The 8th Australian Workshop on Acid and Metalliferous Drainage was held in Adelaide, South Australia between 29 April and 2 May 2014 where Dr Dave Allen (Principal Environmental Geochemist) presented a paper titled The Mt Gordon Challenge: Impacts of Historic Legacies, Highly Variable Climatic Conditions and Tough Economic Conditions on Management of Acid Mine Drainage. An abstract of this paper and links to download the full paper and powerpoint presentation slides are presented below.
K. SellA, D. AllenA and J. CowieB
A MBS Environmental Pty Ltd
BBirla Mt Gordon Pty Ltd
Aditya Birla Minerals purchased the historic Mt Gordon Copper Project, previously known as Gunpowder Copper, in November 2003. Copper has been mined from two open cut pits and two underground mines periodically from the project since the early 1900s with various processing methodologies used including heap leach, pressure leaching and copper sulfide flotation. Environmental protection requirements have undergone significant changes since the time of commencement of mining operations and the current project experiences considerable environmental legacies arising from actions taken that would not be allowed under modern environmental protection requirements.
During the 2008/09 wet season, higher than average rainfall was experienced in the Mt Isa region. By mid April 2009, the site had received 1,310 mm of rainfall equating to a 1 in 500 year ARI, two month rainfall event. This followed a period of four years of drought conditions where the site was experiencing severe water shortages. A decision to cease mining for economic reasons had already been made in early January 2009 prior to experiencing large rainfall events. The subsequent above average rainfall forced closure of all operations and the site was formally placed on care and maintenance in February 2009.
The Esperanza Pit and Mill Creek Dam collected about 5 GL of runoff from the project area during the 2008/09 wet season, effectively containing all potentially contaminated water on site. With a pH of 2.7, acidity of 3,200 mg CaCO3/L, copper concentration of 250 mg/L and sulfate concentration of 5,500 mg/L, the challenge for Aditya Birla Minerals to manage the water effectively and meet regulatory requirements began.
This paper will discuss:
- Options identified for water treatment and water reduction given the site was on care and maintenance.
- Actions taken between 2009 and present to manage accumulated poor quality water.
- The impacts of climate on the options available for water reduction.
- When does stored water cease to be seen as a resource and become a liability?
- The use of ecological risk assessment as a tool in decision making.