Sala Silver Mine

Sala Silver Mine 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 neighbouring Bronäs Mine. Geology 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. Approximately 100 meters away from the mine, more pure white dolomitic marble poor in skarn minerals is extracted at the Tistbrottet dolomite quarry. History The mine has had three major heydays, 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 more than 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.