The Ahmadabad hematite/barite deposit is located to the northeast of the city of Semnan, Iran. Geostructurally, this deposit lies between the Alborz and the Central Iran zones in the Semnan Subzone. Hematite-barite mineralisation occurs in the form of a vein along a local fault within Eocene volcanic host rocks. The Ahmadabad deposit has a simple mineralogy, of which hematite and barite are the main constituents, followed by pyrite and Fe-oxyhydroxides such as limonite and goethite. Based on textural relationships between the above-mentioned principal minerals, it could be deduced that there are three hydrothermal mineralisation stages in which pyrite, hematite and barite with primary open space filling textures formed under different hydrothermal conditions. Subsequently, in the supergene stage, goethite and limonite minerals with secondary replacement textures formed under oxidation surficial conditions. Microthermometric studies on barite samples show that homogenisation temperatures (TH) for primary fluid inclusions range from 142 to 256°C with a temperature peak between 200 and 220°C. Salinities vary from 3.62 to 16.70 NaCl wt% with two different peaks, including one of 6 to 8 NaCl wt% and another of 12 to 14 NaCl wt%. This indicates that two different hydrothermal waters, including basinal and sea waters, could have been involved in barite mineralisation. The geochemistry of the major and trace elements in the samples studied indicate a hydrothermal origin for hematite and barite mineralisation. Moreover, the Fe/Mn ratio (>10) and plots of hematite samples of Ahmadabad ores on Al-Fe-Mn, Fe-Mn-(Ni+Co+ Cu)×10, Fe-Mn-SiX2 and MnO/TiO2 – Fe2O3/TiO2 diagrams indicate that hematite mineralisation in the Ahmadabad deposit occurred under hydrothermal conditions. Furthermore, Ba and Sr enrichment, along with Pb, Zn, Hg, Cu and Sb depletion, in the barite samples of Ahmadabad ores are indicative of a low temperature hydrothermal origin for the deposit. A comparison of the ratios of LaN/YbN, CeN/YbN, TbN/LaN, SmN/NdN and parameters of Ce/Ce* and La/La* anomalies of the hematite, barite, host volcanic rocks and quartz latite samples to each other elucidate two important points: 1) the barite could have originated from volcanic host rocks, 2) the hematite could have originated from a quartz latite lithological unit. The chondrite normalised REE patterns of samples of hematite barite, volcanic host rocks and quartz latite imply that two different hydrothermal fluids could be proposed for hematite and barite mineralisation. The comparison between chondrite normalised REE patterns of Ahmadabad barite with oceanic origin barite and low temperature hydrothermal barite shows close similarities to the low temperature hydrothermal barite deposits.
Adachi, M., Yamamoto, K. & Sugisaki, R., 1986. Hydrothermal charts and associated silicious rocks from northern Pacific: their geological significance as indication of ocean ridge activity. Sedimentary Geology 47, 148–125.
Alavi, M., 2005. JAM Geology Map 1:100,000, Geological Society of Iran. Tehran Iran.
Alexander, B.W., Bau, M., Andersson, P. & Dulski, P., 2008. Continentally derived solutes in shallow Archean seawater: rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa. Geochimica et Cosmochimica Acta 72, 378–394.
Bhattacharya, H.N., Chakraborty, I. & Ghosh, K., 2007. Geochemistry of some banded iron formations of the Archean supracrustal, Jharkhand-Orissa region, India. Journal of Earth System Science 116, 245–259.
Bodnar, R.J. & Vityk, M.O., 1994. Interpretation of micro thermometric data for H2O – NaCl fluid inclusions. [In:] B. De Vivo & M.L. Frezzotti (Eds): Fluid inclusions in minerals – methods and applications. Virginia Tech., Blacksburg, 117–130.
Bolhar, R., Kamber, B.S., Moorbath Fedo, C.M. & Whitehouse, M.J., 2004. Characterization of early Archean chemical sediments by trace elements. Earth and Planetary Science Letters 222, 43–60.
Bonatti, E., Kraemer, T. & Rydell, H., 1972. Classification and genesis of submarine iron-manganese deposits. [In:] Horn, D. (Ed.): Ferromanganese deposits on the ocean floor. Natl. Sci. Found, Washington, 149–166.
Boynton, W.V., 1984. Geochemistry of the REE meteorite studies. [In:] Henderson, P. (Ed.): REE Geochemistry. Elsevier, 63–114.
Bozkaya, G. & Gökce, A., 2004. Trace- and rare-earth elements geochemistry of the Karalar (Gaipasa-Antalya) barite-galena deposits, Southern Turkey. Turkish Journal of Earth Sciences 13, 63–75.
Clark, H.B, Poole, F.G. & Wang, Z., 2004. Comparison of some sediment hosted, stratiform barite deposits in China, the United States, and India. Ore Geology Reviews 24, 85–101.
