This may be the author’s version of a work that was submitted/accepted for publication in the following source: Frost, Ray& Xi, Yunfei (2012) Raman spectroscopy of selected tsumcorite Pb(Zn,Fe3+)2(AsO4)2(OH,H2O) minerals-Implications for arsenate accumulation. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 86, pp. 224-230. This file was downloaded from: https://eprints.qut.edu.au/47766/ c Consult author(s) regarding copyright matters This work is covered by copyright. Unless the document is being made available under a Creative Commons Licence, you must assume that re-use is limited to personal use and that permission from the copyright owner must be obtained for all other uses. If the docu- ment is available under a Creative Commons License (or other specified license) then refer to the Licence for details of permitted re-use. It is a condition of access that users recog- nise and abide by the legal requirements associated with these rights. If you believe that this work infringes copyright please provide details by email to [email protected] License: Creative Commons: Attribution-Noncommercial-No Derivative Works 2.5 Notice: Please note that this document may not be the Version of Record (i.e. published version) of the work. Author manuscript versions (as Sub- mitted for peer review or as Accepted for publication after peer review) can be identified by an absence of publisher branding and/or typeset appear- ance. If there is any doubt, please refer to the published source. https://doi.org/10.1016/j.saa.2011.10.028 3+ 1 Raman spectroscopy of selected tsumcorite Pb(Zn,Fe )2(AsO4)2(OH,H2O) 2 minerals –implications for arsenate accumulation 3 4 Ray L. Frost and Yunfei Xi 5 6 Chemistry Discipline, Faculty of Science and Technology, Queensland University 7 of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. 8 9 Abstract 10 The presence of arsenic in the environment is a hazard. The accumulation of arsenate 11 by a range of cations in the formation of minerals provides a mechanism for the 12 accumulation of arsenate. The formation of the tsumcorite minerals is an example of a 13 series of minerals which accumulate arsenate. There are about twelve examples in 14 this mineral group. Raman spectroscopy offers a method for the analysis of these 15 minerals. 16 The structure of selected tsumcorite minerals with arsenate and sulphate anions were 17 analysed by Raman spectroscopy. Isomorphic substitution of sulphate for arsenate is 18 observed for gartrellite and thometzekite. A comparison is made with the sulphate 19 bearing mineral natrochalcite. The position of the hydroxyl and water stretching 20 vibrations are related to the strength of the hydrogen bond formed between the OH 3- 21 unit and the AsO4 anion. Characteristic Raman spectra of the minerals enable the 22 assignment of the bands to specific vibrational modes. 23 24 Keywords: Raman spectroscopy, gartrellite, tsumcorite, thometzekite, arsenate, 25 sulphate 26 Author to whom correspondence should be addressed ([email protected]) P:+61 7 3138 2407 F:+61 7 3138 1804 27 Introduction 28 The tsumcorite mineral group are a set of minerals which in their formation 29 accumulate arsenic as arsenate. Tsumcorite was named after the TSUMeb 30 CORporation mine at Tsumeb, in Namibia, in recognition of the Corporation’s 31 support for mineralogical investigations of the ore body at its Mineral Research 32 Laboratory. The tsumcorite mineral group are well known [1-5]. Many of the 33 minerals were found in the oxidised zones of the famous Tsumeb ore deposit [6]. At 34 the Puttapa Mine in Australia it occurs with adamite, mimetite, smithsonite, goethite 35 and quartz. At the Kintore Open Cut, Broken Hill, Australia it occurs with segnitite, 36 beudantite, carminite and mawbyite. Many new minerals have been discovered in 37 these oxidised zones in mineral deposits in other parts of Australia [7-11]. Many of 38 these minerals are based upon arsenates of lead and zinc in combination with other 39 cations. 