BHP Billiton CEO Marius Kloppers will step down as the head of the world's largest mining group - the fourth major mining company boss to leave in the past six months - after it reported a 58 percent decline in half-year profits.

Kloppers will leave his CEO and director roles on 10 May and retire from the company on 1 October, BHP said in a statement published late Tuesday on its website. He'll be replaced by the group's current head of non-ferrous metals, Andrew MacKenzie. In a separate statement, BHP said net income for the six months ending in December fell 58 percent from a year earlier to $4.2bn (£2.7m/€3.1bn), including around $1.4bn in one-time charges. Group revenues fell 14.1 percent to $32.2bn, BHP said.

"Marius was appointed Chief Executive just prior to the global financial crisis," said BHP chairman Jac Nasser said in the statement. "Despite an exceptionally difficult economic environment during his tenure, Marius and his team have delivered for shareholders, significantly outperforming our peers in terms of total shareholder returns. He leaves BHP Billiton a safer and stronger company."

Since Kloppers took over as CEO on 1 October 2007, BHP stock has risen 27.5 percent, compared to a 12.5 percent decline for rival Rio Tinto plc and a 40 percent decline for Anglo American.

"Deciding the right time to retire was never going to be easy," said Kloppers. "However after almost twenty years with BHP Billiton, twelve as a senior executive and nearly six as CEO, I believe now is the right time to pass the leadership baton."

Kloppers, 50, is the fourth major mining CEO to leave in last six months, following the shock resignation of Rio Tinto's Tom Albanese in January and the announced resignation of Anglo American's Cynthia Carroll in October. Xstrata CEO Mick Davis was forced out of the combined merger between his company and Glencore by Ivan Glasenberg in November.

Albanese left after a multi-billion writedown to the value of key mining assets that he directed the company to purchase less than five years ago. Rio Tinto marked down the value of its Rio Tinto Alcan and Pacific Aluminium units by between $10bn and $11bn and its coal operations in Mozambique - Riversdale Mining Ltd. - by $3bn.

Anglo American posted a full year pre-tax loss of $239m (€178.7m/£154m) last week after the world's biggest platinum miner was forced to take a multi-billion dollar writedown on the value of a key project in Brazil.

BHP Billiton shares closed at 2,235.01 pence each in London Tuesday after a 0.7 percent advance on the session. The shares have risen 7.5 percent over the past year.