Thungela Resources, the South African coal business spun out of Anglo American, fell sharply on its first day of trading as investors in the US and Europe dumped the stock.

Shares in the miner, which is quoted in London but has its main listing in Johannesburg, opened at 150p but fell back to 113p, giving it a market capitalisation of just over £150m.

The listing of Thungela was billed as a test of investor appetite for coal mining stocks, which have fallen out of favour amid growing climate concerns. In a report published last week, the company’s corporate broker Liberum said Thungela was worth between 230p and 490p a share.

Traders said most of the selling had come from big institutional funds that cannot hold Thungela either because it is not eligible for inclusion in FTSE indices or large enough to meet their investment mandates.

On the eve of the demerger, Anglo American was accused by a short seller of having “massively underestimated” the environmental liabilities of Thungela.

Boatman Capital Research, which has also waged a long-running campaign against engineer Babcock International, claimed that the clean-up costs for Thungela’s seven mines could be as much as $1.36bn, or nearly three times the amount of money it has currently set aside, because of proposed regulations.

“Given that Thungela’s mines have remaining lifespans of five to 11 years (assuming no extensions), this is now a pressing issue for the company and its shareholders,” the report said, setting an equity value of zero.

Anglo hit back at Boatman’s claims, saying that the $480m clean-up provision on Thungela’s balance sheet was “over and above” the regulatory guidance for miners in South Africa.

It also said provisioning for environmental liabilities based on draft regulation did not accurately “reflect the actual or likely sums needed to discharge such liabilities”.

“It is precisely because these sums are considered to be artificial, and arbitrarily inflated, that the draft has remained under review since 2015,” the company said. “This is an industry-wide matter in South Africa, so the regulations on which the Boatman report apparently draws its conclusion are far from being finalised.”

Big miners are under pressure from investors to divest from coal because of its contribution to climate change. Thermal coal is burnt in power stations to generate electricity, a process responsible for about 30 per cent of global carbon dioxide emissions.

Rio Tinto sold its last coal mine in 2018, while BHP is also looking to divest its thermal coal business.

The spin-off will allow Anglo to focus on producing metals that will be in demand during the shift towards clean energy, such as copper and platinum.

Thungela, which means to “ignite” in isiZulu, is one of South Africa’s largest thermal coal exporters. Under the demerger, investors will receive one Thungela share for every 10 Anglo American shares they hold.

The demerger of Thungela follows a sharp increase in South African thermal coal prices, which have risen 25 per cent to $113 a tonne this year.

Anglo is providing a $180m capital injection to Thungela, which started its first day of trading with no debt. It has also agreed to provide “contingent capital support” until the end of 2022 if thermal coal prices fall below a certain threshold.