Sphalerite at the Cisma deposit (Baiut ore district, Eastern Carpathians, Romania) occurs in two generations formed in different environments. Sphalerite-1 is characterized by a negative correlation between Fe and Mn and precipitated under equilibrium conditions. Sphalerite-2 was deposited in a non-equilibrium environment; it contains chalcopyrite inclusions and shows positive correlation of Fe and Mn. Fluid inclusion data on quartz identify boiling and point to depositional temperatures of 270 to 316^oC in the Bandurita vein and 143 to 344^oC in the Cisma vein at a paleo-depth of 500-800 m. Salinity (Na- and Mg-chloride) is less than 10 wt.% eq. NaCl for both veins. The various zoning patterns in sphalerite derive from a combination of boiling, cooling, and dilution of the ore-forming fluid.