Numerous Pb-Zn occurrences are known in Triassic sediments of the Eastern and Southern Alps as well as along the Periadriatic Lineament (e.g. Topla, Bleiberg, Mežica) but the origin of these deposits is still somewhat controversial. The Mežica Pb-Zn ore deposit represents a classic example for this type of mineralization. The deposit is located in the Northern Karavanke geotectonic unit of the Eastern Alps in Slovenia. The mineralization is hosted by Triassic platform carbonates. The deposit was formed in Late Triassic to Early Jurassic by thermally driven fluid flow during the crustal extension. Galena and sphalerite are the main ore minerals while calcite and dolomite are the most common gangue minerals. Obtained fluid inclusion data suggest that the main mechanism for formation of the Pb-Zn Mežica deposit is mixing of metal-bearing brines with deluted fluids of presuamably meteoric origin. The decreased salinity destabilized metal-chloride complexes and reduced the fluid capacity to transport base metals, enabling precipitation of ore minerals. Post-ore carbonates formed under the influence of CO2 originating from oxidation of organic matter, indicating that organic matter from host dolomite might have contributed to reductive conditions in the system. Fluid inclusions data obtained from wulfenite and supergene carbonates revealed that the descending fluids were deluted hot water.