Environmental review of the Mary Kathleen uranium mine

Costelloe, Marina (2003) Environmental review of the Mary Kathleen uranium mine. Masters (Research) thesis, James Cook University.

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Abstract

The major aim of this project has been to investigate the current environmental status of the historic Mary Kathleen mine site including the open pit; D Stockpile, Crusher, Goldings West, West Tip, Southern Tip and North Waste Tip pile; evaporation ponds and tailings dams; tailings dam seepage and Cameron Creek. This study will provide data for an integrated assessment of the site and comparison to current ANZECC water, soil and stream sediment guidelines.

In the Mary Kathleen open pit, skarn type U-Th-REE mineralisation is hosted in amphibolite grade metamorphosed talc-silicate, mafic to intermediate igneous and sedimentary rocks. Elevated gamma-ray readings in the open pit correspond to exposed ore lenses (26 mSv/year) and the abandoned ore stockpile (10.7 mSv/year). Surficial oxidation of ore and adjacent sulphide-bearing calc-silicate rocks has led to contemporary precipitation of mineral efflorescences on the pit walls. The open pit lake contains saline (0.15%) surface waters which are Ca2+, SO4 rich with elevated Cu (1170 ug/L), Fe (3230 Ug/L), Mn (1050 4ug/L), Ni (688 ug/L) and U (460 ug/L) at a pH of 6.11.

Waste rock piles are up to 30 m thick and several, which were only partly covered or ripped for seeding, have high radiation levels (25 mSv/year). Stream sediments accumulating below waste rock piles are acidic (pH 3.8-7) and results (mean values) show enrichment of Cu (323 ppm), Mn (945 ppm), Ni (90 ppm), Ce (806 ppm), La (531 ppm) and U (82 ppm) indicating active weathering and erosion of waste materials into the local drainage system. Biogeochemical analyses indicate that Enneapogon lindleyanus (grass), Cymbopogon bombycinus (grass), Aerva javanica (kapok bush), Aristida longicollis (poaceae) and Acacia Chisholmii (wattle) accumulate Cu, Mn, Ni, REE and U at mined and disturbed areas.

Gamma-ray measurements over the rehabilitated tailings dam demonstrate an intact cover. However, seepage of acid (pH 5.86), saline (0.31%) waters occurs from the toe of the tailings dam into the evaporation ponds and local drainage system. Seepage waters are Ca2+, SO4 rich with elevated Fe (250 mg/L), Mn (328 mg/L), and U (303 μg/L). Abundant sulphate efflorescences and Fe-oxyhydroxide flocculants with elevated radiation (1300 cps), high REE (Ce 6840 ppm, La 3750 ppm) and U (901 ppm) levels precipitate at the seepage point. Thus radionuclides are mobilised into surface seepage waters, and are coprecipitated with Fe flocculants. Runoff from the mine area drains into Cameron Creek. Seepage of saline waters occurs from the tailings dam and evaporation ponds into Cameron Creek via surface and subsurface flows as indicated by salt-encrusted creek banks.

When sampled during the dry season, pools in the Cameron Creek system were shallow, saline (0.3-3%), alkaline (pH 8.3-8.6), and strongly enriched in SO4 (25.8 mg/L) and U (5.1 mg/L) but fish and aquatic plant life were still sustained locally in lower salinity regimes. Elevated metal loadings of soils and sediments, radionuclide mobility, weathering and erosion of waste dumps and bioaccumulation of elements do not occur beyond the former mine site. Measured radiation levels are at or below Australian Radiation Protection Standards (20 mSv/year averaged over five consecutive years) in most areas. In contrast, seepage of waters from the tailings storage area and evaporation ponds causes seasonal salinisation and impacts on the water quality of Cameron Creek during the dry season.

Item ID: 11370
Item Type: Thesis (Masters (Research))
Keywords: Mary Kathleen Uranium mine, tailings dam seepage, environmental pollution, water pollution, radiation pollution, uranium waste, radionuclide mobility, uranium mining sites, uranium, water quality, soil quality, water salinity
Date Deposited: 26 May 2010 22:57
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050204 Environmental Impact Assessment @ 100%
SEO Codes: 96 ENVIRONMENT > 9610 Natural Hazards > 961005 Natural Hazards in Fresh, Ground and Surface Water Environments @ 33%
96 ENVIRONMENT > 9611 Physical and Chemical Conditions of Water > 961103 Physical and Chemical Conditions of Water in Fresh, Ground and Surface Water Environments (excl. Urban and @ 34%
96 ENVIRONMENT > 9610 Natural Hazards > 961009 Natural Hazards in Sparseland, Permanent Grassland and Arid Zone Environments @ 33%
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