BHP Group has just hours to launch a blockbuster bid to buy smaller mining rival Anglo American — or put its audacious takeover plan on the shelf.

The proposal by the world’s biggest miner to spin off two units and then buy the remainder of Anglo would create a global copper behemoth, heralding the industry’s return to mega—deals after more than a decade. Anglo has already rejected two non-binding offers from BHP — the last worth $43-billion — and unveiled its own plans for a radical restructuring.

Under UK takeover rules, BHP now faces a deadline of 5 p.m. London time on Wednesday to announce a firm intention to make an offer. If CEO Mike Henry instead decides against, he will have to stay away for at least six months.

The catch is that Anglo’s CEO Duncan Wanblad has so far refused talks with BHP, criticising a plan the target company feels is too complex and undervalues its stock.

BHP’s discussions over the past days have focused on whether it can table an offer attractive enough to get Anglo’s shareholders to push the company toward talks, people familiar with the matter said at the weekend. Ditching the proposal remained a strong possibility, the people said, with BHP wary of bidding against itself in a vacuum.

At current prices, the latest informal approach from BHP values Anglo at roughly £29.49 a share. Yet Anglo’s stock closed on Tuesday at £26.87 in London — suggesting investors remain skeptical that the current deal will reach the finish line.

Henry has made no secret of BHP’s desire to expand in copper, and Anglo’s copper mines have long been viewed as prize assets in a sprawling portfolio. The metal’s rally in recent weeks to a record has lent a dramatic backdrop to the public tussle between the two mining giants.

BHP wants Anglo to first spin off its South African platinum and iron ore businesses before proceeding with a takeover. Under Anglo’s alternative plan, the firm would focus on copper and iron ore by exiting platinum, diamonds and coal, and slowing a fertilizer project.

The Sydney-listed shares of BHP have risen for six consecutive sessions, and were trading up 0.5% on Wednesday as of 1:37 p.m. local time to A$46.285.