Brown and blue schorl from the Spiš-Gemer granite, Slovakia: composition and genetic relations
Schorl is a widespread accessory mineral in Sn-bearing S-type rocks of the Spiš-Gemer granite suite (SGG), E. Slovakia. Schorl content increases from Sn-, B-poor biotite-(muscovite) to highly evolved Sn, B-rich albite-muscovite leucogranite, locally with greisenized parts in granite cupolas. Optical, EMPA and OES data reveal two populations of tourmaline: (1) brown schorl with low X-site vacancy, and (2) X-site deficient blue schorl, enriched in Pb and Sn. A Fe/(Fe + Mg)at ratio varies between 0.75-0.97. The Mössbauer spectra determined Fe3+ <10% for both populations which indicate a low fO2 conditions. Overgrowths of the blue variety on smoky cores and the trace-element chemistry indicate a two-stage evolution of SGG schorl: older brown schorl crystallized during magmatic stage with quartz, feldspars and micas, whereas younger blue schorl originated during late-magmatic to hydrothermal stage and it is a product of breakdown of brown schorl and biotite. Presenve of schorl indicates B-rich protolite in the source rocks of SGG represented by illite- or muscovite-rich marine sediments.
SNIP (Scopus, 2015): 0.700
IF (ISI, 2015): 1.326
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