Indium in the Lagoa Salgada Orebody, Iberian Pyrite Belt, Portugal

Daniel P. S. de Oliveira, Diogo R.N. Rosa Instituto Nacional de Engenharia, Tecnologia e Inovação (INETI) Geological Data Centre, Apartado 7586, 2721-866 Alfragide, Portugal and CREMINER (Centro de Recursos Minerais, Mineralogia e Cristalografia), Edifício C6, piso 3, 1749-016 Lisboa, Portugal

João X. Matos Instituto Nacional de Engenharia, Tecnologia e Inovação (INETI), Dept. of Economic Geology, Rua Frei Amador Arrais, 39 R/C, 7801-902, Beja, Portugal

Fernanda Guimarães Laboratório Instituto Nacional de Engenharia, Tecnologia e Inovação (INETI), Rua da Amieira, 4465-021, S. Mamede de Infesta, Portugal

M.O. Figueiredo, Teresa P. Silva Instituto de Investigação Científica Tropical (IICT), Cryst. Miner. Centre and INETI Geological Data Centre, Apt. 7586, 2721-866 Alfragide, Portugal

Abstract. The Iberian Pyrite Belt (IPB) is one of the most 2009), the IPB at the beginning of the 21st century may outstanding ore provinces in Europe hosting some of the have lots more to offer than the traditional base and largest concentrations of massive sulphides and 22% of precious metals. Neves Corvo, a giant in terms of copper the world-class (>32 Mt) VMS orebodies. A significant content and supergiant with respect to tin tonnage, has number of (pyrite) mines are now inactive but some well documented occurrences of indium (Benzaazoua et orebodies still remain unexploited; this is the case of Lagoa Salgada. It is the most NW orebody known and al. 2003). The presence of accessory high-tech elements occurs beneath approximately 130 m of Cenozoic (In as well as Ge and Se) in inactive mines and sediments which limits interpretation solely to borehole unexploited orebodies would create a strong incentive to intersection data. The orebody is folded and interpreted look at these with a fresh point of view. Lagoa Salgada is to occur on the subvertical-overturned and intensely one of such unexploited orebodies located in the NW faulted limb of a SW verging anticline. It is hosted within Iberian Pyrite Belt sector (Oliveira et al. 1998) also a thick IPB volcanic sedimentary sequence and is made contains interesting quantities of In. Herein, we report on up of a central stockwork and a massive sulphide lens. the indium contents and mode of occurrence at Lagoa An electron microprobe study revealed consistent trace Salgada. amounts of indium in sphalerite, thus contrasting with the neighbouring Neves Corvo mine where indium is known to occur associated with stannite and stanoidite. 2 Lagoa Salgada: Deposit geology The occurrence of elevated trace amounts of indium in sphalerite from Lagoa Salgada could make this orebody The Lagoa Salgada deposit is the most north-westward an attractive economic target beyond the traditional tin - ore body of the IPB and occurs beneath approximately base metal suite so far extracted in the Iberian Pyrite 130 m of Cenozoic sedimentary cover (Fig. 1), thus Belt. limiting the interpretation solely to borehole data. The

Keywords: Iberian Pyrite Belt; massive sulphides; deposit is folded and interpreted to occur mostly on the indium; Lagoa Salgada subvertical - overturned and intensely faulted limb of an SW verging anticline. Lagoa Salgada is further offset by a E-W trending Alpine fault in the north, with 50 m 1 Introduction subsidence of the northern block, but whose horizontal amount and sense of displacement is unknown (Matos et The Iberian Pyrite Belt (IPB), with more than 1600 Mt al., 2000). The deposit has been described as composed of massive sulphides originally in place and about 250 Mt of stockwork ore is one of the most outstanding ore provinces in Europe, hosting one of the largest concentrations of sulphides in the earth’s crust and 22% of the world-class (>32 Mt) VMS orebodies (Tornos 2006). The IPB hosts 82 inactive or working mines, as well as more than 38 ore showings of massive sulphides or stockworks (Tornos et al. 2000). Many of these inactive mines and the more recently discovered but yet unexploited orebodies remain in this state mainly due to economic constraints. Given the growing worldwide consumption and short static depletion times of high- tech elements, particularly for indium (Reiser et al.

