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 que estes elementos acrescentam valor aos concentrados de zinco, significantly stimulated their extraction output, adding economic sendo por isso pagos pela generalidade das metalurgias do zinco. interest to critical metal sources that a few years ago were either Neste estudo, são apresentados os mais recentes dados disponíveis unknown, or unconsidered. In addition to Cu (Sn and Ag as by- relativos à distribuição metálica e mineralogia do índio e selénio nos products), recent surface drill programs looking for further minérios maciços de zinco e de chumbo-zinco do depósito de Neves development of the Neves Corvo mine have defined, by the end of Corvo. Este depósito pode vir a representar no futuro um alvo 2013, 113 Mt of zinc resources @ 5.3% Zn, which turned the deposit promissor para metais de alta tecnologia tais como o índio e o into one of the world’s largest undeveloped zinc resources. selénio. Promising by-products can possibly include some high-tech metals Palavras-chave: Índio, Selénio, Depósitos VHMS, Neves Corvo, such as In and Se. In Neves Corvo there is a general positive Faixa Piritosa Ibérica. 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 1CREMINER/LARSyS, University of Lisbon, Faculty of Sciences, Geology to 1100 ppm (1.1 kg/ton), whereas selenium grade commonly ranges Department, Edifício C6, Piso 4, Campo Grande, 1749-016 Lisboa, Portugal. between 20 and 40 ppm, although in some lead-rich domains 2University of Toronto, Department of Earth Sciences, 22 Russell Street, selenium grades can reach up to 8000 ppm Se (avg. 500 ppm). Toronto, Ontario, M5S 3B1, Canada. Despite the general copper-indium coupling in the deposit, there is an 3SOMINCOR, Sociedade Mineira de Neves–Corvo, S.A., Apartado 12, 7780- obvious interest in evaluating the potential of the zinc-rich ores in 909 Castro Verde, Portugal. terms of high-tech metals contents as these elements are widely *Corresponding author / Autor correspondente: [email protected] 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 1. Introduction Neves Corvo deposit. This deposit may represent in the future a promising target for high-tech metals, such as indium and selenium. Over the last decades, the global demand for indium Keywords: Indium, Selenium, VHMS deposits, Neves Corvo, continuously increased, especially due to the critical need Iberian Pyrite Belt. of this metal for the production of flat panel displays (over

Resumo: O crescente aumento do consumo de índio e selénio tem 70% of the world In output). Predicting whether indium estimulado significativamente a sua taxa de extração, conferindo will be in a deficit or in an oversupply situation is rather interesse económico a fontes de metais críticos que, há poucos anos difficult. The exact production and consumption figures atrás, eram desconhecidas ou não consideradas. Em adição ao Cu (Sn for indium are uncertain, and the future trends are e Ag como subprodutos), um recente programa de sondagens visando influenced by many factors such as the world economy in o futuro desenvolvimento da mina de Neves Corvo, permitiu definir, general, or more specific industry trends (i.e. the mining, 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 electronics or energy sectors). Notwithstanding, the nível mundial. Alguns subprodutos prometedores podem incluir steadily increasing consumption that we observe today has metais como o In e o Se. Em Neves Corvo, existe uma correlação significantly stimulated the extraction output, adding positiva geral entre o In e o Cu à escala do depósito, que contrasta economic interest to indium sources that a few years ago com a maioria dos restantes depósitos VHMS ricos em índio, onde were not even known or considered. Up to now, indium 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 has been mainly a by-product of base metal production and em selénio variam normalmente entre 20 e 40 ppm, ainda que alguns as such, clear production data is not readily available. For domínios ricos em chumbo possam atingir valores de 8000 ppm Se primarily economic reasons, indium was originally only (500 ppm, em média). Apesar da correlação positiva entre o cobre e o extracted from zinc and lead concentrates containing at índio ao nível do depósito, existe um interesse óbvio na avaliação do least 500 ppm In. Due to improvements in the extraction potencial dos minérios zincíferos em termos de metais de alta technology, combined with the economics of higher prices, tecnologia, uma vez que existe um reconhecimento generalizado de 826 A. Pinto et al. / Comunicações Geológicas (2014) 101, Especial II, 825-828 indium is now recovered also as a by-product of a wider Branco. Since 1988, the Neves Corvo mine has been a range of base metals including tin, copper, and other significant copper producer, representing the present-day polymetallic ores, which concentrates may contain largest base metal-mining operation in Western Europe. indium grades as little as 100 ppm. Some of the mines The deposit stands out among the volcanic-hosted currently producing indium are VHMS deposits (e.g., massive sulphide (VHMS) deposits of the world. In Kidd Creek, Ontario, Canada, avg. 270 ppm In in the addition to Cu (plus Sn and Ag as by-products), recent