Aitik Copper Mine, Sweden

Located near Gällivare, northern Sweden, the low-grade Aitik copper deposit was discovered in the early 1930s. Bulk-mining technology made exploitation feasible in the 1960s and mining at Europe’s first large, low-grade open pit copper mine started in 1968 at a production rate of 2Mt/y of ore. Since then, a series of pushbacks have increased output to approximately 19Mt/y. The concentrator, expanded in parallel, ships over 200,000t/y to the Ronnskär smelter.

Since the consolidation of Outokumpu’s copper and zinc mining and smelting activities into New Boliden in January 2004, Aitik has been wholly owned by Boliden.

Boliden approved the investment of Skr5.2bn ($790m) for the expansion of the operations (Aitik 36) which will see significant increases in capacity and production.

Boliden says that the expansion will result in one of the world’s most efficient mines becoming even more efficient. On average, ore is mined at the rate of 1t/manhour. Boliden says that production at Aitik is now at 43t/manhour but will increase to 55t/manhour.

The company said recently it also expected life of mine cash costs to fall from $0.80/lb to $0.43/lb.

All this extends the mine life from 2016 to 2025, while increasing copper, gold and silver production and adding new production of molybdenum. By lowering costs, ore reserves have been tripled.

The mine currently employs 430 people, of which 280 are in the mine. This number is expected to increase significantly in line with the expansion.

GEOLOGY AND RESERVES

The orebody is hosted by a basin of volcanic rocks surrounded by granitic intrusions, within a supracrustal metamorphosed shear zone of precambrian age. Biotite schists in the volcanic sequence contain disseminated chalcopyritic mineralisation averaging less than 0.40% copper plus gold and silver values.

Mining started on the basis of a 50Mt reserve, but by 1998 Aitik had yielded 300Mt of ore. As of November 2006, total proven reserves were 520Mt grading 0.31% copper, 0.2g/t gold and 2.0g/t silver, while 110Mt of probable reserves have similar precious metals grades and 0.28% copper. Measured resources at January 2006 were 635Mt grading 0.30% copper, 0.2g/t gold and 2g/t silver. Indicated plus inferred resources totalled 350Mt at similar grades.

MINING

Aitik is a single open pit divided into a southern section, where mining reached a final depth of 250m, and a northern area where mining is proceeding towards an ultimate 400m. The strip ratio is just below 1:1 – 1.8Mt/month of waste and 1.6Mt/month of ore in mid-2004. During the 1989–91 expansion, Roxon installed an in-pit crushing station, linked to the concentrator by underground conveyors.

Extraction starts with drilling mainly 311mm holes bored by rotary rigs, in preparation for Nonel blasting – as Aitik is prone to violent thunderstorms. Aitik recently reintroduced large electric rope shovels, with new rotary and DTH drills, all equipment that was obtained from the closed Los Frailes mine in Spain. Supplementary drilling and clean up around the main shovels is contracted out.

ORE PROCESSING

Autogenous and ball mill grinding is followed by conventional flotation, the system design being typically ‘Boliden’. It has been enhanced by the installation of Microcel flotation columns. The plant’s capacity is around 250,000t/y and the whole plant is managed by an ABB distributed process control system, optimised using Svedala CISA software. The recently announced expansion will raise the throughput to match the mine’s higher output.

Pressure filtered concentrate is transported in purpose-designed containers to Boliden's Ronnskär smelter at Skelleftehamn on the Baltic coast. A new rail link from the mining area to the main line may be used to ship out crushed mine waste rock for aggregates, as well as eliminating the previous truck haul to Gallivare.

PRODUCTION

A new concentrator to be built as part of the expansion will see capacity doubled to 36Mt. All environmental permits have granted and operations at Aitik 36 will commence in 2010. There is a four-year construction period, which Boliden says will achieve 33Mt annual capacity, ramping up to 36Mt between 2011 and 2014.

Enhancing the economics of Aitik 36, the new concentrator will include a molybdenum recovery circuit, providing Boliden with a new metal revenue source. Additionally, much of the stockpiled waste rock may become a commercial product in the future to be used in the construction of roads and as aggregate ballast. Attention is also focusing on producing products more suited to the construction industry from the waste rock mined in the future.

In 2006, concentrator throughput was18.5Mt and 21.9Mt of waste rock was removed. At feed grades of 0.4% Cu, 0.25g/t Au and 2.72g/t Ag in 2006, the mine produced 240,000t of copper concentrate. This concentrate contains 66,100t of copper, 35,700kg of silver and 2,340kg of gold.