Silver futures for the December delivery dropped nearly 5% to $15.635, their lowest price since February 2010, according to Bloomberg . The decline occurred thanks in part to the Bank of Japan, which helped strengthen the U.S. dollar when it bolstered its stimulus by increasing its annual target for enlarging the monetary base to 80 trillion yen, or $723 billion, up from a range of 60 to 70 trillion yen.