The Brazilian company Vale, the world’s biggest iron ore producer, said on Wednesday that it had begun testing equipment at its largest mine, in the Brazilian Amazon. Tests began with a nearly six-mile-long conveyor belt that takes iron ore from the mine’s open-cut pit to a processing facility, said Jamil Sebe, project director for the company’s Amazon iron assets. The mine has a planned capacity to produce 90 million metric tons of high-grade ore a year.