The Bafq metallogenic district in the Kashmar-Kerman zone, or Posht-Badam block, in the Central Iran structural zone, hosts large iron oxide-apatite deposits hosted in Early Cambrian volcanic, subvolcanic, and sedimentary rocks, as well as in Precambrian metamorphic rocks. The proposed models vary from orthomagmatic to hydrothermal and sedimentary. Different generations of apatite have been identified based on their size, morphology, and paragenetic relationships with magnetite and the host rock. Microthermometric studies were carried out on two main generations of apatite (referred to as Ap-I and Ap-II) from the main stage of mineralization, and on the late calcite, quartz and chlorite in the samples from Chadormalu, Esfordi, and Gazestan deposits. For Chadormalu, the homogenization temperature (Th) and fluid salinity for the liquid-vapor (LV) fluid inclusions in Ap-I and Ap-II were determined to be 266-580 °C and 138-460 °C, and 0.5-10.7 and 12.8-19.6 wt.% NaCl eq., respectively. For Ap-I and Ap-II from Esfordi, the Th and salinity were between 167 to >500 °C and 2.5-6.7 wt.% NaCl eq., and 165-464 °C and 9.8-23.5 wt.% NaCl eq., respectively. The halite-bearing inclusions in Ap-II from Esfordi yielded Th and salinity >500 °C and 36-37 wt.% NaCl eq. For Ap-II in Gazestan, the Th and salinity were measured at 416 to over 500°C, and 19.8 to 25.8 wt.% NaCl eq, respectively. The late calcite coexisting with pyrite from Gazestan yielded Th and salinity at 183-310 °C and 40-41 wt.% NaCl eq. The eutectic temperatures (Te) for various inclusions were measured at -21 to -53°C, implying the presence of complex ternary salts in the ore fluids. The results suggest the involvement of two different fluids in the evolution of the iron ore systems: a magmatic fluid, with relatively high temperature (150 to >500 °C) and low-moderate salinity (0.5-25.8 wt.% NaCl eq.), and a fluid with lower temperature (183-310 °C) but higher salinity. The role of the two fluids is supported by the oxygen isotopic composition of magnetite for the former and the sulfur isotopic composition of pyrite for the latter.
 
Introduction
The Bafq metallogenic district in the Kashmar-Kerman Zone (Ramezani and Tucker, 2003) or Posht-Badam Block (Haghipour, 1977b) in the Central Iran Structural Zone embraces several Kiruna-type magnetite-apatite deposits, including Chadormalu, Choghart, Gazestan, and Esfordi (e.g., Samani, 1988; Daliran, 2002; Moore and Modabberi, 2003; Jami, 2005; Torab and Lehman, 2007; Stosch et al., 2011; Heidarian et al., 2016; Heidarian et al., 2017). The origin of the deposits is debated, with models ranging from orthomagmatic (e.g., Foerster‌ and Jafarzadeh, 1994; Mücke and Younessi, 1994; Mokhtari et al., 2013) to hydrothermal (Daliran, 2002; Moore and Modabberi, 2003; Jami et al., 2007; Heidarian et al., 2017) and sedimentary, related to the late Precambrian glacial event (Aftabi et al., 2009; Mohseni and Aftabi, 2015). This study investigates the physicochemical properties of ore-forming fluids by fluid inclusion microthermometry on apatite and several other nonmetallic minerals in selected samples from Chadormalu, Esfordi, and Gazestan deposits. The results are compared with published fluid inclusion data and discussed, in an attempt to tackle the source and evolution of the ore fluids.
 
Materials and methods
Mineralogical and paragenetic studies were conducted on samples from ore and host rocks in outcrops and drill cores from Esfordi, Chadormalu, and Gazestan deposits. Some 20 samples were selected for doubly-polished sections and fluid inclusion petrography and microthermometry. The experiments were performed at the Iranian Mineral Processing Research Center (IMIDRO), utilizing a Linkam TMHS 600 heating-freezing stage on a Zeiss Axioplan-2 microscope. The stage was calibrated with cesium nitrate (melting point 414°C, accuracy ±0.6°C) and n-hexane (melting point -94.3°C, accuracy ±0.2°C). The fluid inclusion studies were focused on two main generations of apatite; limited measurements were performed on actinolite, and late chlorite, calcite, and quartz.
 
