The Bom Futuro Frenzy
In 1987, a wildcat prospector, or garimpeiro, discovered one of the world's largest deposits of cassiterite (SnO₂) in the Amazonian state of Rondônia. The site, named Bom Futuro ("Good Future"), triggered a massive and chaotic tin rush. Within a year, an estimated 30,000 miners had descended upon the area, transforming the rainforest into a sprawling area of open pits, mud, and makeshift camps. Between 1988 and 1990, their efforts made Brazil the world's top tin producer.
The mining methods were brutally effective and destructive. Garimpeiros used high-pressure water cannons and dredges to blast away riverbanks and topsoil, creating vast pits and washing tons of sediment into the waterways. At the peak of the rush, the Bom Futuro garimpo was a lawless frontier. From 1987 to 1989, the area saw more than ten homicides per week. The boom was short-lived for most. As surface-level deposits were exhausted, large mechanized companies moved in, pushing out the individual miners and leaving behind a scarred environment and settlements.
A Legacy of Silt and Mercury
The environmental cost of the cassiterite rush is measured in cubic meters and micrograms. At Bom Futuro alone, mining operations discharged over 800,000 cubic meters of waste into local streams and rivers every month. This massive siltation choked the river system for a radius of more than 200 kilometers, blocking sunlight, disrupting photosynthesis, and causing widespread imbalances in the aquatic ecosystem.
Although tin mining does not directly use mercury, the garimpeiros often used it to separate gold, a common byproduct found alongside cassiterite. This liquid mercury entered the environment, where bacteria convert it into highly toxic methylmercury. This compound accumulates in the food chain, reaching dangerous concentrations in fish, a primary food source for local and indigenous populations. Studies in the broader Amazon region have found mercury levels in some communities far exceeding the safe limits established by the World Health Organization. The toxic metal persists in river sediments today, a contaminant from a temporary rush for wealth.