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Neves Corvo |
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Portugal |
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Cu Zn Pb Ag Sn
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Super Porphyry Cu and Au
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the Neves Corvo volcanic hosted massive sulphide deposit lies within the Iberian Pyrite Belt and is located 220 km southeast of Lisbon and 17 km southeast of the city of Castro Verde in the Alentejo district of Portugal.
The Iberian Pyrite Belt lies within the Herecyinian Fold Belt of the southern Iberian Peninsula, and extends for some 230 km in a generally east-west strike direction, from Seville in Spain to the east, to Casa Verde in Portugal to the west, with a width ranging from 35 to 50 km. It contains around 85 known deposits containing a mined + reserve tonnage of some 1.756 Gt of ore with 14.6 Mt Cu, 13 Mt Pb, 34.9 Mt Zn, 46 188 t Ag and 887 t Au. The massive sulphide deposits are part of a Devonian to Carboniferous (Famennian to early upper Visean) volcanogenic-sedimentary complex comprising calc-alkaline felsic volcanics (three sequences of dacitic-rhyolite pyroclastics, lavas and reworked tuffs dated at 385±40 Ma) and intercalated tholeiitic-alkaline mafic volcanics (basic lavas, dykes and sills), sediments (purple-blue shale, pelitic black shale and sandstone), sedimentary 'exhalites' (chert and jasper) and manganese rich beds. This whole complex is overlain by the thick turbidites of the Culm facies.
The massive sulphides of the Iberian Pyrite Belt occur within two mineralised stratigraphic levels (the lower or middle of the three dacitic-rhyolite sequences of the volcanogenic-sedimentary complex) and are found either directly in the black shale unit of the volcanogenic-sedimentary complex, or resting on rhyolitic volcanic facies, commonly separated from the felsic volcanics by a thin pelitic layer. Mineralisation appears to be within shallow submarine facies.
In the Neves Corvo area, there is an allochthonous and an autochthonous unit, both encompassing rocks of upper Devonian to lower Carboniferous age. Both units are divided throughout the Iberian Pyrite belt into a lower Phyllite-Quartzite group, a Volcanic-Siliceous group and an upper Flysch group. The host Volcanic Siliceous complex is in the autochthonous unit and comprises black shales, siliceous shales, tuffites and cherty rocks with the massive sulphide mineralisation and footwall stockworks with chloritic alteration. This complex also contains felsic tuffs and related pyroclastics, locally with strong chloritic and quartz-sericite alteration. Neves Corvo lies on a major lineament that controlled the development of volcanism in the region.
The volcanic, volcaniclastic and sedimentary lithofacies directly hosting the Neves-Corvo mineralisation comprises a rhyolitic dome-cryptodome-hyaloclastite complex. Facies interpretation indicates that volcanic activity occurred at moderate water depth (below storm-wave base) in variably subsiding basins of different orders. Several syn- and post-ore modification events included gravity-driven mass transport processes and subsequent low-angle thrusting and asymmetric detachment folding, which shaped the present deposit.
Studies of the Corvo orebody suggest that ore formation resulted from a long-lived hydrothermal system which included two main genetically related mineralising systems fed by two spatially independent stockworks, namely:
i). An early stage of stringer and massive cassiterite-stannite, ores which took place almost exclusively within a structural alignment bounded by synvolcanic faults known as the "tin corridor". Textural analysis and geochemical data both suggest a minimal fluid-rock interaction during ascent of the tin-bearing fluid. It has been interpretted that the massive and semi-massive cassiterite ores at Corvo were formed by venting into seawater and/or replacement in unlithified water-laden sediments and early hydrothermal products that mantled the footwall volcanic sequence.
ii). A subsequent episode of massive sulphide and related hydrothermal alteration, which at in Corvo is essentially strata bound. The permeability contrasts in the uppermost portion of the footwall succession played an important role in controlling the fluid flow. Hydrothermal alteration is zoned and comprises an inner chlorite/donbassite-quartz-sulphide-(sericite) core that grades outward into successive enveloping K-sericite-quartz-sulphide and Na-sericite-quartz-sulphide halos. Textural evidence, from the macro to the microscopic scale, and mass-balance considerations suggest that extensive silicate replacement in the coherent volcanic rocks of the footwall sequence and disseminated replacement mineralisation in the uppermost volcaniclastic and/or sedimentary units were responsible for the massive sulphide deposition at Corvo. The ore is mineralogically variable, although the dominant minerals are pyrite, chalcopyrite, sphalerite, galena, tetrahedrite and arsenopyrite, present as 'banded ore', 'massive sulphide', and 'fissure and breccia' ore.
