Teck Resources has come full circle: After a tumultuous seven months kicked off by an unsolicited takeover offer from Glencore Plc that sent the Canadian firm’s stock soaring, its shares are now back where they began.

Teck’s stock had traded largely range-bound for months, as investors await the outcome of a plan to split out its coal business, while metals prices broadly have come under pressure. But a 9.1% plunge on Tuesday, after the company increased the cost estimate for its flagship copper project by an additional $600-million, erased the last of the gains since Glencore’s $23-billion bid was made public in early April.

Teck shares closed at C$48.38 each on Tuesday — below the March 31 closing price of C$49.25 — before paring some of those losses Wednesday.

Teck refused Glencore’s takeover proposal and has instead pushed ahead with a strategy to separate from its coal business and become a standalone metals producer, which makes the success of its Chilean copper project particularly crucial. Glencore has offered to buy Teck’s coal business for about $8 billion, and Teck says it is engaging with other interested parties as well.

Despite Tuesday’s sharp drop, Teck has still outperformed most of its rivals this year, as the mining industry broadly comes under pressure from slumping metals prices and rising costs.

But the company’s shares have fallen further than Glencore’s since the bid was announced, so that Teck is now trading well below the value of Glencore’s original all-stock proposal, suggesting investors are increasingly skeptical about the chances of a deal.

The stock slide puts more pressure on Teck to deliver on projects like Quebrada Blanca 2 that will be key to growing its metals business, while investors continue to wait for answers on the future of the coal mines. On a conference call Tuesday, Chief Executive Officer Jonathan Price said the Vancouver-based company still hopes to make a decision about the coal unit by year end, but did not provide any new details.