Mineral exploration in Sweden could be enjoying a modest renaissance in the next few years as
This year’s exploration season will see Boliden’s own efforts turn from target selection to drilling, as well as a large grassroots exploration campaign in the Garpenberg area and continued feasibility work on properties in the Skelleftea camp.
Boliden divides its exploration dollars a number of ways: the mine departments have their own exploration budgets, used for drilling to bring inferred resources into measured and indicated categories, and into minable reserves. The exploration department has budgets for “resource” exploration on showings, used for drilling off inferred resources, and for more grass-roots “field” exploration.
The company has budgeted US$7 million for resource and field exploration in Sweden this year. Boliden’s mining divisions are spending another US$600,000 on mine-scale exploration, and a joint venture with
David Rigg, Boliden’s manager of Swedish exploration, thinks Boliden’s exploration budgets may go farther than those of other explorers because of the company’s long-time dominance in northern Sweden. The Boliden exploration database goes back to the 1920s, and has been carefully preserved. One of its virtues is that a lot of information can be drawn out without extensive (or expensive) field work, but there is another: if exploration budgets fall, the staff can still be productive without breaking the bank, as they have in the past two years.
During those lean times, Boliden cut back programs but did not cut back on staff. The result is that new funding now has projects to go to, developed by Boliden geologists whose job over the past year has been to comb the company’s large database for untested or poorly defined exploration targets.
“We’ve maintained our staffing levels, and it’s really paying off,” says Rigg. The coming exploration season will see drilling on the new targets, and some old ones.
Another factor that may provide more for the exploration dollar in the coming years is the introduction of wireline drilling in Sweden, which is cutting costs-per-metre in half. A third, says Rigg, is the saving that has come from international tendering of laboratory contracting.
The money now available for exploration gives Boliden’s exploration department 30,000 metres of drilling for new discoveries.
Skelleftea, historically, has been a camp of relatively small volcanogenic massive-sulphide deposits: one or two million tonnes of ore. That has contributed to making it an orthodox central-mill operation, with the small deposits feeding the Boliden concentrator. And it has allowed the area to flourish, with multiple small mines coming into production as they were discovered and developed. Since the Boliden discovery, in the 1920’s, 27 mines have come into production in the area.
The camp is, in Rigg’s words, “challenged.” Its 5.5 million tonnes of reserves — split among six mines — represent a 5-year life, and the existing inventory needs to be built up.
Boliden controls a land package of about 1,400 sq. km in the Skelleftea district, which measures about 140 km from Kristineberg in the west to Skellefteahamn on the coast.
Most of the past discoveries have had surface showings, or been geophysical discoveries, suggesting that there may be opportunities to discover some blind or buried deposits. For the most part, Boliden’s drill holes have been relatively shallow (100 metres and less), and, considering the plunging morphology of most of the camp’s known orebodies, the camp should have potential for deeper mineralization.
The largest undeveloped deposit in the area, Rakkejaur, has been dormant for years, owning to its arsenopyrite-rich mineralization. Still, it has 17 million tonnes that grade an average of 2.3% zinc, 0.3% copper and 45 grams silver and 1 gram gold per tonne.
In the complexly folded Kristineberg area, a large part of the resource-exploration budget will go into defining the recently discovered Einarsson massive-sulphide zone, at depth below the Kristineberg mine workings.
There will also be some field exploration to test a possible new mineralized horizon. Three phases of folding have been identified in Kristineberg’s volcanic host rocks, and some mineralized showings and drill intersections have been discovered off the known ore horizons.
The joint venture with Inmet covers a 150-sq.-km land package surrounding Boliden’s Garpenberg zinc mine in southern Sweden, about 150 km northwest of Stockholm. The agreement excludes the immediate mine area but will step up prospecting in the Proterozoic volcano-sedimentary belts of the Bergslagen district.
The Bergslagen area is a similar geological setting to the Skelleftea district, with rocks of a similar age (mainly around 1.9 billion years). But the Garpenberg orebodies (Garpenberg, discovered in the 1300s and still operating, and a rather newer mine at Garpenberg Norra) are mainly steeply dipping sulphide lenses in both felsic volcanic rocks and limestones. There are multiple ore types, but most of the orebodies resemble skarns rather than volcanogenic massive-sulphide bodies.
The two operating mines have produced about 20 million tonnes of ore between them, and their reserves at the end of 1999 were 5.9 million tonnes grading 4.1% zinc and 114 grams silver. Two other known deposits, Tyskgarden and Dammsjon, lie between the two producing mines, and the four deposits taken together have another 16 million tonnes of resources.
Boliden did a lot of work in the Bergslagen area between 1962 and 1986 and has a large collection of data — precisely what attracted Inmet’s interest. “We can do a lot with our exploration dollar in the Garpenberg structure,” says Rigg. The partners will be looking hardest for deposits that can be operated as satellites of the Garpenberg mill.
In another joint venture, this time in the Skelleftea belt, Boliden and
The project has two base metal deposits at the advanced exploration stage: Storliden, just north of Mala, and Norrliden, about 40 km to the southeast. Storliden, an airborne-geophysical discovery, is the more advanced of the two, with an indicated and inferred resource of 1.8 million tonnes showing average post-dilution grades of 10.3% zinc, 3.5% copper, 24 grams silver and 0.25 gram gold.
Consulting firm Micon International’s prefeasibility study on Storliden concluded that an 850-tonne-per-day underground operation could be profitable, based on a net smelter return of US$110 per tonne. The operation would have a mine life of six years.
Initial metallurgical tests achieved recoveries of around 90% by flotation, producing separate copper and zinc concentrates. Under Micon’s scenario, the proposed mine would not feed the Boliden concentrator; the prefeasiblity study includes a mill sending concentrate to the smelter at Ronnskar.
The capital cost estimates for a mine and mill range from US$35 million to US$50 million. The estimates vary depending on mining methods, on whether the operation uses new or used equipment, and on how much of the work will be done by outside contractors. Operating costs have been estimated at US$32-40 per tonne.
More recently, Micon finished a prefeasibility study on the smaller, Norrliden deposit. At Norrliden, which was first discovered by the Swedish Geological Survey, North Atlantic has drilled an inferred resource of 775,000 tonnes with grades of 7.8% zinc, 0.8% copper, 0.7% lead, 100 grams silver and 1.1 grams gold.
The smaller resource yields a 30-month mine life, and the capital costs of putting in a mine (which would feed the Storliden concentrator) would run between US$7 million and US$10 million. Norrliden’s lower grades mean a net smelter return of around US$60 per tonne, and operating costs per tonne are expected to run between US$30 and US$35.
Initial metallurgical tests on Norrliden have been positive, suggesting that copper, zinc and lead-silver concentrates can be produced fairly easily. The gold and some of the silver reports to the copper concentrate.
The partners have a mine permit for Storliden in place, and have applied for one for Norrliden. Environmental baseline studies are under way, and environmental approvals for Storliden are expected in the last half of this year.
Be the first to comment on "Boliden considers extensive exploration"