Acta Musei Moraviae

Characteristics of the chemical composition of tourmalines from phyllites near Štítnik (Slovak Republic)

The zonal metamorphic tourmalines with detrital cores were identified in the phyllites near Štítnik (Bôrka Nappe, Western Carpathians). The younger metamorphic tourmalines of dravite composition (Drv₂) have preserved older detrital cores of schorl or dravite composition (Drv₁). Dravite cores (Drv₁) have slightly reduced Si⁴⁺ (up to 5.95 apfu) compared to schorl cores (6.00 apfu). Dravite cores have increased Al³⁺ values (up to 6.54 apfu) compared to schorl cores (up to 5.85 apfu). Schorl cores have higher Fe²⁺ (up to 1.91 apfu), Ti⁴⁺ (up to 0.19 apfu) and Na⁺ (up to 0.88 apfu), compared to dravite cores (up to 1.08 apfu Fe²⁺; up to 0.09 apfu Ti⁴⁺; up to 0.61 apfu Na⁺). Mg²⁺ values are higher in dravite cores (up to 1.80 apfu) compared to schorl cores (up to 1.66 apfu). Vacancy values in schorl cores range from 0.03–0.19 apfu in contrast to dravite cores (0.28–0.31 apfu), the values of OH^– in the W position in schorl cores are in the range of 0.89–0.95 apfu, in contrast to dravite cores (0.59–0.63 apfu). Dravite rims (Drv₂) show slight differences in Al3+ contents (5.86–6.17 apfu), with lower Al³⁺ values than dravite cores (Drv₁) and higher Al³⁺ values than schorl cores. Mg²⁺ values in dravite rims (up to 1.78 apfu) are comparable to dravite cores. Fe²⁺ contents in dravite rims (up to 1.44 apfu) are lower compared to schorl cores and higher compared to dravite cores. Na⁺ values in dravite rims (up to 0.92 apfu) are higher compared to dravite cores. Vacancy values in dravite rims (up to 0.18 apfu) are lower compared to dravite cores. OH^– values at the W position in dravite rims (up to 1.00 apfu) are higher compared to dravite cores. The chemical zoning of tourmalines documents its polystadial development, which reflects the conditions of regional metamorphism within the studied area of Bôrka Nappe. The identified mineral association of the studied phyllites consists of muscovite, Mg-chlorite, albite, quartz and calcite. From the point chemical analyses of Mg-chlorites in the phyllites near Štítnik, the temperatures in the interval 309–331 °C ± 4 °C were calculated, which confirms metamorphism in the greenschist facies conditions.