Geochemical data, ground water

Toran L.. and A. Sjoreln. 1996. CHEMFORM A fonnatting program for geochemical data. Ground Water. 34(3) 552-53. 

The Koongarra U deposit in the Northern Territory of Australia has been studied to evaluate the processes and mechanisms involved in the geochemical alteration of the primary ore zone, and to model the formation of the secondary U ore zone and dispersion fan (Duerden 1991 Duerden Airey 1994). Studies of the distribution of the U in the dispersion fan (Murakami et al. 1991) have provided data on the fixation of U leached from the primary ore deposit. Their work has shown that, for this system, fractures are not only preferential pathways for ground-water movement but also contain secondary minerals with high sorption capacity for elements such as U. Even in the monsoonal climate, in which this deposit is located, a significant proportion of the uranium has not been released from the vicinity of the primary ore body. 

The system associates a quality variable q x with each parameter, x, of the analysis. Each quality variable is assigned an initial value of zero. When there is evidence to support or contradict the reliability of the parameter value, the quality variable is incremented or decremented. Consider the calcium concentration in an analysis. Initially its quality variable, q calcium, is set to zero. Assume that the carbonate species concentrations have been shown to be reliable but that the geochemical model shows calcite to be oversaturated by several tenths of a unit. The sample is of a limestone ground water, and so should be calcite saturated. Assuming that the program and thermochemical data used are correct, the calcite oversaturation can be interpreted as indicating an erroneous calcium analysis. q calcium is therefore decremented because of this evidence that the calcium value is incorrect. The overall quality... 

In principle, such an expert system could also consider the extent to which a wide variety of minerals would influence ground-water chemistry at various temperatures and reaction times, as well as the natural variability and experimental uncertainties associated with the thermochemical data used to model geochemical equilibrium. To develop a consensus in the geochemical community about the categories of information required to evaluate mineral reactivity and the properties appropriate for each of many minerals, would be a time consuming task. Thus, in the near future at least, such enhancements will probably be limited to consideration of tightly defined problems of simple mineralogy. 

Detailed interpretation of kinetic test data collected for environmental purposes has allowed criteria for ground and surface water geochemical exploration to be selected. Parameters predicted from kinetic testing to be anomalous in both ground and surface waters were observed to occur reflecting the presence of both molybdenum mineralization and natural acid rock drainage. Kinetic testing is very expensive and careful use of the acquired... 

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