(IDEX Online) - Gem Diamonds, which operates the highest dollar per carat kimberlite diamond mine in the world, reported a slump in first-half profits from $18.7m to just $2.5m.The London-based miner has been hard hit by the coronavirus pandemic and saw revenue slip from $93.1m in H1 of 2019 to $69.5m. It had to close its Let?... ?eng mine (pictured) in Lesotho from 28 March to 26 April because of a government lockdown and returned to normal production on 27 May.The company recovered 43,275 carats in H1, down from 56,668 carats in the first half of 2019.The company was, however, optimistic about demand returning for high quality rough. "It is anticipated that in the medium to long term, rough diamond prices are expected to be supported by favourable demand and supply fundamentals, which are underpinned by continued growth in demand from market such as China and India, contrasted with the projected falloff in rough diamond supply," it said in its interim business review."This dynamic is expected to benefit high-quality diamonds in particular, where shortages of certain categories of these rough diamonds have already been seen during the period."