The limestone in Surnadal has been of significant importance for the local community for generations. Around the turn of the century (19th to 20th) industrialists started securing limestone deposits in Surnadal for themselves. Some exploration was carried out towards the end of First World War, but operations did not start before 1927.

Three mines were in operation in the area, with only one continuing doing so in the present. Around 1950 there were a good 100 men employed by the three mines. Today only Glærum Kalksteingruve is in operation, with 5 employees.

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Until 2002 Glærum Kalksteingruve was owned by the employees. The mine was taken over by the employees in 1991, from Hydro Aluminium Ltd. In 2002 the Belgium company Lhoist purchased the mine. Finally in December 2009, the Norwegian company Norock & Co purchased the mine from Lhoist, and is now running the production.

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Glærum Kalksteingruve was established in 1944. When the Germans during the occupation (1940/41) were preparing to embark on the expansion of their aluminium production in Norway, they needed large quantities of limestone for the planned production of  alumna. The mines and quarries in operation at that time were too small to provide the necessary quantity, and it was decided that Nordag themselves should start their own quarrying or mining operations. The choice felt on Glærum in Surnadal. The initial plans aimed at an annual production of 1,2 mill tons limestone, but this was later reduced to 500,000 tons per year. The plant costed 16 mill. kroner and was almost ready when the war finished. It has since been partly rebuilt and expanded in 1957, 1970 and 1972.

The deposit is extracted in two main access points at levels 86z and 10z (meters above sea level). The first years, some of the deposits were excavated, but this system has been abandoned, to avoid flooding and harm to the scenery.

 

Until 1987 selective mining has proved to be the most suitable method of extraction. A 1-metre thick layer of limestone was left on hanging walls and a half metre thick layer on footwalls, to avoid contamination to the limestone with slate. Bolting was carried out on both hanging walls and footwalls.

Loading was from mechanized chutes into 6 and 8 tons Granby cars, which automatically tip their loads into a mine silo on level 86, where most of the operations take place today. An accumulator-driven locomotive provided the traction.

The stopes are about 75 meters long and about 80 meters high. A regular pattern of pillars is left.  The chutes were built with a centre-to-centre distance of 15 meters, and were operated by compressed air.
The entire crushing plant and production silos for the old facility are underground, and use the full height from 10z to 86z.

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In 1987, the production in the stopes was stopped. Instead conventional tunnelling with modern tunnel-rigs started. The transportation is now based on dumpers, and wheel-loaders take care of loading.

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Since the beginning the limestone was sold to carbide factories, cellulose factories, smelters and the building industry as granular additive and as filler. In recent years there has been a large increase in sales for agricultural purposes. In 1972 a new fine fraction plant was built on the surface to supply limestone to the industry and for agricultural purposes. Here there are five silos, each with a capacity of 500 tons for the following fractions: 0-1 mm, 1-4 mm, 3-8 mm and 8-16 mm.