Abstarct: The Poshteh barite-baxse mextals deposit occurred at 18 kilometers east of Semnan in the Alborz magmatic arc within Eocene volcano-sedimentary sequence. The host sequence from bottom to top involves three major parts: 1) part 1: sedimentary rocks including conglomerate, limestone and sandstone, 2) part 2: lava-rich, and 3) part 3: tuff-rich. Mineralization occurred at top of the part 2 and baxse of the part 3. The host rocks consists of dominantly andesitic and dacitic tuff and lava. Four ore facieses are observed within the orebodies, from bottom to top: 1) vein-veinlet-breccia or feeder facies (stringer), 2) massive sulfide, 3) sulfide-bearing laxyered barite, and 4) banded iron-manganese-rich exhalative sediments. Textures and structures observed in the orebodies are vein and veinlet, brecciated, bedded, massive and disseminated. The mineralization involves primary minerals of barite, pyrite, sphalerite, galena, chalcopyrite, argentite, pyrolusite and pesilomelan, and secondary minerals of malachite, azurite and Mn-Fe oxides and hydroxides. Generally, four ore horizons were distinguished in the deposit: ore horizon 1, consists of a sulfide-rich stringer zone overlaid by a massive sulfide lens and a sulfide-bearing laxyered barite ore and Fe-Mn exhalative unit at top. Ore horizon 2, involves a baritic stringer zone and a manganese-rich exhalite unit at top. Ore horizon 3 is comprised of a baritic stringer and stratiform zone overlaid by an exhalite unit. In the ore horizon 4, only a baritic stringer zone crops out, the rest is covered by alluviums. Main wall rock alterations consist of choloritic, sericitic-Argilic, silicic and epidotic. baxsed on geochemical studies, volcanic rocks and sills show andesitic, basaltic, trachytic and rhyolitic compositions, and calc alkaline nature. The maximum amount of silver is 45 ppm belonging to massive ore facies, and the maximum amount of gold is 390 ppb belonging to the sulfide-bearing laxyered barite ore. Overall, Pb and Zn show the most enrichment in the stringer facies, while Cu, Cd, As and Ag were mostly enriched in the massive sulfide ore, Sb and Sr indicate maximum enrichment in the laxyered barite ore and Mn shows the maximum amounts in the exhalative faceis. Microthermometery study of fluid inclusions on barite, quartz and calcite shows that the most frequency of homogenesis temperature is from 100 to 150 centigrade and salinity is from 8 to 18 Wt% NaCl equivalent, and the frequency of density is from 0/5 to 1/1 and the pressure is lower than 50 atmosphere. Regarding to boiling evidences, the depth of water was lower than 1000 meters. baxsed on structural, stratigraphic, geometry of orebodies, alterations, texture and structure, mineralogy, fluid inclusion and geocemical studies, it seems that the Poshteh barite-baxse mextals deposit formed trough submarine volcanic-exhalative activities within an intra-arc basin as volcanogenic massive sulfide (VMS) mineralization. By comparison of this mineralization with other VMS types, the Poshteh barite-baxse mextals deposit shows the most similarity to the Kuroko-type deposits. In this study, for the first time in Iran, fragments of black and white chimneys and ore fluid cundoits were distinguished.