The plates of the Book of Mormon may have had the appearance of gold, but they were surely not 24 carat gold. In places like Oaxaca, Mexico and also among the Inca ruins, we have evidence of the inhabitants using an alloy of mostly copper, but with some gold also mixed in. With the copper and gold together, they could make a nice foil that was really quite rigid. They then rinsed it in a light citric or vinegar acid. That leached out the top molecules of copper, leaving, in effect, a very thin but pure exterior of gold plating.
Those plates ended up with the rigidity of copper, but the color of gold. When they scratched the surface of the gold, it actually went through the gold down into the copper, making it much more legible because they had a different color for contrast, especially after the copper had oxidized. We find examples of this kind of gold-copper alloy, called Tumbaga, in Mesoamerica in that time period. This may have well have been the kind of metal that the Nephites used for the plates of the Book of Mormon.
Other metal plates can be found all over the ancient world, including the ancient Near East and the Mediterranean. For example, Brigham Young University owns a set of Roman brass plates dating from the first century AD. These plates were a military retirement diploma given to soldiers who had served for 25 years in the Roman Army as a retirement bonus for their service, and certified their award of Roman citizenship.
As you may know from the New Testament, Roman citizenship was worth an enormous amount, and the citizenship rights also extended to sons and daughters of the soldier as well. The interesting thing about these plates is that on the outside, there is the full text of the grant by the Roman Emperor, and on the back, there are seven names. These are the Roman officials whose seals would have been put on the back. And through two holes in the middle, they would wrap and twist a wire to seal the two plates shut. Should the outside become damaged, a judge could break the seal and open it up. What he would find inside is a duplicate copy of the outside text. It is called the interior or sealed portion. There are many examples of plates just like these in museums all over Europe. Similar sealed documents with inside and outside information have also been found on papyrus, on parchment, and on clay going back into the middle of the second millennium BC. It was a fairly standard, legal way of formalizing and protecting documents.
How hard would it have been to make metal plates of any kind? First of all, the creator would need some substantial metallurgical training and skill. Such records needed to be made of the right material and in the right way to remain durable. The brass plates, for instance, made it across the ocean, and Lehi prophesied that they "should never perish; neither should they be dimmed any more by time" (1 Nephi 5:19). In contrast, papyrus would not likely have survived the waves dashing over the sides of the ship in a storm—how would you keep anything dry in a boat like the one Nephi’s family must have built? But metal would survive and it had to be some kind of metal that would not rust. Even silver will corrode. But gold will not rust, and brass will not rust.
Book of Mormon Central, "Is the Book of Mormon Like Other Ancient Metal Documents? (Jacob 4:2)," KnoWhy 512 (April 25, 2019).
Book of Mormon Central, "What Kind of Ore did Nephi Use to Make the Plates? (1 Nephi 19:1)," KnoWhy 22 (January 29, 2016).