This is the author’s version of a work that was submitted/accepted for publication in the following source: Frost, Ray L., Xi, Yunfei, Scholz, Ricardo, & Tazava, Edison (2013) Spectroscopic characterization of the phosphate mineral florencite-La – LaAl3(PO4)2(OH, H2O)6, a potential tool in the REE mineral prospection. Journal of Molecular Structure, 1037, pp. 148-153. This file was downloaded from: https://eprints.qut.edu.au/61339/ c Copyright 2013 Elsevier B.V. All rights reserved. This is the author’s version of a work that was accepted for publication in Journal of Molecular Structure. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and toher quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Molecular Structure, [1037, (2013)] http://dx.doi.org/10.1016/j.molstruc.2012.12.045 Notice: Changes introduced as a result of publishing processes such as copy-editing and formatting may not be reflected in this document. For a definitive version of this work, please refer to the published source: https://doi.org/10.1016/j.molstruc.2012.12.045 Spectroscopic characterization of the phosphate mineral florencite-La – LaAl 3 (PO 4 ) 2 (OH, H 2 O) 6 , a potential tool in the REE mineral prospection Ray L. Frosta•, Yunfei Xia, Ricardo Scholzb, Edison Tazavab a School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. b Geology Department, School of Mines, Federal University of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, MG, 35,400-00, Brazil • Author to whom correspondence should be addressed (r.frost@qut.edu.au) P +61 7 3138 2407 F: +61 7 3138 1804 1 Abstract We have studied bluish green crystals of the mineral florencite-(La) from Serra dos Carajás, Pará, Brazil. Qualitative chemical analysis shows a La and Al phosphate with traces of Ce, Nd and Pr in substitution for La. Two sharp Raman bands at 987 and 1021 cm-1 assigned to the PO 4 3- and HPO 4 2- symmetric stretching modes. Raman bands at 1064, 1112 and 1221 cm1 are attributed to the PO 4 3- and HPO 4 2- antisymmetric stretching modes. Raman bands at 404, 464, 524 and 526 cm-1 are assigned to the PO 4 3- ν 4 bending modes; An intense Raman band at 614 cm-1 with shoulder bands at 680 and 647 cm-1 are assigned to the PO 4 3- ν 2 bending modes. A sharp Raman band observed at 3649 cm-1 is assigned to the stretching vibration of the OH units. Raman bands at 2906, 2988, 3158 and 3440 cm-1 and infrared bands at 2808, 2956, 3117 and 3416 cm-1 are attributed to water stretching vibrations. The spectra in the OH stretching region support the concept of both hydroxyl and water units in the structure of florencite-La, thus confirming the formula as LaAl 3 (PO 4 ) 2 (OH, H 2 O) 6 . Key words: florencite-La, Raman spectroscopy, infrared spectroscopy, phosphate, alunitejarosite group, molecular structure 2 Introduction The most common minerals containing rare earth elements (REE) are related to the monazite, bästnesite and alunite-jarosite groups (florencite subgroup). The REE are important chemical elements in the high technology industry, with special application in ceramics, glasses, lasers, electronics, aluminum alloys and nuclear batteries. Florencite-La is one of the members of the homonymous subgroup that divide the alunite-jarosite group, which is composed by sulphates, arsenates and phosphates of trigonal structure [1]. Other member in the florencite subgroup include the Nd, Ce and Sm analogues of florencite-La, and a number of arsenates such arsenoflorencite-(Ce), graulichite-(Ce) and arsenowaylandite. The first report concerning “florencite” as a mineral was published by Hussak and Prior [2] in sediments from Diamantina region, Brazil. Latter a number of occurrences where described in the literature [3-6]. In a systematic study about florencites, Kato [7] has described the Ce, La and Nd analogues. The type material for florencite-La was considered those described from the Shituru mine, in the copper deposits of Katanga, Democratic Republic of Congo in data published by Lefebvre and Gasparrini [8]. Florencites occur in different geological environments. It can be found in hydrothermal deposits related to carbonatites [9], in lateritic crusts and weathered rocks [10, 11] and as a diagenetic mineral in sediments [12]. In recent years, due to the industrial and strategic importance of REE florencite subgroup minerals are subject of a number of geological studies [13, 14]. To the best knowledge of the authors, studies concerning the spectroscopic characterization of phosphates of the florencite group are rare restricted to the database of the University of Arizona (rruff.info), however no interpretation is given. However, in recent years, the application of spectroscopic techniques to understand the structure of phosphates has been increasing [15-17]. Farmer (1974) [18] divided the vibrational spectra of phosphates according to the presence, or absence of water and hydroxyl units in the minerals. In aqueous systems, Raman spectra of phosphate oxyanions show a symmetric stretching mode (ν 1 ) at 938 cm−1, the antisymmetric stretching mode (ν 3 ) at 1017 cm−1, the symmetric bending mode (ν 2 ) at 420 cm−1 and the ν 4 mode at 567 cm−1. The value for the ν 1 symmetric stretching vibration of PO 4 units as determined by infrared spectroscopy was also described [19-21]. The position of the symmetric stretching vibration is mineral dependent and a function of the cation and crystal 3 structure. The fact that the symmetric stretching mode is observed in the infrared spectrum affirms a reduction in symmetry of the PO 4 units. The vibrational spectroscopic characterization of REE minerals can be an important tool applied to the mineral exploration, where rocks and soils with potential of mineralization can be easily submitted to IR or Raman study. In this work, samples of the REE phosphate mineral florencite-La from the Igarapé Bahia mine, located in the municipality of Parauapebas, Brazil has been carried out. Studies include spectroscopic characterization of the structure with infrared and Raman. Chemical study via Scanning electron microscope (SEM) was applied in the mineral characterization. Experimental Samples preparation and description Bluish green florencite-(La) crystals from Serra dos Carajás, Pará were obtained from the collection of the Geology Department of the Federal University of Ouro Preto, Minas Gerais, Brazil, with sample code SAA-085. The sample is from the Igarapé Bahia mine, located in the municipality of Parauapebas. The mine is an important Iron Oxide-Cu-Au (IOCG type mineralization) ore deposit in the Carajás mineral district in Brazil, one of the most important mineral provinces around the world. It is hosted by a low-grade metamorphosed volcanosedimentary sequence, the Igarapé Bahia Group of Archaean age [22]. The economically extracted ore at Igarapé Bahia is largely developed as a supergene enrichment within the 150200 m thick oxide profile [23, 24]. The oxide zone is characterized by supergene enrichment and hematite, goethite, gibbsite and quartz and has traces of secondary copper minerals and REE-rich phosphates (florencite, crandalite, and rhabdophane) [25]. The original reserves of oxidized gold ore were 15 Mt of high-grade ore (5 g/t Au) and 14 Mt of low-grade ore (1.4 g/t Au). To date, total production of gold is approximately 92 t, exclusively from supergeneenriched ore in the oxidized zone [25]. This is underlain by a transition zone that may be up to 50 m thick with enriched supergene malachite, azurite, cuprite, native copper and goethite and minor amounts of digenite and chalcocite. The primary copper-gold mineralization occurs below 200 m and consists mainly of Fe chlorite, siderite, and magnetite rich breccias hydrothermally altered [22]. The total resource of primary ore is 219 Mt at 1.4 percent Cu and 0.86 g/t Au. 4 The 2575 ± 12 Ma SHRIMP age was obtained of hydrothermal monazite from the Igarapé Bahia mineralization [22]. The sample was gently crushed in an agate mortar and to remove contaminate