Journal of Geochemical Exploration 165 (2016) 81–93 Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/gexplo Major and minor element geochemistry of chromite from the Xerolivado–Skoumtsa mine, Southern Vourinos: Implications for chrome ore exploration E. Tzamos a,⁎, A. Filippidis a,A.Rassiosb, G. Grieco c, K. Michailidis a,A.Koroneosa, K. Stamoulis d, M. Pedrotti c, P.N. Gamaletsos e,1 a Department of Mineralogy–Petrology–Economic Geology, School of Geology, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece b Institute of Geology and Mineral Exploration, Lefkovrisi, Kozani, 501 00 Kozani, Greece c Department of Earth Sciences, Università degli Studi di Milano, Via Botticelli, 23, Milano, Italy d Geologist, Kastania, Servia, 505 00 Kozani, Greece e Department of Metallurgy and Materials Technology, School of Mining and Metallurgical Engineering, National Technical University of Athens, Zographou Campus, Heroon Polytechneiou str. 9, 157 80, Greece article info abstract Article history: The concentration of major (Cr, Al, Mg, Fe) and minor (Ti, V, Mn, Ni, Zn) elements was studied in chromitite ores Received 29 October 2015 and accessory chrome spinels within serpentinite host rocks from the Xerolivado–Skoumtsa mine (Southern Revised 19 February 2016 Vourinos, Western Macedonia, Greece) by means of electron microprobe techniques. Chrome ores in the mine Accepted 28 February 2016 occur in seven extensive ore bodies. Chromite was analyzed with respect to its position within or between ore Available online 5 March 2016 bodies, including the following classifications: chromitite (schlieren ore) band, accessory chromite in intercalat- Keywords: ed serpentine within the ore bodies, disseminated chromite in non-ore bearing host rocks, and chromite within Chrome ore serpentinites intermediately adjacent to ore bodies. Chrome spinel originally forms at temperatures of around Mineral chemistry 1300 °C, but their hosts undergo ductile deformation to temperatures down to around 700 °C, thus facilitating Geochemistry solid state re-equilibration. Results showed that Mg in chromite was found to be substituted during re- Vourinos ophiolite complex equilibration mainly by Fe and, to a minor extent, by Mn and Zn. Cr is mainly substituted by Al and, to a minor extent, V. Compositions were found to vary in accessory chromite crystals as a function of their distance from chromitite bands. Specifically, the average concentrations of Cr and Mg are higher in spinels within chromitite ores than for the disseminated spinels in serpentine gangue layers within chromitites. Chrome spinels in schlieren ore layers have higher Mg and Cr concentrations compared to the disseminated chromites in the serpentinites immediately adjacent to the chromite ore bodies and also slightly higher concentrations of Mg and Cr than the disseminated chromites in the host serpentinites. Fe2+, Mn, Zn, Al and V cations show exactly the oppo- site trend. We attribute these variations in the spinel chemistry to subsolidus reactions between chromite, silicate mineral phases and fluids. Geochemical maps presenting the spatial variation of these elements in disseminated Cr spinels of the Xerolivado mine can serve to delineate the precise position of the chrome ore bodies. © 2016 Elsevier B.V. All rights reserved. 1. Introduction chromitites of various types (e.g., Irvine, 1967, 1977; Pearce et al., 1984; Roeder and Reynolds, 1991; Arai, 1992; Arai, 1997; Malpas Chromite chemistry within ophiolitic suites has long been used as a et al., 1997; Zhou and Robinson, 1997; Arai and Matsukage, 1998; petrogenetic indicator for establishing their geotectonic environment, Barnes and Roeder, 2001; Kamenetsky et al., 2001; Ahmed and the composition of the parental magma(s) and the genesis of Economou-Eliopoulos, 2008; Pagé and Barnes, 2009; Kapsiotis et al., 2011; Kapsiotis, 2013; Grieco et al., 2014; Rollinson and Adetunji, 2015; Uysal et al., 2015; Zhou et al., 2015). Chromite chemistry can be ⁎ Corresponding author. affected during subsolidus reactions by re-equilibration processes with E-mail addresses: [email protected] (E. Tzamos), [email protected] (A. Filippidis), silicate mineral phases and fluids (Irvine, 1967; Arai, 1980; Ozawa, [email protected] (A. Rassios), [email protected] (G. Grieco), 1985; Roeder and Campbell, 1985; Auge, 1987; Christodoulou and [email protected] (K. Michailidis), [email protected] (A. Koroneos), Michailidis, 1990; Rassios and Kostopoulos, 1990; Van der Veen and [email protected] (K. Stamoulis), [email protected] (M. Pedrotti), Maaskant, 1995; Peltonen, 1995; Filippidis, 1997). In general, Mg and [email protected] (P.N. Gamaletsos). 