Indonesia introduced in January its controversial ban on exports of unprocessed minerals and ore. Under a revision of the tax, Freeport will pay a 7.5 percent duty on its copper concentrate exports, but that rate falls as it spends on its smelter, hitting zero once investment in the project exceeds 30 percent of total cost.

The ban on exports forced Newmont to declare force majeure on copper sales from Indonesia earlier this year, putting roughly 80 percent of its Batu Hijau mine employees on leave at reduced pay. Disputes and confusion over the new mining rule have halted closely $500 million of monthly mineral ore and concentrate exports.