Rio Tinto has been accused of being involved in political bribery relating to its Oyu Tolgoi copper mine in a secret lawsuit that reveals the toxic relationship between the resources giant and the Mongolian government.

Rio and officials in Ulaanbaatar have squabbled for almost two decades over how to share Oyu Tolgoi’s wealth, and the company’s departing chief executive, Jakob Stausholm, has spent close to $8.5 billion on buying out minority shareholders and waiving government debts to resolve the tension.