Mining group Xstrata agreed to merge with commodities trading giant Glencore, in a $90 billion recommended all-share deal, the mining sector's biggest to date.

The miner said on Tuesday that shareholders would receive 2.8 new Glencore shares per Xstrata share held, excluding Xstrata shares already owned by Glencore, which the companies said represented a premium of 15.2 percent over Xstrata's closing price on February 1.

Xstrata, the world's fourth-largest diversified miner, last week revealed it was in discussions with Glencore, already its single largest shareholder, confirming talks were back on after years of on-off negotiations.