Geochemical Characteristics, Origin, and Evolution of Ore‐Forming Fluids of the K hut Copper Skarn Deposit, West of Y azd in Central I ran

The K hut copper skarn deposit is located at about 50 km northwest of T aft City in Y azd province in the middle part of the U rumieh‐ D okhtar magmatic arc. Intrusion of granitoid of O ligocene– M iocene age into carbonate rocks of the T riassic N ayband Formation led to the formation of marble and a calcic skarn. The marble contains high grade Cu mineralization that occurs mainly as open space filling and replacement. Cu ‐rich sulfide samples from the mineralized marble are also anomalous in Au , Zn , and Pb . In contrast, the calcic skarn is only weakly anomalous in Cu and W . The calcic skarn is divided into garnet skarn and garnet–pyroxene skarn zones. Paragenetic relationships and microthermometric data from fluid inclusions in garnet and calcite indicate that the compositional evolution of skarn minerals occurred in three main stages as follows. (i) The early prograde stage, which is characterized by Mg ‐rich hedenbergite ( Hd 53.7 Di 42.3 – Hd 86.1 Di 9.5 ) with Al ‐bearing andradite (69.8–99.5 mol% andradite). The temperature in the early prograde skarn varies from 400 to 500°C at 500 bar. (ii) The late prograde stage is manifested by almost pure andradite (96.2–98.4 mol% andradite). Based on the fluid inclusion data from garnet, fluid temperature and salinity in this stage is estimated to vary from 267 to 361°C and from 10.1 to 21.1 wt% NaCl equivalent, respectively. Pyrrhotite precipitation started during this stage. (iii) The retrograde stage occurs in an exoskarn, which consists of an assemblage of ferro‐actinolite, quartz, calcite, epidote, chlorite, sphalerite, pyrite, and chalcopyrite that partially replaces earlier mineral assemblages under hydrostatic conditions during fracturing of the early skarn. Fluids in calcite yielded lower temperatures ( T