Geochemical characterisation of surface waters and precipitates in Nenthorn historic gold mine, East Otago, New Zealand
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Authors: David, L Open access courtesy of:
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DOI https://doi.org/10.36487/ACG_repo/2315_088
Cite As:
David, L 2023, 'Geochemical characterisation of surface waters and precipitates in Nenthorn historic gold mine, East Otago, New Zealand', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2315_088
Abstract:
Nenthorn is one of the historically mined gold districts in East Otago, Southern New Zealand. After mining ceased in the early 1900s, the mine battery and adits have exposed fresh schists and mineralised gold-bearing quartz vein that has undergone continuous chemical weathering and alteration reactions mainly involving, arsenopyrite(AsFeS) and calcite (CaCO3); producing alkaline waters (pH range of 7.5 to 8) with elevated trace elements. Oxidation and dissolution of sulphide (ore) minerals usually results in elevated sulphate and other heavy metal concentration in mine waterways, hence creating a potential environmental concern. However, with semi-arid climates like East Otago, the occurrence of ochreous precipitates and efflorescence are common. Water samples and precipitates were collected from the mine workings and the adjacent creek to determine the major and trace element content in a one-time sampling program. The analytical data shows elevated concentration of trace elements in precipitates than the water samples, however, the study site was identified as not extremely concentrated or contaminated with heavy metals. The ochreous precipitates samples used for this study most likely formed from the precipitation of supergene alteration minerals like iron hydroxysulphates and iron oxyhydroxides, and primary minerals like arsenopyrite due to the elevated concentration of Iron, Arsenic, and Manganese. The sorption of metals like Copper, Lead, and Zinc to oxyhydroxides of Iron and Manganese sulphates could explain the absence of these metals in the water samples. The circumneutral pH of the water is caused by calcite dissolution, leading to very high Calcium (Ca) concentration in all the samples analysed, however highly undersaturated concerning halite, gypsum, and calcite. Conclusively, it was observed that in the Nenthorn area, arsenic concentration is above the maximum acceptable values for inorganic determinants of health significance in New Zealand. Contamination of surface waters quality in the abandoned Nenthorn mines is small enough that it does not affect the Deighton Creek just downstream. However the study does reflect the potential for even small mineral deposits to actively engage with the surrounding geochemical environment.
Keywords: Historic gold mine, trace elements, heavy metals, arsenopyrite, iron oxyhydroxides
References:
Abanda, PA, & Hannigan, RE 2007, ‘Mineral control of minor, trace, and rare earth elements during black shale weathering at near-neutral pH’, In D. Sarkar, R. Datta and R. Harringan (Eds.), Developments in Environmental Science, pp.273-303, DOI: 10.1016/S1474-8177(07)05011-5.
Bibby, CJ, 1997, ‘Macraes Ecological District: Survey report for the Protected Natural Areas Programme. New Zealand Protected Natural Areas Programme’, Department of Conservation, Dunedin, pp. 158.
Chester, R 2009, ‘The transport of material to the oceans: the fluvial pathway in Marine geochemistry’, John Wiley & Sons, pp. 11-52.
Craw, D, & Kerr, G 2017, ‘Geochemistry and mineralogy of contrasting supergene gold alteration zones, southern New Zealand’, Applied Geochemistry vol. 85, pp. 19-34, DOI: .
Craw, D, Mortensen, J & Mackenzie, D 2009, ‘Source of Metals for Gold Deposits in the Otago Schist’, In Proceeding from the AusIMM New Zealand Branch Annual Conference’, .
Craw, D 2003, ‘Geochemical changes in mine tailings during a transition to pressure-oxidation process discharge, Macraes mine, New Zealand’, Journal of Geochemical Exploration, vol. 80, no. 1, pp. 81-94. Doi: 10.1016/s0375-6742(03)00184-5.
Craw, D 2000, ‘Water-rock interaction and acid neutralization in a large schist debris dam, Otago, New Zealand’, Chemical Geology, vol.171, no. 1-2, pp. 17-32, Doi: 10.1016/s0009-2541(00)00231-x.
Craw, D, & Norris, RJ 1991, ‘Metamorphogenic Au‐W veins and regional tectonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand’, New Zealand Journal of Geology and Geophysics, vol. 34, pp. 373-383.