concentrate; Polaris, Northwest Territories, Canada, avg. surface drill programs looking for further development of 100 ppm In in the concentrate (Rodier, 1990; Schwarz- the mine have defined, by the end of 2013, 113 Mt of Schampera & Herzig, 2002). Indium minerals such as zinc resources @ 5,3% Zn, turning the deposit into one of roquesite (Cu In S2) are quite rare and, thus, most indium the world’s largest undeveloped zinc resources. Other is allocated in minerals where this metal does occur as a promising by-products can possibly include some high- trace component. Indium tends to concentrate in base tech metals such as In and Se. metal sulphide/sulfosalt minerals, especially those having The distribution and mineral allocation of indium and tetragonal coordination (e.g. sphalerite, stannite, selenium in the Neves Corvo ores have been object of stannoidite and other stannite group minerals, evaluation throughout the last years (Pinto, A., tetrahedrite-tenantite, pyrrhotite, bornite, chalcopyrite Somincor’s unpublished internal reports). Some and others). The formation of indium-bearing sulphides is preliminary and partial results have already been favoured by a number of mechanisms, such as: i) primary published (e.g., Benzaazoua et al., 2003; Pinto et al., co-precipitation from hydrothermal fluids; ii) 1994; 1995 and 2013; Carvalho et al., 2013) and a remobilization and recrystallization due to hydrothermal general overview, embracing all orebodies, and all types zone refining or metamorphic overprinting; iii) of ores are being prepared (Pinto et al., in prep.). enrichment by replacement of primary low temperatures At Neves Corvo, indium grades vary within the range sulphides; iv) diffusion processes and coupled 20 to 1100 ppm (1.1 kg/ton), whereas selenium grade substitution at high T. The main substitution mechanisms commonly ranges between 20 and 40 ppm, although in for indium include: Zn replacement by Cu+In, in some lead-rich domains selenium grades can reach up to sphalerite; Fe3+ replacement by Cu+In, in chalcopyrite; 8000 ppm Se (avg. 500 ppm). Unlike other In-bearing and Cu+Sn replacement by (Fe,Zn)+In, in the stannite VHMS deposits, where indium follows the zinc-rich ores, group minerals. in Neves Corvo there is a general positive correlation Selenium is one of the chalcogen elements having between In and Cu at the deposit scale (Pinto et al., 2013; semiconductor properties. It is chemically similar to Carvalho et al., 2013). Indium couples with Cu grades in sulphur for which it substitutes in many minerals and the Cu-rich ores (especially in the bornite ores and in synthetic compounds. Once again, there are no primary some stringer ores), whereas Se associates either with the “selenium ores”. Primary selenium is produced mainly as copper or the lead-zinc-rich massive ores (Pinto et al., a by-product of base-metal mining and processing. More 2013; Carvalho et al., 2013). than 90% of the selenium supply is presently derived Here we present the most recent data available on the from copper ores, and most of the remaining 10% comes metal distribution and mineralogy of indium and out from lead ores. Selenium is used in many selenium in the massive zinc and lead-zinc ores of the applications, some of the major ones being: decolourizer Neves Corvo deposit. for glass, metallurgical additive to some varieties of ferrous and nonferrous alloys, constituent in cadmium 3. Massive zinc and lead-zinc ores: mineralogy sulfo-selenide pigments, photoreceptor in xerographic This study refers to two massive sulphide ore types in the copiers, and semiconductor in electrical rectifiers and photocells. The production of selenium should easily be Neves Corvo deposit: the massive zinc ore –MZ – and the sustainable. The resources are adequate and the massive lead-zinc ore - MZP. The mineralogy and the In- Se geochemistry of these ores have been evaluated ground production process appears to incur no environmental issues that cannot be resolved. The use of selenium on more than 7000 samples that represent five orebodies of appears unlikely to outgrow the supply. Presently, the the Neves Corvo deposit (Neves, Corvo, Graça, Zambujal and Lombador). From a mineralogical point of view, both larger worldwide producers of selenium are Belgium, Canada, USA and Japan, which collectively represent ca. the MZ and the MZP ores are formed by predominant 83% of the global supply. pyrite, sphalerite and galena, in variable proportions, and subordinate, but variably abundant chalcopyrite and arsenopyrite. Minor constituents also include fahlores, 2. Neves Corvo bournonite, stannite and junoite. The later mineral is a Pb- The Neves Corvo deposit is located at the southeastern Bi sulfosalt (Pb3 Cu2 Bi8 [S,Se]16), which is here described termination of the Rosário-Neves Corvo antiform, in the for the first time either at the Neves Corvo deposit, or at Portuguese part of the Iberian Pyrite Belt. Seven massive the Iberian Pyrite Belt (Pinto et al., 2013), (Table 1; Fig. and stringer sulphide orebodies have already been 1). In these two types of ore, gangue minerals represent identified in the Neves Corvo camp: Neves, Corvo, less than 7% in volume, and are mainly composed of Graça, Lombador, Zambujal, Semblana and Monte quartz, phylossilicates and carbonates. High-Tech Metals in Neves Corvo Zinc Ores 827

