Research project: Distribution, origin and mineralogy of cave formations at Jenolan Caves, New South Wales
- Start date:
This long-running project started as a general mineral survey of Jenolan Caves, New South Wales, a former continental shelf reef limestone system. However, with the increasing complexity of the findings, the project was divided into sections, each of which ran over several years.
A study of the mineralogy and chemistry of cave formations and sediments revealed several unreported phosphate (crandallite), chloride (sylvite), sulfate-phosphate (ardealite) and silicate (illite) minerals in addition to others already published. Radiometric dating of illite/kaolinite clays from suspected reworked volcanic origins by CSIRO Division of Petroleum, plus fission-track dating of extracted zircons, showed the caves were much older than expected, having been formed 3,400 million years in the Carboniferous.
The mineralogical research uses X-ray diffraction, fluorescence and spectrometry, sulfur and oxygen stable isotopes, ICPMS trace element analysis, ultraviolet fluorescence, and SEM, photography and optical microscopy. Two separate sets of sulfate (gypsum) and sulfate-phosphate (ardealite and gypsum) minerals were revealed. One set (gypsum) resulted from purely geological origins by breakdown of pyrite (iron sulfide) in the Devils Coach House, for instance, and the other resulted from chemical reactions during leaching of relatively recent deposits of bat guano (making cave formations called 'The Potatoes' in Lucas and Chifley Caves). Each group has separate oxygen and sulfur isotope signatures.
These results have thrown light on cave-forming processes themselves, and the timing of the Carboniferous Kanimblan Orogeny. Palaeoclimate inferences can also be drawn, as some carbonate O/C isotope figures may be compatible with cooler past climates. Work commencing this year focuses on cave aragonite (calcium carbonate), dolomite and 'moon milk', whose genesis may all be related. 'Moon Milk' is a moist, soft, mainly carbonate material with the consistency of cottage cheese. It can contain carbonate minerals calcite, aragonite, hydromagnesite and huntite, plus possible bacterial agents. Study of this material will involve cross-discipline research, with input from Microbiology.
Project results so far gave crucial support to the case for World Heritage status for the Greater Blue Mountains region, and provided inputs into cave management and conservation, environmental management and tourism.
Ross Pogson , Collection Manager, Mineralogy