News Item: The Northern Territory, Australia, government declared that the fate of one of the territory's largest mines now lies with its owner, Swiss giant Xstrata. Northern Territory Mines Minister Kon Vatskalis has sent Xstrata back to the drawing board in its A$66 million bid to redevelop the McArthur River Mine, 900 km south-east of Darwin. He wants the company to address environmental concerns before he makes a final decision on the proposal—keeping the door open on Xstrata's controversial do-or-die bid to transform the zinc and lead underground mine into an open cut operation.

The company threatened to close the mine—which employs 270 people—and regional businesses launched an advertising blitz to try to change the government's mind. Today, the two government ministers declared the fate of the mine was back with Xstrata, which can now lodge an amended proposal addressing the nine environmental issues raised, including diverting 5.5km of the major river. (I have not been able to establish what the nine issues are.)

"Approval of this mine now would be a slap in the face to the indigenous traditional owners of the region who have argued strenuously that the mine will ruin their environment and local economies," Greens Senator Rachel Siewert said.

The Draft Environmental Impact Statement and the Executive Summary describe in detail what is proposed. The best summary is from the McArthur River Mine website which lists these Q&As:

What is proposed?

Xstrata Zinc has announced its intention to convert the underground zinc-lead mine at McArthur River to an open cut operation to enable the mine to continue production. The conversion to an open pit mine will extend the mine’s life by 25 years and entails an investment of A$66 million. The McArthur River ore body remains one of the largest deposits of zinc and lead in the world.

The conversion will mean that a surface pit covering 83 hectares will be constructed to access the ore, instead of accessing the orebody from the extensive network of underground tunnels and rooms.

The development of open pit mining within the existing mine lease will necessitate the rechannelling of a 5.5 kilometre section of the McArthur River and about 2.5 kilometres of Barney and Surprise Creek around the open pit. No additional infrastructure will be constructed at the site.

What changes are expected from a shift from underground to open cut mining?

The current mine occupies about 12 square kilometres. The change to open pit operations will double this area to about 24 square kilometres. An 83 hectare open pit will be created by removal of surface material and mining excavation operations. About 5.5 kilometres of the McArthur River will be rechannelled, partly into an old water course, to allow the river to flow around the open pit. About 2.5 kilometres of both Barney and Surprise Creeks will be rechannelled around the open pit. A flood protection bund will be built around the pit and facilities as protection against flooding which sometimes occurs in the wet season.

Will the conversion to an open pit mine impact on local biodiversity and any vulnerable or endangered species in the area?

Only one endangered fauna species occurs in habitats potentially affected by the project - the freshwater sawfish. This species has been recorded at five locations in the McArthur River in 1975 and in the river estuary in 2004. No significant impacts on this species are expected from the open cut project. No flora species with declared ‘vulnerable’ status were identified by surveys within the proposed project area.

The following two vulnerable species have habitats potentially affected by the project: (a) Red Goshawk: tentatively recorded in the project area in 1992 but not sighted in any subsequent surveys. (b) Australian Bustard: present in low numbers in open woodland and grassland habitats on the McArthur River floodplain.

What will be the impact of rechannelling the McArthur River?

McArthur River flows for 300 kilometres. The 5.5 kilometre section being rechannelled accounts for about 1.6 per cent of the river. The river is actually an intermittently running or dry creek much of the year, with several permanent waterholes near the mine. During the Wet season, the river sometimes floods (three times in the past 10 years) and can be as wide as 15 kilometres.

The realigned channel will be designed to have similar hydraulic characteristics to the existing river channel so it is stable during floods. The lower channel bank will be stabilised against erosion and the banks and berms will be revegetated. This will minimise the risk of erosion and allow the riverine fauna corridor to re-establish.

What impact will this have on the floodplains, especially during the wet season?

Floods less than 1 in 5 year levels will be contained within the realigned channel. Floods greater than one in five years will extend over the McArthur River floodplain as happens at present.

The presence of the mine will result in increased flood water levels upstream of the mine (eg levels will increase by 1.4 metres for a 1 in 100 year flood). This increase will not have any adverse environmental effects but will increase the extent and duration of upstream flooding. The only significant impact will be on the Carpentaria Highway, which closes now during severe flooding. The highway’s closure times will increase.

What will be the impact on fish generally and threatened species such as the Freshwater Sawfish?

The realigned river channel will be designed so there is no physical or hydraulic obstruction to fish passage. A variety of substrates and micro habitats will be provided along the channel to minimise impacts on fish.

What impact will the open pit have on groundwater systems?

A system of groundwater extraction bores will be built around the open pit to prevent groundwater flowing into the pit, which would interfere with mining activities. The extracted groundwater will be used as process water in the process plant.

Extracting the groundwater will cause groundwater levels surrounding the pit to drop. At the end of the mine’s life, groundwater levels could have dropped by up to one metre in permeable aquifers up to 2.3 kilometres from the pit.

What will happen to the mine at the end of its life? Key elements of the mine closure strategy will include:

  • The river will continue to flow along the realigned river channel.
  • The flood bund will be breached and the open cut allowed to fill with flood water.
  • The processing plant and infrastructure facilities will be removed and the areas remediated and revegetated.
  • The overburden emplacement facility and the tailings storage facility will be topsoiled and revegetated.

Australian Opinion

The news never tells it all so here is an opinion from an Australian who shall remain nameless:

Xtrata have a poor profile with the government in Australia – they are guilty of buying out a newly operating Vanadium Mine, firing all the staff and stripping the mine so that it is unviable to re-start. While this is their right as owners what they were doing was shoring up their other vanadium producing mines elsewhere in the world. Aussies don’t like being taken advantage of in this way.

Being a lead zinc mine their biggest problem is surely going to be the environmental impact of their waste rock dumps given the proximity to the MacArthur river notwithstanding the proposed diversion.

My guess is that there has been a bunch of corner cutting on the part of the mine.

More Background Information About this Project From Infomine Files

Xstrata is a major global diversified mining group with position in six international commodity markets: copper, coking coal, thermal coal, ferrochrome, vanadium and zinc, as well as additional exposures to gold, lead and silver. Its operations span four continents and six countries: Australia, South Africa, Spain, Germany, Argentina and the UK.

The McArthur River district is situated within a belt of sedimentary rocks of Middle Proterozoic age. Similar rocks host the significant orebodies of Mount Isa, Hilton, Lady Loretta, Dugald River and the Century deposit.

The "Here's Your Chance" (HYC) zinc-lead-silver deposit at McArthur River occurs in the HYC Pyritic Shale Member, a package of interbedded pyritic siltstone, sedimentary breccia and tuff.

The HYC deposit consists of seven orebodies, stacked one on top of the other, each separated by dolomitic siltstones and sedimentary breccias. Thin tuff bands are also common throughout the sequence which has an average thickness of 55 metres.