Notes From the Underground On April 30, Rio Tinto officially opened the new Argyle underground diamond mine in a move that will extend the small diamond producer’s life until 2020. The East Kimberley, Australia, mine, which produces 20 million carats a year of mostly smaller stones, previously had been an open-pit producer. The extension of the mine will cost $2.2 billion. The Argyle mine has produced some 800 million carats of rough diamonds in the past 25 years, including the highly desirable Argyle pinks, which the miner sells in a widely watched annual tender. Argyle is one of the largest contributors to the East Kimberley economy, a statement said, with 70 percent of the workforce living locally. “A new chapter begins at Argyle and I am proud to acknowledge the many men and women who have contributed to [its] discovery and development,” said the mine’s managing