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A brief description of the geology and drainage of the Northern limestone at Jenolan Caves is introduced. Approaches to karst geochemistry are given. The reasons are given for the choice of complete chemical analyses followed by calculations of the thermochemical parameters (saturation indices with respect to calcite and dolomite, SIc and SId, and the partial pressure of carbon dioxide PCO2) for the Jenolan groundwaters. The methods of chemical analysis and thermochemical calculations are reported. The results of the groundwater survey are presented both as the raw chemical data and the derived thermochemical data. The raw data give more useful information than the calculated parameters. The results obtained by this survey are consistent with observations and the previous knowledge of the underground drainage of the Northern limestone. The water chemistry reflected the rock type and the residence time of the water in bedrock and gravels. It is concluded that the Jenolan underground River and Central River have different types of source and that Central River is not a braid of the Jenolan Underground River.
Drips in the forward part of the Murray Cave between 5 and 50m below the surface were sampled about once a month for 2 years, carbon dioxide in the soil above and in the cave air being measured also. Mean soil CO2 content was fifteen times atmospheric, summer yeilding higher values than winter though the dry 1972-3 summer had low values. Greater depths in the soil had more CO2 than shallower ones. Cave air had on the average little more CO2 than the atmosphere but river flooding of the cave was followed by large CO2 fluctuations. There was a slight tendency for drips to be warmer and to vary less in temperature inwards. Drip pH was greater in summer than winter because of high CO2 production. The (Ca+Mg)/(Na+K) ratio of the drips was nearly ten times that of the Blue Waterholes, showing that igneous rock weathering around the Plain supplies more of the Na and K in the spring output than was envisaged before. The drip Mg/Ca ratio lies close to that of the Blue Waterholes, underlining the dominance of the limestone in the output hydrochemistry. The mean total hardness of 141 mg.L-1, not significantly different from earlier Murray cave drip measurements, sustains the previous estimate that the superficial zone provides about 2/3 of the limestone solution. The summer value (149 mg.L-1) is significantly greater than the winter mean (132 mg.L-1), including high values in the dry 1972-3 summer when CO2 values were low. Lagged correlation on a weekly and three weekly basis of individual drip hardness on air temperature and precipitation yielded few significant results. Only a weak case for dominance of hardness by temperature through rhizosphere CO2 was evident but neither was the conflicting hypothesis of hardness in such contradictory ways that more detailed observations over equally long time periods are necessary to elucidate their influence.
Water samples taken from a spring and six locations on the stream fed by it were analysed in order to determine the factors responsible for the deposition of tufa along the channel. The spring water, whilst carrying a large quantity of dissolved carbonates, proved to be almost at equilibrium with calcite. The considerable amount of dissolved carbon dioxide necessary for such a load to be carried underwent rapid degassing after emergence of the water. In consequence, about one quarter of the initial load of dissolved carbonate was deposited in the first 430m of subaerial flow. This deposition did not however keep pace with the degassing of CO2, and calcite supersaturation increased progressively downstream.
Carbon dioxide enriched atmospheres are not uncommon in Australian caves and have posed a safety problem for cavers. Carbon dioxide enrichment of a tourist cave's atmosphere is a management problem which can only be approached when standards for air quality are applied. In Gaden - Coral Cave two types of carbon dioxide enrichment are recognised; enrichment by human respiration and enrichment from an external source. Standards for air quality in mines and submersible vehicles are applicable to tourist caves. A maximum allowable concentration of 0.5% carbon dioxide is recommended as the safe, but not the most desirable, air quality standard for tourist caves.
Water Vapour determines the volume percentage of component gases in cave atmospheres. This is particularly significant in foul air caves where carbon dioxide and oxygen concentrations are measured and used to diagnose foul air types. The variation in atmospheric composition brought about by systematic change in carbon dioxide and oxygen levels is examined and shown on the Gibbs triangle. The current three foul air types are readily identifiable in this visualisation of data, and the boundaries of these types are mapped. Further, these diverse data can be combined into a Cave Air Index by which foul air atmospheres may be assigned to type in a rapid and objective manner. The use of these concepts in evaluation of published data on Wellington and Bungonia Caves and with mine and soil data is shown.
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