Typomorphic features of tourmaline from some types of hydrothermal deposits

Category Mineral processing
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Baksheev, Ivan۱; Prokof’ev, Vsevolod۲; Ustinov, Vladimir۳; Zaraiskii, Georgii۴
Holding Date 17 September 2008

We have studied tourmalines from schist-type emerald (Malyshevo, Russia), Sn greisen (Sherlovaya Gora, Russia and Cornwall, UK), Sn volcanic-related (Mramorny district, Russia), Cu-porphyry (Aktogai, Kazakhstan; Kafan, Armenia), ultramafic talc (Shabry and Syrostan, Russia), and different-depth gold (Berezovsky and Darasun, Russia) deposits. In the Emerald Mines, tourmalines can be classed as dravite to "fluor-dravite" with different values of XFe 0.12-0.37 and F 0-0.75 apfu. The Fe3+/Fetot ratio is low and ranges from 0.04 to 0.08. Calculated δ18OH2O and δDH2O values of fluid responsible for the tourmaline formation range from +7.7 to +8.3‰ and from -65 to -59‰, respectively, indicating magmatic source. In general, tourmalines from Sn greisen deposits can be classed as schorl to "fluor-schorl" with XFe 0.43-1.0 and F 0-0.58 apfu. The Fe3+/Fetot ratio is low and is ~0.05. The δ18O (SMOW) value of studied tourmaline from Cornwall is +12.0‰. Among cations in emerald and greisen tourmalines, the major type of substitution is MgFe-1. Tourmalines from Sn volcanic-related deposits can be classed as schorl to "oxy-" and "flour-schorl" of two generations with XFe 0.86-0.95 and F 0-0.57 apfu for tourmaline-I associated with cassiterite and XFe 0.51-0.75 and F 0-0.25 apfu for tourmaline-II associated with sulfides. The Fe3+/Fetot ratio is higher than in the greisen and emerald deposits ranging from 0.11 to 0.25. Among cations, the major type of substitution is AlFe-1. The δ18O (SMOW) value varies from -7.2 to +9.5‰ indicating significant influx of meteoric water in mineralizing fluid. Tourmalines from the studied Cu-porphyry deposits can be classed as schorl-dravite with XFe 0.47-0.75 and F 0-0.35 apfu. The Fe3+/Fetot ratio is 0.59. Among cations, the major type of substitution is AlFe-1. The δ18O (SMOW) value of tourmaline from Kafan is +6.5δ. Tourmalines from talc deposits may be classed as dravite with XFe 0.23-0.46 and F 0-0.20 apfu. The Fe3+/Fetot ratio ranges from 0.39 to 0.55. Among cations, the major type of substitution is MgFe-1. Calculated δ18OH2O and δDH2O range from +7.6 to +11.1‰ and from -62 to -31‰, respectively, indicating magmatic fluid source with probable influx of metamorphic water. Early tourmalines from deep-seated gold deposits (P 1.7-2.5 kb) are schorl-dravite with XFe 0.08-0.46 and F 0-0.20 apfu. The Fe3+/Fetot ranges from 0.12 to 0.60. Calculated δ18OH2O and δDH2O range from +2.9 to +5.7‰ and from -61 to -57‰, respectively, indicating magmatic fluid source probably with influx of metamorphic water. Early tourmalines from the shallow gold deposits (P 0.5-1.5 kb) are schorl ("oxy-schorl")-dravite ("oxy-dravite"), with XFe 0.09-0.74 and F 0-0.37 apfu. The Fe3+/Fetot ranges from 0.50 to 0.85. Among cations, the major type of substitution is AlFe-1. Calculated δ18OH2O value varies from +0.1 to +7.7‰ indicating significant influx of meteoric water.
This work has been supported by IGCP-540.