Background and definition of the case to be discussed

The Falun Copper Mine and the Falun area in central Sweden are unique for at least two reasons:

• It was probably the most long-term continuous mining operation in the world, extracting mixed sulphidic ores (mainly containing copper, zinc and lead), for more than a millennium - in industrial scale for at least 450 years - until the operation ceased in 1992.

• From no other place in Sweden have so many and so large quantities of metals and acidifying substances been released to the environment as from the Falun Copper Mine. Thus, the region can be said to have a kind of "record" of long-standing and severe environmental damage.

Since industrial-scale exploitation of the Falun sulphidic ore started in the middle of the 16th century, the total output of metals from this ore has been about 0.4 Mt of blister copper, about 0.5 Mt of zinc, 0.16 Mt of lead, 380 t of silver and 5 t of gold. It may be mentioned that the mining operations were run by what is assumed to be the world's oldest limited company, Stora Kopparberg Bergslag, limited at least since 1288, according to existing documentation.

The ore body has been severely weathered, especially during the glacial periods, when the rock was fragmented and spread around. Parts of the glacial till around the Falun mine therefore contain naturally high concentrations of metals and sulphur. This matrial decomposes steadily, so the groundwater and the watercourses in the neighbourhood exhibit naturally elevated levels of metals and sulphate. However, the additional - sometimes sharp - increase in these concentrations, caused by the mining operations, is the main subject of the subsequent discussion.

Over the centuries, various kinds of mining wastes, more or less rich in extractable valuables, have accumulated in the close surroundings of the Falun Mine. Among the different waste types, that can still be found in large heaps around the mine or as fill materials on which the city of Falun was built, are the rock overburden or gangue, the poorer parts of the crushed ore (called "cobbing"), tailings from the modern concentration procedures, roasted pyrite and slags. Only the slag from ore smelting has been estimated at an amount of at least 6 Mt. The weathering of all this waste material has constituted an enormous source of metal and sulphur emissions to the environment. As if this was not enough, a great cave-in occurred in the main ore body in 1687, which created a wide, gaping hole nearly 100 metres deep and beneath this, a huge amount of mineral-rich rubble down to a depth of nearly 350 m. As a result of this "Great Cave-In", the innards of the Copper Mountain were exposed to atmospheric oxygen, which accelerated the weathering process. Rainwater percolating through the rubble carried the weathering products to the bottom of the mine, from where they were pumped to the surface and discharged into the Gruvbacken Creek, which empties into River Faluan, Lake Tisken and Lake Runn, before the water reaches River Dalalven (cf. map in Figure 4.2).

The pumping and discharge of the heavily polluted mine water to the Gruvbacken Creek continued until 1987, when purification of the mine water was initiated.

0 0

Post a comment