Abstract: Şaplıca alunite deposit is located near the Şebinkarahisar town (Giresun) within Pontide belk Alunite mineralization exists at the vicinity of the vein type sulfide deposits. Alunite deposit and part of sulfide veins occur in intensly alterated volcanites of late Cretaceous. The alunite deposit is exclusively confined by the volcanites. Alunite mineralization is controlled by E - W and NE - SW trending normal faults which are barren. They form the channel - wayof H2SO4 rich magmatic hydrothermal fluids. Alunites are produced by the base leaching of phenocrysts (typically alkali feldspar) of rhyolitic and rhyodacitic host rocks. Alunite minerals typically occur as aggregates of bladed or lathlikecrystals up to 1 mm. long, replacing alkali feldspar and groundmass, intergrown with quartz. Alunite is locally abundantin the centre of the advanced argillic alteration zones which develop throughout the late Cretaceous volcanites. As thealunite zone develops vertically downward, advanced argillic alteration zone develops laterally outward from the aluniteborder. Kaolinite is the dominant clay mineral of this extensive alteration type. The alunite zone is ringed by kaolinite zone. The acid sulfate alteration is typically characterized by a mineral assemblage of predominantly alunite, kaolinite,silica (as quartz and chalcedony), pyrite and sericite. Alunitization is a subset of this advanced argillic alteration.Sulfur isotope analyses have been performed on monomineralic concentrates from Şaplıca alunites and associated sulfides. The alunites (+ 8,9 %o + 10,7 %o + 12,8 %o) are enriched 34s, relative to sulfides (-1,3 %o; -2,9 %c; -5,3%6) which are depleted in 34 S . Calculated isotopic fractionation factors (a * = 1,007 - 1,018) and isotopic differences(A34s = 6,93 - 17,83) of associated alunit - sulfide pairs indicate the hypogene origin of alunites. This result is supported by the textural and mineralogical features of Şaplıca alunite deposit. It is most likely that requisite amounts ofH2SO4 must have been generated by a magmatic hydrothermal environments.