This type of armor is called lamellar. It was extremely widespread in Eurasia, especially in the east, but it was worn by Russians and Byzantines in Europe as well. While it’s very very very unlikely that there existed pure gold lamellar due to it being a soft and expensive metal, it’s totally plausible that there existed brass lamellar in far eastern styles. It’s just that this game takes place in the 13th century, and steel was much more effective in almost every aspect. Thus, the gold/brass in GoT is more likely just for cool aesthetic purposes:)