Nestled deep in the mountains of South Korea, in a remote part of the country's east, is one of the world's largest deposits of a critical mineral.

The Sangdong mine contains millions of tons of tungsten, known as a war metal that can withstand extraordinary temperatures, something the United States desperately needs for defense.

Mining company Almonty Industries has reopened the mine after it was shut down more than 30 years ago when China priced almost every other tungsten producer out of business

"The U.S. is right to do this, there is no choice," Lewis Black, CEO of Almonty Industries, told CBS News. "The status quo cannot be returned to."

But China now dominates the rare earths and critical minerals industries that are necessary to power much of the technology that is used today. During the recent trade war, China threatened to use it as a stranglehold and cut off supply, which is why the U.S. is now desperately searching for alternative supplies.

Tanks, fighter jets, armor-piercing ammunition, bunker-busting bombs and artificial intelligence missile guidance systems all need tungsten. Black guaranteed a supply on his visit last week to the White House.

When asked by CBS News if he will be able to meet the U.S. government's demand for tungsten, Black told CBS News, "For U.S. national security, yes."

This is not the first time tungsten has been used at the center of the war machine. During World War II, Allied countries fought to stop the flow of Spanish deposits to Nazi Germany.

In May, the U.S. signed a minerals deal with Ukraine that at the time was described by Ukrainian officials as an equal partnership between the two countries to develop mineral, oil and gas projects in Ukraine. Under the deal, the U.S. would provide either direct financial assistance or new military assistance to Ukraine, which in turn would contribute half of any royalties from future oil, gas and mineral licenses. Leading up to the agreement, President Trump had framed it as a way for Ukraine to repay the U.S. for the military support it has received in its war with Russia.

In the labyrinth of tunnels underground in the Sangdong mine, CBS News was taken to the latest deposits. A UV lamp illuminates the tungsten embedded in the rock.

The weight of gold, with the fragility of ceramic, makes tungsten is extremely difficult to mine. But once fully operational in the new year, Black says this mine will produce 1.2 million tons of tungsten ore per year, ensuring a guaranteed supply to the U.S. for decades to come.

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