Sphalerite is the main ore-mineral of the vein-type mineralization of Longobucco (LGB) and Fonte Argentila (FAR), outcropping within granodiorite of the Sila Batholith (Calabria, southern Italy). Such mineralization are of historical importance, but not deeply investigated yet (Fregola et al., 2023). We have examined the crystal chemistry of sphalerite through a combination of optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), μ-Raman spectroscopy (μ-RS), single crystal X-ray diffraction (SCXRD), and X-ray powder diffraction (XRPD). Textural and paragenetic observations using optical microscopy allowed us to discriminate three distinct generations of sphalerite from LGB and FAR, corresponding to different mineralization episodes of the ore deposit. Sp-1 is light coloured (from light-yellow to brown), Sp-2 is dark coloured (from reddish-brown to dark brown), whilst Sp-3 is colourless. Colour variation is mainly due to different Fe-content, with the darker Sp-2 being the Fe-richest one (up to 11.3 wt.%; 0.21 mol% FeS). Sphalerite contains also minor amounts of Cd (up to 0.7 wt.%). The phase composition of sphalerite samples has been confirmed by XRPD. Data from μ-Raman spectroscopy, collected from sphalerite Sp-1, Sp-2 and Sp-3, have been correlated to the corresponding Fe concentrations. The colourless Fe-poorest Sp-3 shows the typical spectrum of almost pure ZnS sphalerite, with the main band at about 350 cm-1 (h3, A3; Raman band due to Zn-S bond vibrations). Raman spectra of Sp-1 and Sp-2 show a further band at about 300 cm-1 (h1, A1; Raman band due to Fe-S bond vibrations) becoming gradually dominant with increasing Fe-content, with respect to the Zn-S band. By plotting the obtained ratios of band intensities (h1/h3) and areas (A1/A3) against the corresponding FeS mole fractions, our results are in good agreement with the calibrated curves reported by the literature (e.g., Osadchii & Gorbaty, 2010). The refined unit cell parameters, measured by SCXRD on Sp-1 and Sp-2 sphalerite of different colours (from pale yellow to reddish-brown), range between 5.4158 Å and 5.4230 Å. Using these cell parameters and the corresponding mol% FeS values in the equation by Chareev et al. (2017), we have estimated sphalerite formation temperatures in the range 117-141°C for the light Sp-1, and up to 192°C for the dark Sp-2. Such values are in good agreement with those obtained from our preliminary fluid inclusion analyses performed on quartz, as well as from our geochemical analyses of sphalerite trace element composition (Ciccolella et al., 2024). Chareev D.A. et al. (2017) - Single-crystal Fe-bearing sphalerite: synthesis, lattice parameter, thermal expansion coefficient and microhardness. Phys. Chem. Minerals, 44, 287-296, https://doi.org/10.1007/s00269-016-0856-z. Ciccolella A. et al. (2024) - The Zn-Pb(-Cu-Fe) mineralization in the northern Sila Massif (Calabria, southern Italy): Genetic constrains from trace element concentrations in sphalerite. EGU General Assembly 2024, Vienna, Austria, 14-19 Apr 2024, EGU24-3657, https://doi.org/10.5194/egusphere-egu24-3657. Fregola R.A. et al. (2023) - Review of polymetallic mineralization in the Sila and Serre Massifs (Calabria, southern Italy). Minerals, 13, 439, https://doi.org/10.3390/min13030439. Osadchii E.G. & Gorbaty Y.E. (2010) - Raman spectra and unit cell parameters of sphalerite solid solutions (FexZn1-xS). Geochim. Cosmochim. Ac., 74, 568-573, https://doi.org/10.1016/j.gca.2009.10.022.
Sphalerite from Longobucco and Fonte Argentila mineralization (Sila Massif, Calabria, southern Italy): crystal chemistry and genetic implications
Fregola R. A.
;Ciccolella A.;Ruggieri G.;Ventruti G.;Schingaro E.
2024-01-01
Abstract
Sphalerite is the main ore-mineral of the vein-type mineralization of Longobucco (LGB) and Fonte Argentila (FAR), outcropping within granodiorite of the Sila Batholith (Calabria, southern Italy). Such mineralization are of historical importance, but not deeply investigated yet (Fregola et al., 2023). We have examined the crystal chemistry of sphalerite through a combination of optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), μ-Raman spectroscopy (μ-RS), single crystal X-ray diffraction (SCXRD), and X-ray powder diffraction (XRPD). Textural and paragenetic observations using optical microscopy allowed us to discriminate three distinct generations of sphalerite from LGB and FAR, corresponding to different mineralization episodes of the ore deposit. Sp-1 is light coloured (from light-yellow to brown), Sp-2 is dark coloured (from reddish-brown to dark brown), whilst Sp-3 is colourless. Colour variation is mainly due to different Fe-content, with the darker Sp-2 being the Fe-richest one (up to 11.3 wt.%; 0.21 mol% FeS). Sphalerite contains also minor amounts of Cd (up to 0.7 wt.%). The phase composition of sphalerite samples has been confirmed by XRPD. Data from μ-Raman spectroscopy, collected from sphalerite Sp-1, Sp-2 and Sp-3, have been correlated to the corresponding Fe concentrations. The colourless Fe-poorest Sp-3 shows the typical spectrum of almost pure ZnS sphalerite, with the main band at about 350 cm-1 (h3, A3; Raman band due to Zn-S bond vibrations). Raman spectra of Sp-1 and Sp-2 show a further band at about 300 cm-1 (h1, A1; Raman band due to Fe-S bond vibrations) becoming gradually dominant with increasing Fe-content, with respect to the Zn-S band. By plotting the obtained ratios of band intensities (h1/h3) and areas (A1/A3) against the corresponding FeS mole fractions, our results are in good agreement with the calibrated curves reported by the literature (e.g., Osadchii & Gorbaty, 2010). The refined unit cell parameters, measured by SCXRD on Sp-1 and Sp-2 sphalerite of different colours (from pale yellow to reddish-brown), range between 5.4158 Å and 5.4230 Å. Using these cell parameters and the corresponding mol% FeS values in the equation by Chareev et al. (2017), we have estimated sphalerite formation temperatures in the range 117-141°C for the light Sp-1, and up to 192°C for the dark Sp-2. Such values are in good agreement with those obtained from our preliminary fluid inclusion analyses performed on quartz, as well as from our geochemical analyses of sphalerite trace element composition (Ciccolella et al., 2024). Chareev D.A. et al. (2017) - Single-crystal Fe-bearing sphalerite: synthesis, lattice parameter, thermal expansion coefficient and microhardness. Phys. Chem. Minerals, 44, 287-296, https://doi.org/10.1007/s00269-016-0856-z. Ciccolella A. et al. (2024) - The Zn-Pb(-Cu-Fe) mineralization in the northern Sila Massif (Calabria, southern Italy): Genetic constrains from trace element concentrations in sphalerite. EGU General Assembly 2024, Vienna, Austria, 14-19 Apr 2024, EGU24-3657, https://doi.org/10.5194/egusphere-egu24-3657. Fregola R.A. et al. (2023) - Review of polymetallic mineralization in the Sila and Serre Massifs (Calabria, southern Italy). Minerals, 13, 439, https://doi.org/10.3390/min13030439. Osadchii E.G. & Gorbaty Y.E. (2010) - Raman spectra and unit cell parameters of sphalerite solid solutions (FexZn1-xS). Geochim. Cosmochim. Ac., 74, 568-573, https://doi.org/10.1016/j.gca.2009.10.022.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
