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Carmen de Cobre

Chile

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The Carmen de Cobre IOCG deposit is located in the Carmen-Sierra Áspera district of the Chilean Coastal Cordillera, ~40 km northeast of the Mantoverde deposit, some 360 km south of Antofagasta and 140 km north of the town of Copiapo in northern Chile.

The deposits of the Carmen-Sierra Áspera district are associated with subsidiary splays/second-order faults associated with the north-south Atacama fault system that is the major structural control of IOCG mineralisation in the Chilean Coastal Cordillera. Iron oxide mineralisation is predominantly hosted by volcano-sedimentary sequences of the Mid- to Late-Jurassic La Negra Formation and Early Cretaceous Punta del Cobre Formation, intruded by Early Cretaceous granitoids of the Coastal Batholith (Lara and Godoy, 1998, and references therein).

Mineralisation at Carmen de Cobre is represented by hematite breccia that occurs in the hanging wall of the Carmen Fault, hosted by andesitic rocks of the La Negra Formation, and intruded by diorite that is regarded to be related to the Sierra Áspera Complex. Magnetite, with associated apatite, occurs as early phase subvertical veins up to a metre-thick in the deeper parts of the deposit at >60 to 250 m depths (Herrera et al., 2008; Loyola Espinoza, 2016). These veins are generally coarse-grained, and become more pronounced in the eastern-most part of the deposit, where they form a swarm that strikes NE-SW. Individual veins reach thicknesses of up to 10 m and lengths of more than a kilometre.

Hematite-rich Cu mineralisation is superimposed on the magnetite-apatite phase, and comprises large, up to ~10 m thick, lenses of north-south striking and east dipping breccias. Dated Ti-bearing hematite is younger than the spatially associated magnetite bodies it crosscuts (Verdugo-Ihl, et al., 2022). These hematite breccias form moderately dipping to flat, tabular, mineralised zones above a shear zone that is part of the Carmen fault system. The breccias are composed of host andesite fragments set in a fine-grained, hematite-rich matrix with Cu-(Fe) sulphides. Two distinct styles of alteration are recognised, i). alkali-calcic and ii). hydrolytic. The latter is represented by a sericite-chlorite-siderite assemblage (Herrera et al., 2008; Loyola Espinoza, 2016).

Carmen de Cobre contrasts with other deposits in the district, such as Mantoverde Norte, at Mantoverde, 40 km to the SW, where large magnetite (±chalcopyrite) bodies are found at depth, but without associated magnetite-apatite mineralisation. Nevertheless, hematite-rich IOCG Cu-Au mineralisation, that is considered late relative to early magnetite, occurs at both deposits. However, in contrast to Mantoverde Norte, tha magnetite mineralisation is located in the same structural block as the hematite relative to the Carmen fault. A tabular, massive IOA-type magnetite-apatite body occurs at Carmen de Fierro, ~5 km further north of Carmen de Cobre (Tornos et al., 2020), although there is no apparent structural relationship between mineralisation in the two deposits. Alteration at Carmen de Cobre is comparable to that described for the Mantoverde district, whilst similar S isotope signatures of chalcopyrite and pyrite (δ34SCDT ranges from -4 to -0.8‰) are also interpreted as representative of a magmatic S source (Loyola Espinoza, 2016).

Verdugo-Ihl, et al. (2022) studied hematite from Carmen de Cobre, which yielded a date of ~108 Ma, which is younger than either the magnetite-apatite dyke at Carmen de Fierro, or actinolite from the IOCG system at Todos los Santos (~10 km N), and corresponds to a period that postdates that of the main phase of Andean IOCG mineralisation systems that occurred between ~125 and 110 Ma (Richards et al. (2017). This suggests the hematite belongs to a younger episode of IOCG mineralisation in the area. This hematite is Ti-rich, containing up to 10.8 mol.% ilmenite (~Fe
1.89Ti0.11O3) but lacks ilmenite exsolutions. This is interpreted to imply minimum crystallisation temperatures of ~500°C, above the solvus of the FeTiO3-Fe2O3 system, supporting a magmatically derived fluid source. Nanometer-scale, K-Si-Al-Cl bearing inclusions in hematite suggest an alkali alteration event during hematite formation. In addition to measurable U, the Ti-bearing hematite also contains growth zones with W and Sn, elements which are regarded as part of a 'granitophile' signature (Verdugo-Ihl, et al., 2022).

Published resources at Carmen de Cobre are: 70 Mt @ 0.65% Cu, 0.05 ppm Au (Verdugo-Ihl, et al., 2022).

The most recent source geological information used to prepare this summary was dated: 2022.    
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:
Verdugo-Ihl, M.R., Ciobanu, C.L., Courtney-Davies, L., Cook, N.J., Slattery, A., Ehrig, K., Tornos, F. and Hanchar, J.M.,  2022 - U-Pb Geochronology and Mineralogy of Hematite from Mantoverde and Carmen de Cobre, Northern Chile: Constraints on Andean IOCG Mineralization: in    Econ. Geol.   v.117, pp. 943-960.


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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