424 "Smart Science for Exploration and Mining" P. J. Williams et al. (editors) Figure 1. Geological setting of the Iberian Pyrite Belt and the (EPMA) was carried out using a fully automated JEOL location of the Lagoa Salgada orebody as well as a few other JXA-8500F microprobe equipped with five wavelength mines within the IPB. A – Aljustrel; NC – Neves Corvo; B – dispersive (WDS) and one energy dispersive (EDS) Barrigão. (Adapted after Rosa et al. 2009). spectrometers. 20 kV and 20 nA were used to produce an

electron beam with a diameter of 1 μm to analyse major of a Central Stockwork and a Massive Sulphide Lens in and minor elements - S, Fe, Cu, Zn, Pb, Cd, As, Se, Sb, the NW (Matos et al. 2003). Bi – plus trace elements - Mn, Ge, W, Ag, Hg, In, Sn.

Special care was taken when defining the analytical The Lagoa Salgada central stockwork occurs within a conditions to account for the interference of tin upon thick; > 700 m, Volcanic Sedimentary Complex (VSC) indium detection. sequence of which the base is not known (Matos et al. Table 1 illustrates the analytical results for pyrite, 2000). The true thickness of the stratigraphic sequence tetrahedrite and sphalerite from six borehole samples - is difficult to determine, due to disruption and repetition LS, Lagoa Salgada; locations (1 to 22) as indicated in of the VSC stratigraphy by several thrust faults. The Fig. 7 of Oliveira et al. (1998); depths in meters – at mineralization in the central stockwork occurs in a points corresponding to pyrite, tetrahedrite and relatively thick (>300 m) interval, as metric semi- sphalerite grains. EPMA study showed that the highest massive sulphide lenses and related stockwork indium contents were associated with sphalerite as structures, and is mainly hosted by thick (up to 250 m) noticed by preceding authors using transmission electron and strongly chloritised quartz-phyric rhyodacite unit. microscopy (e.g., Pattrick et al. 1993). However, under Additionally, there is a feldspar- and quartz-phyric the instrumental conditions up to now used it was not rhyodacite that dominates the sequence hosting the possible to detect discrete In-bearing mineral phases in Massive Sulphide Lens in the NW. The two rhyodacites sphalerites from Lagoa Salgada. are distinguished by their phenocryst content and geochemical signature. Table 1. Data obtained for samples from 6 Lagoa

Salgada boreholes. Sample reference indicates the 3 Lagoa Salgada: Ore mineralogy borehole number and the depth at which the sample was collected. A dash (-) indicates non-detection of the The ore mineralogy in the Lagoa Salgada massive element. sulphide deposit is strongly controlled by NNW-SSE fault zones. Deformation caused intense ore brecciation and pyrite annealing but primary colloformic and Sample LS5 - LS6 - LS22 LS1 - 441.5 LS14- 155.7 179.7 - 156 226.3 LS4 - 172.7 framboidal textures are still locally preserved in pyrite 2 4 5 3 11 17 4 9 Point (Gaspar et al. 1993; Matos et al. 2000). The sub vertical Pyrite Tetrahe. Sphalerite deposit consists of two main ore assemblages: massive S 52.70051.860 52.370 51.860 24.910 33.550 33.060 33.320 sulphides and gossan (paleo weathering alteration). As 0.041 0.753 - 0.189 0.236 - - - Massive sulphides – Pyrite is the dominant ore Fe 46.62046.840 46.860 47.020 2.570 3.270 4.000 4.260 mineral. Interstitial with pyrite occur sphalerite, Sb - 0.030 0.051 0.059 29.430 - - - arsenopyrite, tetrahedrite-tennantite, galena, löllingite, Zn 0.011 0.008 0.015 - 5.230 61.540 62.310 61.630 chalcopyrite, cassiterite, stannite, meneghinite and In 0.008 0.004 0.007 0.004 0.010 0.021 0.019 0.027 pyrrhotite. Sphalerite commonly presents inclusions of Cd - - - 0.020 - 0.514 0.493 0.344 chalcopyrite and rarely stannite (Gaspar et al. 1993; Se - - 0.006 0.024 - 0.001 0.014 0.034 Oliveira et al. 1998, Matos et al. 2000). Arsenopyrite Mn - - - - 0.010 - - - occurs first in the paragenetic sequence relative to Hg - - 0.024 - 0.116 - - - sphalerite, chalcopyrite and galena in the massive Ag 0.017 - 0.053 0.013 0.162 - - - mineralization. The orebody is eroded and the Ge - - 0.008 - - - - - palaeosupergene alteration is represented by chalcocite Cu 0.014 - 0.075 0.016 37.330 0.015 - - and covellite phases below the oxidation zone Sn - - - 0.014 - - - 0.009 (haematitic gossan). Bi 0.052 0.178 0.114 0.201 0.074 - - - Gossan - In the gossan zone oxidised massive sulphides W 0.019 0.044 0.022 0.039 - - - - are represented by goethite, haematite, Ag-Hg amalgam, Pb - - - - - 0.107 0.034 - chalcocite, neodigenite, covellite, bornite and mimetite Total 99.48 99.72 99.60 99.46 100.08 98.74 99.93 99.62 (Gaspar et al. 1993; Oliveira et al. 1998). 5 Comments and discussion 4 Indium in Lagoa Salgada Benzaazoua et al (2003) showed that discrete, albeit very As in Neves Corvo, the Lagoa Salgada deposit also small, grains of indium-carrying phases occur in selected contains indium. Whole rock analyses of several samples samples from the Neves Corvo ore deposit in tin-and collected for this study from boreholes showed contents copper-minerals, namely stannite (CuFeSnS4) and up to 90 ppm In. stanoidite (Cu8Fe3Sn2S12). At Lagoa Salgada present Polished sections of massive sulphide orebody electron microprobe data indicate that indium is samples were first studied in reflected light under the preferentially hosted in Fe-rich sphalerite, possibly as optical microscope to identify domains of interest for the submicron inclusions (nanophases, as prospectively electron microprobe study. Electron-probe microanalysis referred by Figueiredo et al. 2007).