Results
Magnetite is the main ore mineral in the Bafq district, partially replaced by hematite at surface and shallow depths. Associated minerals include apatite, actinolite, tremolite, diopside, albite, quartz, dolomite, calcite, chlorite, talc, and minor sulfides dominated by pyrite. Ore textures vary from massive to breccia in central parts of the main ore bodies to pegmatoid comb textures in the peripheral veins. A banded, cumulate-looking ore texture with alternating magnetite and actinolite-rich bands was identified in Chadormalu (Fig. 8A). Two generations of apatite, here referred to as Ap-I and Ap-II, were identified in the selected deposits based on the textures and paragenetic relations. The Ap-I occurs mostly as euhedral to subhedral crystals of varying sizes in the massive ore (Fig. 5A, C and G). The Apatite-II occurs as coarse to pegmatoid crystals commonly associated with magnetite in vein-type ores with comb textures at the margins of the massive ores and/or within the altered host rocks (Fig. 5B, D and F).
Fluid inclusions were classified based on the phases present at room temperature as: single-phase liquid (L) (Fig. 6A and B), single-phase vapor (V) (Fig. 6C and D), two-phase liquid-rich (LV) (Fig. 6E and F), two-phase vapor-rich (VL) (Fig. 6H), three-phase liquid-vapor-halite (LVH) (Fig. 6J and I), and multi-phase inclusions (LVHS) (Fig. 6K) where S stands for unknown solid. The heating-freezing measurements were performed mostly on the LV and LVH inclusions in apatite, with limited experiments on actinolite, dolomite, and late chlorite, calcite, and quartz.
The Th values for the LV inclusions ranged from 138 °C to >500 °C (Table 2). For Chadormalu, the Th values for the primary and secondary fluid inclusions in Ap-II from the vein-type ore ranged between 268–454 °C and 138–217 °C, respectively. For the banded ore, fluid inclusions in actinolite and in the late dolomite and chlorite yielded Th values exceeding 500 °C, 280–330 °C, and 147–157 °C, respectively. For Esfordi, the LV inclusions in Ap-I and Ap-II homogenized between 167–350 °C and 165–464 °C, respectively. For Gazestan, the Th values for the vein-type Ap-II, and for the late calcite and quartz in breccia ore ranged between 416 °C to >500 °C, 190–270 °C, and 250–390 °C, respectively. For the LVH fluid inclusions in the calcite, homogenization occurred with halite dissolution between 290–330 °C; vapor disappearance occurred between 183–320 °C (Thd > Tvd). In contrast, for the LVH inclusions in the Esfordi Ap-II, halite dissolution occurred between 274 to 291 °C, with vapor disappearance at >500 °C (Tvd > Thd) (Fig. 11). In apatite from the Choghart massive magnetite-apatite ore, halite-bearing inclusions in Ap-I homogenized to the liquid phase (Tvd≤Thd), with halite dissolution occurring between 418 and 430 °C. (Fig. 11) (Hosseini et al., 2022).
A wide range of salinities, ranging from <1 wt.% to ~41 wt.% NaCl eq. was observed for fluid inclusions in various minerals (Table2). For Chadormalu banded ore, salinities were measured for the LV inclusions at 1.7-14 wt.% NaCl eq. in dolomite, and <1 to 2.4 wt.% NaCl eq. in chlorite. Higher salinities at 12.8-19.6 wt.% NaCl eq. were found in Ap-II from the vein-type ore. For Esfordi, the LVH inclusions in Ap-II yielded salinities at 36.1-37.1 wt.% NaCl eq., whereas LV inclusions displayed lower values at 9.8-23.5 wt.% NaCl eq. In contrast, lower salinities (1-6.7 wt.% NaCl eq.) were measured for LV inclusions in Ap-I. For Gazestan, the LVH inclusions in calcite from breccia ore yielded the highest salinities recorded (40-41 wt.% NaCl eq.). Significantly lower values (3.3-5.1 wt.% NaCl eq.), however, were observed for the LV inclusions in quartz from the breccia ore. Hosseini et al. (2022) for the LVH and LV inclusions in apatite-I reported 42.9- ~45 wt.% NaCl eq. and 11.5-13.8 wt.% NaCl eq., respectively, from the Choghart deposit.
 
