Alcoa Deal Not Certain

He also points out that Rio Tinto and BHP are classic "rock crushers," whereas Alcoa has downstream operations where products are semifabricated.

On the off chance that the deal is further along than fundamentals suggest it should be, one long time deal-watcher sounds a note of caution.

"Managers, directors and investors should view this [type of possible] transaction cautiously," says Bob Bruner, dean of the University of Virginia's Darden Graduate School of Business Administration and author of the book Deals From Hell. "We know that the worst deals are hatched near the peak of the M&A cycle."

The big question is whether we're closing in on such a peak now. In part, that would be determined by how long the flow of cheap capital keeps running.

BHP and Rio Tinto are remaining predictably tight-lipped. Alcoa wasn't saying much either.