Aluminium maker Alcoa said it will investment $1.1bn into a planned $10.8bn aluminium complex in Saudi Arabia in the next four years.

The announcement follows news that some partners in the consortium had considered leaving the company if it did not increase its investment from the previous $900m it had set in December 2010.

Alcoa, however, said Australia’s Alumina is the only company that has not dropped out of the project.

State-run Saudi Mining (Maaden) will own 74.9% of the joint venture and Alcoa’s stake will be 25.1%, which can be increased by 15%, according to a filing with the Securities and Exchange Commission.

In December last year Alcoa and its consortium partner Aluminum Financing said they would each contribute $900m over four years and Alcoa would have a 20% stake in the project.

Alcoa and Maaden entered into a 60/40 agreement in December to build and operate an integrated bauxite mine, alumina refinery, aluminium smelter and a rolling mill in Saudi Arabia.

Alcoa will own a 60% stake in the mining and refining company with the rest being held by Alumina, while the smelting and the rolling mill company will be wholly owned by Alcoa.

Maaden’s deal with Alcoa provides for a 1.8 million ton-a-year refinery, a 740,000 ton-a-year smelter, a bauxite mine with an annual capacity of four million tons and a rolling mill with a capacity of up to 460,000t.

The company said the smelter and mill will begin production in 2013, while the refinery and mine will be operational in 2014, according to Reuters.