Jim is correct. Silver coins in general began to disappear not only from casinos, but in everyday pocket change as the price of silver began it's meteoric rise in value.

Clad quarters which were issued beginning in 1965 were soon replacing the 1964 and earlier silver quarters in slot machines as well. By 1980, silver had reached $50 per ounce and folks were lined up at coin stores and jewlery stores prior to their 9 a.m. opening time accross the nation to turn in family heirloom silverware, jewlery, sterling silver, wedding rings and Silver Certificates for their melt value. Coins that had been languishing unsold in dealer's show cases for years priced at a couple of bucks each suddenly became worth $20, $30, $40 each in melt value silver. Even silver and gold coins with holes in them became valuable.

The Franklin Mint began manufacturing $1 slot tokens during the mid-60's to replace the disappearing cartwheels and the Nevada legislature hastily approved using tokens instead of the mandated disappearing silver coins ... which the bulk of ore was mined from Nevada's silver mines.

Today's price of silver is currently under $5 per ounce and many circulated common date silver dollars sell in the neighborhood of $8-$9.