Contaminant dispersion at the rehabilitated Mary Kathleen uranium mine, Australia |
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| Authors: | B G Lottermoser P M Ashley M T Costelloe |
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| Institution: | (1) School of Earth Sciences, James Cook University, P.O. Box 6811, Cairns, QLD, 4870, Australia;(2) Earth Sciences, University of New England, Armidale, NSW, 2351, Australia |
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| Abstract: | This study reports on the transfer of contaminants from waste rock dumps and mineralised ground into soils, sediments, waters
and plants at the rehabilitated Mary Kathleen uranium mine in semi-arid northwest Queensland. Numerous waste rock dumps were
partly covered with benign soil and the open pit mine was allowed to flood. The mineralised and waste calc-silicate rock in
the open pit and dumps has major (>1 wt%) Ca, Fe and Mg, minor (>1,000 ppm) Ce, La, Mn, P and S, subminor (>100 ppm) Ba, Cu,
Th and U, and trace (<100 ppm) As, Ni, Pb, Y and Zn values. Consequently, chemical and physical weathering processes have
acted on waste rock and on rock faces within the open pit, mobilising many elements and leading to their dispersion into soils,
stream sediments, pit water and several plant species. Chemical dispersion is initiated by sulfide mineral breakdown, generation
of sulfuric acid and formation of several soluble, transient sulfate minerals as evaporative efflorescent precipitates. Radiation
doses associated with the open pit average 5.65 mSv year−1; waste dumps commonly have lower values, especially where soil-covered. Surface pit water is slightly acid, with high sulfate
values accompanied by levels of U, Cu and Ni close to or above Australian water guideline values for livestock. Dispersion
of U and related elements into soils and stream sediments occurs by physical (erosional) processes and from chemical precipitation.
Plants growing in the mine void, on waste dumps and contaminated soil display evidence of biological uptake of U, LREE, Cu
and Th and to a lesser degree of As, Ni, Pb, Y and Zn, with values being up to 1–2 orders of magnitude above background sites
for the same species. Although rehabilitation procedures have been partly successful in reducing dispersion of U and related
elements into the surrounding environment, it is apparent that 20 years after rehabilitation, there is significant physical
and chemical mobility, including transfer into plants. |
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| Keywords: | Uranium Waste Contaminants Migration Mary Kathleen Queensland Australia |
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