Epigenetic origin of celestite deposits in the Tertiary Sivas Basin: new mineralogical and geochemical evidence

Abstract

The occurrence of celestite in the evaporitic Upper Eocene-Miocene deposits of the Sivas (Ulas) Basin is documented. This paper aims to demonstrate that a group of Tertiary sediment-hosted celestite deposits are epigenetic in origin, rather than syngenetic as has been claimed by a number of previous workers. Thin section petrography, fluid inclusion data, mineral and whole rock geochemistry and isotopic compositions (87/86Sr, 180 and 34/32S) are the main tools employed. The celestite occurs as stratabound, vug-filling, nodular and lenticular types. Petrographic, microtextural (SEM), mineralogical and geochemical analyses indicate that the celestite can be classified as pure, calcareous and gypsiferous varieties. The celestite under polarizing microscope shows xenomorph, pseudomorph and acicular-radial crystal structures. Scanning electron microscope (SEM) analyses reveal abundant zonal structures in single crystals. Ore minerals associated with the celestite mineralization include pyrite (especially bravoite-melnikovite), marcasite, limonite, siderite-ankerite, gold (electrum-nabite), psilomelane, realgar-orpiment, antimony and dedritic chromite. X-ray fluorescense analyses indicate that the celestites contain 53-58 wt.% SrO, 0.05-3.70wt.% BaO, 0.02-3.40b wt.% CaO and 35-44wt.% SO 3 . Average minor element contents are: 0.4 wt.% SiO 2 , 0.9 wt.% Al 2 O 3 , 0.03 wt.% MnO, 0.3 wt.% MgO and 0.3 wt.% Na 2 O. The trace elements recognized are: Mo (1.8 ppm), Pb (18 ppm), W (0.8 ppm), As (2.3ppm), Zn (4ppm) and Cu (7ppm). The homogenization temperatures of fluid inclusions in celestite crystals vary between 210 and 390 °C. Salinity (NaCI equ.) values range from 11 to 23 wt.% NaCl. Fig. 1. A Location of the Tertiary Sivas Basin, Turkey. B Location map of the study area in the Sivas Basin. C Simplified geological map of the study area, showing the location of celestite and celestite-barite (Ba, Sr)SO 4 occurrences. The petrographic, mineralogical, geochemical and isotopic characteristics of the celestite deposits in the Sivas (Ulas) basin are compatible with an epithermalhydrothermal, rather than a sedimentary origin as it was previously proposed. A hydrothermal origin is also supported by the Sr isotope data; since the 8 7 Sr/ 8 6 Sr ratio varries between 0.70590 and 0.70718. Besides, the results of the 1 8 O and 3 4 S/ 3 2 S isotope data are in accordance with the hydrothermal origin.