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LITHOEN

Geological process

Intermediate argillic alteration

Clay-dominated alteration formed at lower temperature and lower acidity than advanced argillic alteration.

Outcrop of pale mottled rock crossed by wavy brown mineralised veins, with whitish clay-altered zones adjacent to each vein.
Wall rock beside hydrothermal veins in the Butte quartz monzonite, where the original minerals have been altered to clay. Argillic alteration of this kind is one of the assemblages the USGS porphyry model recognises, and it is also, on its own, one of the least diagnostic: alteration marks where hot water was, which is a far larger thing than where metal accumulated. Locality: Orphan Boy Mine, Butte, Montana, United States, as stated by the source.

James St. John, CC BY 2.0 · CC-BY-2.0 · source · Derivative: Downscaled to 1200 px wide by the Wikimedia thumbnail service; no cropping, no colour or content alteration.

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Record last updated 2026-09-07. Corrections follow the published corrections policy; superseded claims are retained, never silently edited.