* Trafigura says Dauphin undergoing medical treatment
* New CEO is expert in mining and risk management
* Trafigura has grown into one of world's largest traders (Adds Dauphin medical treatment)
By David Sheppard and Dmitry Zhdannikov
LONDON, March 24 (Reuters) - Trading giant Trafigura announced on Monday an abrupt change at the helm of the firm saying it had to bring forward a previously undisclosed succession plan after veteran co-founder and CEO Claude Dauphin required medical treatment.
"Claude is receiving treatment for a medical condition. He intends to continue being hands on and responsible for leadership and business development. New CEO Jeremy Weir will be responsible for day-to-day operations," a Trafigura spokeswoman said.
Claude Dauphin, 63, one of the most famous names in oil trading, began his career with the godfather of contemporary oil trading Marc Rich, who was active throughout 1970s-1990s and died last year at the age 78.
Dauphin set up Trafigura 20 years ago and Australian Jeremy Weir, the firm's head of mining and market risk, was meant to replace Dauphin as CEO in September, the spokeswoman said.
Trafigura was started as predominantly an oil trader with contracts focusing on Angola and Nigeria. But it has lately grown into metals, mining and coal on all continents, making it one of the most diversified players in the trading world.
"Today's announcement marks the latest stage in the evolution of Trafigura's governance and management structure as the company has grown larger and more complex and illustrates the rise of a new generation of senior managers leading the company," the company said in a statement.
Dauphin previously held the dual position of both CEO and chairman. He will now become executive chairman.
"The new structure will strengthen the management team's capacity to oversee a group whose turnover has almost trebled in the last five years and whose operations now span 58 countries," the statement said.
People who know Weir said his background was not that of a physical trader but rather of a risk manager.
"It may show where Trafigura wants to go in the future: more in investment than in trading and speculation," said one person who traded with Weir and knows him personally.
Dauphin is the last of the original founders to retain an executive position in the firm, which was founded in 1993. Trafigura said in January that Dauphin owns "less than 20 percent" of the firm, with no other shareholder, including the four living founders, owning more than 5 percent.
Trafigura has spent around $2 billion on share buybacks in the last three years to return money to its earliest shareholders, a Reuters analysis of accounts for the Swiss-based firm showed in January.
It has said it could spend another $1.5 billion until 2017.
The firm, which employs almost 9,000 people globally, has said it plans to remain privately-owned, with no major independent commodity trader yet copying Glencore's bumper 2011 public offering.
Trafigura also said Mariano Marcondes Ferraz, who has been the head of Trafigura affiliate DT Group since 2009, is also to join the company's management board. (Additional reporting Ron Bousso,; editing by William Hardy and Keiron Henderson)