The Australian majority owners of the Tiwai Point aluminium smelter, Rio Tinto, have written more than half a billion dollars off the value of the ageing plant, leaving it with a value on its books of just $14.8 million, from $606.9 million previously.

The decision was made in February but has been only disclosed today with the lodging of financial accounts with the New Zealand Companies Office for Rio Tinto Alcan NZ, the subsidiary that owns 79 per cent of the smelter, which has operated near Bluff since 1971.

The smelter's future is under a cloud as Rio seeks to sell a clutch of ageing Australasian aluminium production assets, packaged for sale as Pacific Aluminium, of which Tiwai Point is just one. The company has been seeking since last year to renegotiate its long term electricity contracts with state-owned Meridian Energy.

The 18-year contract, negotiated in 2007, took effect from Jan 1, but falling global aluminium prices since the global financial crisis and a glut of new Chinese production saw the smelter trigger review clauses which could see the plant wind down and close before the end of the decade.


In the latest accounts, for the year to December 31, the smelter made an operating, pre-tax loss of $91.5 million.

But when the impact of the write-down and other factors is included, RTA NZ reported a loss for the year of $677.9 million.

The result reflected "sharply lower aluminium prices, the strong New Zealand dollar and high electricity prices," the company said in an accompanying statement.

The Tiwai Point write-down followed Rio Tinto's decision to reduce the carrying values of a number of its global aluminium assets in its 2012 results, due to the deteriorating conditions in global aluminium markets, it said.

It has not been previously apparent how significant the writedowns would be on the group's Pacific Aluminium portfolio. No buyers have emerged for the Australasian assets and Rio is believed to be considering an issue of Pacific Aluminium shares to its existing shareholders to quit the assets.

A 16 per cent decline in the price of aluminium in 2012 and the strong local current "contributed to the $163 million (18 per cent) reduction in consolidated revenues. Production was also reduced due to high spot electricity prices in the year."

Total operating revenues for the year were $756.8 million, compared with $919.3 million a year earlier.

Pacific Aluminium chief operating officer Brian Cooper said the result was disappointing, and was despite significant productivity and efficiency gains achieved at the smelter during the past year.


"We have been working with smelter employees to improve the operations at Tiwai Point to enable the smelter to survive, safeguarding the 800 jobs at the facility and continuing the major economic contribution it makes to the region," he said.

Electricity contract negotiations with Meridian were continuing.

"Tiwai Point is an efficient and well maintained smelter. With the improvements being made at the operation and a globally competitive electricity price the smelter can operate on a sustainable footing for many years to come," Cooper said.

Resolving the electricity contracts is important for the government's plans for the partial privatisation of Meridian later this year, with the smelter its largest customer and accounting for around one-seventh of national electricity consumption.

While Meridian says it could sell the same energy at better margins and would displace more expensive electricity generating competitors, the massive generation overhang created by a wind-down at the smelter would be a major risk factor for investors to consider.

The value write-down is line with market opinion that site remediation costs of around $400 million would accrue to Rio if the smelter were to be closed.