Comparison of arsenic and trace metal contents of discharges from adjacent coal and gold mines, Reefton, New Zealand
L. Hewlett A , D. Craw A C and A. Black BA Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand.
B CRL Energy, PO Box 29 415, Christchurch, New Zealand.
C Corresponding author. Email: dave.craw@stonebow.otago.ac.nz
Marine and Freshwater Research 56(7) 983-995 https://doi.org/10.1071/MF05018
Submitted: 1 February 2005 Accepted: 20 May 2005 Published: 14 October 2005
Abstract
Historic gold and coal mines in the same catchment near Reefton, New Zealand allow comparison of environmental effects of the different mines in the same climate and topography. Gold mine discharge waters (neutral pH) deposit hydrated iron oxide (HFO) abundantly at mine entrances, whereas coal mine discharge waters (low pH) precipitate HFO tens to hundreds of metres downstream as pH rises. Waters leaving historic mines have up to 59 mg L−1 dissolved arsenic, and HFO at gold mines has up to 20 wt% arsenic. Coal mine discharge waters have low dissolved arsenic (typically near 0.01 mg L−1) and HFO has <0.2 wt% arsenic. Minor dissolved Cu, Cr, Ni, and Zn are being leached from background host rocks by acid solutions during sulfide oxidation, and attenuated by HFO downstream of both gold and coal mines. A net flux of 30 mg s−1 arsenic is leaving the catchment, and nearly all of this arsenic flux is from the gold mining area, but >90% of that flux is from background sources. The present study demonstrates that elevated trace metal concentrations around mines in a wet climate are principally from non-anthropogenic sources and are readily attenuated by natural processes.
Extra keywords: acid rock drainage, antimony, attenuation, HFO, trace elements.
Acknowledgments
This study was funded principally by New Zealand Foundation for Research, Science and Technology via contracts to University of Otago and CRL Energy. Additional funding from University of Otago and Australasian Institute of Mining and Metallurgy is gratefully acknowledged. OceanaGold Ltd. provided logistical support and data for the Globe–Progress area. Department of Conservation gave permission to sample several of the areas in the study. John Taylor gave much assistance in finding and understanding historic mine sites. Jenny Webster-Brown assisted with identification of minerals in HFO. Ellen Cieraad and Mark Baldwin provided able field assistance. Damian Walls, Lorraine Paterson and Brent Pooley gave excellent technical assistance. Constructive comments from two anonymous reviewers and Dugald McGlashan substantially improved the presentation of the paper.
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