Hedge funds run by billionaire New York investor George Soros have emerged as a backer of plans by Perth-based Marengo Mining to crack it as a big-time copper and molybdenum producer from its Yandera project, south-west of the Papua New Guinea seaport of Madang.

Soros funds have taken the lion's share of Marengo's $16.3 million in share placements, giving them a 19.9 per cent stake in Marengo, which plans to be a copper/molybdenum producer from a $US1 billion ($A1.2 billion) development of Yandera in 2013.

The entry of the Soros funds and other North American investment funds comes as copper prices approach the $US3 a pound level in response to hopes the worst of the global financial is over and the prospect of cohesive economic growth in the world's major economies has improved.

Hedge fund activity in securing early-stage exposure to potential mine developments also reflects expectations copper supplies could be squeezed in coming years without the development of new mines. At the same time, the new developments require higher than long-term average copper prices.

Copper has recovered from a low of $US1.50 a pound in early March to $US2.87 a pound.

Molybdenum is generally a byproduct of copper production. It adds strength and corrosion resistance to steel products and is finding growing use in the petroleum, nuclear power, automotive and aerospace industries.

The Soros funds pumped $8.34 million into Marengo (9.5 a share). The Cayman Islands-based resources fund manager Sentient remains Marengo's biggest shareholder after increasing its stake to 26.7 per cent. It has also taken up shares at the placement price of 9.5.

Marengo went into a trading halt ahead of its fund-raising exercise and had a last sale price of 10.5 a share.