S. Esmailnezhad; N. Taghipour; A. A. Hassannezhad
Abstract
The Nukeh iron deposit is situated at the north of Semnan and at south of Central Alborz structural zone. Volcano-pyroclastic rocks with Eocene age are the host of this deposit. Iron mineralization occurs as massive, disseminated, vein and breccia types in the Nukeh deposit and magnetite, hematite, pyrite, ...
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The Nukeh iron deposit is situated at the north of Semnan and at south of Central Alborz structural zone. Volcano-pyroclastic rocks with Eocene age are the host of this deposit. Iron mineralization occurs as massive, disseminated, vein and breccia types in the Nukeh deposit and magnetite, hematite, pyrite, chalcopyrite, garnet, epidote, quartz and calcite are the main minerals in this deposit. Fluid inclusions and stable isotopes (O, C, S) have been used to reveal the physico-chemical characteristics of hydrothermal fluids and genesis of the Nukeh Fe deposit. Seven types of fluid inclusions are identified in quartz, according to the phase numbers, which include, liquid inclusions (L), liquid-rich inclusions (L+V), vapor-rich inclusions (V+L), vapor inclusions (V), simple brine inclusions (L+V+S), halite-bearing liquid inclusions (L+S) and opaque-bearing liquid-rich inclusions (L+V+O). The ranges of homogenization temperature and salinity of liquid-rich fluid inclusions in quartz are 100-200˚C and 10-20 wt. % NaCl equivalent, respectively, whereas the ranges of homogenization temperature and salinity of vapor-rich fluid inclusions are 350-500˚C and 10-30 wt. % NaCl equivalent, respectively. Also homogenization temperature and salinities of liquid-rich fluid inclusions in calcite in garnet (type a) and magnetite (type b) zones is 75-125 ˚C but the salinity of fluid inclusions in calcite in garnet zone (15-25 wt. % NaCl) is more than salinity of these inclusions in magnetite zone (10-20 wt. % NaCl). δ13C and δ18O values of calcite (n=15) vary between -1.9 to +0.1 ‰ (VPDB) and -19.4 to -14.9‰ (SMOW), respectively. The average value of δ18OWater is of +17.85‰ (SMOW) in the Nukeh Fe deposit is different from the values for the primary magmatic fluid. Pyrite is the main sulfide mineral in the Nukeh Fe deposit and δ34S values of pyrite (n=9) is within the range of +3.9 to +5.4 ‰ CDT . The source of sulfur is considered to be magmatic on this basis. Fluid inclusions and stable isotopic (O, C, S) data suggest that the ore-forming fluids evolved by the various mixtures of magmatic brines and meteoric water and probably the genesis of the Nukeh Fe deposit is similar to skarn deposits.
