Packed into a thatched-roof meeting hall in the village of Urucurituba, deep in the Brazilian Amazon, hundreds of Mura Indigenous people mulled over whether to allow a massive potash mine on their lands. Some worried it could pollute their rivers, killing the fish they depend on. Others questioned if the mine would really bring prosperity to this corner of Brazil’s Amazonas state. The meeting, held in early April, was the first step in a long-awaited consultation process giving the Mura people a fair chance to weigh in — a right enshrined in Brazilian and international law — on whether the min…