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Capela, Rey de Plata |
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Guerrero, Mexico |
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Ag Cu Zn Au Pb
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Super Porphyry Cu and Au
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The Capela, formerly Rey de Plata, Zn-Pb-Cu-Ag-Au volcanic hosted massive sulphide (VHMS) deposit cluster is located ~150 km and ~8 km SW of Mexico City and Teloloapan respectively, in the state of Guerrero, in southwestern Mexico (#Location: 18° 37' 18"N, 99° 55' 54"W).
The Rey de Plata mine commenced operation in October 2000 under a partnership between Industrias Peñoles (51%), Dowa Mining and Sumitomo Corporation. A steep decline in the zinc price led to a decision at the end of 2001 to suspend operation of the mine. Peñoles acquired the minority interests in December 2004, and in 2008 resumed evaluation and exploration drilling. In 2011, an initial estimate of mineral resources was issued of 18.8 Mt @ 15% Zn equivalent, and in 2012 the construction of the new Capela mining unit was approved. Exploration during 2013 further expanded reserves to 25.2 Mt @ 15.7% Zn equivalent. The mining unit was commissioned in the first quarter of 2020 and commenced operation in the same year.
The Capela deposit lies within the Guerrero Terrane, which is interpreted to underlie much of western Mexico. However, the Mesozoic assemblages that define the Terrane, are only exposed over <5% of the surface area, occurring as scattered erosional windows through the extensive Tertiary and Quaternary volcanic and sedimentary strata of the Sierra Madre Occidental Province and Trans-Mexican Volcanic Belt. Capela falls within the Teloloapan Sub-terrane of the Guerrero Terrane. This sub-terrane is exposed over a north-south interval of ~150 x 50 km and also hosts the Tizapa VHMS deposit, ~80 km to the north. The Capela deposit also lies between the smaller Campo Morado district 10 to 20 km to the SSW and the Tlanilpa-Azulaquez district a similar distance to the north.
The Teloloapan Sub-terrane It is bounded by the Arcelia Sub-terrane and younger cover to the west and by the similar cover sequence and the Mixteco Terrane to the east. The Arcelia Sub-terrane is predominantly composed of deep water, tholeiitic, pillowed mafic volcanic rocks, interlayered with, and overlain by, black shale and chert, and has been thrust east over the Teloloapan Sub-terrane. The Teloloapan Sub-terrane is composed of mainly Cretaceous mafic volcanic rocks, stratigraphically overlain by intermediate to felsic volcanic and volcaniclastic units, with interlayered and overlying fine grained clastic rocks. This succession is capped by a shelf sequence of clastic and carbonate rocks. The volcanic rocks are calc-alkaline. The entire sub-terrane has been metamorphosed to greenschist facies, and is internally imbricated by thrust and low angle normal faults, and thrust eastward over the Cretaceous Albian carbonates and older Palaeozoic clastic strata of the Mixteco terrane.
The Capela deposit is developed near the top of the volcanic arc succession of the Teloloapan Sub-terrane. Two main lithologic assemblages have been recognised in the deposit area: i). an ~3500 m thick basal calc-alkaline basaltic to andesitic pile, and ii). an overlying, ~1500 m thick package of sedimentary rocks. Sulphide mineralisation at Capela is hosted within a 400 m thick sequence of rhyolitic/felsic volcanic and volcaniclastic rocks with interlayered carbonaceous siliciclastic rocks and andesitic volcanic rocks that locally predominate in the upper portion of the volcanic pile.
Sulphide mineralisation occurs as a group of bodies, that may be either of both stockworks and conformable lenses or mantos developed in schists and meta-volcanics of felsic composition. The lens-shaped bodies range in size from 3 to 60 m in thickness, from 300 to 1200 m length, and from 100 to 500 m width (Monter-Ramírez and Zavala-Esquivel, 2011). The ore is composed of pyrite, sphalerite, galena, bornite, chalcopyrite, pyrargyrite, tetrahedrite-tennantite, native gold, arsenopyrite and jamesonite, along with gypsum, barite and calcite as gangue phases (Miranda-Gasca et al., 2001). The main orebody, Tehuixtla, is strongly zoned from: i). a lower zone of mainly pyrite, including framboidal aggregates; ii). chalcopyrite and bornite; and iii). an upper interval of mainly of pyrite, sphalerite, galena, barite and, sporadically, silver sulphosalts (Monter-Ramírez and Zavala-Esquivel, 2011). The sulphide assemblages are predominantly banded, with a weakly developed tectonic foliation. Gold is found in the upper part of the deposit, and is associated with ankerite-rich silicification.
