A Royal Canadian Mint 1 ounce 999 Fine Gold piece.

If authentic, your gold is worth gold spot, $4,331.
Follow up, submitter replied:
"Marc, this is not a 1 ounce solid gold Maple Leaf coin!
This an incredibly scarce antique (a 559 gram gold alloy with one ounce of fine gold) which the Royal Canadian Mint presented to my father almost 50 years ago.
Like the famed 1933 Double Eagle, its collectible/numismatic value far exceeds its gold value."
To which we'll add: I thought the color was funny and questionable. Luke, if you have a 559 gram alloy that contains one ounce of gold, then it's worth far less, as the purity is only in the 1-2 Karat range. It would be a challenge to reclaim that gold. I hope you made a mistake and meant 55.9 grams, then it's at 50%, which makes more sense. Rarity does not always translate to value. You do not have a 1933 double eagle here. And given that the serial number has seven digits, I don't think it's all that scarce. I'm sorry to disappoint you, but we tell people now what they inevitably will find out later. I stand by my original valuation and you might have to work to get even that. If you want to make an appointment to bring it in, I'd be happy to give a complementary appraisal. We can tell a lot more in person; several things you said do not make sense and we can resolve that by seeing it.