Journal of Earth Science & Climatic Change
Open Access

Abstract

T ourmaline is one of the accessory and mafic minerals which occurs in peraluminous granitic pegmatites from the North of Golpayegan (Ochestan area). The mineral assemblage of these pegmatites consists of turbidity K-feldspar (perthitic orthoclase and microcline), plagioclase (albite), quartz, muscovite (primary and secondary), zoned tourmaline (dravite) and biotite (Mg-biotite) in order of decreasing abundances. The leucocratic matrix is dominated by large K-feldspar with broad perthitic exsolution lamellae. Twinned crystals of plagioclase have undergone sericitisation. Anhedral quartz shows intensive oscillatory extinction and subgrain formation. Muscovites present as large and fine grains which sometimes curved and growth next to tourmaline and in or between feldspars. Tourmaline is usually euhedral and shows optical zonation (yellowish green color shifted to yellow at the rim). Small biotite is trapped between quartz and feldspar. Zoned tourmalines in pegmatite are mainly restricted to the sodium replacement and yellow tourmaline are driven from biotite which attacked by boron introduce. Evidences of alkali metasomatism such as coarsening domains in perthite, growth of new micas (sodic metasomatism), replacement of albitic plagioclase by microcline, distinct reddish coloration microclines in hand specimens and turbidity of the feldspar crystals in thin-section (Potassic metasomatism) are seen in these pegmatites. Based on the occurrence of H + metasomatism which follow albitisation process and Quartz +Muscovite + (Na + , K + )=Perthite + H + reaction, there is the possibilithy of tourmalinization through K(Fe,Mg) 3 AlSi 3 O 10 (OH) 2 +1.67KAl 2 AlSi 3 O 10 (OH) 2 +NaCl( aq )+1.67HCl( aq )+3B(OH)3( aq )=Na(Fe,Mg) 3 Al 6 B 3 O 9 Si 6 O 18 (OH) 4 + 2SiO 2 +2.67 KCl( aq )+ 6H 2 O reaction which occurs in the presence of neutral to acidic solutions to form dravite in the studied pegmatites.

Biography

Akramosadat Mirlohi did her Ph.D. in Petrology at the age of 31 years in University of Isfahan, Isfahan, Iran. She has published 5 papers in journals (1 ISI and 4 Iranian Scientific Journals).