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The historic mining district of Bergslagen is located approximately 200 km west and northwest of Stockholm, in the south-central part of Sweden.
Eastern Highlands AB (EH), a fully owned subsidiary of Scandinavian Highlands Holding A/S, holds nine individual exploration licences in the Bergslagen district. The licences cover a total area of c. 175 km2 of which six (6) lie within the same supracrustal belt that contains the famous Falu Copper Mine.
Bergslagen is a roughly 4000 km2 large Palaeoproterozoic magmatic province and mining district. It constitutes the largest concentration of base metal and iron ores in northern Europe and the Bergslagen region has been a major metal producer since the early of Mediaeval. More than 7500 old mines and smaller quarries are known in the district. It is an intensely mineralised part of a large, Early Proterozoic (1.90–1.87 Ga), felsic magmatic province within the Baltic Shield.
The regional geology in the licence area is dominated by Svecofennian metavolcanic supracrustal rocks mainly of rhyolitic and rhyodacitic compositions. The supracrustals have been intruded by Svecofennian orogenic granitoids generally considered to be co-magmatic with the volcanic sequence. During the orogenic build-up the supracrustals have undergone at least two deformational phases and have been metamorphosed to amphibolite facies. Late Svecofennian granitoids and associated pegmatites have been found in conjunction with these metamorphic events. Subsequently the area has been intruded by NNW–SSE trending dolerite dikes.
The magmatic province consists predominantly of a felsic meta-volcaniclastic succession. Mafic volcanics components are generally rare, except in the westernmost part of Bergslagen. The volcanic stratigraphic, with a thickness up to 7 km, is overlaying terrigenous argillite-arenite meta-sedimentary units. The underlying unexposed basement rocks are interpreted to be older continental crust. The supracrustal succession developed in an evolving graben structure under shallow marine to subaerial conditions. Marble units occur sporadically, interbedded with the volcaniclastic rocks and are most abundant in the upper part of the succession. The filling of the graben occurred during a relatively narrow time span, 1904–1891 Ma.
The Bergslagen district contains a diverse range of ore deposits dominated by polymetallic VHMS type sulphide- or VHMS related replacement mineralisation, carbonated or quartz banded iron formations, skarn type iron/manganese oxide mineralisation, apatite-magnetite iron ores, stratiform and strata-bound Zn-Pb-Ag-(Cu-Au) sulphide ores, W-bearing skarn and possibly larger IOCG type mineralisations. Most of the sulphide ore deposits, and a large number of the iron deposits are spatially associated with marble units, skarns, meta-limestones and hydrothermally altered metavolcanic rocks. The gold mineralisations, as found in the Falun area, appear to be related to syn-volcanic hydrothermal systems.
EH has conducted three (3) individual helicopter born time domain electromagnetic surveys (TEM) carried out by SkyTEM ApS, Denmark. EH was the first exploration company to use TEM in the Bergslagen district. The surveys cover an area of c. 120 km2 and have resulted in the discovery of several strong anomalies, of which the most important ones are situated in vicinity to the old Falu mine. Several of the most prominent anomalies have been confirmed by continuous vertical electrical sounding (CVES) geophysical exploration tool.
Eastern Highlands AB holds six (6) exploration licences in the Falun area covering an area larger than 100 km2, virtually from the edge of the old Falu copper mine towards south along the edge of Lake Runn and west towards the town of Borlänge.
The mine has been in production for at least a 1000 year period. It is estimated that during the lifetime of the mine 28 Mt of ore was mined (28.1−30.0 Mt @ 2-4% Cu, 4% Zn, 1.5% Pb, 13−24g/t Ag and 2−4 g/t Au). The main style of mineralisation is massive sulphide ore with ore minerals being sphaterite, galena and chalcopyrite. In addition to the massive sulphides, a Cu-Au stringer mineralisation (termed hard ore) and gold mineralised quartz veins were mined as important by-products. The mine was abandoned in 1992.
The Samuelsdal target was discovered by the TEM surveys and is situated in the immediate vicinity of the Falu mine at a shallow depth of c. 75–100 m. The conductor is approximately 200 x 300 m wide and given the close proximity of the old mine this target area is very promising. In addition to promising TEM data geochemical assays results show significant gold and copper content in till samples.
The Bergslagen region is regarded as an attractive mineral exploration target, with high potential for new discoveries. This is especially true for exploration at depth. In historic times mining levels seldom reached deeper than 200–300 m, and deep-penetrating exploration methods e.g., airborne TEM have been applied only sparingly. This has been underlined recently by the discoveries at Garpenberg by Boliden Mineral (the Lappberget deposit).
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