Investors turn on board as OZ Minerals shares tumble

OZ Minerals has told frustrated shareholders that its share price at a near record low has no effect on the company's underlying value.

The copper miner's board was greeted by hostile investor questions in relation to the plunging values of their shareholdings, including a near halving in just over three months.

Sentiment around OZ Minerals has been buffeted by a weak copper price and rising mining costs that left the company barely breaking even in the March quarter, with a weaker production outlook for the year.

There is also uncertainty about where the company's future production is coming from, although OZ Minerals says it is confident of extending the life of its Prominent Hill mine to 2030.

"Like most resource companies we are trading at a very significant discount to our fundamental value - be that our NTA (net tangible assets) or any net present value calculation," Neil Hamilton, the company's chairman, said at the general meeting in Melbourne.

"I can't tell you why such a discount is justified. It is industry-wide ... perhaps the discount is greater because of where we find ourselves in this life-of-mine program and because we are going through this period of tough cashflow."

The company's shares closed 14¢, or 3.5 per cent, down at $3.86. That is the lowest since the financial crisis, when OZ Minerals was a far bigger beast with many mines that it was forced to offload in a fire sale to pay off debt.

One angry investor at the meeting pointed out the company had thrown away money by buying back $200 million in shares at $10.51 and $9.18 each over the past two years.

"There was no tangible benefit to the average shareholder from those buybacks ... for the same $100 million per year, the dividend could have been increased by 30 per cent," the shareholder said.

OZ Mineral's Carrapateena copper-gold project in South Australia is highly regarded but no decision to mine has been made. It could cost up to $3 billion to develop.

More doubt about Carrapateena was created when Mr Hamilton said the board had decided to delay building an exploration decline until testing had been completed.