high-grading
/ˌhʌɪˈɡreɪdɪŋ/Mining (originally US )
noun
The action or practice of stealing ore, especially high-grade gold ore, from a mine. Also: the practice of stripping the high-grade ore from a mine, leaving the lower-quality ore behind.
Origin
Early 20th century; earliest use found in Anaconda (Montana) Standard. From high-grade + -ing.