Journal of Economic Geology (Feb 2017)
Evaluating the controls on Tourmaline Crystallization in the mylonitic granite-gneiss pluton in the Northeastern of Jan mine (Lorestan province)
Abstract
Introduction The study area is a part of the Sanandaj- Sirjan zone that is located in the NW of Azna city and NE of the dimension stone mine of Jan between 49° 11' 41"and 49° 16' 07" E longitude and 33° 36'35" and 33° 38'12" N latitude., A pluton of mylonitic granite-gneiss is exposed in the area which contains abundant tourmalines as black and patchy or subgrain association. Geochemically, the studied granite-gneiss is A-type, peraluminous to slightly metaluminous and calc – alkaline to slightly alkaline (Moradi et al., 7). The electron microprobe analyses of the tourmalines display shorl-dravite in composition with more tendency to shorl (Moradi et al., 2015). In this paper we try to study the petrological sites of tourmaline formation with associated minerals, controller factors of crystallization using mineral chemistry of tourmaline, comprehensive behavior of trace elements in the tourmaline, synthetic phase diagrams and finally relationships between the associated minerals. Materials and methods The results of trace-element and major-element analyses were obtained from one polished thin section including 2 tourmaline grains. Major-element analyses of tourmaline were obtained at Oklahama City University of America using the JEOL 8200 electron microprobe with a spot size of 5 μm and trace-element analyses were performed on just a sample by Laser Ablation-Inductively Coupled Plasma-Mass Spectroscopy (LA-ICP-MS) a 193nm ArF excimer laser ablation system (MicroLas GeoLas 200Q) in combination with a quadrupole ICP-MS (Micromass Platform ICP) at Utrecht University of Netherland. Representative EMP and LA-ICP-MS analyses of tourmaline samples are presented in Tables1 and 2. Results The results of LA-ICP-MS on tourmalines of Jan mine in the North east of mylonitic granite-gneiss body show that distribution and diffusion of trace elements during the growth of tourmaline trend is positive on the plots of binary Mn versus Fetot / (Fetot +Mg) and it represents the formation of the tourmaline mineral from the melt is along with the progress of the differentiation (Jolliff et al., 1987; Kontak et al., 2002). Also the average composition of tourmaline – bearing mylonitic granite-gneiss pluton normalized spider diagram for the studied tourmaline shows positive anomaly and negative anomaly in Eu that indicates tourmaline minerals surrounded by quartz and feldspar grains (Copjakova et al., 2013). Secondary phases such as zircon and allanite very much effect on the REE patterns (Rollinson, 1993). Therefore, in the final stages of differentiation, allanite appeared earlier than it appeared in areas without tourmaline crystalliziation and LREE soon after tourmaline crystalized and they are deposited (Cuney and Friedrich, 1987). Using a combination of phase diagrams, the controlling factors of creation of tourmaline associated with biotite-tourmaline can be assessed, and the relationship between tourmaline and associated minerals, chemistry of tourmaline – bearing granitoid pluton, and location of petrological minerals tourmaline can be sought (Pesquera et al., 2005). Discussion The results of LA-ICP-MS on tourmalines of mylonitic granite-gneiss body in the north east of Jan mine in Sanandaj – Sirjan Zone represents tourmaline crystallization from the melt along with the progress of the differentiation. Also, the average composition of tourmaline – bearing mylonitic granite-gneiss pluton normalized spider diagram for the studied tourmaline shows positive anomaly and negative anomaly in Eu that indicates that tourmalines are surrounded by quartz and feldspar grains. According to petrographic evidence of tourmaline and biotite, it can be seen with muscovite. Therefore, where tourmaline is dominant, biotite and associated minerals are limited or do not exist. Using a combination of phase diagrams controlling factors of tourmaline crystallization associated with biotite-tourmaline can be assessed, and the relationship between tourmaline and associated minerals, chemistry of tourmaline – bearing granitoid pluton, and location of petrological of tourmaline minerals can be sought. Acknowledgements The authors would like to thank the Shahrekord University for providing the budget for this research. References Copjakova, R., Skoda, R., Galiova, M.V. and Novak, M., 2013. Distributions of Y + REE and Sc in tourmaline and their implications for the melt evolution; examples from NYF pegmatites of the Trebic Pluton, Moldanubian Zone, Czech Republic. Journal of Geosciences, 58(2): 113–131. Cuney, M. and Friedrich, M., 1987. Physicochemical and crystalchemical controls on accessory mineral paragenesis in granitoids: implications for uranium metallogenesis. Bulletin Mineralogie, 110(2-3): 235–247. Jolliff, B.L., Papike, J.J. and Laul, J.C., 1987. Mineral recorders of pegmatite internal evolution: REE contents of tourmaline from the Bob Ingersoll pegmatite, South Dakota. Geochimica et Cosmochimica Acta, 51(8): 2225–2232. Kontak, D.J., Dostal, J., Kyser, K. and Archibald, D.A., 2002. A petrological, geochemical, isotopic and fluidinclusion study of 370 Ma pegmatite–aplite sheets, Peggys Cove, Nova Scotia, Canada. The Canadian Mineralogist, 40(5): 1249–1286. Moradi, A., Shabanian Boroujeni, N. and Davodian Dehkordi, A.R., 2015. Geochemistry and determination genesis of tourmalines in the mylonitic granite-gneiss pluton in Northeastern of Jan mine (Lorestan province(. Journal of Petrology, 23(6): 65-82. (in Persian with English abstract) Moradi, A., Shabanian Boroujeni, N. and Davodian Dehkordi, A.R., 2017. Geochemistry of granitoid pluton in northeastern of mine Jan (province Lorestan). Journal of Economic Geology (in Persian with English abstract). (in print) Pesquera, A., Torres-Ruiz, J., Gil-Crespo, P.P. and Jiang, S. Y., 2005. Petrographic, chemical and B-isotopic insights into the origin of tourmaline-rich rocks and boron recycling in the Martinamor antiform (Central Iberian Zone, Salamanca, Spain). Journal of Petrology, 46(5): 1013–1044. Rollinson, H., 1993. Using geochemical data: evolution, presentation, interpretation. Longman Scientific and Technical, London, 352 pp.
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