WU Shou-rong1, ZHAO Jing-yu2,3, ZHANG Xin1, ZHANG Hui2
(1. General Team No.7 of Non-ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China;
2. Key Laboratory of High-temperature and High-pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: Chemical compositions of tourmalines, determined by electron microprobe, show that tourmalines from the altered country-rock, exo- and internal-contact zones are Ca- and Fe-rich dravite, from the tourmalized pegmatite are Mg- and Fe-rich elbaite, from the early formed textural zones (Ⅰ-Ⅳ) are schorl-elbaite solid solution series, and from the late formed textural zones (Ⅴ-Ⅶ) are elbaite. Tourmalines from the altered country-rock, exo- and internal- contact zones are characterized by low Al, high Mg and Ca in Y site, and very low ratios of Al/(Al+Fe) and Fe/(Fe+Mg), represented by substitution of R3++O2-=R2++OH-, indicating that the origin of tourmalines were associated with interactions between country-rock and exsolved magmatic fluid, and/or between country-rock and pegmatite-forming melt. Tourmalines from the internal textural zones (Ⅰ－Ⅶ) of pegmatite are featured by very low Mg and Ca, high Fe, Al and Li in Y site, and very high ratios of Al/(Al+Fe) and Fe/(Fe+Mg), represented by substitution of ?+Al3+=Na++Fe(Mg)2+ and Li++Al3+=Fe(Mn)2++Mg2+, respectively. Touramlines from the early formed textural zones (Ⅰ－Ⅳ) of pegmatite are magmatic in origin, showing no zonation in chemical compositions, but tourmalines from the late formed textural zones (Ⅴ－Ⅶ) of pegmatite were magmatic-hydrothermal in origin, featured by oscillatory zonation. As solidification of pegmatite from the outer to the inner, it shows that Al, Li and Mn in Y site and Fe/(Fe+Mg) ratio of tourmalines increase with decreasing temperature gradually. As no Mg in Y site of tourmalines from the internal textural zones, it indicates that the magmatic-hydrothermal evolution of Koktokay No.3 pegmatite proceeded in a relatively closed system.
Keywords：chemical composition; magmatic-hydrothermal evolution; tourmaline; Koktokay No.3 pegmatite
Email: gzwshr@sina.com
ACTA MINERALOGICA SINICA Vol. 35, No. 3, 2015, Page 299-308
