What makes you so sure it isn't silver? Did you do some tests? Or is your finding based on appearance only? Modern silver proof coins look different than older silver coins.
It's written on the coin it's silver, so if it's not silver it's obviously a fake. There are no non-silver coins for this type.
I´ve bought this coin from a very experienced dealer in Montevideo, but a price much lower than its silver melt value.
The KM catalogue might have no considered a non-silver issue of this coin. That´s why I´m asking if any of the collectors in Numista knows about a non-silver edition.
I have purchased Silver coins below melt due to dealer error. (And usually my error as well--I wouldn't realize how good a deal i got until I studied the coin later.)
Try weighing the coin. If the weight is not 17.4 grams, then clearly it is not made of silver. If it is 17.4, it could be silver, but if it isn't, then it's definitely not made of silver, at least not in the purity that it should be.
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