Mineralchemistry, mineralogy and behavior of trace and rare earth elements of tourmaline in pegmatites of Tashina area in North of Serkan, Hamedan province

Abstract

Tashina area, as a part of the Sanandaj-Sirjan magmatic-metamorphic Zone, is located in 10 kilometers north of Serkan city and on the southern slopes of Kuhe-Gavbar. The most important geological unit is the Middle Jurassic porphyroid granite. Tourmaline is observable as massive in pegmatites as well as quartz tourmaline observed as vein within granodiorite. Massive tourmalines in the pegmatites are spherical, elliptical, elongated, and radial, and sometimes the amount is so large that it can be of the tourmalinite type. In microscopic scale, the massive tourmalines show brown-green in color, sometimes very intense intefrance and the tourmaline veins are brown-green and blue (indicolite). Indicolite related to the tourmaline delayed phase and is newer than brown-green tourmalines. According to EPMA of tourmaline mineral and with the help of various diagrams, the studied tourmalines show Fe-rich and schorl type. The tourmalines in pegmatites are often alkaline and tend to the vacancy group, and the tourmaline in the quartz-tourmaline veins are vacancy groups. Euhedral forms and lack of chemical zoning, high Al and Fe/Fe+Mg contents, deficiency in X sites, and plentiful tourmaline in host granitic rock which is poor of Li indicate the magmatic origin of tourmaline and its enrichment in B. Based on the geochemical analysis, the presence of Ba, Eu, Nb and Sr negative anomalies in samples and separation of plagioclase and K-feldspar present of important factors in magmatic evolution of rocks in this area. The studies show a good correlation between the results of petrographic studies, trace and REE geochemistry.