Original paper

Sequence of secondary phosphates deposition in a karst environment: evidence from Magurici Cave (Romania)

Onac, Bogdan P.; Vereş, Daniel S.

Abstract

Măgurici Cave hosts a diverse assemblage of minerals. The phosphatization of illite and montmorillonite clay rich sediments, located on the cave's floor, lead to the formation of taranakite and francoanellite. Mineral assemblages precipitated at the boundary between limestone bedrock and guano deposits are dominantly hydroxylapatite, brushite, ardealite, and monetite. A number of sulphate minerals (gypsum, bassanite, mirabilite, and cesanite) were precipitated along with the phosphates, strengthen the physico-chemical conditions of the depositional environment. The major parameters controlling the environments under which these mineral assemblages were deposited are: pH, relative humidity, alkali content, and Ca/P ratio. In addition, this study presents the second worldwide reported occurrence of phosphammite discovered in a cave environment. This rare mineral occurs as small transparent crystals within the guano deposit, precipitated in an early stage from the liquid fraction of guano.

Keywords

phosphatescave mineralsdepositional environmentmagurici caveromania