(Bloomberg) -- Australia’s richest woman has added to her stake in lithium miner Liontown Resources Ltd. for the fourth time in under a month, edging closer to a position that could block a A$6.6 billion ($4.2 billion) takeover by the world’s biggest producer of the metal.

Gina Rinehart’s Hancock Prospecting Pty. now owns 14.67% of Liontown, the target of the Albemarle Corp. bid, according to an ASX filing late Tuesday — closing in on the 15% level that is generally considered to be an effective blocking minority stake. Her holding stood at just under 8% on Sept. 12.

Rinehart, who has amassed a net worth of $18.7 billion thanks to massive iron ore mines in Western Australia, does have existing lithium investments — but Liontown is by far her most significant bet on the battery metal to date. 

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Privately-held Hancock has described the stake as “strategic”, but has not disclosed its ultimate intention. Last month, it described Liontown’s early-stage Kathleen Valley project as facing implementation and market risks. 

“Hancock maintains a long-term approach to its investments and commodity markets,” it said in a Sept. 25 statement. “In line with that long-term approach, Hancock can provide Liontown with the opportunity to manage its project execution and operations ramp-up risks.”

Hancock declined to comment further on Wednesday. Under Australian law, edging over 20% would normally trigger a mandatory offer.

“She’s got to be pretty serious,” said Max Vickerson, an analyst at Morgans Financials Ltd. “She must have been willing to stump up a fair amount of capital to build up that position. Even if the [Albemarle] deal went through, if she’s got that big a chunk of the company, maybe she gets a board seat.”

US lithium giant Albemarle has been circling Liontown for months, hoping to expand in Australia and add production. It was finally granted due diligence in early September after raising its cash offer by 20% to A$3 per share — a level Hancock says it has not exceeded. The next step would normally be to secure a binding deal with Liontown once due diligence is complete, as early as next week.

Liontown stock closed up 0.7% at A$2.97 in Sydney on Wednesday.

The Perth-based miner owns Kathleen Valley, one of the most promising early-stage lithium projects in Australia. It has supply agreements with major automakers including Tesla Inc. and Ford Motor Co., and there is ample appetite for battery materials from jurisdictions that can benefit from US incentives aimed at breaking China’s stranglehold on the supply chain.

Read More: Australia’s Richest Woman Buys Into Lithium Bid Target Liontown

But analysts have expressed caution over a bid that is now close to double where the undisturbed price stood back in March. 

“This is presenting an avenue for Albemarle to gracefully exit from its current pursuit of Liontown,” said Jon Bishop, an analyst at Jarden Securities. “In light of what we perceive to be significant execution and cost inflation risks, it’s probably a saving grace for the company and its shareholders.”

A drop in Liontown’s price, in the event of an Albemarle exit, would present Rinehart with an opportunity to build up the current stake, Bishop said.

Demand for lithium has surged in recent years as automakers, driven by climate policies, attempt to reinvent themselves as electric vehicle manufacturers. While Australia produces more than half of the world’s lithium, it ships almost all of it to China in the form of bulky, low-grade ore, where it is refined into a delicate, battery grade chemical.

Liontown and Albemarle declined to comment.

--With assistance from Harry Brumpton and Andrew Janes.

(Updates shares in paragraph 9, adds analyst comments from paragraph 12)

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