Table 1. Electron Microprobe results of the junoite crystals found in contents in sphalerite range from a minimum of 230 ppm Neves Corvo (3) and comparisons with junoite occurrences in Juno in the MZ ores of the Neves orebody to more than 8000 (Australia) and Kidd Creek (Canada) deposits. ppm in the MZ Lombador ores (Table 3). Although not Tabela 1. Resultados da análise por microssonda electrónica da junoite em representative, indium was occasionally detected as a trace Neves Corvo (3) e sua comparação com as ocorrências de junoite nos element in other sulphides, such as chalcopyrite (up to 600 depósitos de Juno (Austrália) (1) e Kidd Creek, Canada (2). 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 5. MZ and MZP ores: selenium 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 The average selenium content of the MZ and MZP ore overall average indium content for these orebodies is 140 types in the five orebodies studied are listed in Table 2. ppm in MZ ores, and 90 ppm in MZP ore. However, there The overall average selenium content for these orebodies is some variability in the way indium distributes among is 150 ppm in MZ ores, and 650 ppm in MZP ore. Again, the various orebodies, ranging from averaged values of 30 there is some variability concerning to the selenium to 215 ppm. Graça, Lombador, Corvo and Zambujal distribution among the various orebodies, ranging from orebodies have higher average grades in indium - 215, average values of 10 to 3220 ppm. By far, the Zambujal 152, 139 and 134 ppm, respectively - whereas in the Neves orebody have the highest selenium average concentration, orebody, the average indium content is very low - only 33 reaching average values of 3220 ppm in the lead-zinc ppm. A similar low value – 45 ppm – was obtained for the massive ores (MZP). MZ ores of the South sector of Lombador orebody. Regardless of the orebody considered, galena is always The major indium-bearing minerals in the MZ and the major carrier of selenium in the two types of ore MZP ores are sphalerite and stannite group minerals, fact studied. The selenium mineralogy is represented by that, in some point in the future, might be quite convenient selenium-bearing galena containing up to 30% of from a mineral processing point of view. Average indium clausthalite (PbSe) end member. Average selenium contents in galena range from a minimum of 260 ppm in 828 A. Pinto et al. / Comunicações Geológicas (2014) 101, Especial II, 825-828 the MP ores of the Lombador orebody, up to more than Acknowledgements 1.5% in the MZ Lombador ores and 2.3% in the MZ This is a contribution to project ZHINC (PTDC/CTE- Zambujal ores (Table 3). Trace contents of selenium were GIX/114208/2009; Foundation for Science and Technology also detected in sphalerite and in fahlores group minerals. (FCT-MCTES). 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 References in the MZ ore of the Zambujal orebody to 1190 ppm in the Benzaazoua, M., Marion, P., Pinto, A., Migeon, H., Wagner, F.E., MZ ores of the Neves orebody). 2003. Tin and indium mineralogy within selected samples from the Neves-Corvo ore deposit (Portugal): A multidisciplinary study. Minerals Engineering, 16(11), 1237-1325. 6. Final remarks Carvalho, J.R.S., Fernandes, A.S., Moreira, B.B., Pinto, A., Relvas, The Neves Corvo deposit may represent in the future a J.M.R.S., Pacheco, N., Pinto F., Fonseca, R., 2013. Hydrothermal promising target for high-tech metals, such as indium and Alteration and Ore Mineralogy at the Lombador Massive Sulphide Orebody, Neves Corvo, Portugal: an on-going study. 12th SGA selenium. The relative abundance, spatial distribution and Biennial Meeting - “Mineral Deposits Research for High-Tech mineral allocation of these metals in the Neves Corvo World”. Uppsala, Sweden. mineralizing system are currently under detailed Pinto, A., Bowles, J.F.W., Gaspar, O.C., 1994. The Mineral investigation. Deciphering these variables has significant Chemistry and textures of wittichenite, miharaite, carrolite, meanings under several different perspectives, including mawsonite and In-Bi-Hg-Tennantite from Neves Corvo (i) the metallogenic understanding of their occurrence, (PORTUGAL). IMA 94, XVI General Meeting of IMA, Pisa, Italy. spatial distribution and relative abundance, (ii) their Pinto, A., Ferreira, A., Bowles, J.F.W., 1995. Caracterização de mineral processing implications, and (iii) the economic minerais raros do Jazigo de Neves-Corvo e suas implicações metalogénicas. IV Congresso Nacional de Geologia, Universidade impact of their exploitation. The ores from the Kidd Creek do Porto – Faculdade de Ciências Museu e Laboratório deposit, which is now a leading global producer of indium, Mineralógico e Geológico, Memória nº4, 665 – 670. have in average 106 ppm of indium. Indium and selenium Pinto, A., Relvas, J.M.R.S., Carvalho, J.R.S., Pacheco, N., Liu, Y., grades, mineralogy, textures and mineral geochemistry of 2013. Mineralogy and distribution of Indium and Selenium metals the Neves Corvo deposit place various of its ore types and within zinc-rich ore types of the Neves Corvo deposit, Portugal. orebodies as potentially interesting as sources of indium- GOLDSCHMIDT2013, Florence, Italy. and/or selenium-rich concentrates.