A Rare Au-Sb Telluride Pampaloite from the Svetlinsk Gold-Telluride Deposit, South Urals, Russia

Pampaloite AuSbTe, a rare gold-antimony telluride that was first described in 2019 from the Pampalo gold mine, Finland, was found in samples from the large Svetlinsk gold-telluride deposit, South Urals, Russia. Optical microscopy, scanning electron microscopy, electron microprobe analysis, reflectance measurements, electron backscatter diffraction and Raman spectroscopy were used to study eight grains of pampaloite. Pampaloite forms inclusions (5-30 mu m) in quartz together with other tellurides (typically petzite), native gold and, less often, sulfides. In reflected light, pampaloite is white or creamy white in color with weak anisotropism and without internal reflections. The empirical formula calculated on the basis of 3 apfu is Au0.97-1.07Ag0-0.02Sb0.96-1.04Te0.96-1.04 (n = 18). The holotype pampaloite structure was used as a reference and provided the perfect match for an experimental EBSD pattern (12 bands out of 12, mean angle deviation 0.19 degrees). Raman spectra are reported for the first time for this mineral. All studied pampaloite grains exhibit vibrational modes in the range 60-180 cm(-1). Average peak positions are 71, 108, 125, 147 and 159 cm(-1). According to experimental data for the Au-Sb-Te system, we estimate the upper temperature range of pampaloite crystallization at the Svetlinsk deposit to be 350-430 degrees C.