To lose a chairman before he’s even taken the top job is an embarrassment; to lose him inside a month of being named is doubly embarrassing; to lose him ahead of vital full year profit figures and asset sales is even more mortifying — and to do all that without an explanation verges on contempt.

But that’s the best you can say about Rio Tinto’s performance this morning: the worst is that there is some sort of board or other ruction that the incoming chairman, Jim Leng, was made aware of, and he decided not to take the job. It’s either that, or a bout of bad health.

But even then health reasons would not explain the mystery of Mr Leng refusing the job, despite Rio announcing his appointment three weeks ago on January 15. According to Rio, he joined the boards of both the UK and Australian listed companies as “Chairman-designate and a non-executive director”.

Mr Leng had this to say about his new gig in that statement:

“I am absolutely delighted to be joining Rio Tinto and taking up the Chairmanship. Rio Tinto has a superb set of assets and strong prospects. I look forward to working closely with Chief Executive Tom Albanese and his team as we steer the company through the challenges of the current economic climate and beyond.”

So delighted that he departed today.

This morning, all Rio had to say was these two paragraphs:

“Rio Tinto announces that Jim Leng, a non-executive Director, has resigned from the Boards with immediate effect and will therefore not take up the post of Chairman of the Boards in April as previously planned.

“At the request of the Boards, Rio Tinto’s current Chairman, Paul Skinner, has agreed to remain as Chairman until mid 2009, by which time it is anticipated that a successor will be appointed. The process to appoint a new Chairman is underway.”

Nothing more was forthcoming.

Mr Skinner is said to be the preferred candidate to take over as chairman of BP in April, but some UK shareholders have raised concerns about the planned appointment in light of Rio’s woes.

Rio is due to report its annual results on Thursday. Are we therefore to assume that there is something before the board that he couldn’t wear if he became chairman? The company has reportedly been looking at selling assets to big shareholder Chinalco of China and the Japanese trading house, Mitsui and/or raising cash from shareholders via a large rights issue.

An explanation from Mr Leng and the company should be demanded by either ASIC or the ASX.

Rio shares rose this morning on the news and the feeling from US markets of a rebound around the corner with the US banking bailout package on the cards, even if it has been put off a day. The huge stimulus package for the economy will be voted on by the US Senate tonight, hence the day’s delay for the banking package.

As a director of Tata Steel, a major Indian company with investments in Europe (Corus), could it be that Mr Leng would face a conflict of interest if assets and other deals were done with Chinalco?