U.S.-listed shares of Sigma Lithium rose 21 percent in extended trading on Friday after Bloomberg News reported that Tesla was weighing a takeover of the Canada-based battery metals miner.

Tesla has been speaking with potential advisers about a bid, the report said, citing people with knowledge of the matter, and added that Sigma Lithium is one of the many mining options the electric-vehicle maker is exploring as it mulls its own refining.

Tesla and Sigma Lithium did not immediately respond to Reuters requests for comment.

Sigma is finishing construction of a hard rock lithium mine in Brazil that it expects to open by April. The mine will produce spodumene concentrate, which can be used to make lithium hydroxide, a type of the metal preferred by some automakers including Tesla and BMW.

The project would use hydroelectric power, thus helping to greatly reduce its carbon footprint.

U.S. stock of Sigma Lithium, which has a market capitalization of $3.21 billion, nearly trebled in value last year.

Chief Executive Elon Musk said last year Tesla was open to buying a mining company if producing its own supply of electric vehicle metals would speed up worldwide adoption of clean energy technologies.

Tesla and other automakers routinely talk to mining companies of all sizes about potential supplies of lithium and other EV metals without necessarily signing contracts.

Last month, Tesla signed an agreement with Piedmont Lithium for supply of spodumene concentrate from Quebec, starting later this year.

Tesla also has supply contracts for nickel, lithium and a range of other EV metals from suppliers across the globe.

(Cover via CFP)