After shelving its sale of Nickel West, BHP Billiton will be forced to keep the troubled unit out of its $US15 billion spinoff of unwanted assets amid analyst predictions it would damage the new company's credit rating.

Ratings agencies would not view Nickel West's environmental rehabilitation bill of up to $2 billion kindly if it was to be included in BHP's new spinoff vehicle, dubbed "Newco", analysts said.

On Wednesday, BHP told the market the sale of Nickel West - announced in March - had been shelved. But it remains an unwanted asset, and is unofficially on the block.

"It will have to stay within BHP," Mr Young said.

However, he stressed the asset was not material to BHP - it accounts for 0.2 per cent of the miner's NPV and less than 1 per cent of EBIT.

"They can't put it into Newco - it would be too much of a burden. The rehabilitation costs attached to Nickel West would affect rating agencies' assessment and it would struggle to get an appropriate credit rating."

The planned Newco will begin life with about $4 billion in non-current liabilities, so Nickel West would add substantially to that.

Newco was initially met with a frosty reception in London until the big miner smoothed things over by adding a standard listing for London to plans to list it in Australia and South Africa.

BHP's push to simplify its operations to its "four pillar" commodities, plus a potential fifth in potash, will not be fully realised until it rids itself of Nickel West, which remains an odd fit. A suite of BHP's assets are on the block as part of chief Andrew Mackenzie's drive to simplify operations.

On unveiling the demerger In August, Mr Mackenzie said "Nickel West is neither a good fit with BHP Billiton nor with Newco", citing the operation's maturity and complexity.

While BHP's desire to exit Nickel West should not be underestimated, any sale would have had to ensure the miner a clean exit.

Key sticking points in the sales process include the environmental rehabilitation bill attached to Nickel West - which analysts estimate at between $US1 billion and $US2 billion. It would include closures, rehabilitation and future site monitoring plans for the key mines, smelter and refinery sites. As well as the rehabilitation bill, Nickel West requires a capital expenditure outlay of $1.5 billion.

Trading giant Glencore and Chinese nickel major Jinchuan are understood to have tabled formal bids for the Nickel West portfolio, but they were considered far too low by BHP. The Big Australian had been gunning for at least $500 million for the unit and it is thought Glencore offered about $200 million. If a suitor took on the environmental ­remediation bill, the sale price would likely have been dropped.

Consensus analyst estimates value Nickel West at about $US340 million, but UBS has put it at negative $US800 million, given the size of the environmental liabilities.

BHP has no immediate plans to shut the Nickel West unit, which is being starved of capital and will be run at minimum spend.

"It was always going to struggle to attract a buyer when they haven't locked down offtake and filled the smelter," Mr Young said.

Nickel West includes the Mount Keith, Cliffs and Leinster mines and concentrators, Kalgoorlie smelter, Kambalda concentrator and Kwinana refinery.

Mr Young said the "most value-enhancing option" for BHP on Nickel West was to just run it for cash, and try to fill the smelter as quickly as possible, by securing key offtake agreements with local miners in the area.

Less than 50 per cent of the smelter feed is BHP's own.

Another unknown in the sales process was whether BHP could restart its moth-balled ­Perseverance nickel mine using a ­different mining method, to add to supply. 

Sharp volatility in the nickel price this year could have also complicated the process.

Some in the market had speculated that Glencore was interested in buying the asset so it could shut it, as a means of further strengthening its hold in the nickel trading market.

• [Editor:Juan]