Hydrogeochemistry of a calcrete-containing aquifer near Lake Way, Western Australia

• Published in: Journal of hydrology (Amsterdam) Vol. 38; no. 3; pp. 357 - 377
• Main Authors: Mann, A.W., Deutscher, R.L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1978
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/0022-1694(78)90079-3

Twenty-six water samples from representative sampling locations within a calcrete-containing drainage have been chemically analysed and the results processed to obtain information relevant to the genesis of calcrete. Comparison of major-element concentrations with that of Cl − suggests chemical precipitation of Ca 2+, Mg 2+, SO 4 2− and silica within the drainage basin. The HCO 3 − ion concentration is independent of Cl − ion concentration ( r = 0.30). Groundwater pH appears to be determined by interaction of silica minerals with groundwater and to a lesser extent by carbonate equilibria wherever calcite occurs. Calculated solubility indices give an accurate representation of the distribution of calcite, dolomite, aragonite, silica, gypsum and sepiolite within the drainage basin. Carbonate equilibria appropriate to 25° C have been applied to all samples to obtain from the measured HCO 3 − concentration, activities for H 2CO 3, CO 3 2−, and P CO 2 values — the mean P CO 2 is 10 −2·01± 0.28 bar. Equilibration of neutral or slightly alkaline groundwaters with this CO 2 is responsible for the production of CO 3 2− ion activities of the order of 10 −5 required for precipitation of CaMg carbonate.