Kizilcaoren is a vein-type, fault controlled fluorite-barite-rare earth element (REE) deposit and forms the only economic REE and thorium source of Turkey. The ore-bearing veins formed by hydrothermal solutions originating from alkaline volcanism occur in a wide variety of host rocks ranging from metasandstones to pyroclastics. The host rocks show three types of hypogene alteration of varying intensity: silicification, argillic alteration, and sericitization. Three main economic ore types identified were fluorite ore, massive barite ore, and bastnaesite+fluorite+barite ore. Fluid inclusion measurements from barite and bastnaesite show low salinity of 0.5 - 9.5 eq. wt.% NaCl and homogenization temperatures of 105 degrees and 246 degrees C respectively. Fluorite was formed from slightly higher salinity (< 12.4 wt.% NaCl equiv.) fluids at low- and moderate-temperatures (163 degrees-336 degrees C). Relatively low-salinity and low and moderate temperature inclusions might be the result of mixing of deep-saline brines with low-salinity meteoric fluids. Sulphur isotopic composition suggests a source similar to that of the hydrothermal fluids which are compatible with volcanogenic sulphate field.