Rio Tinto's US$3.85 billion exit from one of the world's biggest copper-gold mines, leaving Indonesia state-owned PT Indonesia Asahan Aluminium (Inalum) with 51% ownership, allows Freeport and Inalum to meet new Indonesia foreign ownership rules while enabling the former to meet its stated aim of remaining in charge of operations.

Moody's notes Rio's exit transaction, due to close in the second half of this year, remains subject to the negotiation of "a number of material agreements", and resolution of environmental regulatory matters.

Freeport CEO Richard Adkerson has said the company retaining fiscal and legal stability for Freeport is vital, as is maintaining current environmental conditions.

"While this announcement is credit positive, key elements that will continue to be considered in [Freeport's  Ba2 stable] rating include requirements to build a smelter and funding for same, capital expenditures to continue to develop the underground mine, FCX's financial policy going forward and capital structure objectives, and growth objectives," the ratings agency said.

"Additionally, the terms of the final agreements, particularly with respect to the long-term mining rights will be considerations.

"The divestiture of its interest to roughly 49% does not limit upward rating potential for [Freeport]."

Moody's expects Freeport to continue to benefit from strong earnings and cash flow "at a level not dissimilar to what it would have received over the longer term absent any divestiture".

The company's shares were down 2.8% Friday at $16.80, capitalising it at $24.51 billion.