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Abstract
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Pegmatite bodies with a simple mineral composition are widespread within the Sanandaj-Sirjan Zone (SaSiZ), Zagros Orogen, Iran, however gem-bearing pegmatite bodies are rare. There is a pegmatitic vein within the Hamadan garnet (± andalusite ± staurolite) schist adjacent to the Alvand Plutonic Complex (APC), south of Hamedan city (western Iran), in which large crystals of gem spodumene have been occurred together with quartz, amazonite, beryl, tourmaline, and apatite. This spodumene-bearing pegmatite (SBP) consists of four major zones with slightly different mineral composition from the border to the core. It includes the wall zone of quartz-rich granitoid and the intermediate zone of alkali granite and trondhjemitic compositions near the quartzolitic gem-bearing core zone. All parts of the vein are peraluminous in composition and exhibit the S-type affinity. Two types of spodumenes which have been distinguished in the core zone display vitreous luster, and are very pale yellow and pink, transparent and inclusion-free (eye clean) under 10X magnification loupe. Different color in these minerals can be attributed to the slightly different chemical composition, particularly lower Fe/Mn ratios in kunzite. The δ7Li values of these spodumenes (+5.58 to +6.57‰) are indicative of the incorporation of middle continental crustal components in their genesis. Change in the mineral assemblage from tourmaline-bearing in the intermediate zone to spodumene + tourmaline in the core zone of the SBP is consistent with increasing lithium content from the wall zone to the core. Petrographic, geochemical, and isotopic data indicate that partial melting of middle crustal Al-rich metapelitic source was followed by fractional crystallization to generate these rocks. In this concern, the required Li for the crystallization of spodumenes has probably been supplied by the breakdown of staurolite of the Hamadan schist and/or subsequent fractional crystallization of the parent magma. The results
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