Mineralogy, fluid inclusions and carbon isotopes of the Kaman iron deposits, Central Anatolia, Turkey: Implication for ore genesis and hydrothermal evolution

Abstract

The Kaman iron deposits are located in Central Anatolia and are hosted by the Triassic Bolçadağ Marble and Upper Cretaceous Çelebi granitoid. Magnetite mineralization manifests as rhythmic banded and irregular lenses, which can be massive or disseminated within calcic marble and skarn zones. Six main paragenetic stages of skarn formation and ore deposition have been identified: (1) Na-(Ca) alterations composed of plagioclase (An4–31), and actinolite; (2) a prograde stage representing oxidized mineralogy dominated by diopside (Di62–98Joh0–4), grossular–andradite (Grs15–84Alm4–8Sps1–4) and magnetite; (3) a retrograde stage consisting of epidote (Ep51–62Cli38–49), magnetite, calcite, quartz, and less-abundant sulfides and chlorite; (4) a quartz-calcite-pyrite stage containing pyrite, quartz, calcite, and chlorite; and (5, 6) quartz-carbonate and supergene stages characterized by quartz, calcite, hematite, and chalcedony, goethite.Fluid inclusion and carbon isotope studies have shown that the prograde stage formed from moderate–high-salinity (7.1 to >70 wt% NaCl eq.) and high-temperature (339 to >600 °C) fluids. Liquid and vapor-rich inclusions in an early garnet were homogenized in the liquid and vapor phases in a similar temperature range (513 and 529 °C). The δ18O and δ13C of calcites that accompany rhythmic banded magnetite ranged from 22.82 to 23.50‰ and −4.68 to −5.31‰, respectively. The retrograde stage was formed from low–high-salinity (2.9 to 45.4 wt% NaCl eq.) and low–high-temperature (167 to 459 °C) fluids. The δ18O and δ13C of skarn calcites ranged from 4.34 to 15.86‰ and −3.57 to 0.23‰, respectively. The quartz-calcite-pyrite stage was formed from low-salinity (3.1–7.5 wt% NaCl eq.) and temperature (171–392 °C) fluids. The δ18O and δ13C values were −2.38‰ and 2.43‰, respectively. The quartz-carbonate stage formed from low-salinity (3.6 to 5.7 wt% NaCl eq.) and temperature (129 to 169 °C). In all phases, the eutectic and clathrate melting temperatures ranged from −59.5 to −52.2 °C and +4.4 to +12.0 °C, respectively. This indicates that the solutions contain H2O–NaCl–CaCl2–(±MgCl2)–CO2.These fluid inclusion data suggest that fluid boiling occurred under pressures between ~60 and 70 MPa based on hydrostatic consideration during the prograde stage. The main magnetite deposition occurred following boiling, with rising salinity and temperature magmatic–hydrothermal fluids and in the pressure range of ~15 to 50 MPa. Depletion in δ13C was attributed to high-temperature fluid infiltration and indicates an open-system volatilization process. It is suggested that the retrograde stage had developed in two episodes, with the carbofracturing effect triggered by CO2. The carbon isotope data of calcites indicate the mixing of low-temperature metasomatic and meteoric water in later stages. The mineralogy, microthermometry, and carbon isotope results reveal that Kaman iron deposits were developed by a combination of processes such as contact infiltration metasomatism, fluid–rock interaction, cooling, and fluid mixing as a result of decreasing pressure.