The Björkdal Mine
BJÖRKDAL MINE FACTS
OWNER: Elgin Mining Inc. Canada.
SITUATED: 40 kilometers West of Skellefteå in Västerbotten County.
MINING RATE: About 1 300 000 tons per year, from which 1,3 tons of gold is extracted.
PERSONNEL: 180 persons work at the mine (around half are contractors).
AREA: The open pit covers some 50 hectares. There is about 200 hectares of dams, of which the settling pond covers 27 hectares
MINE SPECIFICS: The Björkdal mine was once the largest gold mine in Europe. Today it is one of two mines in Sweden which mines only gold. The ore body consists of numerous quartz veins and unusually coarse gold. It is probably the only mine in Sweden to use COPROD technique, which allows for drilling through loose rock masses.
From bedrock to gold products
The process from bedrock to gold products is long, costly and requires patience. A lot of know-how and a little bit of luck is needed before you can hold the gold ingot in your hand.
The first link in the chain is exploration. Various methods are used in different stages, from boulder mapping to airborne geophysics to soil sampling and diamond drilling. Once the ore body is known, the process of obtaining all required permits to mine follows.
The ore body is a gallery of vertical or almost vertical, narrow veins of quartz, hosted by dark granodiorites. The veins vary in width from a few centimeters to about two meters. A vein can be hundreds of meters long and more than 100 meters high. The ore bearing zone is controlled by a limestone hanging wall. The distances between the veins are typically 5–30 meters. So far, some sixty veins have been found and the potential of finding more is great.
Mining of the ore requires contribution from several professionals. Geologists indicate where to mine and where the ore is. Mine engineers plan and schedule drilling, blasting, ground support, ventilation and so on, in order to maintain safe, efficient and cost effective mining. Surveyors mark out for drilling and document all workings. The mining process is done using modern, safe and highly efficient machines.
Open pit mining
The Björkdal open pit is about 1 400 meters long and 140 meters deep. Large COPROD rigs drill blast holes in a chessboard pattern. The holes are loaded with emulsion explosives and fired in blasts of about 20 000–80 000 tonnes. Waste rock is transported to rock heaps with the help of excavators and 45–65 tonne trucks. Ore is loaded and transported to a primary crusher situated near the concentrator. In the pit some 650 000 tonnes of ore and 3 000 000 tonnes of waste rock is mined annually.
The underground mining methods are drifting, long hole open stoping and some bench and room- and pillar mining. Cross cuts perpendicular to the strike of the veins are driven with vertical distances of 20 meters. Smaller so called on-vein drifts are then driven along strike of each of the intersected veins, recovering ore. Between these upper and lower on-vein drifts, a 15 meters high slice of ore is mined by upwards drill and blast. The ore is fragmented and collapses into the lower drift, where it is mucked using a remote controlled wheel loader. Some 530 000 tonnes of ore is mined underground per year.
Crushing and upgrading the Gold ore
Ore is hauled to the primary crusher and crushed to less than 10 mm size. Conveyor belts transport the ore to the rod- and ball mill for grinding to 1– 2 mm size.
In the concentrating plant the main part of the gold is extracted by gravimetric methods. Large industrial shaking tables, spirals and Knelson concentrators separate the coarse Gold from other material due to its high density.
The gravimetric concentrate is divided into three different products. The finest grains of Gold are extracted with normal flotation technic.
The Gold sands are dried, weighed and moved into a partitioning device. A representative sample is sent to the mine’s laboratory for analysis. The analysis is used to calculate the grade of gold at the actual mining site. The total amount of concentrated gold is about four kilos per day.
The four different products are sold to smelters in Scandinavia and Europe.
Gravimetric conc, gold content 50%.
Middling conc, gold content 1500 grams/tonne.
Knelson conc, gold content 500 grams/tonne.
Flotation conc, gold content 100 grams/tonne.
The environmental work has an important position in the planning and execution of mining the ore. Björkdal mine’s operations have benefited life in downstream waters through enhancing the number of species by about 30% according to a river-bed fauna investigation carried out in 2007. This is a unique situation with respect to operative mines with emission into nearby water still containing fish and in which salmon species (salmon trout, grayling) are rejuvenated.
Residue sand contains no other element than a typical granite contains, and some limestone.
The sand can simply be compared to normal hardcore material in form of asphalt roads, gravelled surfaces and railway embankments. Residue sand from Björkdalsgruvan releases no harmful heavy metals for the simple reason that there are none there in the first place.
Consequently, the sand can be used at no risk instead of aggregate or crushed material.
1985 The gold deposit is discovered.
1988 Production is initiated and the operation is managed by Terra Mining AB.
1999 The price of gold tumbles from 100 000 to 60 000 SEK/kg. Bankruptcy is a fact. The mine is put on care and maintenance.
2001 The bankruptcy trustee puts up the mine for sale by public auction. The financier Rolf Nordström buys the mine for 15 million SEK. The work consists mostly of processing material from old stockpiles. Regular mining plans starts to grow.
2003 The Irish company MinMet Plc. becomes the principal owner and enlarges the open pit.
2006 The Canadian prospecting company, Gold-Ore Resources Ltd, signs an option to acquire the mine. During the time up to December 2007, they are free to undertake whatever surveys they consider needed in order to come to a decision regarding the acquisition.
2008 Gold-Ore acquires all of the shares and commences underground mining. The underground mine is rapidly developed. Today it has more than 25 kilometers of tunnels.
2010 The mine celebrated that more than 1 million ounces of Gold have been produced since 1988. Only a fraction of the potential gold field has been examined and the potential is very high. ”We see no end to it”
2012 In May, Elgin Mining Inc. completed a business combination with Gold-Ore Resources Ltd. The arrangement resulted in a well-funded, growth-orientated gold producer