The Mariana dam disaster, also known as the Bento Rodrigues or Samarco dam disaster, occurred on 5 November 2015, when the Fundo tailings dam at the Germano iron ore mine of the Samarco Mariana Mining Complex near Mariana, Minas Gerais, Brazil, suffered a catastrophic failure, resulting in flooding that devastated the downstream villages of Bento Rodrigues and Paracatu de Baixo (40 km (25 mi) from Bento Rodrigues), killing 19 people. The extent of the damage caused by the tailings dam collapse is the largest ever recorded with pollutants spread along 668 kilometres (415 mi) of watercourses.The failure of the dam released 43.7 million cubic metres of mine tailings into the Doce River, causing a toxic brown mudflow to pollute the river and beaches near the mouth when it reached the Atlantic Ocean 17 days later. The disaster created a humanitarian crisis as hundreds were displaced and cities along the Doce River suffered water shortages when their water supplies were polluted.

The total impact of the disaster, including the reason for failure and the environmental consequences, are officially under investigation and remain unclear. The owner of the Bento Rodrigues dam, Samarco, was subject to extensive litigation and government sanctions. In 2016, charges of manslaughter and environmental damage were filed against 21 executives, including Samarco's former CEO and representatives from Samarco's owners, Vale and BHP Billiton, on its board of directors. Controversy over the investigation grew after a 2013 report, indicating structural issues in the dam, was leaked.

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe3O4, 72.4% Fe), hematite (Fe2O3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe) or siderite (FeCO3, 48.2% Fe).

Ores containing very high quantities of hematite or magnetite (greater than about 60% iron) are known as "natural ore" or "direct shipping ore", meaning they can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel—98% of the mined iron ore is used to make steel. In 2011 the Financial Times quoted Christopher LaFemina, mining analyst at Barclays Capital, saying that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".