Mineralogy and mineral chemistry of alteration zone in order to determine the tectonic settings and mineralization characteristics in the Choreh-Nab iron deposit (Western Alborz)

The Chore-Nab iron deposit is located in the northwest of the Zanjan-Zaker district. The deposit was formed in quartz monzonite, syenogranite, and granodiorite bodies introded into Lower Cambrian volcanic (andesite) and sedimentary units (siltstone, tuff, and ignimbrite) in the Tarom-Hashtjin metallogenic province. Iron mineralization occurs as brecciated, massive, disseminated, and vein-veinlet types. Major alteration minerals include actinolite, albite, magnetite, epidote, phlogopite, k-feldspar, and biotite. The main sulfide minerals are pyrite, chalcopyrite, and bornite. Based on field and mineralogical studies, sodic-calcic, potassic, propylitic, sericitic, siliceous, and argillic alterations have been identified in the deposit. Sodic-calcic alteration (albite-actinolite-magnetite), characterized by massive and brecciated magnetite in the depth, calcic (actinolite) and potassic (secondary biotite) alteration in the middle levels associated with vein-veinlet sulfide mineralization and finally propylitic alteration (chlorite-epidote) in the shallow levels are observed. Based on the results of chemical analyses, the clinopyroxenes in the alteration zones (mainly sodic-calcic) are mostly augite and less commonly diopside. Plagioclase has a range of albite compositions. Amphiboles are calcic and often tremolite and magnesio-hornblende. Finally, the absence of Cl in the composition of the amphiboles of the Chore-Nab deposit and the presence of at least two Cl-rich amphiboles in all the IOCG deposits of the Carajas mineral province can be attributed to the lack of influence of replacement mechanisms generated by Cl-rich hydrothermal fluids during sodic-calcic alteration.