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* Smelter power prices have doubled since 2014
* Aluminium prices up but oversupply persists
MELBOURNE/LONDON, March 3 (Reuters) - Rio Tinto RIO.AX RIO.L and its partners are cutting output and jobs at the Boyne aluminium smelter in Australia, adding to cuts announced in January, it said on Friday, blaming a jump in power prices.
Rio said output would be cut by 14 percent and that "a significant number of jobs lost".
"Boyne Smelters has been working hard to secure a competitive energy deal. Both parties have been negotiating in good faith but ultimately could not reach agreement," Rio Tinto said in an emailed statement.
The latest production cut follows plans in January to cut output this year by about eight percent, or 45,000 tonnes, because of rising costs of power, 85 percent of which is provided by Gladstone Power Station.
Boyne said in January power prices had doubled since October 2014 and it could not secure an internationally competitive price for the 15 percent of power it needed to supplement its long-term contract. is majority-owned and operated by Rio Tinto and co-owned by Japan's YKK Aluminium, UACJ Corp 5741.T , Mitsubishi Corp 8058.T , Marubeni Corp 8002.T , Sumitomo Corp 8053.T and Sumitomo Chemical 4005.T .
Electricity is a major cost for aluminium smelters who have struggled with poor margins. Aluminium prices have risen this year but oversupply remains an issue. CMAL3 sold its aluminium business in Britain last year, while Russia has put forward the idea of an OPEC-like body to boost aluminium prices.