phases, with the support of a Stereomicroscope Leica Model EZ4, florencite-La crystals were handily selected from a sample in association with goethite and white clay. The florencite-La crystals were phase analyzed by X-ray powder diffraction and Scanning electron microscopy in the EDS mode (SEM/EDS). Scanning electron microscopy (SEM) Experiments and analyses involving electron microscopy were performed in the Center of Microscopy of the Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil (http://www.microscopia.ufmg.br). Florencite-La sample was coated with a 5 nm layer of evaporated carbon. Secondary Electron and Backscattering Electron images were obtained using a JEOL JSM-6360LV equipment. Qualitative and semi-quantitative chemical analyses in the EDS mode were performed with a ThermoNORAN spectrometer model Quest and was applied to support the mineral characterization. Raman microprobe spectroscopy Crystals of florencite-La were placed on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10x, 20x, and 50x objectives. The microscope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a CCD detector (1024 pixels). The Raman spectra were excited by a Spectra-Physics model 127 He-Ne laser producing highly polarized light at 633 nm and collected at a nominal resolution of 2 cm-1 and a precision of ± 1 cm-1 in the range between 200 and 4000 cm-1. Repeated acquisitions on the crystals using the highest magnification (50x) were accumulated to improve the signal to noise ratio of the spectra. Raman Spectra were calibrated using the 520.5 cm-1 line of a silicon wafer. The Raman spectrum of at least 10 crystals was collected to ensure the consistency of the spectra. Infrared spectroscopy 5 Infrared spectra were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart endurance single bounce diamond ATR cell. Spectra over the 4000−525 cm-1 range were obtained by the co-addition of 128 scans with a resolution of 4 cm-1 and a mirror velocity of 0.6329 cm/s. Spectra were co-added to improve the signal to noise ratio. The infrared spectra are given in the supplementary information. Spectral manipulation such as baseline correction/adjustment and smoothing were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, USA). Band component analysis was undertaken using the Jandel ‘Peakfit’ software package that enabled the type of fitting function to be selected and allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentzian-Gaussian cross-product function with the minimum number of component bands used for the fitting process. The Gaussian-Lorentzian ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r2 greater than 0.995. Results and discussion Chemical characterization The SEM image of florencite-La sample studied in this work is shown in Figure 1. The fragment shows an aggregate of crystals up to 10 µm with rhombohedra form. The EDS spectra are shown in Figure 2. Qualitative chemical analysis shows a La and Al phosphate. Traces of Ce, Nd and Pr were also observed in substitution to La. Due to the presence of goethite in association with florencite-La, an intense pick of Fe was also found. Spectroscopy The Raman spectrum of florencite in the 100 to 4000 cm-1 spectral range is displayed in Figure 3a. This figure shows the position of the peaks and the relative intensities of the Raman bands. The spectrum in the 2600 to 3800 cm-1 displays lower intensity than the phosphate spectral region around 1000 cm-1. Clearly, there are parts of the spectrum where no intensity is observed. Thus, the Raman spectrum is divided into subsections depending upon the type of vibrations being observed. In comparison, the infrared spectrum as shown in Figure 3b shows significantly more intensity in the 2500 to 3600 cm-1 spectral range. Again 6 there are parts of the spectrum where no intensity is found, and as a consequence the spectrum is divided into sections for further analysis. The Raman spectrum of florencite-la in the 800 to 1400 cm-1 region is illustrated in Figure 4a. The