Diamond miner and explorer Firestone Diamonds said it is set to become one of only three kimberlite producers in the world excluding the major mining companies in the second quarter as it brings a project in Botswana into production. However, shares in the company were lower after it announced pre-tax losses of £1.4m for the six months to December 31, compared with £1.26m over the same period the previous year.Chief executive Philip Kenny said he was confident about Firestone's prospects in Botswana, particularly given the shortfall in rough diamond supply projected in the coming years.