The front line of America’s scramble for critical minerals lies miles beneath the surface in the cavernous tunnels of Sangdong, South Korea, where miners blast glittering seams of tungsten from craggy rock.

With the highest melting point of any metal and a hardness close to that of a diamond, tungsten is essential to manufacturing semiconductors, construction and oil-drilling equipment, and the missiles and armored vehicles used in modern warfare.

Like many minerals critical to the technologies the world depends on, tungsten is overwhelmingly controlled by China, which produces roughly 85 percent of the global supply. The consequences of that dominance became clear last year when Beijing imposed strict export controls, leading to shortages and sending prices soaring as military demand surged.

At the same time, China has sought to tighten its grip on the market, acquiring the mining rights to the world’s largest open-pit tungsten mine in Kazakhstan. And Chinese buyers are scouring the globe for scrap tungsten.

“What China is trying to do is not just dominate one piece of the supply chain,” said Chris Berry, an independent metals analyst based in Washington. “They want to dominate the entire tungsten supply chain.”

Mr. Berry said China was interested in controlling the mining and import of the raw material as well as the production and export of high-value tungsten materials.

In an effort to catch up, the U.S. government has joined the global race for tungsten. Late last year, the White House helped an American company secure a mining deal with Kazakhstan to develop a large deposit there, hundreds of miles from the Chinese-owned mine. The Defense Department, meanwhile, is preparing to enforce a ban next year prohibiting contractors from using Chinese tungsten and has been searching for suppliers to help stockpile the mineral.

That is why all eyes are now on this mine in South Korea’s mountainous eastern region, operated by Almonty Industries, a Montana-based company whose recent initial public offering raised $770 million. Already in production, the tungsten mine is widely viewed as the one best positioned, as Mr. Berry said, “to put a dent in China’s dominance of the supply chain.”

About 58 million tons of tungsten lies within galleries stretching more than two miles underground. Lewis Black, Almonty’s chief executive, estimates that it will take 45 years to mine the deposit, with the potential of supplying roughly 40 percent of global tungsten demand outside China. Last year, Almonty also secured the mining rights to another tungsten deposit in Montana.

There is already a flurry of activity at the South Korean site. First comes the blast of dynamite. Then gray boulders of ore are loaded onto dump trucks that wind their way back to the surface. There, the rock is broken down until it becomes the fine powder manufacturers are now scrambling to procure.

The competition for tungsten now extends far beyond mines and refineries.

Nick Stevens, the owner of JC Metals, a scrap recycler in New Jersey, said he received a call from Chinese buyers in April offering to pay nearly 30 percent above market prices for all the scrap tungsten he had on hand.

Their message, he recalled, was: “Whatever you have, I’ll take it.”

Mr. Stevens said he had refused to sell because he believed in strengthening the U.S. tungsten supply chain. But some of his peers, he said, have since taken advantage of the higher prices and sold to Chinese companies.

For all the talk of reducing dependence on China, the world’s tungsten supply chains remain deeply entangled.

Mr. Black illustrated the point during a recent interview by reaching for one of tungsten’s most consequential uses — a .50-caliber armor-piercing round made from the metal. Much of the tungsten used in the ammunition sent to Ukraine, he said, still originates from the very countries it is fighting against.

“That is the absurdity of the situation,” he said.

A Mine Reborn

This is not the first time that the United States, suddenly cut off from Chinese tungsten and in desperate need of the material, has turned to the mine in Sangdong.

After North Korea invaded South Korea in 1950, Washington feared that war with the Soviet Union could be imminent and began stockpiling critical minerals. The United States had come to rely on cheap Chinese tungsten exports, but amid the Chinese civil war, Beijing halted shipments to countries outside the Communist bloc.

The United States dispatched an American geologist to Sangdong to determine whether the mine could be a viable alternative, instructing him to deliver a survey report directly to Dean Acheson, the secretary of state, and Gen. Douglas MacArthur, according to Jaeyoung Ha, a postdoctoral fellow at Tsinghua University.

The U.S. government signed an agreement with South Korea allowing Americans to manage the mine and buy its output. When the deal expired in 1954, after an armistice had ended the fighting in the Korean War, the mine was returned to South Korean control.

That push-and-pull of demand, shaped by global conflicts and the availability of cheap Chinese exports, has defined the tungsten market for decades.

In the mine’s heyday, it accounted for 70 percent of South Korea’s economic output. But by the 1990s, a flood of cheap Chinese concentrates had again swamped the market, forcing several mines, including Sangdong, to close.

When Mr. Ha saw tungsten prices start to spike after China imposed export restrictions, he thought reopening the mine would become “inevitable.”

“Chinese tungsten had been the main competitor with the Sangdong tungsten since its beginning,” he said.

In the years after the mine closed, the nearby village steadily shrank. Storefronts along once busy streets were abandoned. Roofs caved in, doors were boarded up and mail carriers stuffed fliers into the letter boxes of stores with broken windows. As recently as 2023, Mr. Ha recalled, he saw signs posted by villagers urging companies to reopen the mine.

“I don’t want to see this town die” was the sentiment he heard, he said.

Inside the Mine

On a recent Tuesday, trucks carrying boulders of ore trundled up a hill at the mine and deposited the boulders onto heaping stockpiles.

Below ground, miners in steel-toe rubber boots and hard hats drilled through rock and toted away the remnants. Some were extracting and examining another heat-resistant metal found in the mine, molybdenum. Others were breaking through walls to reconnect older passages from the mine’s early days, which are now used to ventilate the underground network.

In the darkness, tungsten ore glitters beneath an ultraviolet lamp, shimmering from gray slabs of rock that will eventually be blasted apart.

Once extracted from the galleries, the ore is either added to stockpiles or sent directly for processing, a multistep process that grinds the rock into ever-smaller pieces.

A mountain of ore is held back by thick black metal chains until it is ready to be crushed into fist-size pieces or smaller. The pile is then released, tumbling down a ramp where the pieces are sifted and sorted by size.

The rock is carried by a conveyor belt into a cavernous room filled with towering silver-and-yellow machinery, where it is milled into even finer particles. Finally, it is mixed with chemicals in large vats, allowing workers to separate the tungsten from other metals and sediments.

The final product is tungsten concentrate, a gray powder that is bagged and shipped to Almonty’s clients, chief among them a Pennsylvania company that makes “components across thousands of different products across hundreds of sectors,” Mr. Black said, including armor-piercing munitions.

“It takes years of investment, permitting and technical work to bring a mine into production,” he said. “You can’t race to the finish line in a democracy; you’ve got to walk.”