But Xstrata investors hoping for an improvement to the all-share offer are likely to be disappointed, at least for now.

That is because of technical changes set to support Glencore shares over the coming weeks, share sales by prominent naysayers and stake-building by Qatar, whose sovereign wealth fund now has more than 9 percent of Xstrata and is expected to back the deal.

Glencore, which already owns almost 34 percent of the miner, is offering 2.8 new shares for every Xstrata share held to conclude its long-standing plan to create an integrated mining and trading powerhouse.

Those terms will likely be confirmed in the documents, due out by Thursday, though Glencore can still increase the bid up until a few days before shareholders vote.

"Qatar seems reasonably likely to approve the 2.8 ratio. So given that, the chances of an increase in the ratio from 2.8 to something modestly above have probably lessened slightly, and the probability the deal will get done has increased," Nik Stanojevic, an analyst at Brewin Dolphin, said.

Glencore shares closed on Friday at almost 346 pence, with Xstrata at about 912 pence, below the level implied by the offer.

The time value of money - a convention that says money held now has a higher value than money promised in future - implies investors are expecting the deal to go through roughly on current terms.

"We continue to see negligible scope for a "bump" to the terms and larger downside risks for Xstrata shareholders in the increasingly unlikely event that the deal is voted down," Liberum analysts said in a note on Friday.

Ingredients that helped Glencore, they said, included an increased focus on the rising cost of new greenfield projects - a bonus for the trading giant which has bet on low capital intensity, brownfield growth.

But the last round of meetings after the documents are published will be crucial for Glencore, which needs the backing of minorities thanks to the deal structure.

It requires at least 75 percent of shareholders excluding Glencore to approve the offer, meaning opposition from investors representing more than 16.5 percent of Xstrata's total shareholding would be enough to derail it.

And there is still opposition to the deal on current terms.

"They want control of the assets and to control them in a different way - but we are not being paid for that change of control. It's pretty clear what is in this for Glencore but not so much for Xstrata," one top-20 shareholder said this month.

Yet at least two of Glencore's most vocal opponents on the Xstrata shareholder register, Standard Life and Schroders, have been selling down their stakes, according to regulatory filings.

MONEY MATTERS

Investors are expecting the documents to lay out minutiae of the deal, including payments due to the two sides' advisers, remuneration details and an update on discussions with antitrust authorities, with the European Union and China a focus.

Remuneration - including details of any retention package for Xstrata's Mick Davis, who will stay on as chief executive of the combined group - will be closely watched after more than a third of voting shareholders rejected pay plans at Xstrata's annual shareholder meeting this month.

Xstrata and Glencore last month delayed timing of the documents for shareholders to the end of May, a month later than planned, as the two sides sought more time for discussions with regulators - including Brussels, to which a merger notification is expected to be filed imminently.

Once that notification is received, the European Commission has 25 days to approve the deal or begin an in-depth probe into the plan to create the world's fourth-largest miner.

An in-depth probe -- Phase II -- is considered unlikely, but would be a significant setback for Glencore. The deal would technically lapse, under UK rules, and could only be restarted once clearance is granted -- a bruising delay.

(Additional reporting by Sinead Cruise; Editing by David Hulmes)

• A Permanent Economic Emergency