Tailings
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In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material that overlies an ore or mineral body and is displaced during mining without being processed.
Phosphogypsum stack located near Fort Meade, Florida. These contain the waste byproducts of the phosphate fertilizer industry.
Red mud near Stade (Germany)
Bauxite, an aluminium ore (Hérault department, France). The reddish colour is due to iron oxides that make up the main part of the red mud.
Gangue
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In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed, and from tailings, which is rock already stripped of valuable minerals.
Crystals of cassiterite, a commercially valuable ore mineral, in a matrix of quartz, the gangue
Banded Zn-Pb ore sample with sphalerite (brown) and (silver-grey) galena as main ore minerals and (white) calcite as main gangue mineral
Native gold partially contained within a quartz gangue, visible at lower left.