(IDEX Online) - Underground mining for sapphires has resumed in Montana, USA, after four decades.The long-dormant Yogo Mine, close to the town of Utica, is being revived. And after two years of surface mining, operators Yogold USA are now going underground.They've dug a 3,000ft tunnel and are extracting up to 100 tons of ore today, in search of Yogo sapphires which range in color from deep cornflower blue to lilac. They have high clarity and few if any inclusions, but tend to be small, with few above 0.5 carats.Yogold USA said it was re-opening the mine in two phases."1) beginning with the reprocessing and redeposition of the historic tailing and a total restoration of Yogo Creek back to its original natural beauty and splendor"2) development of an environmentally responsible underground mining operation designed to mine and process several million tons of inferred sapphire bearing dike material that is known to extend for more than five miles."Pix, courtesy Yogold, show miners with rough and polished sapphires from the mine.