[Larousse2]

I'm not quite sure I understand what you mean by the term "poor."

I understand Mexico to be wealthy in natural resources.

[quadrant]

Poor, of course, is a relative term.
If one measures natural resources, Japan is poor in relation to Mexico, but Japan is a rich country.
Mexico is rich in natural resources but is a (perhaps the) classic example of a rich country that has impoverished itself.