U-series Dating of Authigenic Gypsum and Anhydrite: A new Sample-Dissolution Technique Using Cation-Exchange Resin

Abstract

In principle, authigenic gypsum and anhydrite are excellent candidates for dating by the uranium-series decay scheme yet have been neglected because of cumbersome dissolution requirements. We present a simplified and manageable procedure for sample dissolution of sulfate minerals using cation-exchange resin. Calcium sulfate is shown to dissolve readily in the presence of cation-exchange resin in the hydrogen form by exchange of Ca 2+ for H + . Uranium and thorium isotopes associated with the mineral are released from the solid and fixed on the resin during dissolution. The isotopes are then readily eluted for isolation and analysis by standard alpha spectroscopy techniques.

Geochronology of Phreatophytic Mounds on the Atmur El Kibiesh, Egypt: With Descriptions of Plants Collected During the Expedition to the Eastern Sahara, Egypt, and Sudan (Appendix I)

“…Gypsum is a common evaporate mineral of playa deposits that with time converts to anhydrite under the high temperature and dry conditions of this hyperarid area of the eastern Sahara. Whereas chemical charts list gypsum as soluble in mineral acids, it is in fact very difficult to dissolve this way (Fitzpatrick and Bischoff 1994). The Tarfa Mound…”