' 17"S, 69° 4' 13"W).

Escondida is currently the largest copper producing mine complex in the world with an annual output of more than 800 000 tonnes of fine copper, and capacity of 1.2 Mt pa. The deposit contains in excess of 30 Mt of copper metal.

The Escondida deposit falls within the 50 km wide Cordillera de Domeyko morpho-tectonic province of the northern Chilean Andes, characterised by north-south elongated ranges and intervening shallow gravel filled basins at elevations varying from 2000 to 4500 m asl. It is one of a string of deposits associated with Upper Eocene to Lower Oligocene porphyry intrusion in northern Chile.

The basement sequence below the Cordillera de Domeyko represents a complex continental margin of accreted continental fragments and Palaeozoic to Mesozoic volcanic arcs, but overall coincides with the transition from continental Precambrian and Palaeozoic crust to the east and thick Palaeozoic turbidites and volcanic-sedimentary sequences most likely resting on oceanic crust, to the west. During the Mesozoic a magmatic arc developed to the west, while the Cordillera de Domeyko was within an extensional back arc basin. This sequence was in turn followed by three continental margin Andean-type magmatic arcs from the late Cretaceous to late Cainozoic, with associated large porphyry deposits such as Escondida formed mainly between 42 and 31 Ma during the Eocene-Oligocene phase. From 31 Ma onwards uplift, climatic change and low rates of denudation have favoured the development and preservation of enriched blankets over these porphyries.

The Cordillera de Domeyko province is dominated by the Domeyko fault system, which in the Escondida district is characterised by cymoid shapes producing elongated, north-south basins in a 200 x 20 to 50 km zone, probably representing long lived zones of structural activity, varying in character over time. Both Chuquicamata (200 km to the north) and Escondida lie on strike-slip faults of the Domeyko fault system.

Escondida is the largest of six known porphyry deposits in the district. The others include Escondida Norte, Zaldivar, Pinta Verde, Pampa Escondida, Carmen and Ricardo. All fall within a localised zone of north-south striking, sinistral strike-slip faulting that forms a cymoidal shape.

The hydrothermal activity responsible for the hypogene mineralisation is closely associated with a late Eocene to Oligocene dioritic to quartz-monzonite to granodiorite stock complex composed of at least three intrusive stages. This complex intrudes a sequence of Palaeozoic andesite, cut by late Palaeozoic (265 to 270 Ma) rhyolites, marine-continental Mesozoic sediments (calcareous sandstone, red sandstone and conglomerate) unconformably overlain by late Cretaceous to Paleocene andesites. The mineralised intrusive complex is overlain and cut by Oligocene to Miocene rhyolitic sub-volcanic intrusives and extrusives.

At Escondida the mineralised NW-SE trending, 4.5 x 2.5 km quartz-monzonitic to granodioritic porphyry stock complex cuts Paleocene andesites. The complex is composed of at least three phases, the first two of which are distinguished on their phenocryst size, composition and quantity while the third is a porphyry breccia which contains mineralised clasts but is cut by copper rich veins.

Alteration commenced with an early potassic (biotite rich, particularly within the andesites) stage grading out into a propylitic periphery and a silicified shell around the intrusive, with associated magnetite, chalcopyrite and bornite and a hypogene grade of generally less than 0.2% Cu. The second phase corresponded to sericite-chlorite and then to quartz-sericite alteration with chalcopyrite, pyrite and molybdenite carrying 0.4 to 0.6% Cu and chalcopyrite:pyrite ratios of 3:1. The third and final phase comprised an acid sulphate episode which over printed the previous assemblages with a younger advanced argillic alteration and a range of sulphides including bornite, chalcopyrite, pyrite, chalcocite, covellite, enargite, sphalerite tennantite and galena, which produced grades of 0.6 to 1.0% Cu where overprinting the earlier pulses of mineralisation.

