Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/185
Comunicações Geológicas (2014) 101, Especial II, 825-828
IX CNG/2º CoGePLiP, Porto 2014
ISSN: 0873-948X; e-ISSN: 1647-581X
High-Tech Metals in the zinc-rich massive ores of the
Neves Corvo Deposit
Metais de alta tecnologia nos minérios maciços zincíferos do
depósito de Neves Corvo
A. Pinto1*, J. M. R. S. Relvas1, J. R. S. Carvalho1, Y. Liu2,
N. Pacheco3, F. Pinto3, R. Fonseca3
Artigo Curto
Short Article
© 2014 LNEG – Laboratório Nacional de Geologia e Energia IP
Abstract: The increasing consumption of indium and selenium has
significantly stimulated their extraction output, adding economic
interest to critical metal sources that a few years ago were either
unknown, or unconsidered. In addition to Cu (Sn and Ag as byproducts), recent surface drill programs looking for further
development of the Neves Corvo mine have defined, by the end of
2013, 113 Mt of zinc resources @ 5.3% Zn, which turned the deposit
into one of the world’s largest undeveloped zinc resources.
Promising by-products can possibly include some high-tech metals
such as In and Se. In Neves Corvo there is a general positive
correlation between In and Cu at the deposit scale, which contrasts
with most other In-bearing VHMS deposits, where In typically
follows Zn. At Neves Corvo, indium grades vary within the range 20
to 1100 ppm (1.1 kg/ton), whereas selenium grade commonly ranges
between 20 and 40 ppm, although in some lead-rich domains
selenium grades can reach up to 8000 ppm Se (avg. 500 ppm).
Despite the general copper-indium coupling in the deposit, there is an
obvious interest in evaluating the potential of the zinc-rich ores in
terms of high-tech metals contents as these elements are widely
acknowledged as adding value to the zinc concentrates, thus being
payed by most zinc smelters. In this study, we present the most
recent available data on the metal distribution and mineralogy of
indium and selenium in the massive zinc and lead-zinc ores of the
Neves Corvo deposit. This deposit may represent in the future a
promising target for high-tech metals, such as indium and selenium.
Keywords: Indium, Selenium, VHMS deposits, Neves Corvo,
Iberian Pyrite Belt.
Resumo: O crescente aumento do consumo de índio e selénio tem
estimulado significativamente a sua taxa de extração, conferindo
interesse económico a fontes de metais críticos que, há poucos anos
atrás, eram desconhecidas ou não consideradas. Em adição ao Cu (Sn
e Ag como subprodutos), um recente programa de sondagens visando
o futuro desenvolvimento da mina de Neves Corvo, permitiu definir,
em finais de 2013, 113 Mt de recursos de zinco @ 5,3% Zn, tornando
o depósito um dos maiores recursos zincíferos ainda por explorar, a
nível mundial. Alguns subprodutos prometedores podem incluir
metais como o In e o Se. Em Neves Corvo, existe uma correlação
positiva geral entre o In e o Cu à escala do depósito, que contrasta
com a maioria dos restantes depósitos VHMS ricos em índio, onde
este metal segue tipicamente o Zn. Em Neves Corvo, os teores em
índio variam entre 20 e 1100 ppm (1,1 kg/ton), enquanto os teores
em selénio variam normalmente entre 20 e 40 ppm, ainda que alguns
domínios ricos em chumbo possam atingir valores de 8000 ppm Se
(500 ppm, em média). Apesar da correlação positiva entre o cobre e o
índio ao nível do depósito, existe um interesse óbvio na avaliação do
potencial dos minérios zincíferos em termos de metais de alta
tecnologia, uma vez que existe um reconhecimento generalizado de
que estes elementos acrescentam valor aos concentrados de zinco,
sendo por isso pagos pela generalidade das metalurgias do zinco.
Neste estudo, são apresentados os mais recentes dados disponíveis
relativos à distribuição metálica e mineralogia do índio e selénio nos
minérios maciços de zinco e de chumbo-zinco do depósito de Neves
Corvo. Este depósito pode vir a representar no futuro um alvo
promissor para metais de alta tecnologia tais como o índio e o
selénio.
