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Centinela - El Tesoro |
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Chile |
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Cu
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Super Porphyry Cu and Au
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El Tesora is a large exotic secondary copper deposit developed within Tertiary gravels approximately 70 km to the south of Chuquicamata. It is 3 km NW of the Esperanza mine. Both Esperanza and El Tesora belong to the Centinela cluster of deposits and have been merged into the same operation.
(#Location: 22° 57' 1"S, 69° 4' 52"W)
Regional and District Setting
The regional geology surrounding the deposit comprises Palaeozoic intrusives and volcanic rocks overlain by several Mesozoic sedimentary and volcanic sequences, all of which have been intruded by Cretaceous granitoids. An Early Tertiary volcanic sequence follows unconformably, while a series of Middle to Late Eocene flow domes are the youngest bedrock. The cover sequence comprises a thick development of moderatley consolidated Middle to Late Tertiary gravels which are blanketed by a 10 Ma ignimbrite. The regional Domeyko fault system dislocates all of the above, including the ignimbrites, as does a NNE trending fault set.
See the separate Esperanza record for a more complete description of the regional and district setting.
Deposit Geology and Mineralisation
The deposit is completely contained within the Tertiary gravel sequence, and comprises two main NNE trending, NW dipping lenses with a maximum thickness of 150 m and an areal extent of some 5x2.5 km.
The host gravel is predominantly a crudely stratified, pebbly to blocky unit interbedded with coarse grained sand and silt, some of which are calcareous. The clast composition allows a stratigraphic subdivision into two main units, Gravas I and Gravas II. The basal Gravas I includes several sub-units of which the Gravas de Pórfido is the main host to exotic Cu. Gravas II is essentially post mineralisation.
The mineralised gravel is overlain by barren gravel with a contains a 10 Ma ash bed and covers the buried palaeo-relief to a thickness of 350 to 800 m below the surface.
The copper mineralisation within Gravas I, occurs as several 10 to 50 m thick tabular horizons within the overall gravels that are locally hundreds of metres thick. These horizons dip at 10 to 20° conformable with the host gravels.
The copper mineralogy is principally paratacamite and atacamite with subordinate chrysocolla and wad occuring as impregnations of the gravel matrix, the clasts of which are not mineralised. The host gravels commonly contain rounded clasts of sericitic quartz porphyry suspected to represent the assumed porphyry source and often contain encapsulated chalcocite and Co-oxides.
There is a crude mineral zoning where paratacamite and atacamite are dominantin the upper parts of the deposits and chrysocolla is found in the lower sections.
A series of alteration zones within the basement which extend for tens of kilometres to the north and south have been encountered in the vicinity of the deposit.
Reserves and Resources
Published reserve and resource estimates at the end of 2005 were as follows (Antofagasta PLC website, 2006):
total measured + indicated + inferred resource - 179 Mt @ 0.73% Cu; including
total proved + probable reserve - 123 Mt @ 0.79% Cu.
Published reserve and resource estimates at 31 December, 2010 were as follows (Antofagasta PLC website, 2012):
total measured + indicated + inferred resource - 155.0 Mt @ 0.80% Cu; including
total proved + probable reserve - 130.2 Mt @ 0.83% Cu.
Published ore reserve estimates at 31 December, 2015, for Tesoro Central, Tesoro NE, Mirador and Esperanza Oxides were as follows (Antofagasta PLC Annual report, 2015):
Proved + probable reserve - 188.5 Mt @ 0.44% Cu.
The most recent source geological information used to prepare this decription was dated: 2004.
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.
El Tesoro
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Selected References:
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Fernandez-Mort, A.,Riquelme, R., Alonso-Zarza, A. M., Campos, E., Bissig, T., Mpodozis, C., Carretier, S., Herrera, C., Tapia, M., Pizarro, H. and Munoz, S., 2018 - A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile: in Mineralium Deposita v.53, pp. 775-795.
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Mora R, Artal J, Brockway H, Martinez E and Muhr R, 2004 - El Tesoro exotic copper deposit, Antofagasta region, northern Chile: in Sillitoe R H, Perello J and Vidal C E (Eds.), 2004 Andean Metallogeny: New Discoveries, Concepts and Updates Society of Economic Geologists, Special Publication 11, pp 187-197
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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
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Munchmeyer C 1996 - Exotic deposits - products of lateral migration of supergene solutions from copper deposits: in Camus F, Sillitoe R H, Petersen R (Eds), Andean Copper Deposits: New Discoveries, Mineralisation, Styles and Metallogeny Soc. Econ. Geologists Spec. Publ. No. 5 pp 43-58
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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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