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Earth and Space Sciences · Glossary

What is Supergene enrichment, gossan?

Also known as: supergene enrichment · gossan

Definition 29.10 University Earth and Space Sciences — Year 2 · Chapter 29 — Ore Deposits

Supergene enrichment is the concentration of a metal by descending ground water: above the water table, oxygenated, acid water dissolves the metal from the sulfides of an orebody, and below it, in reducing conditions, deposits it again, mostly by replacing the primary sulfides. A gossan is the porous, iron-oxide rich rock left at the surface over a weathered sulfide body, its sulfides replaced by goethite, hematite and jarosite.

Left: a supergene profile over a copper sulfide body (a drawing, not to scale): acid water leaches copper above the water table and redeposits it as chalcocite below, leaving a gossan at the surface. Right: a volcanogenic massive sulfide mound in section (a drawing): sea water heated in the crust rises through a stockwork and vents as a black smoker; the mound is zoned from iron and copper at the hot base to zinc, iron, lead and barium at the top and margins.
Left: a supergene profile over a copper sulfide body (a drawing, not to scale): acid water leaches copper above the water table and redeposits it as chalcocite below, leaving a gossan at the surface. Right: a volcanogenic massive sulfide mound in section (a drawing): sea water heated in the crust rises through a stockwork and vents as a black smoker; the mound is zoned from iron and copper at the hot base to zinc, iron, lead and barium at the top and margins.
Left: a supergene profile over a copper sulfide body (a drawing, not to scale): acid water leaches copper above the water table and redeposits it as chalcocite below, leaving a gossan at the surface. Right: a volcanogenic massive sulfide mound in section (a drawing): sea water heated in the crust rises through a stockwork and vents as a black smoker; the mound is zoned from iron and copper at the hot base to zinc, iron, lead and barium at the top and margins.
Gossan from the Flambeau massive sulfide deposit, Wisconsin: a porous rock of iron hydroxy-oxides left by the weathering of pyrite, chalcopyrite, chalcocite and bornite in a Palaeoproterozoic volcanic arc; the small orange specks are native copper. Photograph: James St. John (CC BY 2.0).
Gossan from the Flambeau massive sulfide deposit, Wisconsin: a porous rock of iron hydroxy-oxides left by the weathering of pyrite, chalcopyrite, chalcocite and bornite in a Palaeoproterozoic volcanic arc; the small orange specks are native copper. Photograph: James St. John (CC BY 2.0).
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