(Bloomberg) -- Canada’s Teck Resources Ltd. rejected a proposal from Glencore Plc to buy the company for shares and then spin off their combined coal businesses, in the latest sign of dealmaking heating up across the mining industry.

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Glencore’s proposal on March 26 represented a 20% premium at the time, and would be worth about $23 billion at Friday’s closing prices, according to Bloomberg calculations. The approach was first disclosed by Teck and then confirmed by Glencore, which said on Monday its proposal remains in place and reiterated its interest.

Teck jumped as much as 11% in Toronto, while Glencore traded 1.4% lower.

The news is the clearest indication yet that the world’s biggest miners are shifting back into dealmaking mode after years on the sidelines. It also reflects how large producers of coal like Teck and Glencore are grappling with the future of those business: mining companies are seeking to focus more on metals like copper and nickel that will benefit from the clean-energy transition, and yet coal still remains a big profit driver.

Teck, which is controlled by Canada’s Keevil family through a dual-class share structure, has an attractive suite of copper mines that have long been coveted by rivals. The company announced in February it plans to split its own business into coal and base metals companies, in a move that spurred speculation that it could become be a target — that is, if the Keevils were willing to sell. Shareholders are set to vote on that plan on April 26.

For Glencore, the proposal represents the first concrete indication that it could be looking to get out of thermal coal. The company has continued to reap massive profits from the most-polluting fuel, even as rivals retreated. Until now had simply said it would keep running its mines until they are empty, by 2050.

The proposal from Glencore envisaged creating a new publicly traded company to own Glencore’s vast thermal coal operations and Teck’s coking coal mines. The remaining company, to be named “GlenTeck,” would include Glencore’s and Teck’s base metals operations as well as Glencore’s oil and other commodity trading business, other than coal trading and marketing.

Both Teck and Glencore published the letters sent by their respective boards, in which they disclosed the two companies had held previous discussions about a similar transaction. In his letter of proposal, Glencore Chief Executive Officer Gary Nagle said the deal had the backing of key former and current employee shareholders — meaning it has support from former boss and top investor Ivan Glasenberg — and said Glencore would be willing to proceed without any due diligence.

However, both Teck and the controlling Keevil family were clear in their rejection on Monday. Chief Executive Officer Jonathan Price said that the spinoff structure proposed by Glencore would expose Teck shareholders to the other company’s large thermal coal business and oil trading business. Norman Keevil, who holds the role of chairman emeritus, said that “now is not the time to explore a transaction of this nature.”

The Keevil family, which has been involved with the firm for six decades, has long controlled Teck through majority ownership of Class A shares, which carry more voting control than the company’s Class B shares.

Glencore has proposed offering 7.78 Glencore shares for each Teck Class B subordinate voting share and 12.73 Glencore shares for each Teck Class A common share, a 20% premium for both on the date of the offer.

The larger company argued that the proposed merger and spinoff would create two stronger and more diversified companies, with the potential to save as much as $5.25 billion.

Glencore, under new CEO Gary Nagle, has been working to simplify its business in recent years and had talked down the prospect of major deals. Yet in an interview last month, Nagle said there were some obvious combinations in the industry, including putting together copper mines owned by Teck and Glencore in Chile.

In a nod to the need for Canadian government approval to any deal, Glencore said it would put the headquarters for the combined metals-mining business in Canada. The coal business would stick to its plans to exit thermal coal by 2050.

Glencore also noted that the proposed “CoalCo” would have no ongoing financial obligations to the remaining company. In Teck’s plan to split off its coal business, the remaining Teck Metals would continue to benefit from coal, as it would own a royalty on the coal spinoff’s revenue as well as preferred shares in the company.

Teck owns four copper mines in South America and Canada that produced 270,000 tons last year. The company expects to double copper output after the second phase of its Quebrada Blanca project in Chile ramps up to full capacity by the end of this year. It also owns coking coal mines that it plans to spin into the new company, Elk Valley Resources.

Teck is being advised by bankers Barclays and Ardea Partners, while its special committee was being advised by BMO Capital Markets, Goldman Sachs and Origin Merchant Partners.

--With assistance from Mark Burton and Jack Farchy.

(Updates with Glencore comments)

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