Surviving pump shaft and 1842 headframe building at Sala Silvergruva, an active heritage mine and visitor attraction.
Gustav III:s schakt is a shaft at Sala Silvergruva, Sweden's foremost historic silver mine, located near Sala in Västmanland. Sinking of the shaft commenced in 1775, initially to a depth of 90 metres, for the purpose of ventilating the mine workings. The shaft had no surface superstructure at this stage.
A second phase of sinking began in 1832 under the direction of Bergshauptman Jacob Henrik af Forselles, extending the shaft to its present depth of 267 metres for use as a dedicated pump shaft serving the northern part of the mine. Power for the pumps was transmitted mechanically from water wheels in the Nya Hjulhuset, 275 metres to the east, via a stånggång — a reciprocating rod linkage. Wooden pumps in use during the nineteenth century required frequent replacement of their packings.
In 1903 the mechanical pump arrangement was replaced by an electrical installation and the stånggång was removed. A headframe building — the lave — was erected over the shaft in 1842, during the period of the second sinking, and survives as a historic structure on the mine site. Active mining at Sala Silvergruva ceased in 1962 and the entire complex is now a heritage destination, designated a byggnadsminne in 2014.
The shaft continues to pump water from the mine today.
Gustav III:s schakt forms part of the Sala Silvergruva complex, a site with organised silver extraction dating from the fifteenth century and the most important silverfyndighet — silver deposit — in Sweden. The mine operated with three recognised periods of great productivity: the early sixteenth century, the mid-seventeenth century, and the late nineteenth century. Over more than four centuries of working it reached a depth exceeding 300 metres and developed a network of galleries and chambers totalling more than 20 kilometres. The town of Sala was founded by Gustav II Adolf in 1624 specifically to serve the mine.
The shaft now known as Gustav III:s schakt was begun in 1775. Its first phase of sinking reached 90 metres in depth and was undertaken primarily for ventilation of the underground workings. At this stage the shaft was open at the surface with no headframe or covering structure.
A second phase of development began in 1832, undertaken during a period of major investment in the northern part of the mine complex. This work was led by Bergshauptman Jacob Henrik af Forselles, one of the most prominent and energetic directors in the mine's history. The sinking was extended to 267 metres — the depth the shaft retains today — and its purpose was now defined as that of a dedicated pump shaft to keep the northern workings free of groundwater. Power to drive the pumps was taken from water wheels located in the Nya Hjulhuset, 275 metres to the east of the shaft, and transmitted underground via a stånggång — a system of reciprocating wooden rods that transferred the motion of the water wheels to the pump mechanisms below ground. During the nineteenth century the pumps themselves were of wooden construction, with packings of birch bark or leather that wore rapidly and required frequent renewal.
As part of the development works of the 1832 period, ground to the east of the shaft was levelled by filling with mine waste — varp — to create a uniform surface extending to the Materialskrivarbostället, the building now known as Direktörsbostaden. On this prepared surface the lave — the headframe building — was erected over Gustav III:s schakt in 1842. This structure survives on the site.
In 1903 the mechanical pump transmission was replaced by an electrical pump installation, and the stånggång was dismantled. The shaft continued in its pumping function under the new arrangement. The mine's last phase of active extraction ended in 1962, when the Bronäsgruvan — the final working section — closed. The pump function of Gustav III:s schakt has continued into the present: the shaft currently extracts an average of 200,000 litres of water per day from the mine, maintaining the workings in a dry condition to a depth of 155 metres for visitor access. The mine site as a whole, comprising around fifty historic buildings, was designated a byggnadsminne — a protected building monument — in 2014. Sala Silvergruva is one of Västmanland's largest visitor attractions and the schakt complex around Gustav III:s lave is open to visitors during the summer months.