Carbonate-bearing phosphohedyphane–“Hydroxylphosphohedyphane” and cerussite: Supergene products of galena alteration in Permian aplite (Western Carpathians, Slovakia)

Abstract

A unique assemblage of hedyphane-group minerals of the apatite supergroup associated with galena, cerussite, and calcite occurs in a Permian aplite dike crosscutting orthogneisses belonging to the pre-Alpine basement of the Veĺký Zelený Potok Valley in the Veporic Unit, Western Carpathians, Central Slovakia. The secondary Ca-Pb phosphates include phosphohedyphane Ca₂Pb₃(PO₄)₃Cl and (OH)-dominant “hydroxylphosphohedyphane” Ca₂Pb₃(PO₄)₃OH. Detailed EPMA and Raman spectroscopy of the hedyphane-group minerals reveal the presence of Pb, Ca, P, and Cl as major constituents; the systematic presence of (CO₃)^2– (up to 2.6 wt.% CO_2calc; 0.65 apfu C) substituting for (PO₄)^3– (B-type) is the first reported carbonate-bearing phosphohedyphane in nature. There is also significant localized halogen deficiency (0.38–0.49 apfu Cl+F) which suggests the potential for a new mineral, “hydroxylphosphohedyphane”. The secondary assemblage described herein results from very low-temperature sulfide-carbonate reactions and further near-surface supergene alteration of primary magmatic or metamorphic phosphate minerals (mainly apatite) and hydrothermal galena in the alkaline CO₂-rich groundwater.