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. The operation employs about 350 people.

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.

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 635 Mt grading 0.30% copper, 0.2g/t gold and 2g/t silver. Indicated plus inferred resources totalled 350Mt at similar grades. A US$750m (SEK5.2bn) mine expansion, announced in November 2006, will extend the mine’s life until 2025, with Boliden now evaluating equipment tenders. The company now intends to increase ore production to 36Mt/y.

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. In 1989 Boliden switched from electric rope shovels and diesel-electric drive trucks to hydraulic shovels (two Demag H485s) and Caterpillar mechanical drive trucks, including 789, 789B and later 793B and 797 models. More recently Aitik has 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

Total ore throughput in 2005 was 16.67Mt of ore grading 0.44% copper, 0.22g/t gold and 3.61g/t silver. Mill production of 28% copper concentrate was 237,197t. The metal content in 2005 and (2004) was 65,619t (64,498t) of copper, 41,297kg (44,948kg) of silver and 1,840kg (1,985kg) of gold.

Between them, Boliden’s Ronnskär Harjavalta (Finland) smelters produced 647,700t of copper metal in 2005, compared with 660,000t in 2004. The two units also produced 20,440kg of gold, 468.630kg of silver and 26,700t of lead, plus byproducts such as zinc clinker and sulphuric acid. The zinc clinker typically goes to New Boliden's Odda refinery in Norway.

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