Mineral textures are complex due to the intergrowth between chalcopyrite-tetrahedrite-tennantite-sphalerite-pyrite, produced by multistage replacement phenomena. Sphalerite is frequently replaced by by chalcopyrite, tetrahedrite/tennantite and by stannite. The other principal sulphides include galena, bornite and arsenopyrite, with a wide variety of accessory minerals including kesterite, stannoidite, mawsonite, freibergite, pyrrohotite, bournonite, glaucodot, alloclasite, cobaltite, aikinite, bismuthinite, galenobismutite, kobellite, loellingite, rezbanyite, enargite, native bismuth, electrum, marcasite, carollite, vinciennite, miharaite, wittichinite, naumannite, native gold, galenoclausthalite, nekrasovite, etradymite, joseite, tiemannite, bohdanowitzite, meneghinite, berthierite, boulangerite, roquesite, magnetite, hematite, ilmenite and rutile. Gangue minerals comprise quartz, phyllosilicates (chlorite and sericite), carbonates (dolomite and siderite) and barite.
The operation is based on a number of orebodies linked by zones of thin discontinuous mineralisation, with varying ore types, forming an overall, shallow NE dipping, irregular, massive sulphide zone of some 1.8 x 3 km and locally more than 50 m thick, as follows:
Corvo - 1200 x 700 x 90 m, 60% barren pyrite, with major Cu & Sn ore zones & minor complex sulphide ores.
Graca - 600 x 500 x 80 m, 70% barren pyrite, with major Cu & Sn ore zones & minor complex sulphide ores.
Neves - 1500 x 700 x 50 m, 30% barren pyrite; -and-
North Neves with major Cu ore zones & minor complex sulphide ores;
South Neves with major complex sulphide ore, minor Cu ores with associated Zn and minor Cu-Sn ores.
Zambujal - 600 x 500 x 50 m, 60% barren pyrite, with major complex sulphide ores & minor Cu ores.
Lombardor - 700 x 500 x 50 m, 85% barren pyrite, with major complex sulphide mineralisation.
Each of these bodies exhibit stockwork zones in the footwall host rocks and are located above the thickest pile of felsic volcanic rocks. The display distinct vertical and lateral zonal patterns of metals with Cu-rich sulphides predominating at the base, overlain by zinc-rich sulphides (if present) and 'barren' (lower grade) massive sulphides towards the top. Siliceous chemical sediments of the 'Jaspes e Carbonatos' are enriched in Ci, Sn, Zn, In, Co, Sb and Se.
The total resource + production of the deposits is beleived to be more than 300 Mt, including around 150 Mt of polymetallic massive sulphides. In 1998, the complex of tin, copper and zinc (polymetallic complex sulphide) deposits was estimated to comprise a total of 261 Mt of ore containing 3.44 Mt Cu, 2.88 Mt Sn, 0.6 Mt Pb, 3.74 Mt Zn and 2977 Mt Ag. In 2010 (Carmichael, 2010) quotes the total contained production + reserves/resources as containing 4.68 Mt of Cu metal and 6.81 Mt of Zn metal.
In 2000, the copper ore, which is the principal exploited ore type, comprised 31 Mt @ 8% Cu, 0.2% Pb, 1.4% Zn, while the polymetallic complex sulphide mineralisation (Zinc ore) constituted a further 33 Mt @ 0.46% Cu, 1.13% Pb, 5.72% Zn, 40 g/t Ag. The tin orebodies zone contained 2.9 Mt @ 2.4% Sn, 13.4% Cu, 1.3% Zn.
g/t Ag
Reserve and resource figures at the end of 2007 (Lundin Mining website, 2008) were:
Ore Reserves - copper ore (1.6% Cu cut-off):
Proven + Probable - 17.714 Mt @ 4.4% Cu, 0.9% Zn, 0.2% Pb,
Mineral Resources - copper ore (1% Cu cut-off):
Measured + Indicated - 20.437 Mt @ 5.1% Cu, 1.0% Zn, 0.3% Pb,
Inferred - 3.338 Mt @ 3.4% Cu, 0.8% Zn, 0.2% Pb,
Ore Reserves - zinc ore (4.6% Zn cut-off):
Proven + Probable - 33.511 Mt @ 0.4% Cu, 6.6% Zn, 1.5% Pb,
Mineral Resources - zinc ore (3% Zn cut-off):
Measured + Indicated - 56.512 Mt @ 0.5% Cu, 6.2% Zn, 1.4% Pb,
Inferred - 20.456 Mt @ 0.5% Cu, 4.6% Zn, 1.4% Pb.
Reserve and resource figures at June 30, 2021 (Lundin Mining website, Feb 2022) were:
Ore Reserves - copper ore:
Proven + Probable - 25.09 Mt @ 2.1% Cu, 0.6% Zn, 0.2% Pb, 31 g/t Ag;
Mineral Resources - copper ore:
Measured - 8.985 Mt @ 3.6% Cu, 0.8% Zn, 0.3% Pb, 44 g/t Ag;
Indicated - 51.023 Mt @ 2.1% Cu, 0.8% Zn, 0.3% Pb, 44 g/t Ag;
Inferred - 12.681 Mt @ 1.8% Cu, 0.8% Zn, 0.3% Pb, 34 g/t Ag;
Ore Reserves - zinc ore:
Proven + Probable - 24.774 Mt @ 0.3% Cu, 7.5% Zn, 1.8% Pb, 80 g/t Ag,
Mineral Resources - zinc ore:
Measured - 10.609 Mt @ 0.3% Cu, 7.8% Zn, 1.8% Pb, 66 g/t Ag;
Indicated - 57.742 Mt @ 0.3% Cu, 6.7% Zn, 1.4% Pb, 61 g/t Ag;
Inferred - 4.071 Mt @ 0.4% Cu, 5.7% Zn, 1.6% Pb, 64 g/t Ag.
