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Hossein Kouhestani

محمد ابراهیمی، حسین کوهستانی، احسان شهیدی
بررسی تیپ و خاستگاه کانه زایی آهن در رخداد معدنی مسگر، جنوب زنجان، با استفاده از داده های سنگ شناسی، کانی شناسی و زمین شیمیایی
Investigation on type and origin of iron mineralization at Mesgar occurrence, south of Zanjan, using petrological, mineralogical and geochemical data
Abstract


Mesgar iron occurrence is located in northwestern part of the Central Iran, 115 km south of Zanjan. Rock units exposed in the study area consist of Miocene sedimentary and volcanic-pyroclastic rocks. Iron mineralization occurs as vein and lens-shaped bodies within and along the contacts of pyroclastic (footwall) and andesitic basalt lavas (hanging wall). The lavas show porphyritic texture consisting of plagioclase (up to 3 mm in size) and pyroxene phynocrysts set in a fine-grained to glassy groundmass. Geochemical data indicate a calc-alkaline affinity for the volcanic rocks, associated with active continental margin. Iron mineralization occurs as vein and hydrothermal breccia cements, and shows vein, veinlet, massive, brecciated, clastic and disseminated textures. Hematite is the main ore which is accompanied by minor magnetite and chalcopyrite. Goethite is a supergene mineral. Quartz and chlorite are present in the gangue minerals that represent vein, veinlet, colloform, cockade and crustiform textures. Alteration is restricted to silicified and chloritic altered parts of the ore zones. In the outer parts of the mineralization zones, alteration types are sericite and chlorite-calcite. The ore zones show lower concentrations of Rare Earth Elements (REE), except Ce, relative to fresh volcanic host rocks. Light REE (LREE) are more depleted than Heavy REE (HREE). These signatures indicate high rock-fluid interaction in Mesgar. Comparison of the geological, mineralogical, geochemical, textural and structural characteristics of the Mesgar occurrence with different types of iron deposits reveals that iron mineralization at Mesgar is originally formed as volcano-sedimentary, and then reconcentrated as vein mineralization by hydrothermal fluids.

 

 

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