Madagascar might have a geological advantage, but Brazil is a mining super power that must surely surpass Madagascar in terms of engineering, infrastructure, qualified labor etc. In the end that counts heavily in capex and opex.
I'm not saying that mining cannot be done in poorer countries, it just takes much more investment to overcome the greater risks and costs.
Recall the DNI announcement that they were taking a drill rig from Brazil to Madagascar? Goes to show how massively costs differ.
With that said, let's watch this space because mining is a catalyst for rapid development. Madagascar might be catching up sooner than I expect.