Extract Resources Ltd. (EXT.AU) Thursday upgraded the resource at its Rossing South uranium prospect in Namibia by about a third, confirming the venture as one of the world's most significant uranium discoveries.

A sizable upgrade was largely expected and keeps a target firmly painted on Extract's back, with takeover speculation around the Perth-based miner already running rampant.

Extract said the resource in the first zone at Rossing South increased to 145 million pounds of uranium oxide from the previous statement of 108 million pounds, while the overall resource grade increased to 449 parts per million of yellowcake from 430ppm.

Rossing South is six kilometers away from the massive Rossing uranium mine that's jointly owned by Rio Tinto Ltd. (RIO.AU) and the Namibian government, and which produced 8% of the world's uranium oxide in 2008.

More land is still to be tested at the first zone of Rossing South and the maiden resource for the second zone is due August, Extract said.

"Once the Zone 2 resource estimate is completed, Rossing South is expected to be one of the top 10 global uranium deposits by contained metal," Extract said in a statement.

Extract shares jumped about 5% on the news but settled to close trading Thursday up 0.6% at A$6.28 compared with a 0.1% rise in the benchmark S&P/ASX 200 index. They were hovering around A$1.00 in December.

Promising assay results and corporate activity has driven the share price rally, with major shareholder U.K-based Kalahari Minerals Plc (KAH.LN) and significant shareholders Rio Tinto Ltd. and Stephen Dattels' Polo Resources Ltd. (PRL.LN) all jostling for position on Extract's board.

Interest in uranium is increasing as Asian countries plan to install vast amounts of nuclear power and some European countries lift nuclear power bans.

Consequently, some analysts have suggested Extract could also be bought by Chinese or Indian state interests, France's Areva SA (CEI.FR) or Canada's Cameco Corp. (CCO.T).

Tony Parry, analyst at Resource Capital Research, on 15 June said Rossing South had major exploration upside beyond 250 million pounds, with a minimum 300 million pound resource more likely.

He said Thursday that the Zone 1 resource upgrade is "very positive...and it makes it highly likely they'll be exceeding the 300 million pound resource by the end of this year."

He's valued Extract at A$7.50-A$8.00 a share and noted the valuation doesn't include any potential upside from a takeover offer.

Extract is still searching for a new managing director after Peter McIntyre announced his resignation last month.

His decision came a few weeks after Kalahari Minerals called a shareholder meeting to vote on his removal.

Kalahari ousted Extract's former chairman Bob Buchan in February, also by calling a special shareholder meeting.

AIM-listed Kalahari tried to buy Extract outright last year, but its shareholders became concerned when Rio Tinto built stakes in Extract and Kalahari.

-By Ross Kelly, Dow Jones Newswires; 61-2-8235-2957; ross.kelly@dowjones.com