Palavras-chave: Índio, Selénio, Depósitos VHMS, Neves Corvo,
Faixa Piritosa Ibérica.
1
CREMINER/LARSyS, University of Lisbon, Faculty of Sciences, Geology
Department, Edifício C6, Piso 4, Campo Grande, 1749-016 Lisboa, Portugal.
2
University of Toronto, Department of Earth Sciences, 22 Russell Street,
Toronto, Ontario, M5S 3B1, Canada.
3
SOMINCOR, Sociedade Mineira de Neves–Corvo, S.A., Apartado 12, 7780909 Castro Verde, Portugal.
*
Corresponding author / Autor correspondente: [email protected]
1. Introduction
Over the last decades, the global demand for indium
continuously increased, especially due to the critical need
of this metal for the production of flat panel displays (over
70% of the world In output). Predicting whether indium
will be in a deficit or in an oversupply situation is rather
difficult. The exact production and consumption figures
for indium are uncertain, and the future trends are
influenced by many factors such as the world economy in
general, or more specific industry trends (i.e. the mining,
electronics or energy sectors). Notwithstanding, the
steadily increasing consumption that we observe today has
significantly stimulated the extraction output, adding
economic interest to indium sources that a few years ago
were not even known or considered. Up to now, indium
has been mainly a by-product of base metal production and
as such, clear production data is not readily available. For
primarily economic reasons, indium was originally only
extracted from zinc and lead concentrates containing at
least 500 ppm In. Due to improvements in the extraction
technology, combined with the economics of higher prices,
826
indium is now recovered also as a by-product of a wider
range of base metals including tin, copper, and other
polymetallic ores, which concentrates may contain
indium grades as little as 100 ppm. Some of the mines
currently producing indium are VHMS deposits (e.g.,
Kidd Creek, Ontario, Canada, avg. 270 ppm In in the
concentrate; Polaris, Northwest Territories, Canada, avg.
100 ppm In in the concentrate (Rodier, 1990; SchwarzSchampera & Herzig, 2002). Indium minerals such as
roquesite (Cu In S2) are quite rare and, thus, most indium
is allocated in minerals where this metal does occur as a
trace component. Indium tends to concentrate in base
metal sulphide/sulfosalt minerals, especially those having
tetragonal coordination (e.g. sphalerite, stannite,
stannoidite and other stannite group minerals,
tetrahedrite-tenantite, pyrrhotite, bornite, chalcopyrite
and others). The formation of indium-bearing sulphides is
favoured by a number of mechanisms, such as: i) primary
co-precipitation
from
hydrothermal
fluids;
ii)
remobilization and recrystallization due to hydrothermal
zone refining or metamorphic overprinting; iii)
enrichment by replacement of primary low temperatures
sulphides; iv) diffusion processes and coupled
substitution at high T. The main substitution mechanisms
for indium include: Zn replacement by Cu+In, in
sphalerite; Fe3+ replacement by Cu+In, in chalcopyrite;
and Cu+Sn replacement by (Fe,Zn)+In, in the stannite
group minerals.
Selenium is one of the chalcogen elements having
semiconductor properties. It is chemically similar to
sulphur for which it substitutes in many minerals and
synthetic compounds. Once again, there are no primary
“selenium ores”. Primary selenium is produced mainly as
a by-product of base-metal mining and processing. More
than 90% of the selenium supply is presently derived
from copper ores, and most of the remaining 10% comes
out from lead ores. Selenium is used in many
applications, some of the major ones being: decolourizer
for glass, metallurgical additive to some varieties of
ferrous and nonferrous alloys, constituent in cadmium
sulfo-selenide pigments, photoreceptor in xerographic
copiers, and semiconductor in electrical rectifiers and
photocells. The production of selenium should easily be
sustainable. The resources are adequate and the
production process appears to incur no environmental
issues that cannot be resolved. The use of selenium
appears unlikely to outgrow the supply. Presently, the
larger worldwide producers of selenium are Belgium,
Canada, USA and Japan, which collectively represent ca.
83% of the global supply.
