Tailings

n. act of following

Tailings (also known as tailings pile, tails, leach residue, or slickens) are the materials left over after the process of separating the valuable fraction from the worthless fraction of an ore.Tailings represent external costs of mining. As mining techniques and the price of minerals improve, it is not unusual for tailings to be reprocessed using new methods, or more thoroughly with old methods, to recover additional minerals. Yesterday's tails can be tomorrow's resource, as seen during the 1990s when the extensive tailings dumps of Kalgoorlie / Boulder in Western Australia were re-processed profitably by KalTails Mining.
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Noun
1. the act of following someone secretly
(synonym) shadowing
(hypernym) pursuit, chase, following
(derivation) chase, chase after, trail, tail, tag, give chase, dog, go after, track
Adjective
1. following surreptitiously; keeping under surveillance; "always on guard against shadowing submarines"
(synonym) shadowing
(similar) following

Residue of raw material or waste separated out during the processing of crops or mineral ores.

Rock and other waste materials removed as impurities when minerals are mined and mineral deposits are processed. These materials are usually dumped on the ground or into ponds.