The biggest merger deal so far this year has been given a critical green light today. The board of the Swiss mining company Xstrata has approved a merger offer made by Glencore, a commodities trader.

The combined group will be the fourth biggest mining group in the world, so it won’t be able to push up metal prices on its own. But it does make industrial sense. Xstrata would dig coal, copper, nickel and other metals out of the ground, while Glencore would transport, market and sell them — allowing both companies to cut their costs.

Talks of a merger began more than seven months ago — but were stalled by executive bonus questions and shareholders opposing the deal for not being good enough.

Will the deal happen? Rupert Nathan from the stock market research firm Fat Prophets says he has his doubts. “We still believe that even at the current level, this does undervalue Xstrata as indeed do a few of the major shareholders,” he says.

A vote is expected at the of the month.