Neves Corvo is owned and operated by SOMINCOR, Sociedede Mineira de Neves Corvo, SA, which in November 2006, was fully consolidated into Lundin Mining Corporation.
The most recent source geological information used to prepare this decription was dated: 2007.
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.
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Selected References:
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Carmichael R, 2010 - Zinc Resource Expansion at the Neves-Corvo Mine, Portugal: in Archibald S M (Ed.), 2010 Proceedings of the Zinc2010 Meeting, Cork 2010, Irish Association for Economic Geology pp. 12-15
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de Carvalho D 1991 - A case history of the Neves-Corvo massive-sulphide deposit, Portugal - and implications for future discoveries: in Econ. Geol. Monograph 8 pp 314-334
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Frenzel, M., Bachmann, K., Carvalho, J.R.S., Relvas, J.M.R.S., Pacheco, N. and Gutzmer, J., 2019 - The geometallurgical assessment of by-products-geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal: in Mineralium Deposita v.54, pp. 959-982.
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Gaspar O C 1991 - Paragenesis of the Neves-Corvo volcanogenic massive-sulphide deposits: in Comun. Serv. Geol. Portugal, 1991 t. 77 pp 27-52
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Leca X 1990 - Discovery of concealed massive-sulphide bodies at Neves-Corvo, southern Portugal - a case history: in Trans. IMM, Section B 99, Sept-Dec 1990 pp B139-152
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Leistel J M, Marcoux E, Deschamps Y, 1997 - Chert in the Iberian Pyrite Belt: in Mineralium Deposita v33 pp 59-81
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Luz, F., Mateus, A., Ferreira, E., Tassinari, C.G. and Figueiras, J., 2022 - Pb-Nd-Sr Isotope Geochemistry of Metapelites from the Iberian Pyrite Belt and Its Relevance to Provenance Analysis and Mineral Exploration Surveys: in Aguas Tenidas (Cu-Zn-Pb), Sotiel-Coronada (Cu-Zn-Pb), and La Magdalena Econ. Geol. v.117, pp. 423-454.
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Oliveira J T, Pereira Z, Carvalho P, Pacheco N and Korn D 2004 - Stratigraphy of the tectonically imbricated lithological succession of the Neves Corvo mine area, Iberian Pyrite Belt, Portugal: in Mineralium Deposita v39 pp 422-436
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Pasava J, Vymazalova A and Tornos F, 2007 - PGE distribution in massive sulfide deposits of the Iberian Pyrite Belt : in Mineralium Deposita v42 pp 309-314
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Relvas J M R S, Barriga F J A S and Longstaffe F J, 2006 - Hydrothermal Alteration and Mineralization in the Neves-Corvo Volcanic-Hosted Massive Sulfide Deposit, Portugal. II. Oxygen, Hydrogen, and Carbon Isotopes: in Econ. Geol. v101 pp 791-804
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Relvas J M R S, Barriga F J A S, Ferreira A, Noiva P C, Pacheco N and Barriga G, 2006 - Hydrothermal Alteration and Mineralization in the Neves-Corvo Volcanic-Hosted Massive Sulfide Deposit, Portugal: I. Geology, Mineralogy, and Geochemistry: in Econ. Geol. v101 pp 753-790
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Relvas J M, Tassinari C C, Munha J and Barriga F J 2001 - Multiple sources for ore-forming fluids in the Neves Corvo VHMS Deposit of the Iberian Pyrite Belt (Portugal): strontium, neodymium and lead isotope evidence: in Mineralium Deposita v36 pp 416-427
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Rosa C J P, McPhie J, Relvas J M R S, Pereira Z, Oliveira T and Pacheco N, 2008 - Facies analyses and volcanic setting of the giant Neves Corvo massive sulfide deposit, Iberian Pyrite Belt, Portugal: in Mineralium Deposita v43 pp. 449-466
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Saez R, Almodovar G R and Pascual E, 1996 - Geological constraints on massive sulphide genesis in the Iberian Pyrite Belt: in Ore Geology Reviews v11 pp 429-451
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Soriano C, Marti J 1999 - Facies analysis of volcano-sedimentary successions hosting massive sulfide deposits in the Iberian Pyrite belt, Spain: in Econ. Geol. v94 pp 867-882
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Thadeau D 1989 - Portugal: in Dunning F W, Garrard P, Haslam H W, Ixer R A (Eds.), Mineral Deposits of Europe IMM, London v 4/5: Southwest and Eastern Europe, with Iceland pp 197-218
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Tornos F, 2006 - Environment of formation and styles of volcanogenic massive sulfides: The Iberian Pyrite Belt: in Ore Geology Reviews v28 pp 259-307
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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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