Raman spectrum is dominated by an intense sharp band at 987 cm-1 with a second band at 1021 cm-1. These bands are assigned to the PO 4 3- and HPO 4 2- symmetric stretching modes. The Raman bands at 1064, 1112 and 1221 cm-1 are attributed to the PO 4 3- and HPO 4 2antisymmetric stretching modes. The Raman band at 846 cm-1 is likely to be a water librational mode. The infrared spectrum of florencite-La in the 500 to 1300 cm-1 spectral region is reported in Figure 4b. The spectrum shows complexity especially when compared with the Raman spectrum which shows clearly resolved bands. The spectrum may be resolved into component bands. An intense band is observed at 1026 cm-1 which is the infrared equivalent of the Raman band at 1021 cm-1. The resolved infrared band at 975 cm-1 is likely to be the equivalent of the Raman band at 987 cm-1. The infrared bands at 1075, 1123 and 1214 cm-1 are assigned to the PO 4 3- and HPO 4 2- antisymmetric stretching modes. The Raman spectrum of florencite-La in the 300 to 800 and in the 100 to 300 cm-1 spectral ranges are illustrated in Figures 5a and 5b. The first figure displays the region where the phosphate bending modes are to be found. The bands are found at 404, 464, 524 and 526 cm-1 are assigned to the PO 4 3- ν 4 bending modes. An intense Raman band is observed at 614 cm-1 with shoulder bands at 680 and 647 cm-1. These bands are assigned to the PO 4 3- ν 2 bending modes. The observation of multiple bands in the ν 2 and ν 4 regions proves the symmetry of the phosphate anion is reduced to C 3v or C 2v . The broad band at 310 cm-1 is a metal (La)-oxygen stretching vibration. The two bands at 699 and 716 cm-1 are thought to be related to the OH deformation modes. The Raman bands in the far low wavenumber region at 202, 255 and 270 cm-1 are simply referred to as lattice vibrations. The Raman spectrum and infrared spectrum of florencite-La in the 2600 to 3800 cm-1 spectral range is reported in Figures 6a and 6b. The formula of the mineral is written as LaAl3 (PO 4 ) 2 (OH, H 2 O) 6 and as such has both hydroxyl units and water molecules in the structure. The spectra of these units should be readily observed in the spectra of the OH stretching region. A sharp Raman band observed at 3649 cm-1 is assigned to the stretching 7 vibration of the OH units. This band is not observed in the infrared spectrum. Raman bands found at 2906, 2988, 3158 and 3440 cm-1 are attributed to water stretching vibrations. In the infrared spectrum broad bands at 2808, 2956, 3117 and 3416 cm-1 are attributed to water stretching vibrations. The position of these bands is indicative of a range of hydrogen bonding. The bands at the lower wavenumbers are assigned to very strong hydrogen bonded water molecules. The Raman spectrum of florencite-La in the 1300 to 2000 cm-1 spectral range is illustrated in Figure 7a, whilst the infrared spectrum over the 1300 to 1800 cm-1 region is reported in Figure 7b. This concept is affirmed by the bending modes of water at 1655 cm-1 (Raman) and 1667 cm-1 (infrared). Conclusions The most common minerals containing rare earth elements (REE) are related to the monazite, bästnesite and alunite-jarosite groups (florencite subgroup). The REE are important chemical elements in the high technology industry, with special application in ceramics, glasses, lasers, electronics, aluminum alloys and nuclear batteries. Florencite-La is one of the members of the homonymous subgroup that divide the alunite-jarosite group, which is composed by sulphates, arsenates and phosphates of trigonal structure. Qualitative chemical analysis shows a La and Al phosphate with traces of Ce, Nd and Pr in substitution for La. Due to the presence of goethite in association with florencite-La, an intense pick of Fe was also found. Raman spectroscopy complimented with infrared spectroscopy identified the presence of phosphate, hydroxyl units and water in the structure of florencite-La Acknowledgements The financial and infra-structure support of the Discipline of Nanotechnology and Molecular Science, Science and Engineering Faculty of the Queensland University of Technology, is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation. The authors would like to acknowledge the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br) for providing the 8 equipment and technical support for experiments involving electron microscopy. R. Scholz thanks to FAPEMIG – Fundação de Amparo à Pesquisa do estado de Minas Gerais, (grant No. CRA - APQ-03998-10). 