Visitors have enjoyed the calcite and aragonite decorations of Jenolan Caves for over 170 years, but no-one suspected they also hosted unrecognised minerals of great scientific interest, some formed with help from bats and wallabies.

It was thought that Jenolan Caves had a small range of common minerals and there was not much more to discover, but a 25 year study by an Australian Museum-Sydney University team has proven otherwise, with help from the Australian Museum’s X-ray diffractometer.

This unexpected wealth of minerals, some very rare, has formed through biological and geological processes acting together, with the help of bats and wallabies. These minerals tell us much about the chemical processes that formed them and the climate at the time.

Of the 25 minerals we described, about 8 were previously known but 15 are described for the first time from this locality. They include the rare phosphate mineral kingsmountite, previously only known from one other limestone cave environment, in Mexico.

Some of the minerals we studied had been placed in the Australian Museum Geoscience collection over 100 years ago, so we analysed these with modern laboratory equipment and they suddenly became very important for our work. Museum specimens are like that – they may be in the collection for a long time, but then yield important information in new studies.

Other minerals were collected by us in the caves themselves. You can picture us in overalls smeared with brown clay, and wearing a miner’s helmet with attached lamp as we went ‘off the track’, sometimes having to squeeze into tight places in search of minerals. You may think we had to search through many ‘wild’ or undeveloped caves not shown to the general public, but that was not so. Apart from a small number of such caves, most of our important discoveries were made in the tourist show caves themselves.

These minerals included carbonates: (calcite, aragonite, hydromagnesite, huntite, dolomite, ankerite); silicates: (kaolinite, K-deficient muscovite (“illite”), montmorillonite clays); phosphates, (ardealite, hydroxylapatite, taranakite, leucophosphite, variscite, crandallite, montgomeryite, kingsmountite); sulfate: (gypsum); oxides: (quartz, cristobalite, amorphous silica, hematite, romanèchite); hydroxide: (goethite); nitrate: (niter); and chloride: (sylvite).

Surprisingly, local animals had a helping hand in forming some of the minerals. They formed from chemical reactions between ancient bat guano from the bent-wing bat, Miniopterus schreibersii and limestone & clay (phosphate and sulfate minerals), or leaching of dung from the brush-tailed rock wallaby Petrogale penicillata (chloride and nitrate minerals). Many phosphate minerals came from Katie’s Bower in Chifley Cave, while others, in formations known as ‘potatoes’ came from Lucas and Chifley Caves. Other minerals, such as those from carbonate, silicate, oxide and hydroxide groups formed though non-biological chemical processes, some of the gypsum resulting from acidic chemical breakdown products of pyrite (iron sulphide) reacting with limestone.

We gave the cave clays our special attention. Potassium-argon dating techniques suggested they were extremely old – far older than anyone suspected, from the Carboniferous Period about 320 million years ago. This proved the caves (in 420 million year-old Late Silurian limestone) have been open for much longer than previously thought.

Mineral studies such as this one add to our knowledge of geology of the Greater Blue Mountains World Heritage Area, assist Jenolan Caves Guide training programs, input into cave environmental and conservation studies, and enhance cave visitor experience through geotourism.

Ross Pogson
Manager, Geoscience and Archaeology, Australian Museum Research Institute

Armstrong Osborne
A/Prof, Faculty of Education and Social Work, University of Sydney
Research Associate, Australian Museum Research Institute

David Colchester
Research Associate, Australian Museum Research Institute

More Information:
Pogson, R.E., Osborne, R.A.L. and D.M. Colchester, 2014. Minerals of Jenolan Caves, New South Wales, Australia: Geological and Biological Interactions. Proceedings of the Linnean Society of New South Wales, 136, 1-18.