The possible synglaciogenic Ediacaran hematitic banded iron salt formation (BISF) at Hormuz Island,southern Iran: Implications for a new style of exhalative hydrothermal iron-salt system |
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| Institution: | 1. Department of Mining Engineering, Shahid Bahonar University of Kerman, P.O. Box 76135-133, Kerman, Iran;2. Department of Geology, Shahid Bahonar University of Kerman, P.O. Box 76135-133, Kerman, Iran;1. National Iranian Oil Company–Exploration Directorate, Tehran, Iran;2. Department of Geology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran;3. Kamandab Consulting Engineers Company, Tehran, Iran;4. Université de Paris VI, Paris, France;5. Géosciences and Environnement, Université de Cergy-Pontoise, Paris, France;6. Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran;1. School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea;2. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;1. Institute of Geophysics of the Czech Academy of Sciences, Bo?ní II/1401, 141 31, Prague, Czech Republic;2. Structural Geology, Tectonics and Geomechanics, EMR, RWTH Aachen University, Lochnerstr. 4-20, D-52056 Aachen, Germany;3. Center for Lithospheric Research, Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic;4. Institut de Physique du Globe de Strasbourg (CNRS UMR7516), Ecole et Observatoire des Sciences de la Terre, Universite de Strasbourg, 67084 Strasbourg Cedex, France;5. Geological Survey of Iran, Azadi Square, Meraj Avenue, Tehran, 13185-1494, Iran;6. Institute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43, Prague, Czech Republic;7. Geological Institute, RWTH Aachen University, EMR, RWTH Aachen University, Wüllnerstr. 2, D-52056 Aachen, Germany;1. Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran;2. National Iranian Oil Company, Exploration Directorate, Tehran, Iran;3. Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran;1. Department of Geology, Ferdowsi University of Mashhad, Islamic Republic of Iran;2. Department of Geological Sciences, University of Colorado, USA;3. Department of Geosciences, University of Aveiro, Aveiro, Portugal |
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| Abstract: | The Ediacaran BISF at Hormuz Island is a newly identified glaciogenic iron-salt deposit in the Tethyan margin of Gondwana. The BISF was formed by synchronous riftogenic A-type submarine felsic volcanism and evaporate deposition. The mineralization occurs in a proximal felsic tuff cone and jaspilitic distal zones and contains 1 million tonne of hematite-rich ore with an average grade of 58% Fe. The ore structure shows cyclicity of macrobandings, mesobandings and microbandings of anhydrite, halite, hematite and chert, which marks a new record in BIFs geohistory. The alteration minerals in the proximal and distal zones are actinolite, ripidolite, epidote, sericite, tourmaline, clinochlore, anhydrite and clay minerals. The occurrence of metamorphosed polygenetic bullet-shape dropstones in BISF attests that there was probably a continuous process of ice melting, episodic submarine volcanism and exhalative hydrothermal banded iron salt formation during the Late Ediacaran time. The non-metamorphosed Neoproterozoic stratigraphy, the presence of genus Collenia, U-Pb dating (558 ± 7 Ma) and the marked negative δ13C excursion in cap carbonates are representative of Late Ediacaran glaciation, which has been identified worldwide. The REE+Y display light REE enrichment, unusually strong Tb-Tm anomaly, a weak positive Y anomaly, but no distinguished Eu and Ce anomalies, reflecting the glaciogenic nature of the BISF. The contents of Zr, Hf, Nb, Ta, Th, La, Ce and Y in BISF, dropstones, halite and cap carbonates are similar to those of the Neoproterozoic glaciogenic BIFs. Also, the Ni/Fe, P/Fe ratios and Fe/Ti – Al/Al + Fe + Mn + Ca + Na + K diagram suggest an exhalative hydrothermal Ediacaran-type BISF. The absence of brecciated magnetite in the ore association and the low contents of copper (9–493 ppm) and gold (<5–8 ppb) are not in favor of the IOCG – Kiruna-type iron oxide ores. The co-paragenesis of hematite with several alteration minerals, in particular actinolite, tourmaline and anhydrite, indicates that the exhalative hydrothermal fluids were generated by the interaction of seawater with the felsic rocks and sediments at about 200–500 °C. The interaction of seawater with felsic magma and sediments led to the formation of Mg-rich alteration minerals, leaching Si, Fe, Mn and other elements and forming the potential ore fluids. It is highlighted that the A-type alkaline submarine felsic volcanism could be considered as an exploration target for BISF. |
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| Keywords: | Ediacaran glacial timelines BISF Submarine A-type rhyolitic volcanism Metamorphosed dropstones Hormuz Island |
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