News: RIO U.S. authorities scrutinise Rio's 2013 coal writedown - sources

SYDNEY, Nov 29 (Reuters) - The U.S. Securities and Exchange Commission is investigating a $3 billion impairment charge booked by miner Rio Tinto RIO.L in 2013 on the value of a Mozambican coal asset, two sources familiar with the matter said on Tuesday.

The shock impairment, less than two years after Rio bought Mozambique-focused Riversdale Mining in 2011, helped trigger the departure of the group's then chief executive, Tom Albanese.

The sources, who cannot be named as the matter is not public, said the ongoing discussions on Riversdale with U.S. regulators were around accounting practices and were not related to the group's headline-grabbing troubles around a payment to a high-level adviser in Guinea.

Rio Tinto declined to comment. Earlier this month, Rio reported to U.S., UK and Australian authorities that it had uncovered 2011 emails detailing a payment to a French consultant who had assisted the group in Guinea. That year, Rio had successfully reclaimed the right to mine part of the giant Simandou iron ore project.

It is not clear whether any of those regulators has yet begun a formal investigation, though Rio is carrying out an internal inquiry into the emails and the payment.