Geology
The Garpenberg mine is situated in the mineralized Palaeoproterozoic igneous province of Bergslagen, south central Sweden, which is host to a variety of ore deposits, and especially Fe-oxide and polymetallic sulphide deposits. Garpenberg is the largest sulphide deposit in the region, and comprises several individual ore bodies distributed over a distance of 4 km along a limestone horizon, see Figure 3-3. The main host rock is calcitic marble (limestone) altered to dolomite and Mg +/- Mn-rich skarns. The footwall comprises of strongly phlogopite-biotite-cordierite-sericite-quartz altered felsic volcaniclastic rocks, whereas the hanging-wall comprises relatively unaltered volcaniclastic and sedimentary rocks and dacitic intrusions. The stratigraphic succession is attributed to the volcanic cycle of a felsic caldera complex, and includes rhyolitic to dacitic, juvenile pumiceous, graded mass-flow breccia deposits and rhyolitic to dacitic ash-siltstone and sandstone in the footwall, and polymict conglomerates and juvenile, rhyolitic, pumiceous breccias in the hanging-wall. These pumiceous breccias in the hanging-wall record a climactic eruption that formed a caldera over 500 m deep and over 9 km in diameter in the Garpenberg area. The limestone hosting the ore is interpreted as a stromatolitic carbonate platform, formed in a shallow, marine environment during a hiatus in volcanism.

The ore-host limestone shows a complex geometry due to large scale folding, shearing and faulting. Folding and late faults have locally remobilized the ore into fault- and fracturehosted sulphide veins, some of which have been thick enough and rich enough to mine. These structural features have resulted in complex synforms and antiforms, and have a major influence on the position, geometry and metal grades of the ore bodies. The Lappberget ore body is interpreted as an over 1.5 km long, subvertical anticlinal tube fold with the top of the antiform just below 200z. The initial main stage of mineralization and alteration at all the known Garpenberg ore bodies is interpreted to be essentially syn-volcanic in timing and to pre-date regional metamorphism and deformation (Jansson & Allen, 2011).

The Garpenberg mine encompasses several ore bodies which follow a limestone-marble horizon occurring in a synform structure. The structure is compressed at the southern end and opens to the north. The horizon is strongly isoclinally folded and the structure tectonic and divided into blocks. The ore bodies occur in the contact zone between the limestone and underlying siltstones. The contact zone is heavily altered to skarn and the limestone to dolomite. The structures are consistently steeply dipping

Garpenberg is a Zn-Pb-Ag-(Cu-Au) underground mine where the ore is mined from between 500 meters to more than 1 400 meters below surface. The mine encompasses several polymetallic ore bodies. Almost 80 % of the mined tonnage derives from the largest ore body, Lappberget.

Almost 90% of the mined ore in Garpenberg is extracted by sublevel stoping (also called longhole stoping), where the ore is mined in layers between two drifts vertically 25 m apart. Most areas are mined with transversal longhole stoping, where the development and stope axis are perpendicular to the strike of the orebody. In some more narrow areas, longitudinal longhole stoping is used. The orientation of this method is along or parallel to the strike of the orebody. The ore body is split into primary and secondary stopes, which are mined in a predefined order and pyramid shape sequence. The standard stope dimensions are 24 - 25m high, 10 m wide for primary stopes and 15 m wide for secondary stopes. In Lappberget, the ore body is divided in mining blocks with 6 levels of stopes in each block. The last level of each mining block is the sill pillar, which separates the different mining blocks. This division allows the mine to have several production areas being scheduled and mined at the same time.

Other mining methods include cut and fill and avoca (rill). With the cut and fill method, mining is carried out in slices along the steeply dipping, narrow ore body. The bottom slice is mined first. The excavated area is then backfilled, so mining can continue with the slice above. The rill method used in Garpenberg is in fact similar to longitudinal stopping, but the stopes are split in 20 m long slices. After being blasted and mucked, the stopes are backfilled before the next slice is blasted. This process repeats until the full size of the stope is done.

A liquid emulsion explosive is used for blasting. The emulsion is mixed mechanically when charging. During sublevel stoping, a normal round produces approximately 10,000–20,000 tonnes of loose ore.

Loading ore from the sublevel stoping area takes place using remote-controlled LHD loaders. Loading when drifting and cut-and-fill mining is performed with a wheel loader. The ore is transported using trucks to one of the two underground crushing plants. Ore and waste rock are transported by a contractor.[Fact Sheet 2017 p.8].

Today there are two underground crushing plants at 700 z and 1087 z. Transport to the crushers is done by trucks from the active mining areas. The crushed ore is hoisted to surface in a shaft, unloaded into a bin in the headframe and then transported by conveyor belts to an intermediate ore storage, which can hold approximately a week of production.

Waste rock, which is mined and separated in the mine, are used for back filling in the mine. The
portion of the finely ground waste rock that is separated in the concentrator is known as tailings.
Some of the tailings are mixed with a binding agent and pumped back into the mine for back filling. Surplus tailings are deposited in a pond at the Tailings Management Facility (TMF) from where processed water is recovered [Fact Sheet 2017 p.8].

There are two underground crushing plants where the ore is crushed in jaw crushers. The crushing plants are situated 700 metres and 1,087 metres below ground level. After crushing, the ore is hoisted to surface in a shaft. The machinery for the ore hoist is situated above the shaft installed in the headframe. The ore is unloaded into a bin in the headframe and then transported by a belt conveyor to an intermediate ore storage, which can hold approximately two days’ of production.

The ore is transported on belt conveyors from the ore storage to the grinding circuit. Water is added during grinding and the ore is ground in two stages, with autogenous grinding in the
primary stage and pebble mill grinding in the second. Autogenous grinding means that the ore grinds itself without the addition of external\ grinding media. In the pebble mill, pebbles are added that have been extracted from the autogenous mill. The grinded ore is classified using screens and hydrocyclones. The coarse particles, that have not been ground down sufficiently, are returned to the grinding circuit. The grinding process results in a slurry containing water and finely ground ore.

After grinding, the ore is screened, with the coarse fraction being returned to the primary mill and the fine fraction undergoing gravimetric separation (Knelson) in order to separate coarse gold out at an early stage of the process. Knelson concentrate is collected in big bags. After gravity separation, material is classified using hydrocyclones. The overflow constitutes the main flotation feed, while the underflow undergoes flash flotation in the grinding circuit, from which the concentrate is sent directly to CuPb separation in the flotation plant and the tailings back to the mills.

Flotation is carried out in a three-stage process flotation circuits: CuPb flotation, CuPb separation and Zn flotation. Regrind mills are installed both in the CuPb and Zn circuits. The mineral concentrates are dewatered using thickeners and pressure filters. Three mineral concentrates are produced in flotation: zinc, lead and copper concentrates. The precious metals report primarily ........