Proceedings of the Tenth Biennial SGA Meeting, Townsville, 2009 425 Trace amounts of indium have commonly been deposits: digging deeper into the crystal chemistry of indium detected in sphalerite, which is the main source of the chalcogenides. In: Andrew CJ et al. Digging Deeper. metal (Johan 1988; Kieft and Damman 1990; Pattrick et Proceedings of the Ninth Biennial SGA Meeting, Dublin/Ireland 2007, p. 1355-1357. al. 1993; Scharz-Schampera and Herzig 2002). Indium is Gaspar OC, Oliveira VMJ, Matos JMX (1993) Nota preliminar also reported associated with copper (chalcopyrite) ores sobre os sulfuretos maciços da Jazida da Lagoa Salgada, Faixa (Kieft and Damman 1990). Piritosa Ibérica, Portugal. 11º Cong. Geoquímica Países The formation of In-carrying sulphide phases may be Língua Portuguesa. Mus. Lab. Miner. Geol. Fac. Ciências do fostered by various processes (Schwarz-Schampera and Porto, Memórias nº3: 239-242. Ivanov VV (1963). Indium in some igneous rocks of the USSR (in Herzig 2002): primary precipitation from a mineralising Russian). Geokhimiya, 1101-1110 (Translt. Geochemistry, hydrothermal fluid, remobilisation due to hydrothermal 1963, 1150-1160). zone refining or metamorphic overprinting and local Johan, Z (1988) Indium and Germanium in the structure of enrichment by replacement of primary low temperature sphalerite: An example of coupled substitution with copper. sulphides (namely, sphalerite) as a result from diffusion Mineralogy and Petrology 39: 211-229. processes and coupled substitution at high temperatures. Kieft K, Damman AH (1990) Indium-bearing chalcopyrite and sphalerite from the Gasborn area, West Bergslagen, central In general, chalcopyrite ores contain the largest amount Sweden. Mineralogical Magazine 54: 109-112. of indium, being twice as rich as sphalerites from the Matos JX, Barriga FJAS, Oliveira VMJ, Relvas JMRS, Conceição same deposit (Ivanov et al. 1963). However, sphalerite is P (2000) The geological structure and hydrothermal alteration the most important indium-bearing mineral and indium of the Lagoa Salgada deposit (Iberian Pyrite Belt – Sado metal is mainly extracted from zinc concentrates. Tertiary Basin, Portugal). Volcanic Environments and Massive Accordingly, high indium concentrations are closely Sulfide Deposits – SEG/CODES International Conf. Abstract Vol., Tasmania, Australia, 119-121. associated with elevated copper contents and there is Matos JX, Barriga FJAS, Oliveira V (2003) Alunite veins versus often a strong positive correlation between indium and supergene kaolinite/halloysite alteration in the Lagoa Salgada, copper. There is in addition, evidence that processes such Algares and S. João (Aljustrel) and S. Domingos massive as those responsible for the formation of “chalcopyrite sulphide deposits, Iberian Pyrite Belt, Portugal Ciências da disease” are responsible for the formation of indium- Terra (UNL), Lisboa, V, B56-B59. Oliveira V, Matos JX, Bengala M, Silva N, Sousa P, Torres L bearing, iron-rich sphalerite containing roquesite (1998) Geology and Geophysics as Successful Tools in the (Scharz-Schampera and Herzig 