Peace Dollar mintages varied from a small run of around 360,500 for the key rare date issue to a large run of 49 million on other dates. The highest mintages took place early in the series when heavy production was necessary to fulfill the requirements of the Pittman Act.
The World War I Pittman Act authorized the melting of up to 350 million silver dollars to provide bullion to other countries, which would fill 3/4 of an olympic sized swimming pool! It's interesting to note that another 50 million were melted during WWII to produce additional U.S. coins. 270,232,722 silver dollars which were melted were replaced with new coins struck from U.S. mines, and this resulted in high mintage of the Morgan Dollar series and the early years of the Peace Dollars until 1928. The mint marks are located on the obverse of the coin under the "O" in ONE.
The key dates of the Peace Dollars series are the 1928 and 1934-S since they had the smallest mintage. Here are the mintage numbers for each Peace Dollar year: