JOHANNESBURG (Reuters) - Rio Tinto (>> Rio Tinto plc) has agreed to sell two small coal assets in South Africa to Forbes & Manhattan Coal (>> Forbes & Manhattan) for 440 million rand ($53 million) as part of its strategy to shed smaller operations.

Rio Tinto spokesman David Outhwaite said the coal assets being sold were too small for its portfolio.

Rio Tinto is also divesting from South Africa's largest copper producer Palabora Mining (>> Palabora Mining) but the company has invested elsewhere in the country, doubling its stake in Richards Bay Minerals, a producer of titanium dioxide, earlier this month in a $1.9 billion deal with BHP Billiton .

Forbes Coal in a statement said the acquisition will boost its total production by 39 percent to 2.5 million metric tonnes (2.75 tons) a year.

Forbes Coal is taking a 74 percent interest in the Zululand Anthracite Colliery, a producing anthracite mine, and 74 percent in the Riversdale Anthracite Colliery ("RAC"), an undeveloped mine. The remaining 26 percent stakes in each asset are in the hands of black economic empowerment partners.

Policy uncertainty and a wave of violent strikes in the platinum sector this year have unnerved some foreign investors in South Africa's mining sector.

(Reporting by Sherilee Lakmidas; Editing by Ed Stoddard and Hans-Juergen Peters)