(Corrects margin unit to per contract in lead)
NEW YORK, Nov 9 (Reuters) - CME Group said on Tuesday it will raise its silver futures trading margins by 30 percent to $6,500 per contract from $5,000, effective Wednesday.
U.S. silver futures surged as much as 6 percent before retreating, with volume rising to an all-time high on Tuesday, boosted by extreme price volatility and possible short covering, traders said. [ID:nN0999567]
Exchanges often raise margins to mitigate risks as price volatility increases. (Reporting by Frank Tang; Editing by Marguerita Choy)