Sala Silver Mine
Sala Silver Mine (Swedish: Sala silvergruva) is a mine in Sala Municipality, in Västmanland County in Sweden. The mine was in continuous production from the 15th century until 1908. Additional mining occurred in 1950-1951 and also in 1945-1962 in the neighboring Bronäs Mine.
The Sala ore is mainly known for its high silver content though the ore also contained economic amounts of lead and zinc. The zinc was hosted by the mineral sphalerite while lead was hosted by the mineral galena. Silver occurred as a native phase rarely but was mainly hosted by complex antimonides and sulphosalts, dispersed in the matrices of galena and sphalerite, invisible to the naked eye but visible in microscope. The silver content in typical galena-dominated Sala ore was about 0.15% to 1%, the latter being one of the highest contents of silver in galena ever reported. In the sphalerite-dominated ore, the silver content is only about 0.015-0.02%, which was still enough to exploit and would even be at present days, given that a sufficient tonnage of metallurgically advantageous ore could be found.
The bedrock was created about 1,89 billion years ago during the paleoproterozoic era. The host rock to the mined ore is dominated by white dolomitic marble, proximal to the ores commonly rich in skarn minerals such as tremolite, serpentine, diopside and chlorite, giving the dolomitic marble at Sala a characteristic green colour. ~ 100 meters away from the mine, more pure white dolomitic marble poor in skarn minerals is extracted at the Tistbrottet dolomite quarry.
The mine has had three major heyday, the main one in the early 16th century, a second less significant one in the mid-17th century and a last one in the late 19th century. The last period involved re-organisation of the mine organisation (a transition from state-owned to company-owned) as well as the introduction of several new technological innovations, e.g. leaching methods employed on older mine tailings. These innovations produced temporal production peaks, yet a general lack of high-grade ore made continued production uneconomic which finally led to closure. At most, 5 million tons of rock were mined from which > 200 million ounces of silver and about 35,000 tons of lead were extracted. The maximum depth of the mine is 318.6 metres and the length of the mine is ~ 700 metres, the width is ~ 100 metres.
The town of Sala emerged as a miners settlement near the mine, first in the form of a small mining village in the early days, then moved to its present location on order from the king. The king Gustavus Adolphus of Sweden gave the town its privileges in 1624. Around Sala there are numerous lakes and dams with canals, constructed to supply the mine with hydro-power for driving machines for water pumping, ore hoisting and ore smelting. None of these machines are preserved to present days.
Earlier, granite ('Sala granite') was extracted to be used as bricks for construction material northeast of the mine. Several foundations for the buildings in the mine area are built from Sala granite.
The mine was owned during later years by AB Svenska Metallverken in Västerås and Avesta Jernverks AB that until 1962 extracted lead, zinc and very little silver. The extraction was made in a mine not physically connected to the old mine. Since 1988 the mine is owned by the municipality of Sala and serves as a mining museum.