Supergene enriched ore represents 65% of the total resource at Escondida. The upper surface of the supergene blanket is sub-horizontal and is displaced by faulting, while the base is irregular, with thicknesses varying from a few metres to 400 m. The leached cap extends from the present surface to a depth of around 200 m over the chalcocite blanket to only a few metres over the local copper oxide zone. It carries hematite over the deeper higher grade chalcocite blanket and jarosite over shallower, lower grade sections of the blanket. Over the copper oxides goethite dominates. The copper oxide zone represents around 5% of the resource and is composed of oxides, silicates, sulphates and carbonates of copper, mainly brochantite, antlerite, atacamite, chrysocolla, wad and tenorite.

Sulphides within the zone of supergene enrichment occur as disseminations and in veins and include chalcocite, covellite with minor digenite and idaite replacing pyrite, chalcopyrite and bornite. Chalcocite occurs throughout the blanket, while covellite and digenite appear in the middle, and increase downwards. Copper grades vary from 0.3 to more than 2%, but are highest in the thickest part of the blanket over the best developed hypogene mineralisation, in the zone where strong quartz-sericite and subsequent advanced argillic alteration overprints early biotite.

The total reserve + resource at Escondida and its contiguous mineralised systems amounted to approximately 2.62 Gt @ 1.15% Cu in 2000.

Escondida has reserves (proved + probable) & resources (measured + indicated + inferred) at Escondida in 2002 were as follows (Rio Tinto 2002 Annual Report):
  Sulphide ore - reserve of 1548 Mt @ 1.21% Cu,   +   resource of 579 Mt @ 0.9% Cu,
  Low grade float ore - reserve of 575 Mt @ 0.60% Cu,   +   resource of 815 Mt @ 0.6% Cu,
  Low grade leach ore - reserve none,   +   resource of 666 Mt @ 0.4% Cu,
  Oxide ore - reserve of 198 Mt @ 0.70% Cu,   +   resource of 55 Mt @ 0.5% Cu,
  Mixed ore - reserve of 49.7 Mt @ 1.03% Cu,   +   resource of 62 Mt @ 0.6% Cu,

Escondida Norte has additional resources (measured + indicated + inferred) as follows (Rio Tinto 2002):
  Sulphide ore - resource of 649 Mt @ 1.3% Cu,
  Low grade float ore - resource of 642 Mt @ 0.6% Cu,
  Oxide ore - resource of 142 Mt @ 0.8% Cu,
  Mixed ore - resource of 43 Mt @ 0.8% Cu,

The mine is operated by Minera Escondida, the principal owners of which in 2003 were BHP Billiton 57.5% and Rio Tinto 30%.

JORC compliant ore reserves and mineral resources in the Escondida group of deposits at December 31 2011 (Rio Tinto, 2012) were:
    Escondida sulphide ore - Proven + probable ore reserves - 1.993 Gt @ 0.97% Cu,
          Measured + indicated + inferred mineral resources - 5.762 Gt @ 0.53% Cu,
    Escondida sulphide leach ore - Proven + probable ore reserves - 3.503 Gt @ 0.50% Cu,
          Measured + indicated + inferred mineral resources - 75 Mt @ 0.53% Cu,
    Escondida sulphide oxide ore - Proven + probable ore reserves - 0.111 Gt @ 0.86% Cu,
          Measured + indicated + inferred mineral resources - 33 Mt @ 0.65% Cu,
    Pampa Escondida sulphide ore - Measured + indicated + inferred mineral resources - 7.378 Gt @ 0.47% Cu,
    Pinta Verde sulphide ore - Measured + indicated + inferred mineral resources - 45 Mt @ 0.51% Cu,
    Pinta Verde oxide ore - Measured + indicated + inferred mineral resources - 130 Mt @ 0.70% Cu.

Note: Reserves are additional to resources.

