BEIJING (Reuters) - China's Zijin Mining on Monday revised down its gold production target for 2020 after Papua New Guinea (PNG) refused to extend the mining lease at the Porgera mine it operates with Barrick Gold Corp .Zijin, which produced 40.8 tonnes of mined gold in 2019, was previously targeting output of 44 tonnes this year, rising to 42-47 tonnes in 2021 and 49-54 tonnes in 2022.However, following the PNG decision, Zijin said in a filing it would strive to "maintain the mine-produced..