Carbonate Replacement Deposits (CRD) are bodies of metallic minerals formed by the reaction of hot magmatic fluids with carbonate rocks, such as limestone or dolomite. The hot, metal-bearing fluids are driven upward from the heat source, an igneous intrusion (Glover Mo-Cu Porphyry) and dissolves the reactive carbonate rocks when they encounter them. That reaction changes the chemistry of the fluid, causing it to precipitate metallic sulphide minerals that often contain copper, zinc, lead and significant precious metals such as gold and silver. The metallic sulphide minerals effectively “replace” the carbonate host creating massive sulfide mineralization.

Nearer to the source of the fluids, mineralization is often in the form of copper - gold skarn (The 421 and overlying Canyon Creek Zones), transitioning to zinc - lead - silver mantos (4b Manto Zone; No.3 Manto Zone; No.2 Manto Zone) and chimneys. In the periphery of the system, the cooler fluids drop out precious metals silver and gold veins (No.1 Vein Zone Ag-Au ±Zn±Cu) form in the edges of the system.