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Abstract:

The new data from the Big Hole and its vicinity give some further support to the view maintained previously as to its origin, though an approach through water chemistry proved non-committal. Difficulties attaching to an origin by true phreatic solution of underlying limestone through circulations of groundwater of meteoric provenance remain however. Nevertheless, the possibility, not considered previously, that the Big Hole is due to hydrothermal solution in the manner of many collapse structures associated with uranium ore bodies in southwestern U.S.A. finds no support in the regional geology of the Shoalhaven valley, though it could produce features of the right dimensions. Previous lack of a complete parallel to the Big Hole has been removed by reference to the furnas of southern Brazil where a similar origin to the one proposed here is also inferred.