The Kiruna ore is predominantly magnetite interspersed with apatite, averaging 0.9 percent phosphorus. Before mining began, the ore sheet stretched four kilometers across the surface and averaged 90 meters in width. Geophysical surveys suggest it continues as a coherent body at least 1,500 meters below the surface -- and possibly deeper. As of 2020, the main haulage level sits 1,365 meters below where the ore once outcropped at Kiirunavaara. The origin of this deposit has fueled decades of scientific debate. One school holds that the ore solidified from iron-rich magma; another, championed by geologist Tibor Parak in the 1970s, argues it formed as sediment in a volcanic environment. The geology shares striking parallels with El Laco volcano in Chile, a comparison that has kept the volcanic-origin hypothesis alive. What no one disputes is the scale: this is one of the richest iron deposits ever discovered.

Surface mining came first. Workers carved into the mountainside of Kiirunavaara in the final years of the nineteenth century, and in 1902 the completion of the Kiruna-Narvik railway opened a route to the ice-free Norwegian port of Narvik, making year-round ore shipment possible. By the 1960s, the surface ore was exhausted, and operations shifted underground using sublevel caving -- a method where ore is blasted from below and allowed to collapse under its own weight. Each level goes deeper. Until 1999, the mine reached 775 meters. After the turn of the millennium, it pushed past 1,045 meters. In 1985, reserves were estimated at 1.8 billion tonnes grading 60-65 percent iron. By 2018, proven and probable reserves stood at 683 million tonnes grading 43.8 percent iron -- lower grade, but still enormous, with decades of extraction ahead.

Sublevel caving is efficient but destructive. As underground chambers collapse to release ore, the ground above subsides. By 2004, mining-related subsidence had crept close enough to Kiruna's city center that a decision could no longer be deferred: the town would have to move. Initial proposals in 2007 placed the new center northwest of the mine, at the foot of Luossavaara mountain near Lake Luossajarvi. By 2010, the city council reversed course and chose an eastward relocation toward Tuolluvaara instead. White Arkitekter of Gothenburg and Ghilardi + Hellsten Arkitekter of Oslo, working with researchers from Lulea and Delft universities, won the design contract for the new city. Their vision is deliberately different from the old: denser, more pedestrian-oriented, with green and blue infrastructure replacing the automobile-centered layout of the original town. Physical relocation began in 2014 and is projected to continue until 2040.

LKAB, the state-owned mining company that operates the Kiruna mine, is more than a commercial enterprise -- it is one of the pillars on which modern Sweden was built. Swedish iron ore, shipped through Narvik and the Baltic port of Lulea, fed the steel mills of Europe through two world wars and the postwar industrial boom. The strategic importance of this supply line was so great that both the Allies and Nazi Germany maneuvered to control it during World War II. Today, LKAB has identified what it calls Europe's largest deposit of rare earth elements in the region surrounding Kiruna, suggesting that the mine's significance may extend well beyond iron in the decades ahead. Meanwhile, the city that iron built continues its slow migration eastward, a community reshaping itself around a hole in the ground that grows deeper every year.