At 30 June 2017, the published resources (BHP Annual Report, 2017) amounted to:
  Mineral Resources
    Sulphide ore:
      Measured resource = 5.350 Gt @ 0.63% Cu,
      Indicated resource = 3.510 Gt @ 0.57% Cu,
      Inferred resource = 9.570 Gt @ 0.51% Cu,
    Total Sulphide resource = 18.400 Gt @ 0.78% Cu.
    Oxide ore:
      Measured resource = 104 Mt @ 0.69% Cu,
      Indicated resource = 83 Mt @ 0.57% Cu,
      Inferred resource = 20 Mt @ 0.53% Cu,
    Total Oxide resource = 207 Mt @ 0.63% Cu.
    Mixed ore:
      Measured resource = 70 Mt @ 0.62% Cu,
      Indicated resource = 82 Mt @ 0.47% Cu,
      Inferred resource = 59 Mt @ 0.44% Cu,
    Total Mixed Resource = 211 Mt @ 0.51% Cu.
   TOTAL Mineral resource = 18.818 Gt @ 0.77% Cu.
  Proved + Probable Ore Reserves (included within Mineral Resources)
      Sulphide ore = 5.260 Gt @ 0.70% Cu,
      Oxide ore = 0.298 Gt @ 0.63% Cu,
      Sulphide Leach ore = 2.140 Gt @ 0.40% Cu,
    Total Ore Reserve = 7.688 Gt @ 0.61% Cu.


The most recent source geological information used to prepare this summary was dated: 2011.    
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.


Escondida

Zaldivar

  References & Additional Information
   Selected References:
Alpers C N, Brimhall G H  1989 - Paleohydrologic evolution and geochemical dynamics of cumulative supergene metal enrichment at La Escondida, Atacama Desert, northern Chile: in    Econ. Geol.   v84 pp 229-255
Campos E, Wijbrans J and Andriessen P A M,  2009 - New thermochronologic constraints on the evolution of the Zaldivar porphyry copper deposit, Northern Chile: in    Mineralium Deposita   v.44 pp. 329-342
Lowell J D  1991 - Discovery of the La Escondida orebody: in    Econ. Geol.   Mono 8 pp 300-313
Mpodozis, C. and Cornejo, P.,  2012 - Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes: in Hedenquist J W, Harris M and Camus F, 2012 Geology and Genesis of Major Copper Deposits and Districts of the World - A tribute to Richard H Sillitoe, Society of Economic Geologists, Denver,   Special Publication 16, pp. 329-360
Ojeda-F J M  1990 - Geology of the Escondida porphyry copper deposit, II Region, Chile: in   Pacific Rim 90 Congress AusIMM, Melbourne    pp 473-483
Ortiz F J  1995 - Discovery of the Escondida porphyry copper deposit in the Antofagasta Region, Northern Chile, March 1981: in Pierce F W, Bolm J G (Eds), 1995 Porphyry Copper Deposits of the American Cordillera Arizona Geol. Soc.   Digest 20 pp 613-624
Padilla Garza R A, Titley S R and Eastoe C J  2004 - Hypogene evolution of the Escondida porphyry copper deposit, Chile: in Sillitoe R H, Perello J and Vidal C E 2004 Andean Metallogeny: New Discoveries, Concepts and Updates SEG Special Publication 11    pp 141-165
Padilla Garza R A, Titley S R, Pimental F  2001 - Geology of the Escondida porphyry copper deposit, Antofagasta Region, Chile: in    Econ. Geol.   v96 pp 307-324
Porter T M,  2005 - The Escondida Porphyry Copper Deposit, Northern Chile: Discovery, Setting, Geology, Hypogene Mineralisation and Supergene Ore - A Review: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide,   v.1 pp. 133-149
Richards J P, Boyce A J, Pringle M S  2001 - Geologic evolution of the Escondida Area, Northern Chile: A model for spatial and temporal localization of Porphyry Cu Mineralization: in    Econ. Geol.   v96 pp 271-305
Richards J P, Noble S R, Pringle M S  1999 - A revised late Eocene age for Porphyry Cu magmatism in the Escondida area, northern Chile: in    Econ. Geol.   v94 pp 1231-1248
Sillitoe R H, McKee E H  1996 - Age of supergene oxidation and enrichment in the Chilean Porphyry Copper Province: in    Econ. Geol.   v91 pp 164-179

   References in PGC Publishing Books: Want any of our books ? Pricelist
Porter T M, 2005 - The Escondida Porphyry Copper Deposit, Northern Chile: Discovery, Setting, Geology, Hypogene Mineralisation and Supergene Ore - A Review,   in  Porter T M, (Ed),  Super Porphyry Copper and Gold Deposits: A Global Perspective,  v1  pp 133-149
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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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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