زمین‌ شیمی کانسار منگنز جون‌ آباد، شمال خاش، استان سیستان و بلوچستان

کانسار منگنز جون‌آباد در 16 کیلومتری جنوب‌‌شرق روستای جون‌آباد در شمال خاش و از لحاظ پهنه‌بندی رسوبی ساختاری در بخش میانی زون فلیشی شرق ایران واقع‌شده است. سنگ میزبان لایه‌های منگنز در این کانسار، شیل‌های قرمز‌رنگ است که در قسمت‌های بالایی و به‌‌صورت بین‌لایه‌ای یا به‌‌صورت آغشتگی، کانی‌سازی منگنز در آنها دیده می‌شود. هندسه ماده معدنی به‌صورت لایه‌ای شکل و اغلب هم‌‌شیب و همراه با واحدهای دربرگیرنده (شیل‌های قرمز‌رنگ) است. شیمی عناصر اصلی، نسبت‌های mn:fe، si:al و وجود ضرایب همبستگی مثبت بین al2o3، tio2 و fe2o3 نشان‌دهنده تاثیر هم‌زمان فرایندهای گرمابی در محیطی کم‌عمق همراه با ورود مواد آواری خاکی از جنس مافیک به درون حوضه رسوبی در محل شکل‌گیری کانسار است. نمودارهای عناصر فرعی، همگی بر محتوای پایین کانسنگ از عناصری همچون ni، cu و co دلالت دارند که نمایانگر قرارگیری کانسار در محدوده کانسارهای با منشا گرمابی است. نسبت‌های co:ni، co:zn، lree:hree، غنی‌شدگی عناصر lree نسبت به عناصر hree و آنومالی‌های منفی ce نیز بیانگر نقش سیال گرمابی کانه‌دار در این کانسار است. الگوی پراکندگی عناصر نادر خاکی برای این کانسار، همخوانی زیادی با الگوی توزیع عناصر نادر خاکی در کانسارهای با منشا گرمابی دارد.

Geochemistry of the Joun Abad manganese deposit, north Khash, Sistan and Baluchestan province

