A compound, CuCO₃, that was used as a sulfide scavenger for water-base muds. However, it was found to be corrosive due to spontaneous plating of metallic copper onto metal surfaces, causing pitting corrosion; it has largely been replaced by zinc compounds.

Reference:
Perricone AC and Chesser BG: "Corrosive Aspects of Copper Carbonate in Drilling Fluids,"
Oil & Gas Journal 68, no. 37 (September 14, 1970): 82-85.