Processes affecting the chemical composition of Blue Lake, an alluvial gold-mine pit lake in New Zealand
Shaun L. L. Barker A C D , Jonathan P. Kim B , Dave Craw A , Russell D. Frew B and Keith A. Hunter BA Department of Geology, University of Otago, PO Box 56, Dunedin, New Zealand.
B Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
C Present address: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia.
D Corresponding author. Email: shaun.barker@anu.edu.au
Marine and Freshwater Research 55(2) 201-211 https://doi.org/10.1071/MF03174
Submitted: 17 October 2003 Accepted: 12 January 2004 Published: 31 March 2004
Abstract
Blue Lake is an abandoned, water-filled alluvial gold-mine pit in Central Otago, New Zealand. Alluvial gold mining is generally considered to be chemically benign, unless mercury is added to assist gold separation. The major element, trace metal and isotopic composition of the pit lake was compared to nearby, unaffected streams. Blue Lake was found to be enriched in the major cations, with levels that were 2–5 times higher than in unaffected streams. Furthermore, Cu, Ni and Zn concentrations exceeded 10 nmol L–1 in Blue Lake; these levels were 2–30 times higher than those in nearby, unaffected streams. Processes affecting the lake’s characteristics include evaporative concentration, and the oxidation and dissolution of locally derived sulfide and sulfate minerals. Localised acidification in surface and ground waters around the lake leads to the mobilisation of Zn and Ni, resulting in lake waters being strongly enriched in these trace metals (concentrations greater than 40 nmol L–1), whereas surrounding stream waters have much lower Ni and Zn concentrations (less than 5 nmol L–1). Ongoing evaporative concentration, and the continuing mobilisation of trace metals, implies that metal enrichment in lake waters will continue to occur. The present study demonstrated that the ‘benign’ process of alluvial gold mining can have significant chemical consequences in resulting water bodies.
Extra keywords: alluvial gold mine, pit lake, sulfide dissolution, trace metals.
Acknowledgments
This study was partially funded by University of Otago and the NZ Foundation for Research, Science and Technology. Discussions with Candace Martin improved our techniques and presentation of the material in this paper. Field and laboratory assistance from Mike Barker and Damian Walls is much appreciated. E. Sholkovitz and two anonymous reviewers are thanked for providing constructive reviews.
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