Introduction;Manganese deposits are classified as hydrogenous, diagenetic and hydrothermal deposits based on their mineralogy, chemical composition, and tectonic setting (Hein et al., 1997). Hydrogenous manganese deposits have slowly precipitated from seawater (210 mm/Myr) (Ingram et al., 1990). These deposits contain iron and are poor in manganese oxide. The Mn:Fe ratio is ~1 and Ni and Cu are represented by high concentrations ( >3000 ppm) (Hein et al., 1997; Usui and Someya, 1997). Diagenetic manganese deposits occur as nodules and have precipitated from hydrothermal solutions or pore water within altered sediments (Klinkhammer et al., 1982). These deposits are usually related to organic matter oxidation and formation of Mn carbonate minerals (Polgari et al., 2012). Hydrothermal manganese deposits have directly precipitated from lowtemperature hydrothermal solutions (Hein et al., 1997; Ingram et al., 1990). These deposits are generally laminated and stratabound or occur as irregular bodies and epithermal veins (Hein et al., 1997). Diagenetic and hydrothermal deposits are characterized by high Mn:Fe contents and low trace metal concentrations (Hein et al., 1994; Hein et al., 1996). Although there are similarities between these two deposit types, they are mostly distinguished by their morphologic, tectonic and growth rates (Kuhn et al., 1998). The Joun Abad manganese deposit is located 16 km southeast of the Joun Abad village, 72 km north of the city of Khash in the eastern longitude of 61° 06´ 0.7ʺ and the northern latitude of 28° 51´ 2.3ʺ. This zoning is structuralsedimentary that is located in the middle part of the flysch zone of Eastern Iran. In this paper, major, trace and rare earth element compositions of ores have been used as an approach to determine the conditions of ore formation.; ;Materials and methods;Twenty representative ore samples (~450 g) were selected from the Joun Abad manganese deposit. Geochemical analyses were made of samples taken from different surface mineral outcrops at various locations. Crushed and grounded ores (under 200 mesh) were analyzed at the Kansaran Binaloud Laboratories, Tehran, Iran. Major oxide and trace element contents were determined by XRay Fluorescence (XRF) and Inductively Coupled PlasmaOptical Emission Spectrometry (ICPOES), respectively, and the REEs were analyzed using the Inductively Coupled PlasmaMass Spectrometry (ICPMS) method.; ;Discussion and results;The Joun Abad manganese deposit is located 16 km southeast of the Joun Abad village, north of the city of Khash, and with respect to structuralsedimentary zoning in the middle part of the flysch zone of Eastern Iran. The host rocks of manganese layers are red shale, manganese mineralization is visible on the upper parts, as interlayers and/or contamination. The geometry of the ore mineral is in layered form and it is often conformable with units including red shales. The chemistry of the major elements, Mn:Fe and Si:Al ratios and the positive correlation coefficients between Al2O3, TiO2 and Fe2O3 indicate that they were affected by hydrothermal processes in a shallow environment together with entering mafic clastic materials in sedimentary basin where the ore formed. All trace element diagrams show low contents of elements such as Ni, Co and Cu in the manganese ores. The deposits of the study area in these diagrams plot in the field of hydrothermal deposits. Co:Ni, Co:Zn, LREE > HREE contents and total REE and negative Ce anomalies also indicate the role of orebearing hydrothermal fluid in the deposit. REE distribution patterns of the deposit are quite similar to those of hydrothermal deposits.; ;References;Hein, J.R., Gibbs, A.E., Clague, D. and Torresan, M., 1996. Hydrothermal mineralization along submarine rift zones, Hawaii. Marine Georesources & Geotechnology, 14(2): 177–203.;Hein, J.R., Koschinsky, A., Halbach, P., Manheim, F.T., Bau, M., Kang, J.K. and Lubick, N., 1997. Iron and manganese oxide mineralization in the Pacific. In: K. Nicholson, J.R. Hein, B. Buhn, and S. Dasgupta, (Editors), Manganese Mineralization: Geochemistry and Mineralogy of Terrestrial and Marine Deposits. Geological Society, Special Publication, London, pp. 123–138.;Hein, J.R., Yeh, H.W., Gunn, S.H., Gibbs, A.E. and Wang, C.H., 1994. Composition and origin of hydrothermal iron stones from central Pacific seamounts. Geochimica et Cosmochimica Acta, 58(1): 179–189.;Ingram, B.L., Hein, J.R. and Farmer, G.L., 1990. Age determinations and growth rates of Pacific ferromanganese deposits using strontium isotopes. Geochimica et Cosmochimica Acta, 54(6):1709–1721.;Klinkhammer, G.P., Heggie, D.T. and Graham, D.W., 1982. Metal diagenesis in oxic marine sediments. Earth and Planetary Science Letters, 61(2): 211–219.;Kuhn, T., Bau, M., Blum, N. and Halbach, P., 1998. Origin of negative Ce anomalies in mixed hydrothermalhydrogenetic FeMn crusts from the Central Indian Ridge. Earth and Planetary Science Letters, 163‌(1–4): 207–220.;Polgari, M., Hein, J.R., Vigh, T., SzaboDrubina, M., Forizs, I., Biro, L., Muller, A. and Toth, A.L., 2012. Microbial processes and the origin of the Urkut manganese deposit, Hungary. Ore Geology Reviews, 47: 87–109.;Usui, A. and Someya, M., 1997. Distribution and composition of marine hydrogenetic and hydrothermal manganese deposits in the Northwest Pasific. In: K. Nicholson, J.R. Hein, B. Buhn, and S. Dasgupta (Editors), Manganese Mineralization: Geochemistry and Mineralogy of Terrestrial and Marine Deposits. Geological Society, Special Publication, London, pp. 177–198.