Gossan is an iron-bearing weathering product that can indicate what underlying feature?

• A. An underlying deposit of sulfide ores
• B. A carbonate vein
• C. A sedimentary bed
• D. A volcanic plug

Answer: (A)

Gossan forms as a rusty, iron-oxide–rich cap that develops above oxidizing sulfide ore bodies. When sulfide minerals in the subsurface orebody weather, iron combines with oxygen and water to form iron oxides and hydroxides (such as goethite or hematite), giving the characteristic rusty color. This surface expression signals there is a buried sulfide ore deposit beneath. It isn’t associated with carbonate veins, typical sedimentary beds, or volcanic plugs, which produce different surface indicators. So the presence of gossan points to an underlying deposit of sulfide ores.