Gossan formation is associated with which process involving iron oxides?

• A. Hydration of iron oxides
• B. Oxidation of iron to magnetite
• C. Dissolution of iron oxides
• D. Deposition of iron carbonate

Answer: (A)

Gossan forms as the near-surface weathering of sulfide ore bodies proceeds in the presence of oxygen and water, producing hydrated iron oxide minerals. As sulfides weather, iron is released and oxidized, and it reacts with water to form hydrated iron oxides such as goethite and limonite. These hydrated oxides give the rusty red-to-yellow coloration and the sturdy, weathered cap characteristic of a gossan.

This is different from forming magnetite, which would require a different oxidation state and conditions; dissolution would remove oxides rather than accumulate them; and deposition of iron carbonate would yield siderite, not the typical rusty oxide-rich cap.