I recall an interesting story about spanish cannons being made with platinum ore.
Iirc, the resulting alloy could withstand far greater bore pressures without fatigue than normal iron/steel/brass cannon.
When it was discovered that they were alloyed with some 30% platinum, they were yanked from the mesoamerican fortress they were installed in, melted, ad reprocessed to recover the platinum.
This is only a story I heard though. I habe no reliable sources.
It's a myth; it was some sort of scam from the '80s similar to the kind of scam where you get sold "damaged money" that just needs to get exposed to a special chemical to turn into real money. The idea was that the cannons were found in a spanish shipwreck and that some sort of low-energy nuclear transmutation had converted radioactive elements in the cannon into platinum or something, and that you could buy bits of this metal and separate out the platinum at home for fun and profit. It was all bunk of course. Platinum is not a radioactive decay product and I believe that it can only be formed by stellar nucleosynthesis.
As for intentionally making cannons out of platinum alloys: the mesoamericans did have some native platinum artifacts but they were tiny and they were all made using cold hammering since platinum has an extremely high melting point. 16th and 17th spanish steel making techniques couldn't have been used to create any kind of usable platinum alloy.
The mining techniques that the Spanish used in the new world for silver, gold and copper were heavily reliant on mercury extraction; mercury forms amalgams with just about every metal and can majorly increase yields from precious metal ores. Mercury will not amalgamate with platinum or mercury, so if the cannons were brass or bronze they can't have contained platinum since there wouldn't have been any in the copper used to make them. Interestingly, mercury will not amalgamate with platinum
or iron.
The Spanish sucked at making cannons in general but they were especially bad at making steel cannons. I'm not aware of any substantial iron mining or any iron/steel cannon foundries in New Spain. Platinum is also 3 times denser than iron, so an iron or steel cannon that was 30% platinum would be about twice as heavy as a regular cannon of the same size-, not something that you would want to put on a ship.