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Mineralogy, geochemistry, and genesis of the volcanic-hosted hydrothermal iron ore deposit in Somea, NW Iran

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Abstract

The Somea iron deposit is located ~ 22 km northwest of Ahar, NW Iran. The lenticular iron ores are formed as open space fillings within the pinch and swell structures of a curved fault in a highly brecciated zone within the host andesitic to dacitic rocks. Fe mineralization comprises magnetite and pyrite in the hypogene zone and hematite, limonite, and goethite in the supergene zone. According to the geochemical analysis results, the average grade of Fe ore is about 53 wt%. Magnetite ore is massive and lenticular in shape. Pyrite is formed as veins/veinlets in the crushed zones and fractures within the magnetite ore, following the continued tectonic movements along the fault. Goethite displays spongy and box-work, as well as botryoidal and colloform textures. Spongy and box-work textures indicate the very high acidity of the leaching fluids, which may be resulted from the oxidation of pyrite veins/veinlets. Banded and colloform textures are produced by colloidal precipitation from fluids. Hematite has formed either due to the alteration of magnetite or by dehydration of goethite at the oxidized zone. The very high Fe/Mn ratio of ore samples may indicate the hypogene genesis of the ore-bearing fluids, which were most likely originated from the neighboring Sheyvardagh granitic–granodioritic intrusion. Sulfur isotopic composition of the pyrite samples reveals a magmatic origin for the ore-bearing fluid and its sulfur content, which further advocates the hydrothermal genesis of the ore body. The δ34S values of the pyrite separates are ranging between − 1.4 and − 0.69‰ (V-CDT).

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Acknowledgements

Authors would like to express their thanks and appreciation to the authorities in the Research Bureau of the University of Tabriz for their financial support. Our appreciation is further expressed to the anonymous reviewers for making critical comments and valuable suggestions on this manuscript.

Funding

This study was financially supported by the Deputy Dean of the Research Bureau of Tabriz University through the grant no. 90213.

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Authors and Affiliations

  1. Research Institute for Fundamental Sciences, University of Tabriz, 29 Bahman Boulevard, Tabriz, 51666, Iran

    Vartan Simmonds

  2. Earth Sciences Department, University of Tabriz, Tabriz, Iran

    Ali Asghar Calagari & Zahra Sadeghi

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  1. Vartan Simmonds
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Correspondence to Vartan Simmonds.

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Simmonds, V., Calagari, A.A. & Sadeghi, Z. Mineralogy, geochemistry, and genesis of the volcanic-hosted hydrothermal iron ore deposit in Somea, NW Iran. Arab J Geosci 11, 82 (2018). https://doi.org/10.1007/s12517-018-3418-5

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