2. Neves Corvo
The Neves Corvo deposit is located at the southeastern
termination of the Rosário-Neves Corvo antiform, in the
Portuguese part of the Iberian Pyrite Belt. Seven massive
and stringer sulphide orebodies have already been
identified in the Neves Corvo camp: Neves, Corvo,
Graça, Lombador, Zambujal, Semblana and Monte
A. Pinto et al. / Comunicações Geológicas (2014) 101, Especial II, 825-828
Branco. Since 1988, the Neves Corvo mine has been a
significant copper producer, representing the present-day
largest base metal-mining operation in Western Europe.
The deposit stands out among the volcanic-hosted
massive sulphide (VHMS) deposits of the world. In
addition to Cu (plus Sn and Ag as by-products), recent
surface drill programs looking for further development of
the mine have defined, by the end of 2013, 113 Mt of
zinc resources @ 5,3% Zn, turning the deposit into one of
the world’s largest undeveloped zinc resources. Other
promising by-products can possibly include some hightech metals such as In and Se.
The distribution and mineral allocation of indium and
selenium in the Neves Corvo ores have been object of
evaluation throughout the last years (Pinto, A.,
Somincor’s unpublished internal reports). Some
preliminary and partial results have already been
published (e.g., Benzaazoua et al., 2003; Pinto et al.,
1994; 1995 and 2013; Carvalho et al., 2013) and a
general overview, embracing all orebodies, and all types
of ores are being prepared (Pinto et al., in prep.).
At Neves Corvo, indium grades vary within the range
20 to 1100 ppm (1.1 kg/ton), whereas selenium grade
commonly ranges between 20 and 40 ppm, although in
some lead-rich domains selenium grades can reach up to
8000 ppm Se (avg. 500 ppm). Unlike other In-bearing
VHMS deposits, where indium follows the zinc-rich ores,
in Neves Corvo there is a general positive correlation
between In and Cu at the deposit scale (Pinto et al., 2013;
Carvalho et al., 2013). Indium couples with Cu grades in
the Cu-rich ores (especially in the bornite ores and in
some stringer ores), whereas Se associates either with the
copper or the lead-zinc-rich massive ores (Pinto et al.,
2013; Carvalho et al., 2013).
Here we present the most recent data available on the
metal distribution and mineralogy of indium and
selenium in the massive zinc and lead-zinc ores of the
Neves Corvo deposit.
3. Massive zinc and lead-zinc ores: mineralogy
This study refers to two massive sulphide ore types in the
Neves Corvo deposit: the massive zinc ore –MZ – and the
massive lead-zinc ore - MZP. The mineralogy and the InSe geochemistry of these ores have been evaluated ground
on more than 7000 samples that represent five orebodies of
the Neves Corvo deposit (Neves, Corvo, Graça, Zambujal
and Lombador). From a mineralogical point of view, both
the MZ and the MZP ores are formed by predominant
pyrite, sphalerite and galena, in variable proportions, and
subordinate, but variably abundant chalcopyrite and
arsenopyrite. Minor constituents also include fahlores,
bournonite, stannite and junoite. The later mineral is a PbBi sulfosalt (Pb3 Cu2 Bi8 [S,Se]16), which is here described
for the first time either at the Neves Corvo deposit, or at
the Iberian Pyrite Belt (Pinto et al., 2013), (Table 1; Fig.
1). In these two types of ore, gangue minerals represent
less than 7% in volume, and are mainly composed of
quartz, phylossilicates and carbonates.
High-Tech Metals in Neves Corvo Zinc Ores
Table 1. Electron Microprobe results of the junoite crystals found in
Neves Corvo (3) and comparisons with junoite occurrences in Juno
(Australia) and Kidd Creek (Canada) deposits.
Tabela 1. Resultados da análise por microssonda electrónica da junoite em
Neves Corvo (3) e sua comparação com as ocorrências de junoite nos
depósitos de Juno (Austrália) (1) e Kidd Creek, Canada (2).
827
contents in sphalerite range from a minimum of 230 ppm
in the MZ ores of the Neves orebody to more than 8000
ppm in the MZ Lombador ores (Table 3). Although not
representative, indium was occasionally detected as a trace
element in other sulphides, such as chalcopyrite (up to 600
ppm) and tetrahedrite (up to 400 ppm).
