Swedish gold - looking for gold at the Bjorkdal mine

Materials World magazine
,
3 Sep 2010
Underground at Bjorkdal mine

Michael Forrest reports on developments at the Bjorkdal mine in Sweden, where a junior Canadian mining company hopes to strike gold.

Choosing an exploration or mining environment has never been easy, either for the investor or mining company. The advantage of a 'new' grass roots country or region can be outweighed by lack of infrastructure, cost or political risk. Even developed countries present some risk, as the ongoing taxation issues in Australia have shown. So where does an entrepreneurial mining company put its capital and exploration dollars? In the case of Gold-Ore Resources, a Canada-based company, the answer is Sweden.

According to Gold-Ore Resources' CEO Glen Dickson, ‘We were looking for a project that suited the financial capability of a junior company, that offered potential for growth through exploration, and ideally had production to fund growth. We found all of these in Sweden’.

At the end of 2007, Gold-Ore became the effective owners of the Bjorkdal mine in the historic Skelleftea mining district. ‘The recent history of the mine reflected low investment in property and plant, and, in particular exploration, exacerbated by poor metal prices,’ says Dickson.

Most of the production from 1988 had been from stockpiles with a little mining from the open pit. It was enough, however, to keep the mine in production for all but the year 2000. Since 1988 some 966,766oz of gold have been recovered at Bjorkdal, with a record 92,498oz produced in 1997.

Geologically promising

Bjorkdal, although a relatively recent discovery, is at the eastern end of the Skelleftea district of northern Sweden, which has over 52 mineral deposits, each exceeding 100,000t of ore, with 24 mined since 1924. The 100x30km mineral belt is bounded to the north by terrestrial metamorphosed volcanic rocks deposited near the southern margin of an Archean-aged continent, and to the south by an extensive palaeo-marine basin that today is represented by gneisses, migmatites and granites. The Skelleftea Group comprises two metavolcanic units, a lower felsic lava overlain by a volcanoclastic sequence followed metasediments, mainly of greywacke composition. At least three generations of granite have intruded the sequence from 1.9-1.78Ga. Throughout the belt area are a number of massive sulphide deposits.

At Bjorkdal, gold mineralisation is at the contact between a dome-shaped granitoid intrusion and the overlying Skelleftea Group where it has intruded a sequence of felsic volcanics and marbles. The gold is associated with steeply-dipping sheeted quartz veins developed in fracture zones perpendicular to the granite/volcanic interface. Mapping shows that fracturing is the main determinant for distribution, with most of the veins in the competent volcanics and a few in the ductile overlying marble.

In general, the gold-bearing veins are 10cm to one metre thick, with relatively simple mineralogy of mainly quartz and minor amounts of sulphide. Tourmaline is present in all veins and appears to more abundant with increasing gold content. The gold is coarse grained and free milling.

Beneath their feet

Production in 2008 and 2009 totalled just over 66,000oz using stockpiles, ore from the open pit and material excavated during underground development. The decision to go underground was not difficult as the open pit, by no means exhausted, did not have the potential to increase reserves. ‘Our drilling confirmed mineralisation with good grades at depth and, as a result, our focus in the past two years has been to plan for underground working,’ explains Dickson.

The underground mining method applied will be long-hole stoping using mechanised mining methods. For the open pit, five-metre benches using standard drill, blast and load are used. Total ore production is slated at 3,200t per day for 350 days per year.

Gold-Ore’s consultants Wardell Armstrong International (WAI) reviewed the mineralisation prior to their work in determining a JORC-compliant resource estimate. The resource calculations by WAI are based on historic records and drilling undertaken by Gold-Ore, which confirmed earlier results.

In 2007, around 3,000m of drilling in a number of holes, all intersected granodiorite-hosted gold mineralisation north of the present open pit, with values up to 10g/t. In 2009, a further 1,027m confirmed gold four kilometres to the northeast, although in a different style of mineralisation. These data were used to revise the resources and reserves determined by WAI in March, splitting them into surface and underground resources (see table).

Wardell Armstrong International used Datamine software and indicator kriging, incorporating all drill data up to March 2009 – a total of 4,475 drill holes with a nominal spacing of 30m. Mineable resources were also calculated using actual operating costs at Bjorkdal and Mine2-4D software for mine design, with an economic cut-off grade of 0.45g/t at a gold price of US$806/oz.

Separate interests

Processing to ore at Bjorkdal involves simple crushing and grinding followed by gravity separation and flotation. The ore is crushed to <10mm fragments and ground to less than 1.2mm for loading onto two in-series Deister shaking tables. Tailings are re-ground. In 2009, a Knelson concentrator was installed to improve recovery. Tailings from the tables and Knelson are then passed to flotation cells with a 60% pulp density where the concentrate is thickened to a filter cake.

Dickson explains, ‘Investment in Bjorkdal provided Gold-Ore with an operating mine and concentrator in a mining-friendly operating environment. The relative simplicity of the ore entails minimal environmental impact (no cyanide), and the mine and plant generate significant cash flow. Our exploration and underground development work have proved additional resources and indicated a lot more, providing comfort for our investors’.

Further information

Gold-Ore Resources Corporate Headquarters, Suite 1140-625 Howe Street, Vancouver, British Columbia, Canada, V6C 2T6. Tel: +1 604 687 8884. Website: www.goldore.ca