2+ 1 Present address: Center for Electron Nanoscopy, Technical University of Denmark, Cr in chromite may be substituted by other bivalent (e.g. Fe ,Ni) 3+ 2800 Kongens Lyngby, Denmark. and trivalent (e.g. Fe , Al) cations, respectively (e.g., Irvine, 1967; http://dx.doi.org/10.1016/j.gexplo.2016.02.013 0375-6742/© 2016 Elsevier B.V. All rights reserved. 82 E. Tzamos et al. / Journal of Geochemical Exploration 165 (2016) 81–93 Fig. 1. Major units of the Vourinos ophiolite complex and location of the Xerolivado–Skoumtsa mine (red circle) (after Grivas et al., 1993). Roeder and Campbell, 1985; Roeder and Reynolds, 1991; Michailidis, suggestions of Rassios and Kostopoulos, 1990) were constructed in 1993, 1995; Peltonen, 1995; Filippidis, 1997; Kapsiotis, 2013). The effort to investigate their spatial distribution as an aid in chrome ore purpose of the present investigation was the study of the substitution exploration. We propose that geochemical mapping could provide an relations between bivalent and trivalent cations –with special emphasis added prospecting methodology that could significantly reduce the on substitution of minor elements– in chromite from chromitite (ore) cost of exploratory drilling. bands (spinel–spinel re-equilibration) and accessory chromite of host serpentinites (spinel–olivine re-equilibration) of the Xerolivado– 2. Geologic setting Skoumtsa mine in the southern part of the Vourinos ophiolitic complex (Western Macedonia, Greece) (Fig. 1). We also examine whether these 2.1. The Vourinos ophiolite complex substitutions and the spatial distribution of the elements show any kind of pattern which could be useful for the implementation of a geochem- The Vourinos Complex in northern Greece (Fig. 1)isamid- ical tool for chrome ore exploration. Geochemical anomaly maps of the Jurassic ophiolitic slab emplaced onto the Pelagonian continental major and minor element concentrations in chromite (following the margin during the upper Jurassic: its emplacement, long considered Fig. 2. Chrome ore samples from the Xerolivado–Skoumtsa mine showing (a) typical schlieren form (parallel dark-gray to black chromitite and serpentinized dunite, oily bands) and (b) folded chromitite band. E. Tzamos et al. / Journal of Geochemical Exploration 165 (2016) 81–93 83 Fig. 3. Distribution and form of the schlieren chromite ore bodies of the Vourinos Xerolivado–Skoumtsa mine (modified after Filippidis, 1996). Samples studied were collected from vertical section +90. Fig. 4. Sampling methodology: (a) samples from chromitites (A), serpentinites near the chrome ore bodies (B) and between the chromitites (C). (b) Samples from chromitites: chromite band samples (1) and serpentine band samples (2). Fig. 5. Back scattered electron images of chromite grains (gray) from the Xerolivado–Skoumtsa mine chromitite. (a) Pull apart texture, (b) pull apart texture, porous texture and alteration to Fe-chromite (light gray). 84 E. Tzamos et al. / Journal of Geochemical Exploration 165 (2016) 81–93 Table 1 Representative microprobe analyses of chrome spinels from the Xerolivado Skoumtsa mine (wt.%). Sample C3/692 C3/717A C4/765 C4/800 C5/692 C6/741 C3/750 C3/800 C4/692 C4/717A C5/738 C6/692 Typea 1111112222 22 SiO2 0.03 0.04 0.01 0.02 0.01 0.02 0.08 0.02 0.00 0.03 0.02 0.01 TiO2 0.12 0.15 0.13 0.15 0.14 0.14 0.16 0.17 0.14 0.14 0.16 0.14 Al2O3 8.67 9.05 9.29 9.69 8.86 9.85 11.83 11.39 8.61 8.14 9.94 8.24 Cr2O3 61.03 60.74 61.13 60.88 61.19 61.64 59.19 59.70 60.78 59.62 60.57 60.70 V2O3 0.09 0.12 0.09 0.10 0.07 0.09 0.11 0.09 0.11 0.09 0.10 0.11 b Fe2O3 4.20 3.87 3.61 3.09 4.19 2.90 2.77 2.92 4.42 4.63 3.55 4.09 FeO 11.45 11.65 12.49 13.57 11.62 12.20 13.27 13.57 14.09 16.04 12.99 15.39 MnO 0.03 0.06 0.09 0.03 0.04 0.04 0.06 0.07 0.09 0.12 0.08 0.14 MgO 14.25 14.16 13.75 13.15 14.26 14.11 13.60 13.41 12.74 11.14 13.58 11.70 NiO 0.07 0.04 0.05 0.05 0.04 0.06 0.11 0.08 0.01 0.05 0.06 0.05 CaO 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.01 0.00 ZnO 0.01 0.00 0.03 0.02 0.03 0.03 0.07 0.06 0.00 0.06 0.02 0.02 Total 99.96 99.87 100.68 100.75 100.45 101.09 101.23 101.47 100.98 100.06 101.08 100.60 Structural formulae based on 32 (O) Si 0.008 0.010 0.003 0.004 0.002 0.004 0.020 0.004 0.000 0.007 0.006 0.004 Ti 0.024 0.029 0.024 0.028 0.027 0.027 0.031 0.032 0.027 0.027 0.031 0.027 Al 2.645 2.759 2.817 2.942 2.689 2.961 3.535 3.406 2.631 2.541 2.999 2.547 Cr 12.487 12.424 12.436 12.405 12.455 12.434 11.864 11.982 12.457 12.483 12.260 12.592 V 0.019 0.025 0.020 0.022 0.015 0.019 0.022 0.018 0.022 0.019 0.021 0.024 Fe3+ 0.818 0.753 0.700 0.599 0.812 0.556 0.528 0.558 0.863 0.923 0.683 0.807 Fe2+ 2.478 2.520 2.688 2.924 2.502 2.604 2.813 2.882 3.055 3.552 2.781 3.376 Mn 0.007 0.012 0.020 0.007 0.009 0.010 0.012 0.015 0.019 0.028 0.017 0.031 Mg 5.498