What is "costeaning"

Costeaning \Cos"tean`ing\, n. The process by which miners seek to discover metallic lodes. It consist in sinking small pits through the superficial deposits to the solid rock, and then driving from one pit to another across the direction of the vein, in such manner as to cross all the veins between the two pits.

n. (context mining English) A process for discovering metallic lodes by sinking small pits through the superficial deposits to the solid rock, and then driving from one pit to another across the direction of the vein, so as to cross all the veins between the two pits.