40 The tsumcorite group of minerals are a mineral group based upon monoclinic and 41 triclinic arsenates, phosphates, vanadates and sulphates of the general formulae 3+ 42 (M1)(M2)2(XO4)2(OH,H2O)2 where M1 is Pb, Ca or Na, M2 is Cu, Zn, Fe , Co or 43 Mn and X is As, P, V and/or S. The minerals gartrellite Pb[(Cu,Zn)(Fe3+, Zn, Cu)] 44 (AsO4)(OH,H2O)2, helmutwinklerite Pb(Zn,Cu)2(AsO4)2.2H2O and thometzekite [12] 3+ 45 are triclinic. The minerals ferrilotharmeyerite [13] Ca(Fe ,Zn)2(AsO4)2(OH,H2O)2 , 3+ 46 lotharmeyerite Ca(Mn ,Zn)2(AsO4)2(OH,H2O)2, mawbyite [10] 3+ 3+ 47 Pb(Fe ,Zn)2(AsO4)2(OH,H2O)2, mounanaite Pb(Fe )2(VO4)2(OH)2, natrochalcite 3+ 48 [14] NaCu2(SO4)2(OH,H2O)2 and tsumcorite [15] Pb(Zn,Fe )2(AsO4)2(OH,H2O) are 49 monoclinic. [15]. Tsumcorite belongs to the monoclinic crystal class 2/m. This means 50 that it has a twofold axis of symmetry along the b axis and a mirror plane 51 perpendicular to this, in the plane containing the a and c axes. The a and c axes are 52 inclined to each other at angle β = 115.3°. The unit cell parameters are a = 9.124 Å to 53 9.131 Å, b = 6.326 Å to 6.329 Å and c = 7.577 Å to 7.583 Å. There are two formula 54 units per unit cell (Z = 2), and the space group is C2/m This means the cell is a C-face 55 centered lattice, with lattice points in the center of the C face as well as at the corners 56 of the cell. 57 58 There are some problems associated with writing the mineral formula in that the 59 formula may change as a function of the degree of solid solution formation and the 60 amount of isomorphic substitution. Both anion and cation substitution may occur. 61 Sulphate, phosphate and carbonate may replace the arsenate. For example it is quite 3+ 62 comprehensible that a formula such as PbCu(Fe ,Cu)(AsO4)2(OH,H2O)2 is found. 63 Variation in mineral composition is expected for gartrellites from different origins. 64 The formula of gartrellite may be written as Pb[(Cu,Fe2+)(Fe3+, Zn, Cu)] 65 (AsO4)(CO3,H2O)2. For example the gartrellite found at Ashburton Downs, Western 2+ 66 Australia has a calculated formula of PbCu1.5Fe 0.5As1.5(SO4)0.5(CO3)0.5(H2O)0.2. Of 67 course Raman spectroscopy will readily determine the presence of carbonate in the 68 mineral. The presence or absence of two moles of water is the determining factor as to 69 whether the mineral is triclinic or monoclinic. 70 71 Tsumcorite crystallizes in the monoclinic space group C2/m with a 9.124 (4), b 6.329 72 (2), c 7.577 (2) β = 115.degree. 17 (2)', Z = 2 [15]. Crystal symmetry is either triclinic 73 in the case of an ordered occupation of two cationic sites, triclinic due to ordering of 74 the H bonds in the case of species with 2 water molecules per formula unit, or 75 monoclinic in the other cases. Crystals of ferrilotharmeyerite, tsumcorite, 76 thometzekite (sulfatian), and mounanaite have monoclinic symmetry, space group 77 C2/m. The triclinic members of the tsumcorite group are gartrellite, zincian gartrellite, 78 phosphogartrellite, helmutwinklerite, and probably (sulfate-free) thometzekite; the 79 space group is P/1, with a pronounced monoclinic C-centered pseudocell. The triclinic 80 distortion is caused by an ordered arrangement of Fe[6]O6 octahedra and tetragonal 81 bi-pyramidal Cu[4+2]O6 polyhedra [13]. 82 83 Of course Raman spectroscopy will readily determine the presence of 84 carbonate in the mineral. The presence or absence of two moles of water is the 85 determining factor in whether the mineral is triclinic or not. It has been shown that 86 crystals of ferrilotharmeyerite, tsumcorite, thometzekite (sulfatian), and mounanaite 87 have monoclinic symmetry, space group C2/m. [13] The triclinic members of the 88 tsumcorite group have the space group is P1, with a pronounced monoclinic C-centred 89 pseudocell. [13] The tsumcorite minerals are often formed in the oxidised zones of 90 arsenic bearing Pb-Zn deposits. The particular mineral formed depends upon the 91 composition of the polymetallic ore deposit. The minerals are of a rare nature. 92 Complex solution chemistry involving mixtures of the cations of lead, zinc, and ferric 93 iron may result in the formation of the tsumcorite group of minerals. The type of 94 mineral formed is a function of concentration, pH, temperature and the available 95 anion present in the mother solution. The complex set of variable requires a 96 multidimensional phase diagram. [16] Raman spectroscopy has proven an excellent 97 technique for the study of oxyanions in both solution and in secondary mineral 98 formation [17-26]. In this work we extend our studies to the arsenates of the 99 tsumcorite mineral group. 100 101 Experimental 102 Minerals 103 The tsumcorite minerals were obtained from Museum Victoria. The selected minerals 104 and their museum number and place of origin are reported in Table 1. Details of the 105 tsumcorite minerals have been published (page 207) [27]. 106 Raman spectroscopy 107 Crystals of the individual members of the tsumcorite mineral group were placed on a 108 polished metal surface on the stage of an Olympus BHSM microscope, which is 109 equipped with 10x, 20x, and 50x objectives.