Decrease in acid mine drainage release rate from mine pit walls in Brunner Coal Measures

ABSTRACT

Wall wash samples were collected from outcrops of Brunner Coal Measures aged between 3 days and 138 years in the Stockton, Denniston and Garvey Creek coalfields of the west coast of the South Island. The purpose of these wall wash samples is to measure differences in the amount of acid and trace elements released as the rocks weather to predict the longevity of acid mine drainage (AMD) from pit wall run-off. The concentration of acid released in wall wash is relatively high and constant for the first year, followed by a rapid decrease that can be fitted with a power function. Data analysis indicates that AMD from pit walls is likely to have an impact on water quality for 64–136 years. The most abundant component of acidity in the wall wash samples from fresh pit walls (c. < 1 year) is Fe. At moderate age sites (c. 3–20 years), Al is the most abundant component of acidity in the wall wash, and at the oldest sites (c. 62–138 years), H⁺ is the most abundant component.

KEYWORDS:

• Acid mine drainage
• AMD
• pit wall
• stream chemistry
• Brunner Coal Measures

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Acknowledgements

This research is funded by the Ministry of Business Innovation and Employment under contract CRLE1403 – Mine Environment Life Cycle Guide. Access to field sites and data were made available by Solid Energy NZ Ltd, Bathurst Resources, New Zealand Coal and Carbon Ltd and Stevenson Mining Ltd.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research is funded by the Ministry of Business Innovation and Employment under contract CRLE1403 – Mine Environment Life Cycle Guide.