(Reuters) - Shares of Alcoa Inc (AA.N) surged on Tuesday in an unusually busy day for the aluminum producer, with the stock rising sharply in late-day trading for its biggest one-day move in nearly two years, though the reasons for the move were unclear.
The stock rose 8.8 percent to close at $9.36 on 93.7 million shares traded, the busiest day for the stock since October 12, 2011, according to Reuters data, and the best day for shares since October 27 of that same year.
Heavy options activity was also seen, with volume rising to more than eight times the recent daily average. The activity was concentrated on upside call option bets expiring on Friday, where the buyer has the right to buy the stock by a given date in the future at a specific price.
Little fundamental news was seen as responsible for the late-day move that also saw gains in Century Aluminum (CENX.O), which rose 17.6 percent. Alcoa declined to comment.
Alcoa has formed a joint venture with VSMPO-Avisma Corp (VSMO.MM), the world's No. 1 titanium producer, to develop high-end aerospace products to feed growing demand from the sector, it said on Tuesday.
Some analysts said this joint venture was the reason for the buying, but the collaboration in a niche aerospace product was announced prior to the open of trading, and activity in Alcoa shares did not pick up until the last two hours of trading. More than 58 million shares traded in the last two hours, according to Thomson Reuters data.
"Not only did Alcoa set a new 52-week high on Tuesday but its share volume was more than four times the normal trading day," said J.J. Kinahan, chief strategist at TD Ameritrade.
Options volume came to 158,000 calls and 84,000 puts traded on Tuesday, according to options analytics firm Trade Alert.
Other factors that might have contributed to the jump in Alcoa shares is broad strength in the metals market as well as news that BHP Billiton is boosting iron ore production, said WhatsTrading.com options strategist Frederic Ruffy.
"There is substantial opening call buying in Alcoa in the October 25 weekly options for the $9, $9.50 and $10 strikes," said Ophir Gottlieb, managing director of options analytics firm Livevol.
More than 18,000 calls in total were purchased on those three strikes alone, with an existing open interest combined of just 328 contracts prior to Tuesday.
Reporting by Doris Frankel and Allison Martel; Editing by James Dalgleish