BHP Billiton announced the surprise retirement of its popular chief financial officer Alex Vanselow and expanded its top management committee on Monday, building on the team of potential successors to its young chief executive.

Vanselow, 49, is quitting in February 2012 to pursue personal business interests, and will be replaced by Australian Graham Kerr, who is just 40 years old.

They're big boots to fill, but I'm sure BHP will adequately source a replacement, and they have in this instance, said Tim Schroeders, a portfolio manager at Pengana Capital, which owns BHP shares.

Kerr, who joined BHP in 1994, was until recently president of the group's diamonds and specialty products division based in Vancouver.

BHP also appointed chief marketing officer Mike Henry, 45, to expand the group management committee to eight members, seen as the pool for the top job at the company.

But no one is expecting 49-year-old Kloppers, chief executive since 2007, to leave anytime soon.

It's a bit early to call that, said Richard Morrow, a director at EL&C Stockbroking.

The new CFO comes in at a tough time, with the euro zone threatening to melt down and the top miners warning that demand is weakening as credit markets tighten.

However, investors said BHP was in a strong position to weather any downturn.

There's probably never an easy time for something like that, but BHP's probably pretty well placed relative to a lot of its competitors in terms of the flexibility it offers in various financial options, said Schroeders.

BHP recently raised $3 billion (1 billion pounds) in the bond market at what bankers considered a good price, in contrast to European nations facing sharply rising bond yields.

BHP shares rose 1.8 percent in early trade, in line with the broader market.

(Reporting by Lincoln Feast)