NT mine gets licence to pump water into river

Vista Gold has been granted a waste discharge licence to discharge wastewater from the Mt Todd mine site to the Edith River.

The licence was granted by the EPA Controller of Water and lasts for approximately 18 months and is due to expire 30 September 2014.

The Mt Todd Gold Mine is located in the Edith River catchment, approximately 55 kilometres north of Katherine. The mine operated between 1994 and 2000 producing gold, with two  changes in mine ownership during this period.

Mining operations ceased in July 2000 without adequate remediation works, leaving the site with a legacy of large volumes of exposed mine waste (tailings and waste rock). These wastes have reacted with rainwater and the atmosphere to generate contaminated water runoff and seepage, consisting of low pH water and elevated toxic metal concentrations. In 2001 the NT Government assumed responsibility for the management of the site.

Since 2007 Vista Gold Australia Pty Ltd (Vista) has operated the site under an agreement with the NT Government.

The impact of contamination has been managed by capturing and controlling the water flowing from the waste sources into a number of retention ponds. Wastewater is released under controlled conditions into the Edith River, although uncontrolled discharges of contaminated water have occurred from the site, including a discharge in late December 2011 and early January 2012 (coinciding with the Edith River train derailment).

Water levels in the retention ponds have increased over time and are now close to capacity.

The NT Government understands there is an elevated risk of uncontrolled discharge from the mine site into the Edith River over the next two Wet seasons if water levels cannot be appropriately managed. Uncontrolled discharge could have a significant impact on the Edith River if it occurs without adequate dilution.

Subject to a final investment decision, Vista is proposing to re-open the Mt Todd mine. An Environmental Impact Statement is expected to be submitted to the NT Environment Protection Authority (NT EPA) in the first half of 2013. The EIS will assess the risks associated with a new mine and will be available for public comment once submitted to the NT EPA. Vista needs to dewater Batman Pit prior to commencing a new mining operation.

Vista has commenced the in-situ treatment of pit waters with calcium carbonate and quicklime to improve water quality in the pit prior to discharge. This is intended to raise the pH of the water and precipitate out metals. Vista expects to be able to commence discharging treated water from Batman Pit late January 2013. Vista may need to discharge untreated water from other retention ponds during the Wet season (Retention Ponds 1 and 7) to avoid uncontrolled discharge. This would be subject to flow in the Edith River providing sufficient dilution of waste waters.

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