Zinkgruvan is in south-central Sweden, approximately 250 km southwest of Stockholm and some 15 km from the town of Askersund. The operation is supported by excellent local road access and is close to the main highway linking Stockholm and Oslo. Lake Vänern, the largest lake in Sweden, is approximately 100 km from site and provides access to coastal shipping via a series of inland canals and the port of Göteborg.
Zinkgruvan mines underground from several orebodies. Mine access is principally via three shafts. The primary P2 shaft provides hoisting and man access to the 800 m and 850 m levels with the shaft bottom at 900 m. A ramp system is used to access mine levels below the shaft with the deepest level now approximately 1,270 m below surface. A ramp connecting the underground workings with surface provides direct vehicle access to the mine. The mine is highly mechanized and uses primarily a combination of longitudinal and transverse longhole panel stoping. In 2013, underhand panel stoping was introduced to the lower sections of some orebodies. At stopes are backfilled with either paste tailings and cement or waste rock.
The plant is located next to the primary P2 shaft and comprises two processing lines. Ore is secondary crushed and then ground in an autogenous grinding (AG) and ball mill circuit. The zinc line has a processing capacity of approximately 1.4 million tonnes per annum (mtpa) following completion of a low-cost project to improve overall mill capacity in June 2017. A bulk concentrate is initially produced from the zinc-lead ore before further flotation to separate zinc and lead concentrates. Concentrates are thickened and filtered and then stockpiled under cover. A separate 0.3 mtpa copper treatment line was commissioned during 2010. This line was further modified during 2011 to allow it the flexibility to treat zinc-lead ore as well as copper ore.
Tailings are pumped approximately 4 km to a dedicated tailings impoundment from which water is returned to be reused in the process. Concentrates are trucked from the mine to a nearby inland port from where they are shipped via canal and sea to European smelter customers.
Geological and Exploration Overview
The Zinkgruvan deposit is located in the southern part of the Bergslagen province of south-central Sweden. The deposit comprises a stratiform, massive zinc-lead deposit situated in an east-west striking synclinal structure within the lower Proterozoic Svecofennian supracrustal sequence. The deposit exhibits distinctive stratification and extends for more than 5,000 m along strike and to depths of 1,600 m. Zinkgruvan orebodies thickness range from 3 to 40 m, are dominated by sphalerite and galena and are generally massive, well banded and stratiform. In the central part of the deposit the zinc-lead mineralisation is stratigraphically underlain by a substratiform copper stockwork. The copper stockwork mineralization occurs in the structural hanging wall of the Burkland deposit. Chalcopyrite is the main copper mineral.
Drilling is the principle means of near mine exploration. Historical exploration has comprised of airborne and extensive ground geophysical surveys, geological mapping, conventional till sampling and geochemical surveying. Since 2000, exploration has predominantly been focused on near mine targets and on replacing mining depletion with new Mineral Resources. Due to the depth of the exploration areas and the relatively complex geometry, exploration is mostly done by underground drilling. Underground mine development provides platforms for drilling to test for possible extensions and further evaluate the potential of these areas. More recently, significant exploration has been done on the Dalby area.