Sulfate and phosphate speleothems at Jenolan Caves, New South Wales, Australia

Abstract

Sulfate and phosphate deposits at Jenolan Caves occur in a variety of forms and compositions including crusts, 'flowers' and fibrous masses of gypsum (selenite), and clusters of boss-like speleothems (potatoes) of ardealite (calcium sulphate, phosphate hydrate) with associated gypsum. This boss-like morphology of ardealite does not appear to have been previously described in the literature and this is the first report of ardealite in New South Wales. Gypsum var. selenite occurs in close association with pyrite-bearing palaeokarst, while the ardealite gypsum association appears to relate to deposits of mineralised bat guano. Isotope studies confirm that the two gypsum suites have separate sources of sulfur, one from the weathering of pyrite (-1.4 to +4.9 δ34S) for gypsum (selenite) and the other from alteration of bat guano (+11.4 to +12.9 δ34S) for the ardealite and gypsum crusts.