From a 2009 article in Resource Investor....

In 1900 there were 12 billion ounces of silver in the world. By 1990, the internationally respected commodities research firm CPM Group say that figure had been reduced to around 2.2 billion ounces of silver. Today, that figure has fallen to less than 1 billion ounces in above ground refined silver. It is estimated that more than 90% of all the silver that has ever been mined has been consumed by the global photography, technology, medical, defence and electronics industries.

If less than 1 billion ounces of above ground refined silver is accurate, the U.S. Gov't is borrowing the dollar eqivalent of it about every 8-9 days.