Discussion
The fluid inclusion data suggest the involvement of at least two distinct fluids in the evolution of the iron oxide-apatite ore systems and associated wall rock alteration/metasomatism in the Esfordi, Chadormalu, Gazestan, and possibly other magnetite-apatite deposits in the Bafq metallogenic district. An evolving fluid source is reflected in the fluid inclusion data from the two main generations of apatite in Chadormalu, where a moderate- to high- temperature fluid (266 to 580°C) with low salinity (0.5 to 10.7 wt.% NaCl eq.) responsible for Ap-I in the massive ore (Heidarian et al., 2017) evolved into a lower temperature (268–454°C) but higher salinity (~13–20 wt.% NaCl eq.) fluid involved in the development of the pegmatoid Ap-II crystals in the vein-type magnetite-apatite ore (this study). The secondary LV fluid inclusions in the Ap-II crystals yielded lower homogenization temperatures (138–217°C) but the same salinities as in the primary fluid inclusions, consistent with a cooling evolution trend. Fluid evolution and multiple fluid sources is also supported by the banded ore in Chadormalu where actinolite developed in the presence of a high-temperature fluid (>500°C), whereas dolomite and chlorite in the same ore evolved through interaction with fluids at lower temperatures, 280-330°C and 147–157°C, and variable salinities, 1.74–14 and 1–2.4 wt.% NaCl eq., respectively. The comparison between massive and vein ore data reveals fluid mixing and evolution from high-temperature, low-salinity to low-temperature, moderate-salinity fluids in the Chadormalu deposit.
At Esfordi, a low to high-temperature (167->500°C) but low salinity (2.5-6.7 wt.% NaCl) fluid contributed to the development of magnetite-rich ore, while apatite-rich ore formed from lower temperature (165 to 464°C) but higher salinity (36-37 wt.% NaCl eq.) fluids. Ore formation in Gazestan occurred from high-temperature and relatively saline fluids, as Th and salinity data from the LV (416– >500°C and ~20–26 25 wt.% NaCl eq.) and LVHS inclusions (485– >500°C, and ~22–25 wt.% NaCl eq.) in apatite from the breccia ore suggest. The lower Th but higher salinity values at 183-310°C and 40-41 wt.% NaCl eq. recorded for the LVH inclusions in the late calcite in textural equilibrium with sulfides in the same ore sample suggests involvement of a second fluid source in the evolution of the ore system in Gazestan. Based on the lowest dissolution temperature of halite (235°C) in calcite fluid inclusions from the Gazestan breccia ore, and apatite-I (418°C) from the Choghart massive magnetite-apatite ore (Hosseini et al., 2022), the minimum trapping pressure is estimated at 90 MPa and 75 MPa, respectively. Considering a density of 2.7 g/cm³, the minimum depth for ore formation in Gazestan was 3.3 km; the apatite-I from Choghart developed at depths of ~2.7 km (Fig. 14).
Results from this study suggest that a high-temperature and low-moderate salinity fluid of possible magmatic origin played a key role in mineralization in the Chadormalu, Esfordi, and Gazestan, and possibly other magnetite-apatite deposits in the Bafq district. With time, the iron ore system interacted with an evolved fluid of low-moderate temperature and relatively high salinity, leading to the development of sulfides and other late-paragenetic minerals. The published sulfur isotopic data for pyrite, ranging between +8.9 to ~ 25 ‰, suggest a basinal brine origin for the evolved fluid.

Acknowledgements
The authors are grateful to the Chadormalu mining complex for providing facilities during field studies in the Bafq district. We sincerely thank Ms. Aghajani from the Iran Mineral Processing Research Center (IMPRC) for providing the microthermometry data for this research.