Celestite mineralization is known from an approximately 80 km(2) area of Karstryggen, on the western margin of Jameson Land in central East Greenland. The Upper Permian Karstryggen and Wegener Halvphi Formations, which host the celestite, contain dominantly limestones and subordinate evaporites deposited in shallow subtidal to supratidal hypersaline environments. Celestite occurs both in a lower (3-10 m thick) algally laminated limestone unit and in a thick (at least 50 m), overlying, karstified conglomerate/ breccia sequence. Celestite replaces calcite, dolomite and gypsum in the algally laminated limestone and constitutes the last diagenetically precipitated mineral phase found in these sediments. However, all other diagenetic products are of very early, near surface origin, weakening the evidence for the timing of the replacement. In the karstified limestone conglomerate/breccia sequence, mineralization occurs as a replacement of algally laminated limestone clasts, as celestite cement in the karst breccias, and as pockets, lenses and veins of celestite-filled karst fractures and caves. The SrSO 4 content is locally up to 80-90% in the karstified conglomerate sequence, but 50-60% is the average grade for an estimated 25-50 x 10 6 T of this sequence in a restricted area around Revdal. This places the Karstryggen celestite occurrence among the largest known in the world. Sr-isotopic values obtained from the celestite show a radiogenic signature for the strontium and preclude a seawater or precursor limestone source of the material. The strontium was apparently delivered by surface and/or subsurface waters derived from the adjacent Caledonian highlands. These waters passed through immediately underlying arkosic redbeds concentrating Sr through the leaching of feldspars. However, in addition to the diagenetic factors, the primary sedimentary history also appears to be important in controlling the location of mineralization. In particular, the localized (tectonically controlled) gypsum basin provided a source of sulfur, whereas early karstification enhanced porosity of the limestones and provided important permeability conduits for subsequent mineralization.