I would date this piece to the 1920's or 1930's because of the use of marcasite in the decoration. Marcasite was very popular during this time and was used to give an inexpensive sparkle to jewelry. It was even called "the poor man's diamond"!
Among other things, St Anthony is well-know for his divine assistance in finding missing items. I admit to using the rhyme
"Holy Tony come on down,
Something's lost and can't be found!"
on more than one occasion!
If you would like to see more views of this medal, please visit my shop, Rosa Mystica.