How do Gossans form?
gossan, also spelled gozzan, rust-coloured oxide and hydroxide minerals of iron and manganese that cap an ore deposit. Gossans form by the oxidation of the sulfide minerals in an ore deposit and they thus may be used as clues to the existence of subsurface ore deposits, especially if distinctive boxworks are present.
What is copper porphyry deposits?
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name.
What are copper deposits associated with?
Most porphyry copper deposits are associated with shallow intermediate to silicic intrusive complexes composed of small plutons and dikes; some are associated wholly with dikes. Representative host-rock types are listed in table 1.
Where is porphyry copper found?
Large porphyry copper deposits are worked in the southwestern United States (where molybdenum is produced as a by-product), the Solomon Islands, Canada, Peru, Chile, Mexico, and other parts of the world.
Where are copper deposits formed?
Copper is a metal that has been deposited from hot sulphur solutions, created in volcanic regions. The hot solutions concentrated the copper up to a thousand times more than would normally be found in rocks. The resultant enriched rocks are called copper ores.
Where are copper deposits found?
The largest copper mine is found in Utah (Bingham Canyon). Other major mines are found in Arizona, Michigan, New Mexico and Montana. In South America, Chile, the world’s largest producer, and Peru are both major producers of copper.
What is ferruginous rock?
Ferruginous deposits are characterized by anomalously high concentrations of iron compared with all other sediments. Whereas an iron-cemented or red-bed type of sediment can contain as much as 10% iron, true ferruginous deposits frequently contain 15% and in some iron-formations more than 30%.
What is gossan?
Gossan. Gossan ( eiserner hut or eisenhut) is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz, often in the form of boxworks (which are quartz-lined cavities retaining the shape…
What is gossan or iron cap?
In the classic gossan or iron cap all that remains is iron oxides and quartz, often in the form of boxworks (which are quartz-lined cavities retaining the shape of the dissolved ore minerals). In other cases, quartz and iron oxides, limonite, goethite, and jarosite, exist as pseudomorphs, replacing the pyrite and primary ore minerals.
Why were gossans important to prospectors?
In the 19th and 20th centuries, gossans were important guides to buried ore deposits used by prospectors in their quest for metal ores. 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 .
What are gossans and leached cappings?
The interpretation of gossans and leached cappings is one of the earliest recognized guide to ore and led to the discovery of many of the important mining districts of the world.