NORTHAM: Laura Lauri, a field exploration manager at the mine, says LKAB was aware of some rare earth deposits back in the 1960s as it was mining the iron ore. LAURA LAURI: We knew that there was something out there, but we didn't know how much and at what depth and things like this.

The discovery led the company to believe there's a huge deposit further underground. They're used in motors that power wind turbines and electric vehicles. Earlier this year, Sweden announced that mixed in with the iron ore were what's known as rare earths, which are critical for the transition to clean energy. NORTHAM: The Kiruna mine is already one of the world's largest sources of iron ore, but they've made a game changing discovery here. And there's some miners here, and it looks like they're just waiting outside the cafeteria 'cause there's got to be food around here.

We are now 4,000 feet under the earth right now, and this is actually quite a brightly lit place.

Our headlights pick up the reflectors on the reinforced gray stone walls. The tunnel is dark with a low ceiling, and it twists and turns as we descend. Now as we're getting lower, I can feel my ears popping, but we're still - we still have a long way to go till we get to the bottom. HUHTANISKA: The first time it felt - I wasn't scared, but it's an awkward feeling. Huhtaniska says there are about 25 miles worth of underground tunnels. There's quite a bit of dust in the air now. It'll be a half-hour drive down to the bottom, and it's a strange experience. She's a communications person at this state-owned iron ore mine, located in Sweden's northernmost city, Kiruna, north of the Arctic Circle. JACKIE NORTHAM, BYLINE: Ulrika Huhtaniska shifts into low gear as the pickup truck we're riding in heads deep into the LKAB mine. ULRIKA HUHTANISKA: So one of the rescue chambers are over there. NPR's international affairs correspondent Jackie Northam went to see the enormous effort Sweden is making to develop its own supply. Around the world, countries are scrambling for them. We're going to take a trip deep underground to a vast mine in Sweden holding minerals that are key in making tech products, from phones to electric cars.

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