"Gold" can be a noun that means the metallic substance itself or a noun that means the color gold. It can also be an adjective that describes something made of the substance or that has the color. "Golden" is only an adjective. It can have either of the same literal meanings that "gold" has when it's an adjective, or it can also have various idiomatic meanings like special, popular, safe from harm, well-positioned, likely to succeed, etc.