From 1940 through 1943 Boliden added plants and mines at Kristineberg, Adak, Bjurfors, Lainejaur and Rävliden. Operations at Laisvall, the most significant source of lead in Europe, began in 1943, when the war threatened to cut off Sweden's supply of lead. Boliden developed it as a wartime measure, but eventually expanded the rich deposit into a permanent facility.
In 1947, a new deposit was discovered at Långsele near Boliden and the sulphide mine at Åkulla went into production. Two years later, the Rönnskär plant was expanded and modernized.
In 1955, the world's then deepest underground electric railway began carrying ore between Långdal and Boliden.
In 1957, Boliden acquired Zinkgruvor AB, a company that owned a small group of mines in central Sweden. The mines included Garpenberg and Saxberget, among others.
The Company continued to grow and prosper in the 1960s, with exploration at the deposits called Udden and Näsliden.
Operations started at the Aitik mine outside of Gällivare in 1968. This open-pit mine was to become one of the largest copper mines in Europe. The concentrate was transported via dedicated rail line 400 kilometres to the Rönnskär smelter.
Throughout the 60s and 70s, the production of chemicals became very important, and Boliden and its subsidiary Supra produced a million tonnes of sulphuric acid annually. The fertilizers produced with the chemicals were among the first of the artificial type called "superphosphates."