International mining giant Rio Tinto, the ultimate owner of the Tiwai Pt aluminium smelter near Bluff, said the outlook for the metal was positive despite a 9 per cent fall in spot prices over 2013.

Rio's aluminium division, Rio Tinto Alcan, last week reported underlying earnings of US$557 million ($665 million) for the year - US$503 million higher than in 2012 - and that margins had improved.

"Market premia on aluminium shipments have continued to perform strongly during 2013," it said.

Salt Funds Management managing director Matthew Goodson said Rio Tinto's comments on aluminium showed the market may be over the worst. "And that of course has major implications for New Zealand because of the major swing factor that it has on electricity demand," Goodson said.


Tiwai is easily the country's biggest power user, being responsible for about 13 per cent of demand.

In August, Tiwai's operator, NZAS, and Meridian Energy confirmed the renegotiation of a long-term electricity supply agreement. The deal involved the Government making a one-off payment of $30 million to Rio.

The smelter is still operating at less than full capacity but Bluff-based port operator South Port said last week NZAS had signalled that potential existed to reinstate the fourth aluminium potline later this year.

In its report, Rio said the 2013 cash London Metal Exchange aluminium price averaged US$1845 a tonne, a decrease of 9 per cent on 2012. "Despite this, the overall demand for primary aluminium was healthy."

Uncertainty over Tiwai has clouded the financial future of the power generators, particularly Meridian, which supplies the smelter.

NZAS is 79.36 per cent owned by Rio Tinto Alcan and 20.64 per cent owned by the Sumitomo Chemical Company.