Gossan

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gossan

[′gas·ən]
(geology)
A rusty, ferruginous deposit filling the upper regions of mineral veins and overlying a sulfide deposit; formed by oxidation of pyrites. Also known as capping; gozzan; iron hat.

Gossan

 

(iron hat), a residual formation that occurs in the surface parts of ore (primary sulfide) deposits of copper, lead, zinc, and other metals as a result of chemical weathering and oxidation of the primary minerals of the ore body. Gossans consist primarily of iron oxides and hydrous iron oxides (goethite, hydrogoethite, hydrohematite, turgite), and as a result they are usually dark or light red, ocherous, or brownish red in color. The formation of gossans is associated with the oxidizing action of surface waters and is accompanied by the secondary enrichment of ore deposits. In the process of weathering, the sulfides of copper, silver, zinc, and other metals oxidize to easily soluble sulfates, after which they are leached and carried to deeper parts of the ore body. At the same time the iron in sulfurous compounds—pyrite, chalcopyrite, and other sulfides—is only partially removed in the form of a soluble salt (sulfate of iron oxide); most of the iron is oxidized and hydrated and remains in place in the form of hydrates of iron oxide (brown iron ores). These secondary brown iron ores, occurring as a result of the transformation of original pyritic and other ores containing iron sulfides, are what form the gossans near the earth’s surface. The depth at which gossans are found beneath the earth’s surface is usually restricted to the groundwater level and may extend to dozens or even hundreds of meters. In comparison with initial sulfide ores gossans are richer in iron in their upper parts and in gold in their lower parts. Contrasting strongly with the enclosing rocks, gossans serve as an important indicator in explorations for sulfide-ore deposits and in identifying the primary ores concealed in the depths.

REFERENCES

Smirnov, S. S. Zona okisleniia sul’fidnykh mestorozhdenii, 3rd ed. Moscow-Leningrad, 1955.
Saukov, A. A. Geokhimiia, 3rd ed. Moscow, 1966.

G. A. SOKOLOV

References in periodicals archive ?
The Iron Cap Zone is a large area of well-exposed gossanous, intensely and pervasisve quartz-sericite-pyrite-altered intrusive and volcanic rock at the northeast corner of the Seabridge claim block.
The Deep Kerr deposit and Iron Cap Lower Zone are core zones of the KSM porphyry deposits and are characterized by higher fluid flux and abundant veining, which generally results in higher grades than the shallower margins of the deposits.
Also, the existing Iron Cap deposit is already designed as an underground block cave mine.
The size of mineralized zones at Iron Cap, Mitchell and Main Copper (discussed below) were expanded into areas of recent glacier retreat which were not accessible by Placer Dome.
Shifting from open-pit to underground panel cave mining in the later years for the Mitchell deposit and also block caving the Iron Cap deposit.
Tenders are invited for Iron Cap Containing At Least 300 Mg Of Ferrous Fumerate/Sulphate/Any Iron Form
The geological composition of the Lekoumou deposit is composed of the upper enriched iron cap or direct shipping ore (DSO), which contains over 50% iron, and the beneficiable DSO found just below the upper iron cap, which contains approximately 41% iron.
Limited Tenders are invited for Procurement Of Iron Cap For Dots Centre
In the past three years, Seabridge has successfully targeted higher grade zones beneath KSM's near-surface porphyry deposits, resulting in the discovery of Deep Kerr and the Iron Cap Lower Zone, two copper-rich deposits that to date have added nearly one billion tonnes of inferred resources to the project at a higher average grade.
In the past two years, Seabridge has successfully targeted higher grade zones beneath KSM's near-surface porphyry deposits, resulting in the discovery of Deep Kerr and the Iron Cap Lower Zone, two copper-rich deposits that have added nearly one billion tonnes of inferred resources to the project at a higher average grade.
40Mm In Diameter Shall Be Of Tough Wood, Well Furnished, 239 Cms In Height With An Iron Ferruel Of Conical Shape At The Lower End And Fitted With An Iron Cap At The Top With Two Leather Washer Underneath It.
In Dia, Shall Be Of Tough Wood, Well Varnished, 180 Cms In Height With An Iron Ferrule At The Lower End And Fitted With An Iron Cap At The Top With Two Leather Washer Underneath It.