Craw, D, & McKeag, SA 1987, ‘Near-surface hydrothermal activity in the eastern Otago schist (Note)’, New Zealand Journal of Geology and Geophysics vol. 30, no. 4, pp. 437-443, DOI: 10.1080/00288306.1987.10427547.
Diehl, FS, Hageman, LP, Smith, SK, Koenig, AE, Fey, DL, & Lowers, HA 2006, ‘What’s weathering in Mine Waste? Mineralogic Evidence for Sources of Metals in Leachates’, In Proceedings of the U.S. EPA Hard Rock Mining Conference, Tucson, Arizona, DOI: 10.2138/rmg.2000.40.7.
Gaillardet, J, Dupré, B, Louvat, P, & Allegre, CJ 1999, ‘Global silicate weathering and CO2 consumption rates are deduced from the chemistry of large rivers’, Chemical Geology, vol. 159, no. 1, pp. 3-30.
Jamieson, HE, Walker, SR, & Parsons, MB 2015, ‘Mineralogical characterization of mine waste’, Applied Geochemistry, vol. 57, pp. 85-105, Doi:10.1016/j.apgeochem.2014.12.014.
Kerr, G, & Craw, D 2020, ‘Metal redistribution during cementation of historic processing residues, Macraes gold mine, New Zealand’, New Zealand Journal of Geology and Geophysics, vol. 0028-8306, pp. 1-13, DOI: 10.1080/00288306.2020.1787472.
Macara, GR 2015, ‘The climate and weather of Otago', NIWA Science and Technology Series, vol. 67, pp. 44, .
Mackie, C, Mackenzie, DJ, Craw, D, 2009, ‘Structural and lithological controls on gold mineralisation at Oturehua on the northeastern margin of the Otago Schist, New Zealand Journal of Geology and Geophysics,, vol. 52, pp. 43–57,.
Mains, D, & Craw, D 2005, ‘Composition and mineralogy of historic gold processing residues, east Otago, New Zealand. New Zealand Journal of Geology and Geophysics’, vol. 48, no. 4, pp. 641-647, .
Martin, A.P, & Simon, C. 2016, ‘On forty-five years of gold exploration at Barewood and Nenthorn, compared with twenty years prior to mining at Macraes, east Otago, New Zealand’, In A.B. Christie (Ed), Mineral deposits of New Zealand: Exploration and research, pp. 199-206, Australasian Institute of Mining and Metallurgy.
Mortimer, N, & Roser, B. P 1992, ‘Geochemical evidence for the position of the Caples–Torlesse boundary in the Otago Schist, New Zealand’, Journal of the Geological Society, vol. 149, no. 6, pp. 967-977.
Plumlee, G.S 1999,’ The environmental geology of mineral deposits’, In: Plumlee, G. S, Logsdon, M.J. (Eds.), and the Environmental Geochemistry of Mineral Deposits,’ Part A: Processes, Techniques, and Health Issues: Reviews in Economic Geology, vol. 6A, pp. 71–116.
Ryder, G & Mandy, T October 2020, ‘Review of Values, Freshwater Restoration Programmes, and Research Needs within the Taieri Catchment’ , Department of Conservation,
Taylor, SR, & McLennan, SM 1985, ’The continental crust: its composition and evolution’.
Weightman, E, Craw, D, Rufaut, C, Kerr, G, & Scott, J 2020, ‘Chemical evolution and evaporation of shallow groundwaters discharging from a gold mine, southern New Zealand’, Applied Geochemistry, vol. 122, no.15. .
Weightman, E, Craw, D, Snow, T, Christenson, H, & Kerr, G 2020, ‘Stratigraphy and mineralogy of tailings at Macraes gold mine, southern New Zealand’, New Zealand Journal of Geology and Geophysics, vol. 17, Doi: 10.1080/00288306.2021.1931360.
White, AF, & Blum, AE 1995, ‘Effects of climate on chemical weathering in watersheds’, Geochimica et Cosmochimica Acta, vol. 59, no. 9, pp. 1729-1747.
Zeman, JS O 2004, ‘Introduction to environmental hydrogeochemistry’, Chapter 3-7, no. 3, Masaryk University in Brno, Faculty of Science.
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