Nakhjirkuh celestite deposit is located at 165 km SE of Tehran. The studied area is a part of Central Iran tectono-sedimentary zone including Mesozoic and Tertiary rock units as well as Quaternary sediments. The Qom Formation which hosts the ore deposit, consists of limestone, marl, mudstone and gypsum. In a general stratigraphic section of Qom Formation, from bottom to top, there are three celestite bearing horizons (I, II, III).
In the horizon (I) country rocks are bioclastic limestone, oolithic limestone and brecciated micrite. Geometry of celestite is lenticular shape and ore textures are Open Space Filling (O.S.F.), disseminated and cross-cutting with a paragenesis of calcite, celestite, gypsum and iron oxides. Facies analysis studies suggest a back-reef lagoon and supratidal to shallow subtidal environments for deposition facies of the horizon. In horizon (I) the celestite has formed in early diagenesis with disseminated texture and in burial diagenesis with O.S.F. and cross-cutting textures.
In the horizons (II) and (III) country rocks are marl and limestone. These horizons have a layered geometry which can be traced about 2km along the strike. In the western part of the mining district, celestite facies laterally grades to gypsum. The ore textures in these horizons (II, III) are Diagenetic Crystallization Rhytmites (D.C.R.s), disseminated, banded, O.S.F. and massive with a paragenesis of celestite, barite, calcite, gypsum, dolomite and iron oxides. The depositional environment of the horizons (II), (III) is shore lagoon. Due to the increasing in salinity, micrite, gypsum and probably celestite precipitated as synsedimentary. In these horizons, during the early diagenesis celestite has been formed from porewater, as primary and replacement mineral (celestite replaced gypsum). In the burial diagenesis a Sr-rich brine obscured the main parts of synsedimentary and early diagenetic features and has been formed D.C.R.s in addition to replacement of celestite after gypsum. Crystallization of the celestite in pressure solution planes, geode formation and inter- layered cross-cutting features are some of the other burial diagenetic textures.