The arrest of the former Mongolian Prime Minister, who worked so diligently with Rio Tinto to secure a $U6 billion investment in growth at Oyu Tolgoi, would seem to take the often challenged relationship between the miner and its host government to a new and risky low.

The arrested man is Saikhanbileg Chimed and his detention was flagged late last week by news that the Mongolia's anti-corruption agency wanted to see him for a chat on his return from the United States.