Maybe another reason is that retail longs on the CME are being squessed by the second increase in margin requirements in as many weeks. At the same time as physical demand is growing.

SAN FRANCISCO (MarketWatch) -- The CME Group late Monday raised margin requirements for its most popular gold, silver, platinum and palladium futures contracts in the U.S. A margin requirement is the money investors must pony up to trade, and in the case of silver the exchange raised the maintenance requirement after a 30% increase last week. For the 100-ounce gold contract, initial and maintenance requirements rose 5.9%. Silver maintenance requirements increased nearly 12%, while silver initial requirement rose 11.5%. Gold for December delivery retreated $16.90, or 1.3%, to $1,351.40 an ounce on the Comex division of the New York Mercantile Exchange on Tuesday. December silver was off 73 cents, or 2.8%, to $25.38 an ounce. The CME owns Comex.