Mineral chemistry, mineralogy and the behavior of trace and rare earth elements of tourmaline in pegmatites of Tashina area (North of Serkan, Hamedan Province)

Abstract

Tashina area, as a part of the Sanandaj- Sirjan magmatic- metamorphic Zone, located 10 kilometers north of Serkan city and on the southern slope of Kuhe- Gavbar. The most important geological unit is the porphyroid granite belonging to the Middle Jurassic. Tourmaline is observed as massive in pegmatites and as quartz tourmaline veins within the host granodiorite. The massive tourmalines are spherical, elliptical, elongated, and radial, and sometimes it is so abundant that it can be as the tourmalinite type. Optically, the massive tourmalines show brown- green in color, sometimes very intense intefrance whereas the tourmaline veins are brown- green and blue (indicolite). Indicolite related to the tourmaline delayed phase and is newer than brown- green tourmalines.The studied tourmalines are Fe- rich and schorl type, base on EPMA data as well as several diagrams. The tourmaline in the quartz- tourmaline veins are the vacancy type while the second type is often alkaline with tendency to this group. Euhedral forms and the lack of chemical zoning, with high Al and Fe/Fe+Mg contents, deficiency in X sites, and plentiful tourmaline in host granitic rock which is Li poor are all indicative of the magmatic origin of tourmaline enriched in B. The presence of Ba, Eu, Nb, and Sr negative anomalies in the studied samples and the separation of plagioclase and K- feldspar can be accounted as important factors in magmatic evolution of the studeid rocks. Overall, the results of petrographic studies are well in accordant with trace and REE geochemistry data.

Keywords

• pegmatite
• schorl
• rare earth elements
• tashina
• serkan