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چکیده
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The economically significant Baba Ali iron ore deposit, is located in the Sanandaj-Sirjan zone, western Iran, is associated with diorite. The mineralization trends in a ENE-WSW direction with thickness that varies from 30 m up to 50 m and a length of about 250 m. The main mineral assemblages are massive magnetite, epidote, actinolite, tourmaline, quartz, calcite, and pyrite. Using different magnetite compositional discrimination diagrams, the low concentrations of Ti (0.11 wt%), Al (0.06 wt%), Cr (19.62 ppm), and Co (20.26) and high Ni/Cr ratios (6.34) are consistent with a hydrothermal origin, similar to typical skarn mineralization. The different elemental compositions of various magnetite generations might be due to an ore-forming fluid that initially a high-T magmatic hydrothermal character, then evolved to a lower temperture meteoric water dominated system. It seems that Fe-bearing saline fluids infiltrated the carbonate host rocks, causing high temperature, acid metalliferous fluids to become neutralized during reaction with carbonates, causing a decrease in iron solubility and saturating as a magnetite with increasing pH and decreasing the temperature. The close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility, triggering ore precipitation and replacement at relatively low temperatures (~300°C), under reducing conditions.
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