By David French and Melanie Burton

(Reuters) -Glencore approached Rio Tinto late last year about combining the two big copper producers but the discussions are no longer active, a person familiar with the matter said.

The talks between Rio, the world's No. 2 miner, and Glencore, one of the world's biggest producers of coal and base metals, were brief and did not go anywhere, the person added.

Bloomberg News reported on Thursday that the two were in early-stage merger talks.

A merger between the firms has the potential to be the largest ever in the mining industry. They have a combined market value of around $158 billion, surpassing BHP's $126 billion.

Rio and Glencore declined to comment.

Global miners have been sizing each other up as they look at ways to bolster their position in metals such as copper that are set to be in high demand as industries shift to cleaner forms of energy.

That was the rationale behind BHP's $49 billion bid for smaller peer Anglo American last year but which failed due to issues with the deal's structure.

Portfolio manager Ben Cleary at Tribeca Investment Partners, which has its largest position in Glencore, said that if Rio was interested, it would have to pay a significant premium.

Glencore, which was last trading at roughly 3.5 pounds per share, is expected to reward shareholders with capital returns this year following a $34 billion merger of its Viterra unit with Bunge.

"Anything under 5 pounds wouldn't make sense for Glencore given ... material capital returns this year," he said adding that Glencore's commodity mix was perfectly leveraged to Chinese stimulus. He also noted a "definite culture clash" between the more conservative Rio Tinto and the more aggressive Glencore.

Rio's U.S.-listed shares fell 0.5% in extended trading after the Bloomberg report, while Glencore's American Depository Receipts closed up 2.4% after jumping nearly 9% at one point.

Rio and Glencore have discussed combining their operations in the past. In 2014, Rio rejected a merger offer from Glencore, saying that it was not in the best interests of shareholders.

RBC analyst Kaan Peker said in a note to clients that a deal for Glencore would provide a clean exit for large investors including its largest shareholder and former CEO Ivan Glasenberg who owns a 9.93% stake.

He added that combining their marketing and sales operations could potentially result in $1 billion in savings.

Peker said Rio would likely be attracted to Glencore's tier-one copper assets starting with Collahuasi in Chile and Antamina in Peru but may be less keen on its copper assets in the Democratic Republic of Congo or its coal business, a sector Rio exited last decade.

The talks extend a years-long streak of merger and acquisition activity among mining companies as they rework their portfolios amid the transition to cleaner energy forms.

Rio last year agreed to buy U.S.-listed lithium producer Arcadium for $6.7 billion with the world's top producer of iron ore seeking to transform itself into a processor of high-end, low-carbon raw materials.

Glencore bought Teck Resources' steelmaking coal unit last year for $6.9 billion.

(Reporting by David French, Melanie Burton, Roushni Nair and Clara Denina; Additional reporting by Urvi Dugar and Shivangi Lahiri; Editing by Devika Syamnath and Edwina Gibbs)