Surviving headframe and processing buildings of the former Aijala copper mine, standing in the quiet village of Aijala in Salo, southwest Finland.
The Aijalan kaivos was a copper mine located in the village of Aijala in the former municipality of Kisko, now part of the city of Salo in Varsinais-Suomi, southwest Finland. The deposit was discovered during systematic exploration by Suomen Malmi Oy in 1945–1947, and acquired by Outokumpu Oy in 1948. The mine shaft reached a depth of 213 metres and the operation extracted 0.84 million tonnes of ore containing copper, zinc, sulphur, and minor quantities of gold and silver.
Underground copper mining ran from 1949 to 1958, with the mine officially active until 1961 when exploration for new ore ended and the shaft was allowed to flood. After its own ore was exhausted, the Aijala concentrator continued to process ore transported from the nearby Metsämonttu zinc mine through the 1950s–1970s. At its peak the mine employed around 400 people.
The main headframe tower and associated processing buildings have survived on the site. In February 2017 a collapse of the underground Itämalmi stope created a large sinkhole at the surface, releasing mine water into the Kiskonjoki river.
The Aijala area has a documented history of small-scale mining extending back to the seventeenth century. Lead ore was extracted at Hopeamäki from 1677 to 1916, totalling some 500 tonnes, and a second lead workings at Aurums operated from 1684 to 1957. Iron ore was extracted at Helbomsissa between 1688 and 1831. These were all small operations with no permanent infrastructure of the kind later associated with the twentieth-century copper mine.
In 1945 Suomen Malmi Oy began systematic mineral exploration in the area. In 1947 two sequential copper ore deposits — referred to as Itämalmi (East ore) and Länsimalmi (West ore) — were identified at Ajosniitty in Aijala village through deep drilling. Estimated ore reserves to 175 metres depth were approximately one million tonnes at a copper grade of around 2 per cent. Outokumpu Oy purchased the deposit in spring 1948 and began construction of the mine. The main shaft, initially sunk to 118 metres, was completed in December 1948 and subsequently deepened to 213 metres during operations, with the main working levels at 115 metres and 175 metres below surface. The shaft was placed approximately 100 metres north of the ore body to avoid rock movement caused by blasting. The shaft and headframe were integrated with the crushing and concentrating plant, sited to take advantage of the natural topography.
Underground mining of copper, zinc, and sulphide ore began in 1949. An annual output target of 100,000 tonnes was set. The Itämalmi deposit on the upper level was initially worked by the magazine method, in which blasted ore was stored in the stope before being drawn off. Following a roof collapse during one extraction cycle, the mine switched to cut-and-fill stoping, where excavated areas were progressively backfilled with waste rock. Ore and waste rock were moved underground primarily by gravity to separate ore bins and then transferred in 3.5 cubic metre rail wagons on a 750mm gauge internal railway, hauled by Valmet Move41 diesel locomotives. Ore was hoisted to surface in 3-tonne skips by an electrically driven Morgårdshammar winding engine, which served two counterbalanced cages — one for personnel, one for materials. Power was supplied on a dedicated 35 kilovolt line from Virkkalaa, with a 1500 kVA transformer at the mine substation. Process water was pumped from the Kiskonjoki river via a pumping station approximately 300 metres from the plant.
The concentrator produced copper and zinc concentrates, with sulphide by-product. Total ore mined between 1949 and 1958 amounted to 835,455 tonnes at grades of 1.59 per cent copper, 0.66 per cent zinc, and 13.98 per cent sulphur, with gold at 0.7 grams per tonne and silver at 14 grams per tonne. As the Aijala ore body neared exhaustion, ore from the adjacent Metsämonttu zinc-lead mine was brought to the Aijala concentrator for processing. This arrangement operated from the early 1950s through to the mid-1970s, giving the Aijala site a processing function extending well beyond the end of its own underground production. The Aijala copper mine's active underground operations ended in 1958. Exploration for additional ore bodies continued until 1961, when these investigations were concluded without result and the shaft was allowed to flood.
At peak employment the mine and its associated works provided around 400 jobs. A residential settlement was established near the mine, including two stone apartment buildings and a row of timber semi-detached houses in the Pyykylä housing area. The mine's headframe and processing complex — a substantial reinforced concrete and masonry structure — became the defining landmark of Aijala village.
Following cessation of ore processing in the 1970s the mine buildings fell into gradual disuse. By the early 2010s the processing building and headframe tower were reportedly used for minor industrial and storage purposes. The tailings impoundment left behind approximately 2 million tonnes of sulphide-bearing tailings on an 18-hectare site discharging drainage through a run-off channel to the Kiskonjoki river. In February 2017 the ground surface above the Itämalmi underground stope collapsed without warning at the intersection of Aijalantie and Pyykyläntie, forming a sinkhole approximately 10 metres deep and 600 square metres in area. Mine water displaced by the collapse was released into the Kiskonjoki river. Emergency services and specialists from Outokumpu and the Finnish Safety and Chemicals Agency (Tukes) attended the site. Environmental investigations carried out since the collapse have confirmed ongoing metal loading to the Kiskonjoki from the former mine area, likely to continue for several centuries given the sulphide content of the tailings and the flooded mine workings.