Mineralogy and comparison of tourmaline chemistry in quartz-tourmaline veins with granitoid host and metapelitic rocks in the Shah-Kuh district (E Iran): An approach to Tin mineralization potential

The Shah-kuh granite batholith (South of Birjand), monozogranite and syenogranite composition, is located on the eastern edge of the Lut block and consists mainly of plagioclase, alkali-feldspar and quartz associated with biotite and tourmaline. The predominant texture of the monozogranite and syenogranite unit is granular to porphyric and granular to micrographic, respectively. Metapelite rocks, host quartz-tourmaline veins, show porphyroblastic texture. Metapelite hosted tourmalines are in the range of dravite and alkaline tourmalines, while granitoid-hosted tourmalines are shorlite type. Presence of properties such as higher Mg content than Fe, low Fe/(Fe + Mg) value, low Al content, tendency towards outside of alkaline depletion and proton depletion vectors and FeO/(FeO + MgO) values less than 0.6 in metapelite host tourmaline veins indicates fluid-rock interaction in an open system far away from the granitoidic body and magmatic-hydrothermal origin. Also, characteristics, such as high Fe/(Fe + Mg) ratio, lack of zoning and proximity to granitoidic body in tourmaline veins with granitoid host rocks, indicates the separation of penomatolitic fluid containing boron (B) from granitic magma and its proximity to B-bearing fluid source. The results of tin analysis in some rock units of Shah-kuh region show that tin mineralization and probably tungsten (more than 500 ppm) are concentrated in quartz-tourmaline veins located in the north and northwest of the study area which is not economic grade (4500 ppm) in the high grade tin deposits.