(Reuters) - Top global miner BHP Billiton will buy U.S. Petrohawk Energy Corp for $12.1 billion in cash, ramping up its bets on the booming but environmentally controversial shale gas industry.

At $38.75 a share, BHP is offering a 65 percent premium to Petrohawk's closing stock price on Thursday. The deal follows BHP's $4.75 billion purchase of Chesapeake Energy's interest in an Arkansas shale gas field in February.

"Their view on their first shale buy was they were buying at bottom-of-the-cycle prices," said Constellation Capital Management portfolio manager Peter Chilton. "I guess they see value here."

Shares of BHP were down 1.5 percent at $90.88 in morning New York Stock Exchange trading, while Petrohawk jumped 63 percent to $38.32.

BHP will use its abundant cash reserves and a new $7.5 billion loan to fund the deal.

The company and others are targeting shale gas as a major source of cleaner-burning fuel in a world looking for alternatives to coal-fired energy.