Table 2. Average indium and selenium grades in the MZ and MZP ores of
the Neves Corvo deposit.
Tabela 2. Teores médios de índio e de selénio nos minérios MZ e MZP do
jazigo de Neves Corvo.
Table 3. Main In-bearing and Se-bearing minerals in the MZ and MZP
ores of the Neves Corvo deposit.
Tabela 3. Principais minerais portadores de índio e portadores de selénio
nos minérios MZ e MZP do jazigo de Neves Corvo.
Fig. 1. Junoite (white) together with fahlore (light gray), sphalerite (dark
gray), chalcopyrite (yellow) and pyrite (pale yellow) in the MZP ores
from the Zambujal orebody.
Fig. 1. Junoite (branco) com cobres cinzentos (cinza claro), esfalerite
(cinza escuro), calcopirite (amarelo) e pirite (amarelo pálido), presente
nos minérios MZP da massa do Zambujal.
4. MZ and MZP ores: indium distribution and mineral
allocation
The average indium content of the MZ and MZP ore types
in the five orebodies studied are listed in Table 2. The
overall average indium content for these orebodies is 140
ppm in MZ ores, and 90 ppm in MZP ore. However, there
is some variability in the way indium distributes among
the various orebodies, ranging from averaged values of 30
to 215 ppm. Graça, Lombador, Corvo and Zambujal
orebodies have higher average grades in indium - 215,
152, 139 and 134 ppm, respectively - whereas in the Neves
orebody, the average indium content is very low - only 33
ppm. A similar low value – 45 ppm – was obtained for the
MZ ores of the South sector of Lombador orebody.
The major indium-bearing minerals in the MZ and
MZP ores are sphalerite and stannite group minerals, fact
that, in some point in the future, might be quite convenient
from a mineral processing point of view. Average indium
5. MZ and MZP ores: selenium distribution and
mineral allocation
The average selenium content of the MZ and MZP ore
types in the five orebodies studied are listed in Table 2.
The overall average selenium content for these orebodies
is 150 ppm in MZ ores, and 650 ppm in MZP ore. Again,
there is some variability concerning to the selenium
distribution among the various orebodies, ranging from
average values of 10 to 3220 ppm. By far, the Zambujal
orebody have the highest selenium average concentration,
reaching average values of 3220 ppm in the lead-zinc
massive ores (MZP).
Regardless of the orebody considered, galena is always
the major carrier of selenium in the two types of ore
studied. The selenium mineralogy is represented by
selenium-bearing galena containing up to 30% of
clausthalite (PbSe) end member. Average selenium
contents in galena range from a minimum of 260 ppm in
828
the MP ores of the Lombador orebody, up to more than
1.5% in the MZ Lombador ores and 2.3% in the MZ
Zambujal ores (Table 3). Trace contents of selenium were
also detected in sphalerite and in fahlores group minerals.
As reported above, junoite, a rare selenium-bearing phase,
was identified in the MZP ores of the Zambujal orebody.
Galena also contains some silver (ranging from 390 ppm
in the MZ ore of the Zambujal orebody to 1190 ppm in the
MZ ores of the Neves orebody).
6. Final remarks
The Neves Corvo deposit may represent in the future a
promising target for high-tech metals, such as indium and
selenium. The relative abundance, spatial distribution and
mineral allocation of these metals in the Neves Corvo
mineralizing system are currently under detailed
investigation. Deciphering these variables has significant
meanings under several different perspectives, including
(i) the metallogenic understanding of their occurrence,
spatial distribution and relative abundance, (ii) their
mineral processing implications, and (iii) the economic
impact of their exploitation. The ores from the Kidd Creek
deposit, which is now a leading global producer of indium,
have in average 106 ppm of indium. Indium and selenium
grades, mineralogy, textures and mineral geochemistry of
the Neves Corvo deposit place various of its ore types and
orebodies as potentially interesting as sources of indiumand/or selenium-rich concentrates.
A. Pinto et al. / Comunicações Geológicas (2014) 101, Especial II, 825-828
Acknowledgements
This is a contribution to project ZHINC (PTDC/CTEGIX/114208/2009; Foundation for Science and Technology
(FCT-MCTES).
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