9 References [1] M.E. Back, J.A. Mandarino, Fleischer`s glossary of mineral species. , Mineralogical Record,, 2008. [2] E. Hussak, G.T. Prior, Min. Mag., 12 (1900) 244-248. [3] P. Devismes, J. Guigues, Y. Laurent, A. Parfenoff, Bull. Soc. Franc. de Min. et de Crist., 91 (1968) 500-502. [4] D. Mckie, Min. Mag., 33 (1962) 281-297. [5] G. Pouliout, H.J. Hofman, Can. Min., 19 (1981) 535-540. [6] B.G. Lottermoser, Neues Jahrb.Min. Mon., 8 (1995) 371-384. [7] T. Kato, Neues Jahrb.Min. Mon., (1990) 227-231. [8] J.J. Lefebvre, C. Gasparrini, Can. Min., 18 (1980) 301-311. [9] S.G. Doroshekevich, S.G. Viladkar, G.S. Ripp, M.V. Burtseva., Can. Min., 47 (2009) 1105-1116. [10] H.G. Dill, A. Fricke, K.H. Henning, App. Clay Sc., 10 (1995) 231-245. [11] I. Valeton, A. Schumann, R. Vinx, M. Wieneke, App. Geochem., 12 (1997) 133-154. [12] B. Rasmussen, J.E. Glover, J. Sed. Res. A64 (1994) 572-583. [13] G. Nagy, E. Draganits, A. Demeny, G. Panto, P. Arkai, Chem. Geol., 191 (2002) 25-46. [14] E. Janots, F. Negro, F. Brunet, B. Goffé, M. Engi, M.L. Bouybaouène, Lithos, 87 (2006) 214-234. [15] L.N. Dias, M.V.B. Pinheiro, R.L. Moreira, K. Krambrock, K. Guedes, F.L. Menezes, J. Karfunkel, J. Schnellrath, R. Scholz, Amer. Min.,96 (2011) 42-52. [16] R.L. Frost, S.J. Palmer, Y. Xi, Spectrochim. Acta, A92 (2012) 377-381. [17] R.L. Frost, Y. Xi, J. Mol. Struct., 1010 (2012) 179-183. [18] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Minerals, The mineralogical Society, London, 1974. [19] R.L. Frost, W. Martens, P.A. Williams, J.T. Kloprogge, J. Raman Spectrosc., 34 (2003) 751-759. [20] R.L. Frost, W. Martens, P.A. Williams, J.T. Kloprogge, Min. Mag., 66 (2002) 10631073. 10 [21] R.L. Frost, W.N. Martens, T. Kloprogge, P.A. Williams, Neues Jahrb.Min. Mon., (2002) 481-496. [22] E. Tazava, C.G.d. Oliveira, Igarape Bahia Au-Cu-(REE-U) deposit, Carajas Mineral Province, Northern Brazil:, Adelaide, 2000. [23] W. Zang, W.S. Fyfe, Econ. Geol, 88 (1993) 1768 - 1779. [24] R.S. Angélica, Mineralogia e geoquímica dos gossans e lateritos auríferos na Região de Carajás, Estado do Pará: Os depósitos de Igarapé Bahia e Águas Claras:, in, Universidade Federal do Pará, Belém, Brazil, 1996, pp. 115. [25] F.H.B. Tallarico, B.R. Figueiredo, D.I. Groves, N. Kositcin, N.J. McNaughton, I.R. Fletcher, J.L. Rego, Econ. Geol., 100 (2005) 7-28. 11 List of figures Figure 1 - Backscattered electron image (BSI) of a florencite-La. Figure 2 - EDS spectra of florencite-La. Figure 3 (a) Raman spectrum of florencite-La over the 100 to 4000 cm-1 spectral range (b) Infrared spectrum of florencite-La over the 500 to 4000 cm-1 spectral range Figure 4 (a) Raman spectrum of florencite-La over the 800 to 1400 cm-1 spectral range (b) Infrared spectrum of florencite-La over the 500 to 1300 cm-1 spectral range Figure 5 (a) Raman spectrum of florencite-La over the 300 to 800 cm-1 spectral range (b) Raman spectrum of florencite-La over the 100 to 300 cm-1 spectral range Figure 6 (a) Raman spectrum of florencite-La over the 2600 to 4000 cm-1 spectral range (b) Infrared spectrum of florencite-La over the 2600 to 4000 cm-1 spectral range Figure 7 (a) Raman spectrum of florencite-La over the 1300 to 1800 cm-1 spectral range (b) Infrared spectrum of florencite-La over the 1300 to 1800 cm-1 spectral range 12 Figure 1 - Backscattered electron image (BSI) of a florencite-La. Figure 2 - EDS spectra of florencite-La. 13 Figure 3a Figure 3b 14 Figure 4a Figure 4b 15 Figure 5a Figure 5b 16 Figure 6a Figure 6b 17 Figure 7a Figure 7b 18