LONDON (AP) - The chief executive of mining giant Rio Tinto PLC and another senior executive are stepping down immediately after the company announced a big loss on a recent acquisition in Mozambique. Rio Tinto said Thursday that CEO Tom Albanese and Doug Ritchie, who led the Mozambique acquisition, were leaving "by mutual consent." Sam Walsh, head of the iron ore division, becomes chief executive. The company disclosed an impairment charge of approximately $14 billion in its 2012 results, including about $3 billion on the acquisition of Rio Tinto Coal Mozambique, and $10 billion or more on the value of the company's aluminum assets. Company chairman Jan du Plessis said the writedown on the Mozambique operation, acquired only in 2011, was "unacceptable."