The world's biggest miner BHP Billiton remained "cautious" about the state of the global economy as governments wound back stimulus measures, outgoing chairman Don Argus said Thursday.

But Argus said BHP was confident it could finalise its proposed joint iron ore venture with Rio Tinto this year, despite "continued uncertainty surrounding world financial markets".

"We do remain cautious about the state of the global economy and note the recent International Monetary Fund (IMF) report which highlighted the gap in growth between developed and developing economies," said Argus, in his final letter to shareholders.

"We are very mindful that most countries have difficult decisions to make regarding a wind back of stimulus packages, against the backdrop of financial services sector reform, and how they boost economic growth."

Argus said it was "imperative" that policy and tax changes by governments be well understood and not hinder investment or capacity for economic growth.

"Governments play a key role in spurring productivity, encouraging investment and fostering international competitiveness," said Argus, who leaves BHP on March 30 after 10 years as chairman.

Iron ore and metallurgical coal exports to China and the Asian region were key to BHP's growth strategy, which would see capital expenditure of about 20 billion Australian dollars (18.5 billion US), he added.

"(That) includes a 5.8 billion US dollar equalisation payment for the Western Australian iron ore production joint venture with Rio Tinto, which we believe we can finalise this financial year," Argus said.

The European Commission is investigating the Anglo-Australian companies' plans to jointly produce iron ore at their Western Australian Pilbara operations, which is expected to result in 10 billion dollars in savings.

The tie-up follows an original hostile takeover bid for Rio by BHP, which was dropped in November 2008 amid global economic turmoil.