Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved ore minerals. Altogether there are sixteen known Iron Oxides and oxyhydroxides Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in In other cases quartz and iron oxides, limonite, goethite, and jarosite, exist as pseudomorphs replacing the pyrite and primary ore minerals. Limonite is an ore consisting in a mixture of hydrated Iron(III oxide-hydroxide of varying composition Goethite, named after the German Polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low temperature environments Jarosite is a basic hydrous Sulfate of Potassium and Iron with a chemical formula of KFe(III3(OH6(SO42 Frequently gossan appears as a red stain against the background rock and soil due to the abundance of oxidized iron and the gossan may be a topographic positive area due to the abundance of erosion resistant quartz and iron oxides. Topography ( topo-, "place" and graphia, "writing" is the study of Earth 's Surface features or those of Planets Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind
In the 19th and 20th centuries gossans were important guides to buried ore deposits used by prospectors in their quest for metal ores. Prospecting is the physical search for Minerals Fossils precious metals or mineral specimens and is also known as Fossicking. An experienced prospector could read the clues in the structure of the gossans to determine the type of mineralization likely to be found below the iron cap.
References
- Guilbert, John M. and Charles F. Park, Jr (1986) The Geology of Ore Deposits, W. H. Freeman, pp 799-830, ISBN 0-7167-1456-6
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