The Cuerpo Superior or Upper Orebody, contains disseminated, semi-massive and massive pyrite, chalcopyrite, bornite, covellite and chalcocite at the bottom, passing up into sphalerite, galena and sporadic silver sulphosalts at the top. Barite veinlets and a chalcopyrite, pyrite and gold-bearing stockwork have been developed in the central part of this orebody (Monter-Ramírez and Zavala-Esquivel, 2011). The Cuerpo Intermedio and Cuerpo Inferior, i.e., the Intermediate and Lower orebodies, exhibit similar mineralogy, zoning and structure, although, galena-rich associations in the upper parts generally have very high silver contents of >1000 g/t Ag. Both the ores and host rocks have been subjected to plastic deformation, developed mylonites locally, and have undergone greenschist facies metamorphism.
Alteration varies through the deposit. Chlorite is pervasively developed, but is restricted to the andesitic and basaltic rocks, both below and above sulphide lenses. Sericitisation is also pervasive, but is restricted to the metamorphosed rhyolite protoliths. Silicification is more intense directly below the thickest portion of the main Tehuixtla Orebody. Quartz and sulphides veinlets are abundant beneath the Tehuixtla Orebody.
Temperatures of crystallisation of chlorite and the homogenisation temperatures of fluid inclusions indicate that conditions of >300°C were achieved below the sulphide lenses and that they decreased upward to as little as 140°C, at the edges of the sulphide lenses.
Reserves and Production
Miranda-Gasca et al. (2001) quote reserves at Rey de Plata as
3.006 Mt @ 8.7% Zn, 2.16% Pb, 0.52% Cu, 239 g/t Ag, 1.41 g/t Au.
Production during financial year 2022 (Industrias Peñoles Annual Report, 2022) totalled:
1.302 Mt of ore milled for 0.72 t of gold, 80.08 t of silver, 3335 t of lead, 27 042 t of zinc, 3377 t of copper, equating to a head grade of,
1.22 g/t Au, 97.21 g/t Ag, 0.59% Pb, 2.87% Zn, 0.60% Cu.
Remaining Reserves at Capela as at December 2022 were (Industrias Peñoles Annual Report, 2022)
- 20.788 Mt @ 2.99% Zn, 0.67% Pb, 0.77% Cu, 87.77 g/t Ag, 1.13 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2017.
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.
Capela
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Selected References:
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Camprubi, A., Gonzalez-Partida, E., Torro, L., Alfonso, P., Canete, C., Miranda-Gasca, M.A., Martini, M. and Gonzalez-Sanchez, F., 2017 - Mesozoic volcanogenic massive sulfide (VMS) deposits in Mexico: in Ore Geology Reviews v.81, pp. 1066-1083. doi.org/10.1016/j.oregeorev.2015.07.027.
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Miranda-Gasca, M.A., De La Garza, BV., Tellez, R. and Hernandez, A., 2001 - The Rey de Plata Cretaceous Zn-Pb-Cu-Ag-Au Volcanogenic Massive sulphide Deposit, Guerrero, Mexico: in 2001 New Mines and Discoveries in Mexico and Central America, SEG Special Publication, v.8, doi.org/10.5382/SP.08.17
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Mortensen, J.K., Hall, B.V., Bissic, T., Friedman, R.M., Danielson, T., Oliver, J., Rhys, D.A., Ross, K.V. and Gabites, J.E., 2008 - Age and Paleotectonic Setting of Volcanogenic Massive Sulfide Deposits in the Guerrero Terrane of Central Mexico: Constraints from U-Pb Age and Pb Isotope Studies: in Econ. Geol. v.103, pp. 117-140.
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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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