HANOI: Some 80km north of Hanoi, in Thai Nguyen province, a massive open-cut mine tears into the landscape.

Ringed by dense, green hills, the vast, stepped crater is raw gray and brown. Along its sides, huge trucks creep along, while a murky pool lies stagnant at the bottom. This is Nui Phao, a mine that’s key to Vietnam’s foothold in the global critical minerals market.