Roundness of mineral particles in subsea tailings from copper mining
Copper mines obviously yield copper, but they also produce waste material – tailings – which must be disposed of somehow. In Norway, tailings have often been dumped in fjords as an alternative to disposal on land. The environmental impact of this practice over time is not known.
Ulveryggen Cu mineralisation in Repparfjord within Kvalsund municipality in Arctic Norway was discovered around 1900. Mining operations took place from 1972 to 1978, when about 3 megatonnes of 0.66% Cu was produced from four open pits. The adjacent Nussir Cu ore deposit, discovered in 1979, contains 25 megatonnes at 1.16% Cu. Tailings from mining in the 1970s were deposited at the bottom of Repparfjord. The same strategy is being considered for mines to be opened in the near future. Therefore, it is of interest to assess the environmental impact of submarine tailings disposal.
Submarine tailings disposal is the discharge of mining tailings below sea level. Three different types can be defined: coastal shallow-water disposal or land reclamation; submerged disposal in water shallower than 100 m; and disposal in deeper water. Norwegian authorities consider submarine tailings disposal to be a legitimate and viable alternative to terrestrial storage.
Globally, submarine tailings disposal has been practised on a large scale in several mines since the 1970s. Papua New Guinea has three active sites, while Indonesia, France, Greece and Turkey all have one each. In contrast, submarine tailings disposal is illegal in the United States and Canada and is considered “unsuitable” in Australia.
In Norway, submarine tailings disposal has long been used to get rid of waste from mining and ore-enriching facilities, and seven sites are currently active. Two more mines are being planned with submarine tailings disposal sites, one of them in Repparfjord.
Coarse masses larger than 200 µm will be used in various ways, but the plan is to dispose of the finer tailings – about a million tonnes per year – using submarine tailings disposal.
Mining produces vast volumes of waste – rocks from overburden, access tunnels, adits, and shafts – in addition to tailings from processed ore. Tailings are a by-product of the process of extracting ore through crushing, milling and subsequent flotation. In copper mining and extraction, the tailings account for as much as 99% of the total mined ore.