Corliss, J.B. & Dymond, J., 1975. Nazca Plate metalliferous sediments: I. Elemental Distribution patterns in surface samples. EOS Transactions, American Geophysical Union 56, 445.
Crerar, D.H., Namson, J., Chyi, M.S., Williams, L. & Feigenson, M.D., 1982. Manganiferous cherts of the Franciscan Assemblage: I. General geology, ancient and modern analoques and implications for hydrotermal convenction at oceanic spreading centers. Economic Geology 77, 519–540.
Evans, A.M., 2009. Ore Geology and Industrial Minerals. An Introduction. Wiley, 389.
Ghorbani, M., 2013. The Economic Geology of Iran. Springer, 570 pp.
Guichard, F., Church, T.M., Treuil, M. & Jaffrezic, H., 1979. Rare earth elements in brites: distribution and effects on aqueous partitioning. Geochemica et Cosmochemica Acta 49, 983–997.
Hajalilou, B., Vusuq, B. & Moayed, M., 2014. REE geochemistry of Precambrian shale-hosted barite-galena mineralization, a case study from NW Iran. Journal of Crystallography and Mineralogy 22, 39–48.
Hein, J.R., Zierenberg, R.A., Maynard, J.B. & Hannington, M.D., 2007. Barite–forming environments along a rifted continental margin, southern California borderland. Deep Sea Research part 2. Tropical Studies in Oceanography 54, 1327–1349.
Jewell, P.W & Stallard, R.F., 1991. Geochemistry and paleoceanographic setting of central Nevada bedded barites. Journal of Geology 99, 151–170.
Jurković, I., Garašić, V. & Hrvatović, H., 2010. Geochemical characteristics of barite occurrences in the Palaeozoic complex of south-eastern Bosnia and their relationship to the barite deposits of the mid-Bosnian Schist Mountain. Geologia Croatica 63, 241–258.
Kato, Y. & Nakamura, K., 2003. Origin and global tectonic significance of early Archean cherts from the Marble Bar greenstone belt, Pilbara Craton, Western Australia. Precambrian Research 125, 191–243.
Kato, Y., 1999. Rare earth elements as an indicator to origins of skarn deposits:Examples of the Kamioka Zn-Pb and Yoshiwara-Sannotake Cu (-Fe) deposits in Japan. Resource Geology 49, 183–198.
Kesler, S.E., 2005. Ore-forming fluids. Elements 1, 13–18.
McDonough, W.F., Sun, S.S., 1995. The composition of the earth. Chemical Geology 120, 223–253.
Murray, RW., Buchholtz ten Brink, M.R., Jones, D.L., Gerlach, D.C. & Russ, G.P., 1990. Rare earth elements as indicators of different marine depositional environments in chart and shale. Geology 18, 268–271.
Nicholson, K., 1992. Contrasting minerological-geochemical signatures of manganese oxides: Guides to metallogenesis. Economic Geology 87, 1253–1264.
Noguchi, T., Shinjo, R., Ito, M., Takada, J. & Oomori, T., 2011. Barite geochemistry from hydrothermal chimneys of the Okinawa Trough: insight into chimney formation and fluid/sediment interaction. Journal of Mineralogical and Petrological Sciences 106, 26–35.
Palinkas, L.A. & Jurkovic, I., 1994. Lanthanide geochemistry and fluid inclusion peculiarities of the fluorite form the barite deposits south of Kresevo (Bosnia and Herzegovina). Geologia Croatica 47, 103–115.
Roedder, E., 1984. Fluid inclusions. Reviews in Mineralogy, vol. 12. Mineralogical Society of America, 644 pp.
Rona, P.A., 1978. Criteria for recognition of hydrothermal mineral deposits in oceanic crust. Economic Geology 73, 135–160.
Ruhlin, D.E. & Owen, M., 1986. The REE geochemistry of hydrothermal sediments from the East Pacific rise: Examination of a seawater scavenging mechanism. Geochemica et Cosmochemica Acta 50, 393–400.
Shepherd, T.J., Ranbin, A.H. & Alderton, D.H.M., 1985. A practical guide to fluid inclusion studies. Blackie, Glasgow, 239 pp.
Ulrich, M.R. & Bodnar, R.J., 1988. Systematics of stretching of fluid inclusions II: barite at 1 atm confning pressure. Economic Geology 83, 1037–1046.
Zamanian, H. & Radmard, K., 2016. Geochemistry of rare earth elements in the Baba Ali magnetite skarn deposit, western Iran – a key to determine conditions of mineralization. Geologos 22, 33–47.
Zarasvandi, A., Zaheri, N., Pourkaseb, H., Chrachi, A. & Bagheri, H., 2014. Geochemistry and fluid-inclusion micro thermometry of the Farsesh barite deposit, Iran. Geologos 20,201–214.