1997). Discovery of the Lagoa Salgada Orebody (Sado Tertiary Basin Also, indium-bearing deposits are commonly closely - Iberian Pyrite Belt), Grândola, Portugal. Mineralium associated with porphyritic, felsic to intermediate Deposita, 33: 170-187. volcanic and intrusive host rocks that display evidence of Pattrick RAD, Dorling M, Polya, DA (1993) TEM study of alteration processes, e.g. silicification, sericitisation and indium-and copper-bearing growth-banded sphalerite. Canadian Mineralogist 31: 105-117. chloritisation (Schwarz-Schampera and Herzig 2002). Reiser F, Rodrigues C, Rosa D (2009) High-technology elements The occurrence of significant trace amounts of for thin-film photovoltaic applications: A demand-supply indium in sphalerite from the Lagoa Salgada coupled outlook on the basis of current energy and PV market growth with the fact that this orebody seems to contain some of scenarios. Proceedings of the Fith User Forum Thin-Film the key host rock and mineralogical characteristics – Photovoltaics. Würzburg, Germany, 120-125. namely, chloritised intermediate volcanic host rocks Rosa DRN, Finch AA, Andersen T, Inverno CMC (2009). U-Pb geochronology and Hf isotope ratios of magmatic zircons from (Matos et al. 2000; 2003) - could make it an attractive the Iberian Pyrite Belt. Mineralogy and Petrology 95, 47-69. economic exploration target beyond the traditional tin - Schwarz-Schampera U, Herzig PM (1997) Geochemistry of base metal suite that is extracted in the Iberian Pyrite indium in VMS deposits: Implication from active Belt. hydrothermal vents in the southern Lau Basin (SW- Pacific). Research focused on the identification of discrete In: Papunen H (ed.) Mineral Deposits: Research and Exploration – Where do they meet? Proceedings of the fourth indium nanophases in sphalerite from Lagoa Salgada is Biennaial SGA meeting, Turku, Finland, 379-382 in progress. Schwarz-Schampera U, Herzig PM (2002) Indium. Geology, Mineralogy and Economics. Springer-Verlag Berlin Acknowledgements Heildelberg New York, 257p. Tornos F (2006) Environment of formation and styles of volcanogenic Massive sulfides: The Iberian Pyrite Belt. Ore This work was financially supported by the Portuguese Geology Reviews 28: 259-307. Foundation for Science and Technology (FCT-MCTES) Tornos F, Barriga F, Marcoux E, Pascual E, Pons JM, Relvas J, through project PTDC/CTE-GIN/67027/2006 (INCA - Velasco F (2000) The Iberian Pyrite Belt. In: Large, R.R., Characterisation of crucial mineral resources for the Blundell, D.J. (Eds.), Database on Global VMS Districts, development of renewable energy technologies: The CODES-GEODE, pp. 19–52. Iberian Pyrite Belt ores as a source of indium and other high-technology elements).

References

Benzaazoua M, Marion P, Pinto A, Migeond H, Wagnere FE (2003) Tin and indium mineralogy within selected samples from the Neves Corvo ore deposit (Portugal): A multidisciplinary study. Minerals Engineering 16: 1291–1302. Figueiredo MO, Silva TP, de Oliveira DPS, Rosa DRN (2007) Searching for In-carrier minerals in polymetallic sulfide

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