Australia: The Land Where Time Began

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The Northern Flinders Ranges, South Australia - the Paralana Hot Springs, an Active Amagmatic Hydrothermal System 

The Mt Painter Inlier, of Mesoproterozoic age, in the Northern Flinders Ranges, South Australia, is located in a zone where heat flow is anomalously high and the heat production has been attributed to high radioactive elements concentration in the inlier. Large volumes of uraniferous breccias and siliceous sinter were produced in the Palaeozoic, and secondary uranium deposits that have been mined in sandstones from the Tertiary to the east of the mine, the inlier. The only remaining hot spring along the Paralana Fault is the Paralana Hot Springs (PHS), which is the focus of long-standing hydrothermal activity, as indicated by ephemeral precious metal deposits of copper-iron and iron-uranium. In this paper the authors1 presented the results of their study of the water of the PHS, as well as other groundwaters in the Mt Painter Inlier, with the aim of constraining the primary source of the water and heat in the PHS, and the exploration of the relationships between fossil ore deposits and modern groundwaters in the province.

The water of the PHS is discharged at 16 L/s and a temperature of 57oC, and is of neutral (pH 7-8) and contains total dissolved solids (TDS) of 1144 mg/L, which is towards the lower end of the range of the cold water springs that are nearby and groundwater bores (1,000-3,041 mg/L TDS). Concentrations of elements in the spring are relatively high, with Fluorine 5 ppm, molybdenum 33 ppb, tungsten (wolfram) 11 ppb, cesium 16 ppb and rubidium 200 ppb. The PHS water is indicated by δ18O and δD values to be of meteoritic origin and δ13C values of CO2 (g) emanating from the springs and dissolved HCO3- suggest organic matter, such as soil or plants, is the carbon source. At the springs the radon concentrations are very high, a localised radiogenic source at shallow depth is implied by radiation of 10,952 Bg/m3.

According to geothermometric calculations the temperature of the most recent water-rock interaction is 95±5oC. A circulation depth of between 1.4-2.4 km are suggested by high geothermal gradients, that have been attributed to high concentrations of radiogenic elements, are required to produce this temperature. The PHS is the result of the circulation of meteoric water through hot rocks, and is the expression at the surface of a hydrothermal system that is of low temperature and non-volcanic. The authors1 suggest 2 possible sources of meteoric water for the springs have been identified - Mt. Painter Domain and a local aquifer of the Great Artesian Basin. The Mt. Painter Domain is indicated as the source of the water by the flow rate variability, the low temperature of the last equilibrium fluid-rock interaction, and the geochemistry of the springs.

Negligible uranium (0.07 ppb) is contained in the PHS, though uranium is enriched, 300-600 ppb, in some shallow ground waters in the basement. It has been shown by reactive transport modelling that Beverly-style mineralisation could be produced by these waters upon reaction with carbon and/or sulphides that have been reduced, though the water of the PHS could, upon cooling, produce jasperoidal mineralisation containing traces of sulphides that outcrop along the Paralana Fault. Therefore, the present day groundwater chemistry may be related to palaeowater chemistry that produced the major mineralisation events in the region, though the formation of the major deposits may have required particular circumstances that affected fluid flow and fluid chemistry, such as climate, tectonism or magmatism.

Sources & Further reading

  1. Brugger, Jol, Ngaire Long, D. C. McPhail, and Ian Plimer. "An Active Amagmatic Hydrothermal System: The Paralana Hot Springs, Northern Flinders Ranges, South Australia." Chemical Geology 222, no. 12 (10/20/ 2005): 35-64.
Author: M. H. Monroe
Last Updated 24/08/2013

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