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Geochemistry of skarn and porphyry deposits in relation to epithermal mineralization in the Arasbaran metallogenic zone, NE Tabriz, Iran

Alavi Ghafour, Radmard Kaikhosrov, Zamanian Hassan, Hosseinzadeh Mohammad Reza, Khalaji Ahmad Ahmadi

Geological Quarterly

2020

Vol. 64, No. 1

141--164

The Arasbaran metallogenic zone in northern Iran is part of the Alborz-Azerbaijan magmatic zone, which developed along the southern margin of Eurasia during the Early Mesozoic-Late Cenozoic. This region hosts precious and base metal mineralization, including porphyry, skarn, and epithermal copper, molybdenum, and gold deposits. Rare earth element variations across all the deposits are similar, indicating a similar source for these elements. The north-west trending belt comprising the Nabijan to the Sonajil deposits consistently shows chiefly alkaline conditions of formation. Fluid inclusion studies indicate that both high and low temperature hydrothermal fluids participated in the formation of all of the deposits. The mineralization age decreases from north to south and east to west and, although metal zonation is complex, the Cu-Au association post-dated the Cu-Mo mineralization reflecting that the ore fluid evolved in terms of both cooling and chemical changes due to fluid-fluid and fluid-rock interactions. In this region most deposits record a concentric zonation, with the centres preserving porphyry and skarn deposits and deposits becoming progressively epithermal toward the outer parts of the mineralizing system. According to this, the mineralization age decreases from the porphyry and skarn deposits to the epithermal deposits. The homogenization temperature and salinity both decrease from the centre to the outer zone. The pattern of homogenization temperature zonation, which is concordant with salinity zonation, suggests that fluids migrated up-dip and towards the margins of the zonation system.

Constraints on ore formation conditions at the Mazra’eh Shadi epithermal deposit, NE Tabriz, Iran : evidences from geochemistry, sulphur isotope, quartz textures and fluid inclusion studies

Radmard Kaikhosrov, Zamanian Hassan, Hosseinzadeh Mohammad Reza, Khalaji Ahmad Ahmadi

Geological Quarterly

2019

Vol. 63, No. 2

230--247

The Mazra'eh Shadi deposit is one of the most representative gold deposits in the Ahar-Arasbaran Belt. The main minerals are galena, sphalerite, pyrite and chalcopyrite. Concentrations of Au-Ag occur mainly within quartz veins. Five textures (crustiform, comb, microcrystalline, cockade, and mosaic) are distinguished by field reconnaissance and hand specimen observations. The δ34S values suggest an increasing role of meteoric water from the deepest levels to the shallow level and surface. Fluid inclusion data show that the mineralisation at the Mazra'eh Shadi deposit can be classified as a volcanic-rock-hosted intermediate-sulphidation epithermal deposit. Fluid inclusions in vein quartz can be distinctly divided into three types according to interpretation of petrographic features: intense boiling, gentle boiling and non-boiling conditions. The presence of intense and gentle boiling among different substages at the same level in the Mazra'eh Shadi deposit indicates that the base of the boiling zone likely shifted upward and downward during vein formation. The concentrations of Au-Ag occur mainly within quartz veins in the shallow level with gentle boiling (max. 813 ppb Au) and with intense boiling (max. 2420 ppb Au), whereas lower Au-Ag concentrations are associated with base metal-rich (Pb-Zn) in the deepest levels with non-boiling fluids (max. 52 ppb Au).