Anglo-Australian mining giant Rio Tinto returned to the black Thursday with a US$3.67 billion annual net profit after a major cost-cutting drive including the sacking of 4,000 workers and slashing of capital spending. "We have achieved underlying earnings of $10.2 billion, exceeded our cost reduction targets and set production records," said Rio chief Sam Walsh of the "strong" results, which compare with a loss of US$3.03 billion in 2012.