Rio Tinto Ltd's $15.2 billion rights offer, the fifth-biggest on record, generated strong demand from UK investors, putting the world's top iron ore miner back into growth mode after a debt-funded purchase of Alcan had brought it to its knees.

Rio revealed on Thursday that shareholders had stumped up for almost all its London shares on offer. The UK tranche would have raised about 7.1 billion pounds ($11.66 billion), more than a fifth of the market value of the UK-listed company.

Results from the Australian offer were still to be released.

Strong take-up of the rights offer would place Rio in a much stronger position, though the mining group will still need to sell off non-core assets, analysts said.

The high take-up reflects that the offer was attractively priced, said Ross Barker, managing director of Australian Foundation Investment Co, which manages about A$3.5 billion including Rio shares.

It also confirms our view that shareholders were wanting to participate in Rio's recapitalization to get through with the issues that it had with the Alcan purchase.

Barker's fund was among those shareholders who agitated earlier this year against a planned $19.5 billion tie-up with China's state-owned Chinalco .

Chinalco, Rio's top shareholder, took up its full entitlement in a sign it is far from severing ties with Rio.

Relations between Rio and the Chinese group soured last month after the miner called off a bigger equity partnership and opted instead for the rights issue and an iron ore joint venture with rival BHP Billiton , prompting China's state media to brand Rio as a dishonorable woman.

Chinalco owns about 9 percent of the combined Rio Tinto group and would have spent $1.5 billion to take up all its rights -- trimming its average holding cost in Rio to around 44 pounds a share. Chinalco bought its initial stake at 60 pounds in February 2008, near the top of the market.

Rio, listed in both London and Australia, said it had acceptances for 96.97 percent of the new London stock.

The indebted miner is raising money to cut a $38 billion debt mountain it accumulated when it bought Canadian aluminum group Alcan at the top of the commodities market in 2007.

Rio's market value has slumped 64 percent in little over a year, partly due to the debt-funded Alcan buy. Rio also rejected an all-scrip takeover offer from BHP, triggering broad criticism of Rio management.

People still view Rio as having very good assets, and don't want to be diluted. But you'd want the board to be considering what it was that led up to the Alcan purchase and try and improve the processes so that sort of thing doesn't happen again, Barker added.

Rio's Australian shares gained 1.4 percent on Thursday to A$52.32, outpacing a 0.4 percent rise on the benchmark S&P/ASX 200 index <.AXJO>.

Rio offered 21 new shares for every 40 held, priced at a steeply discounted A$28.29 per Australian-listed share and 14 pounds per London-listed share. The London shares closed on Wednesday at 21.55 pounds.

($1=A$1.25) ($1=.6091 Sterling)

(Editing by Ian Geoghegan)