You can patent your process to make the bronze sword or or not tell anyone and keep it a trade secret. But you can't patent a mineral you can alloys.
Patents cover how something is made and not the material 99% of the time unless it's a new material.
You people seem to think OMG I patented air you fuckers need to pay me to breathe! This isn't like patenting genes or software, this is patents on how things are created, not omg a chemical reaction it's how you get to the point the stuff forms is what most patents claim.