Global miner Rio Tinto is considering spinning off part of its Australian aluminum assets as a planned carbon tax would raise costs and lower margins, a local newspaper reported Monday.

Rio has been working with Macquarie Group and PricewaterhouseCoopers to consider its options for the business, the Australian Financial Review said.

Rio Tinto declined to comment on Monday. However, Rio chief financial officer Guy Elliott told investors last week there were some assets in its aluminum portfolio which were not aligned with its strategy.

These are assets that we would consider divesting if it makes sense. Of course, we would want to achieve good value if we decided to sell them, Elliott told investors, reiterating comments made previously.

Through the divestment of non-core assets, together with aggressive targets for cost reduction and production creep, plus targeted investment in growth, we are confident that the aluminum business will achieve a 40 percent EBITDA margin.

Rio's aluminum business in Australia is made up of three refineries, three smelters and two bauxite mines, the paper said, adding Rio would hold onto the mines as they offer the highest margins.

Rio last week told investors it plans to achieve 40 percent earnings before interest, tax, depreciation and amortization margin from the aluminum business through the sale of two non-specified assets, the paper said.

Rio Tinto shares were trading 3.6 percent weaker on Monday at A$60.37.

(Reporting by Narayanan Somasundaram and Michael Smith; Editing by Balazs Koranyi)