A Chinese private equity firm on Tuesday announced a hostile takeover bid for Australia-listed Discovery Metals, valuing the copper miner at Aus$830 million (US$857 million), Discovery said.

Shanghai-based Cathay Fortune Corp. said the offer, made with the China-Africa Development Fund, an investment fund specialising in Africa, "represents compelling and certain value at an attractive premium".

The offer of Aus$1.70 per share came "at a time when there is significant uncertainty over the current and expected cash costs and mine expansion plans of the Boseto Cooper Project" in Botswana, Cathay's founder and largest shareholder Yong Yu said in a statement posted on the Australian stock exchange.

Cathay Fortune already has a 13.78 percent stake in Discovery, an exploration and production company focussed on assets in Botswana, including its 100 percent owned Boseto Copper Project.

The move is the latest attempt by a Chinese firm to buy stakes in Australia's mining firms that have sparked intense debate in the country over whether to allow Beijing's state entities to increase their control over its resources.

Cathay's bid follows an indicative, non-binding conditional proposal sent in late September at the same price, which Discovery rejected as insufficient.

That offer did not reflect the value of the company's operations and expansion plans and the potential to increase the resources on the firm's tenements through further exploration, Discovery said Tuesday.

But Cathay Fortune said Discovery had not provided any information to justify a valuation above Aus$1.70 per share.

"The decision of the Discovery Board to refuse access to due diligence and further engagement without any reasonable basis has prompted CFC's decision to bypass the Discovery Board and present the offer directly to shareholders," Yong Yu said.

Discovery said no formal documents about the latest bid had been received.

"The company will inform the market upon service of a bidder's statement," it said in a statement to the Australian Securities Exchange.

China is the world's biggest purchaser of copper as it embarks on a huge modernisation drive, with demand forecast to remain strong despite a recent slowdown in its economic growth.

Steep falls in some commodity prices -- largely due to weakening demand from China -- have driven down the stock prices of many mining companies, prompting speculation of a wave of deals.

But copper prices have remained robust due to supply pressures.

Cathay Fortune owns 75 percent of the bid vehicle, with the remainder held by the China-Africa Development Fund.