(Reuters) – BHP Billiton and a consortium led by Glencore-owned Kazzinc are the only contenders for Tajikistan’s largest silver field after three Chinese rivals withdrew their bids, a government official said. The licence to develop the Konimansuri Kalon deposit should be awarded by the end of this year, Rahmonbek Bakhtdavlatov, first deputy head of Tajikistan’s government agency for geology, told reporters on Wednesday.