International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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PHYLLOSILICATES FROM HYDROTHERMALLY ALTERED GRANITOID ROCKS IN THE PEZINOK Sb-Au DEPOSIT, WESTERN CARPATHIANS, SLOVAKIA

Published: Jun 2001

Pages: 127 - 138

Authors: DANIEL MORAVANSKY, MARTIN CHOVAN, JOZEF LIPKA

Abstract: Biotites from altered granitoid rocks on Pezinok-Kolarsky vrch Hill Sb-Au deposit belong to the phlogophiteannite series with the ratio Fetot/Fetot + Mg) = 0.44–0.55. Mg-biotites are the dominant type and can be classified as phlogopites (Phl30.09–45.79Ann26.67–36.00Eas22.93–10.22Sid20.31–8.02). Fe-biotites (annites, Phl34.79–41.13Ann39.20–46.39Eas12.22–5.86Sid13.79–6.62) are present in the more altered rocks. The chemical composition of the studied biotites is governed by Tschermak´s substitution, dioctahedral-trioctahedral substitution and A-1(Si+1Al-1)IV-substitution. Interlayer deficient occupancy of A site is probably caused by postmagmatic hydrothermal alteration and can be explained by A-1(Si+1Al-1)IV-substitution. The studied tri-trioctahedral chlorites come from the clinochlore-chamosite isomorphic series and they originated from biotites. According to the classification of Wiewióra & Weiss (1990) or Weiss (1991), they can be divided into two groups: ferrous clinochlores (schematic formula Mg34.39–36.32Fe28.31–37.07X24.02–35.39) and magnesium chamosites (schematic formula Mg34.33–37.90Fe34.76–39.32X23.18–28.30). Ferrous clinochlore is the dominant type of chlorite. The chemical composition of chlorites is governed by dominant FeMg-1-substitution and also by Tschermak´s substitution and dioctahedral substitution. The content of impurities (K, Ca, Na) is very low. White K-micas were formed mainly by alteration of alkali feldspars or plagioclases and can be divided into: phengitic muscovites and illites. Phengitic muscovites in the phengitic component (Brigatti et al. 2000) range from 0.17 to 0.25. The content of Ti is 0.016–0.020 a.p. 11 oxygens and indicates postmagmatic to hydrothermal origin (Miller et al. 1981). The content of interlayer occupancy (K + Ca + Na) ranges from 0.905 to 0.964 a.p. 11 oxygens and agrees with data from Konings et al. (1984), Piantone et al. (1994) and others. The chemical composition of phengitic muscovites is governed by Tschermak´s substitution, dioctahedral-trioctahedral substitution and A-1(Si+1Al-1)IV-substitution. The phengitic component for illites is 0.02–0.14. The content of Ti (0.005–0.019 a.p. 11 oxygens) indicates hydrothermal origin (Miller et al. 1981). The content of K ranges from 0.770 to 0.926 a.p. 11 oxygens and agrees with data from Cathelineau & Izquierdo (1988), Aja et al. (1991a,b), Srodon & Erbel (1984) and others. The chemical composition of illites is governed by substitutions A-1(Si+1Al-1)IV-substitution, dioctahedral-trioctahedral substitution and Tschermak´s substitution.

Keywords: Sb-Au deposit, granitoid rocks, illite, phengitic muscovite, magnesium chamosite, ferrous clinochlore, annite, phlogopite

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