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Mantos Blancos

Chile

Main commodities: Cu Ag
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The Mantos Blancos copper-silver deposit is located in the Coastal Range of northern Chile, some 45 km NE of the Pacific coastal city of Antofagasta in northern Chile (#Location: 23° 25' 52"S, 70° 3' 22"W).

It lies within the Atacama Fault Zone and is hosted by a Triassic sequence of acid volcanics, mainly rhyolites and dacite which dip at 10 to 45° SE and, cut upper Palaeozoic sediments and metasediments. These are in turn overlain by Jurassic clastics and limestones, Jurassic andesites and Cretaceous andesites and dacites. In the mine area the host volcanics are intruded by a sill like sub-volcanic andesite body, by sheets of dacite and abundant andesite dykes.

The Mantos Blanco mineralisation displays two superimposed hydrothermal events, namely:

i). an older phyllic alteration probably related to felsic magmatic-hydrothermal brecciation at ~155 Ma, and
ii). a younger (141-142 Ma) potassic, propylitic and sodic alteration phase, coeval with dioritic and granodioritic stocks and sills, and dioritic dykes.

The principal ore formation is genetically related to the second hydrothermal event, and comprises hydrothermal breccias, disseminations and stockwork-style mineralisation, associated with sodic alteration.

The ore stage alteration is dominated by albitisation and silicification that is distributed homogeneously through the volcanic sequence. Specular hematite is found in the barren upper levels and red hematite in the mineralised zones. These represent four principal alteration types, namely:

i). Na metasomatism manifested by albitisation of feldspars as well as albite veining and pore filling;
ii). incipient to intense addition (or locally removal) of Mg and Fe, reflected by chloritisation or bleaching;
iii). intense hematisation in the form of disseminated and stringer specularite and by intense pervasive red hematisation to many of the rocks within the deposit; and
iv). silicification, represented by quartz phenocrysts, microcrystalline aggregates in the groundmass and as occasional veinlets and amygdule fillings.

The mineralisation occurs as irregular bodies of oxide and sulphide copper with economically significant associated silver. The oxide minerals atacamite and chrysocolla are common in the upper levels of the sulphide body associated with faulting and intense brecciation.

The hypogene sulphide assemblages have distinctive vertical and lateral zoning, centred on magmatic and hydrothermal breccia bodies, which are interpreted to constitute feeders to the main mineralisation which is largely distributed in irregular, lenticular bodies roughly parallel to stratification. A barren pyrite root zone is overlain by pyrite-chalcopyrite, and followed upwards and laterally by chalcopyrite-digenite or chalcopyrite-bornite. A digenite-supergene chalcocite assemblage characterises the central portions of high-grade mineralisation in the breccia bodies. Silver is found in the lattices of both the oxide and sulphide minerals and correlated with the Cu grade.

Economic grade ore is found over an interval of 3 x 1.5 km and to a depth of 450 m. In 1995 the pre-mining resource was calculated at 170 Mt, of which 91 Mt were oxide ore @ 1.4% Cu and   89 Mt of sulphide ore @ 1.6% Cu and 17 g/t Ag.

Remaining mineral resources at 31 December, 2014 at a 0.2% Cu Total cutoff (Anglo American Annual Report, 2015) were:
  Sulphide ore (flotation)
      Measured + indicated resource - 90.8 Mt @ 0.64% Cu at a 0.2% Cu
Total,
      Inferred resource - 22 Mt @ 0.56% Cu
Total,
  Oxide ore (Vat and Heap Leach)
      Measured + indicated resource - 18.4 Mt @ 0.43% Cu
Acid Sol.,
      Inferred resource - 16.3 Mt @ 0.29% Cu
Acid Sol.,
  Oxide ore (Dump Leach)
      Measured + indicated resource - 11.0 Mt @ 0.17% Cu
Acid Sol.,
      Inferred resource - 70.7 Mt @ 0.18% Cu
Acid Sol..

The mine is operated by Minera Mantos Blancos S.A., which was initially an Anglo American Group company, but was sold to be part of Mantos Copper S.A. in 2015.

The most recent source geological information used to prepare this summary was dated: 2001.    
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.


Mantos Blancos

  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
Espinoza S, Veliz H, Esquival J, Arias J, Moraga A  1996 - The cupriferous province of the Coastal Range, Northern Chile: in Camus E, Sillitoe R H, Peterson R (Eds), 1996 Andean Copper Deposits: New Discoveries, Mineralisation, Styles and Metallogeny Soc. Econ. Geol.   Spec Pub no. 5 pp 19-32
Haynes D W,  2000 - Iron Oxide Copper (-Gold) Deposits: Their Position in the Ore Deposit Spectrum and Modes of Origin: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.1 pp. 71-90
Maksaev V and Zentilli M,  2002 - Chilean Strata-bound Cu- (Ag) Deposits: An Overview: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v.2 pp. 185-205
Oliveros V, Feraud G, Aguirre L, Ramirez L, Fornari M, Palacios C and Parada M,  2008 - Detailed 40Ar/39Ar dating of geologic events associated with the Mantos Blancos copper deposit, northern Chile: in    Mineralium Deposita   v43 pp 281-293
Palacios C, Ramírez L E, Townley B, Solari M and Guerra N,   2007 - The role of the Antofagasta-Calama Lineament in ore deposit deformation in the Andes of northern Chile : in    Mineralium Deposita   v42 pp 301-308
Ramirez L E, Palacios C, Townley B, Parada M A, Sial A N, Fernandez-Turiel J L, Gimeno D, Garcia-Valles M and Lehmann B,  2006 - The Mantos Blancos copper deposit: an upper Jurassic breccia-style hydrothermal system in the Coastal Range of Northern Chile: in    Mineralium Deposita   v41 pp 246-258
Ramirez Rodriguez R D  1995 - Geology of Mantos Blancos Mine: in Green S M, Struhsacker E, (Eds), 1995 Geology & Ore Deposits of the American Cordillera, Field Trip Guidebook compendium, 1995 Geol. Soc., Nevada    pp 466-481


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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