Size 80 x 70 mm, height 13 mm
Who knows about the existence of these moulds?
I was told it could be a amulet, but it seems very unlikely with the Small Seal Script characters on the back of the mould.
How could I tell its authenticity?
Who knows about its rarity and the possible value?
It is possible that these were used to make clay moulds where the coins would be cast from.
However, please check if yours is copper or really iron (not just copper mixed with some or a little iron) as they should all be copper.
They are not very common but are not exceedingly rare either. They cost between US$150 and US$600 depending on rarity level. Many years back, they used to cost US$800 and above.
Let me know if yours is iron. I would be able to authenticate it if I had a clear photographic image in front of me.
Finally, yours has the four characters on the reverse ta pu qian wan meaning "large spade thousand, ten thousand" or "large spade 10 million".
As such, it may also be a fantasy!