In 1964 the United States Mint used the equivalent of 67% of today’s total silver mining production to mint dimes, quarters and half dollars for every day use.
In 1964, the U.S. Mint used 549,549,066 ounces of silver to make dimes, quarters and half dollars for every day use.*
In 2013, the U.S. Mint used 43.475 million ounces of silver** to mint and sell silver coins for investment purposes (vs. the 549.5 million ounces of silver the U.S. Mint used to produce dimes, quarters and half dollars to place in circulation for everyday use).
Charts and more data: http://smaulgld.com/amount-silver-used-u-s-coins-1964/