Australia's Altura Mining said on Thursday its former biggest investor and one-time suitor, China's Shaanxi J&R Optimum Energy, has sold its entire remaining 11.8% stake in the lithium miner.

At Altura's latest closing price, the stake would have been worth A$24.1-million ($16.60-million). It wasn't immediately clear who bought the shares from the indebted Shenzhen-based battery maker: As a block, the shares would be equal to the miner's second biggest shareholding.

A Shaanxi J&R spokesman confirmed the pullout, and said it was possible the company's debt situation would affect its ability to buy its contracted supply from Altura.

Altura shares jumped as much as 20% after the sale was announced, reflecting relief at the departure of an investor hobbled by a restructuring plan that prompted Shaanxi J&R to start cutting its holding from the 14.4% stake it held as of February. That stake had made it the no.1 investor in the lithium miner.

Shaanxi J&R had been its major customer, and even envisaged buying out Altura at one stage. But it ended up scrapping those ambitions when it was forced into restructuring after being badly hit by changes to China's subsidy policy for electric vehicles.

It also agreed late last year to halve its minimum contracted supply from Altura to 50 000 tonnes a year from 2019.

Chinese battery giant Ganfeng Lithium is Altura's biggest customer, having signed a deal late last year.

One of China's biggest battery makers for electric vehicles, Optimum Nano, a unit of Shaanxi J&R, slashed production levels to around 20% of capacity as the company sought to pay off debt last year.