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The Neves-Corvo Deposit, Iberian Pyrite Belt, Portugal: Impacts and Future, 25 Years after the Discovery

By
Jorge M.R.S. Relvas
Jorge M.R.S. Relvas
Creminer, Dept. Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C2, Piso 5, Campo Grande, 1749-016 Lisboa, Portugal
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Fernando J.A.S. Barriga
Fernando J.A.S. Barriga
Creminer, Dept. Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C2, Piso 5, Campo Grande, 1749-016 Lisboa, Portugal
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Álvaro Pinto
Álvaro Pinto
Creminer, Dept. Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C2, Piso 5, Campo Grande, 1749-016 Lisboa, Portugal
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Alfredo Ferreira
Alfredo Ferreira
Somincor, Sociedade Mineira de Neves-Corvo, S.A., Mina de Neves-Corvo, 7780 Castro Verde, Portugal
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Nelson Pacheco
Nelson Pacheco
Somincor, Sociedade Mineira de Neves-Corvo, S.A., Mina de Neves-Corvo, 7780 Castro Verde, Portugal
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Paulo Noiva
Paulo Noiva
Somincor, Sociedade Mineira de Neves-Corvo, S.A., Mina de Neves-Corvo, 7780 Castro Verde, Portugal
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Gonçalo Barriga
Gonçalo Barriga
Somincor, Sociedade Mineira de Neves-Corvo, S.A., Mina de Neves-Corvo, 7780 Castro Verde, Portugal
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Rui Baptista
Rui Baptista
Creminer, Dept. Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C2, Piso 5, Campo Grande, 1749-016 Lisboa, Portugal
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Delfim de Carvalho
Delfim de Carvalho
Instituto Geológico e Mineiro, Ap. 7586 Zambujal, 2720 Alfragide, Portugal, and R. Frei Amador Arrais, 39 r/c, 7800 Beja, Portugal
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Víctor Oliveira
Víctor Oliveira
Instituto Geológico e Mineiro, Ap. 7586 Zambujal, 2720 Alfragide, Portugal, and R. Frei Amador Arrais, 39 r/c, 7800 Beja, Portugal
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José Munhá
José Munhá
Centro de Geologia, Dept. Geologia, Faculdade de Ciências, Universidade de Lisboa, Edifício C2, Piso 5, Campo Grande, 1749-016 Lisboa, Portugal
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W. Hutchinson Richard
W. Hutchinson Richard
Department of Geology and Geological Engineering, Colorado School of Mines, Golden, 80401, Colorado>
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Published:
January 01, 2002

Abstract

Neves-Corvo, the jewel in the crown of the Iberian pyrite belt, was the most important massive sulfide discovery of the last three decades, both in gross value and significance to exploration for these ores. The deposit consists of five orebodies, which lie beneath a 230-to 800-m-thick succession of rocks of Upper Devonian and Carboniferous age. The massive sulfide orebodies were dated at ca. 350 Ma (Rb-Sr) and are hosted by rhyolitic to rhyodacitic volcanic and volcaniclastic rocks, which are part of a relatively thin Volcanic-Siliceous Complex (≤600 m). The latter is overlain by a thick cover of younger flysch and rests on older, Upper Devonian metasedimentary rocks. Low-angle thrusting has complicated the stratigraphic relationships between these major units. The deposit contains more than 300 million metric tons (Mt) of massive sulfides with about 100 Mt of mineable grade, the balance being highly pyritic. Like most other Iberian pyrite belt deposits, the Neves-Corvo deposit combines many distinctive characteristics of volcanic-hosted massive sulfide (VHMS) deposits worldwide, including very fine grained and metallurgically complex Zn-Pb-(Cu) ores, prominent metal zoning, and hydrothermal alteration of its footwall rocks; with some features akin to those of sedimentary exhalative (SEDEX) deposits. The uncommonly low ratio of volcanic versus sedimentary rocks in the overall footwall succession of the Iberian pyrite belt, the extremely homogeneous lead isotope signatures of the ores throughout the whole district, and the gigantism of many deposits are among the reasons that account to envisaging these deposits as hybrids linking those two major types of massive sulfide mineralization.

In addition to these Iberian pyrite belt-like features, the Neves-Corvo deposit possesses some unusual characteristics as well. Among these stand out its uncommonly high copper-to-zinc ratio, which more than doubles that of typical Iberian pyrite belt deposits; its extremely copper rich ores that reflect zone refining within the deeper parts of the orebodies and late enrichment by remobilization phenomena; and its remarkably high tin content. The Neves-Corvo deposit is unique among massive sulfide deposits, as it encloses primary, extremely high grade, stringer and massive cassiterite ores, which may reach 60 wt percent Sn in small lenses of almost pure cassiterite. Additionally, about 200,000 t of tin metal occurs as lower grade cassiterite disseminations in the copper-rich parts of the deposit (avg 0.25 wt % Sn).

These exceptional features of the Neves-Corvo ores call for unique ore-forming processes, which probably included a history of metal supply involving multiple sources. Its abnormal ore geochemistry, together with both stable and radiogenic isotope data, suggests that its generative sea-floor hydrothermal system may have included metal and fluid contributions from a deep-seated magmatic or metamorphogenic source, as well as mainly modified seawater, which leached the footwall rocks.

The ongoing deposit-scale research in Neves-Corvo has put in evidence critical geologic and genetic factors that determined both the size and the extraordinary ore geochemistry of this deposit and, thus, ultimately, its high value. Relevant insights to integrated exploration have emerged from the identification and characterization of these factors. Also, these insights significantly widen the constraints that must be considered and applied in metallogenic modeling, thereby broadening the number and range of geologic relationships for consideration and application in future exploration projects. The collective consideration of all these understandings is especially significant in defining areas of remaining high exploration potential in long-studied districts like the Iberian pyrite belt and others worldwide.

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Contents

Special Publications of the Society of Economic Geologists

Integrated Methods for Discovery: Global Exploration in the Twenty-First Century

Richard J. Goldfarb
Richard J. Goldfarb
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Richard L. Nielsen
Richard L. Nielsen
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Society of Economic Geologists
Volume
9
ISBN electronic:
9781629490335
Publication date:
January 01, 2002

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