I saw this on TV, so I could not be sure whether if it is an animated movie or TV show, but due to the climax I could assume it is a full-length movie. It was around 10-15 years ago when I saw it.

I only saw the climax and ending, so I cannot give much information. The story is set somewhere in the Americas (apparently), and follows a boy associated with a family of white descent, but is dressed as a native (reminds of Yukari). The story also involves a lost, ancient city of an indian tribe, and that some people want to become the tribe’s next chief, or something. The antagonist is a white man who seeks the city’s ancient powers, which involves a disk/medallion split into two parts. The kid-protagonist has one of the halves. The antagonist gets that power, but is then defeated and the kid leaves the disk/medallion in the city and returns home.