Evolution of the Mo-rich scheelite skarn mineralization at Kozbudaklar, Western Anatolia, Turkey: Evidence from mineral chemistry and fluid inclusions

Abstract

The Kozbudaklar scheelite skarn deposit in the Tavşanlı Zone, located approximately 22km southeast of Bursa, is hosted by the Triassic calcic İnönü Marble and Eocene Topuk Pluton. At least four stages have been recognized through skarn evolution. Scheelite skarn distributed close to the Topuk Pluton occurred during the early (stage 1) and late (stage 2) prograde substages. The early prograde endo and exoskarn are composed of hedenbergite (Hd96Joh4)–plagioclase (An55–64) and hedenbergite (Hd61–94Joh4–7), accompanied by calcic garnet (Grs38–94Sps1–5Alm0) and scheelite (Pow1–6). The second stage represents a relatively oxidized mineralogy dominated by diopside (Hd16–48Joh0–9), subcalcic garnet (Grs24–92Sps0–11Alm0–31) and scheelite (Pow7–32). The stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing.Fluid inclusions from skarn rocks are indicative of multiple fluid events: (1) low-moderate salinity (5–16wt.%NaCl equiv.) inclusions homogenized dominantly by a high-temperature (308°C to >600°C) liquid phase in stage 1. Fluid inclusions in an early garnet homogenized over a similar temperature range (440°C and 459°C) into both liquid and vapor phases. Eutectic temperatures ranging from −61.7°C to −35.0°C that indicate the presence of H2O–NaCl–(±MgCl2±CaCl2)–CO2 solutions; (2) coexisting daughter mineral-bearing high salinity (29.5≥70wt.%NaCl equiv.) and vapor-rich moderate salinity (11.5–16.7wt.%NaCl equiv.) inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range (308°C to >600°C) in stage 2. Eutectic temperatures range from −67.9°C to −51.8°C that shows the presence of H2O–NaCl–CO2–(±CH4/N2) solutions; (3) low-moderate salinity (12.5–7.6wt.%NaCl equiv.) and temperature (320°C to 215°C) inclusions homogenized by the liquid phase in stage 3. Eutectic temperatures range from −59.5°C to −44.2°C indicating the presence of H2O–NaCl–(±MgCl2±CaCl2)–CO2 solutions; (4) inclusions of low salinity (9.9–0.9wt.%NaCl equiv.) and homogenization temperature (183°C to 101°C) in stage 4.These data show that the Kozbudaklar skarn deposit was formed in a magmatic–hydrothermal system. In this model, carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization. Fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440°C and 459°C and pressures ranging from 50MPa to 60MPa based on hydrostatic considerations. Early scheelite was precipitated with relatively reduced mineral compositions. As a result of depressurization, Mo-rich scheelite with oxidized minerals formed via high salinity and vapor-rich inclusions. The second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1.5MPa. At shallow depths (<1.5MPa) with increasing permeability, sulfide and oxide minerals were deposited in the retrograde stage, greatly assisted by meteoric water. Finally, as a result of the diminishing of ore-forming fluids, post-depositional barren quartz and calcite veins were formed.