Mineralogy of speleothems from four caves in the Purcăreţ - Boiu Mare Plateau and the Baia Mare Depression (NW Romania)

The Purcăreţ Boiu Mare Plateau and the southern edge of the Baia Mare Depression, in Sălaj and Maramures Counties, NW Romania, host over 200 caves located in limestones ranging in age from Upper Eocene to Badenian. The carbonate rocks are interposed with non-karst rocks consisting of shales, sandstones and marls. Four caves hosted by limestones of different lithologies have been investigated for secondary minerals in the composition of their speleothems. Calcite, gypsum, goethite, jarosite, brushite, hydroxylapatite and taranakite were found in the composition of crusts, crystals, aggregates and earthy masses. The mineral association was characterized by means of X-ray diffraction and scanning electron microscopy. Gypsum, goethite and jarosite resulted from sulfide oxidation, whereas the phosphate associations formed through the interaction of phosphoric acid from bat guano with the limestones and detrital sediments. In Lii Cave, hydroxylapatite was also identified in black crusts deposited on fossil rib fragments within the limestones.