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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