Mega-everything: the world’s biggest open cut mine
OnLine opinion By Sandra Kanck – 24 August 2009
The expansion of the Olympic Dam mine at Roxby Downs will see environment as the biggest loser. The draft Environmental Impact Statement (EIS), for which public comment closed early in August 2009, has serious deficiencies.
It has been stated, and indeed boasted, by both the proponents and the South Australian Government, that this expansion will result in the construction of an open-cut pit that will become the largest in the world. For those who know Adelaide, this is larger than the whole of the City of Adelaide, including North Adelaide.
There are no plans for filling it at the end of its life: the EIS states “The void created by the new open pit mine would remain as a permanent land feature”. The use of the word “feature” leaves one marvelling at the wonders of spin-doctoring.
Up to 350 metres of overburden weighing 44 billion tonnes will be removed from the pit to expose the ore. Thereafter up to 390 megatonnes of rock will be removed each year for the next 40 years. Most of this material would be dumped in what will be known as a rock storage facility (RSF). The EIS says it will be visible from a 30km distance, and “would be the most prominent feature in the local and regional landscape”. The proponents propose to shape it so that it will look like a natural feature of the landscape……………….
As would be expected from the creation of the world’s largest open cut mine, ore-processing will see the construction of the world’s largest tailings dam – one that will be deliberately designed to leak three megalitres of radioactive waste each year!
The environmental impacts of the expansion will be enormous – from climate change impacts to destruction of biodiversity. In particular, it appears that BHP Billiton has underestimated the amount of native vegetation it will destroy…………
Energy use and associated climate change impact
The use of fossil fuels and associated climate change impact will be immense. While BHP Billiton claims the expansion will account for a not inconsiderable 9.8 per cent of South Australia’s CO2 emissions within just 11 years, the real figures may be closer to 14 per cent…………….
The pit will be 4.1km x 3.5km x 1km deep, i.e. 14.35 cubic kilometres. If we very generously assume only 90 per cent of what will be taken out of the pit will go into the RSF, it will have a volume of almost 13 cubic kilometres. But with an expansion factor of 1.7 this becomes roughly 22 cubic kilometres.
So the RSF, if 1km high, would have a base of 22 sq km. In turn, if the RSF was to have a base three times that (66 sq km) the height could be reduced to 1/3 of a kilometre, i.e. 333 metres. This is still more than twice the 67 sq km by 150m size envisaged in the EIS……………