The Hemerdon tungsten mine on the edge of Dartmoor in Devon will exploit what is said to be the world's fourth-largest deposit of the metal.
Australian owners Wolf Minerals hope to produce about 3,000 tonnes of tungsten and tin per year.
The opening coincides with a fall in the world tungsten price, but bosses claim the price will recover.
Robin Shail, from the Camborne School of Mines, said: "It's important regionally and nationally. We have a world-class resource based here in the south west.
"This mine site is going to be responsible for between 3-4% of tungsten production worldwide."
Russell Clark, managing director of the company, said: "When the world is developing and growing it's consuming tungsten and it needs supply.
Mr Clark said: "Metal prices go through cycles and this mine will be here for the next 10 to 15 years.
"We're very confident the price will come back and when it does this project will be in a prime spot."
He said the price had "eaten into our margins" but would recover as tungsten was an element "that can't be substituted".
About 200 people are employed at the mine, with many of the senior team from Cornwall's Camborne School of Mines.
Mr Clark's outlook is underpinned by the mine's relatively low operating costs.
It is an open-pit operation because at Hemerdon, near Plymouth, the mineral lies close to the surface.
The price of the metal tends to move in cycles and if it stays low, or falls farther, Wolf Minerals believe other tungsten producers worldwide with higher costs will cease production, reducing supplies of the mineral and encouraging the price to go back up.
The price of tungsten was about $400 for a 10kg unit in November 2013, but it has since dropped to about $200 a unit.
The recent decline has been linked to a fall in Chinese industrial activity.
The first metal mine to open in Britain for more than 40 years has officially opened at a cost of £130m.