Zonality of schorls from pegmatite veins of the Turkestan Range (Kyrgyzstan)

V.K. Gerasimov ^a*, L.A. Sergeeva ^b**, O.N. Lopatin ^b***, A.V. Mukhametshin ^b****

^aTomsk State National Research University, Tomsk, 634050 Russia

^bKazan Federal University, Kazan, 420008 Russia

E-mail: ^*1.gerasimov@mail.ru, ^**lsergeeval1996@gmail.com, ^***Oleg.Lopatin@kpfu.ru, ^****adib.mv@gmail.com

Received June 8, 2018

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Abstract

In the course of a long-term field research within the borders of the Turkestan Range located in the southwestern part of Kyrgyzstan (high-altitude Tien Shan), pegmatite veins of a rare-metal genetic type have been found. Along with quartz, feldspars, and micas, one of the most common minerals of these pegmatite veins is black tourmaline, schorl. The petrographic study of the thin sections of black tourmaline crystals under a microscope has revealed their zonal structure. The central parts of almost all the schorl crystals are colored blue or green, while the peripheral areas are brown. Using the optical spectroscopic microprobe scanning, in the highly sensitive mode of photon counting, a complex experimental study of schorl zonality has been performed. Based on the analysis of the optically active centers manifested in the optical absorption spectra, changes in the genetic conditions of pegmatite formation have been confirmed, namely, the change in the reducing environment to oxidative one and the decrease in the total iron content of the pegmatite formation environment. The informative character of the changes in the crystallochemical features of tourmalines in the genetic aspects of the evolution and formation of the pegmatite complexes of the Turkestan Range in the southwestern Tien Shan has been shown.

Keywords: tourmaline, pegmatite complexes, optical spectroscopy, energy dispersive spectroscopy, crystallochemical features of schorls

Acknowledgments. We sincerely thank B.M. Galiullin, PhD in Physics and Mathematics, Kazan Federal University, for the energy dispersive X-ray spectroscopy of the samples.

Figure Captions

Photo 1. The thickened petrographic section of the black tourmaline having a zonal structure. The section is perpendicular to the C axis of the crystal.

Photo 2. The contact of the central green zone and the peripheral brown zone of the schorl crystal. The section is perpendicular to the C axis of the crystal.

Fig.1. The optical absorption spectra of schorls.

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For citation: Gerasimov V.K., Sergeeva L.A., Lopatin O.N., Mukhametshin A.V. Zonality of schorls from pegmatite veins of the Turkestan Range (Kyrgyzstan). Uchenye Zapiski Kazanskogo Universiteta. Seriya Estestvennye Nauki, 2018, vol. 160, no. 3, pp. 459–466. (In Russian)

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