Relict Geothermal Features

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Relict Geothermal Features

Relict Geothermal Features:
Geothermal features left behind by processes which are now absent
Other definitions:Wikipedia Reegle

Relict geothermal surface feature, include the mineral formations left behind by hot springs, fumaroles, and geysers as well as the alteration of minerals by geothermal waters (e.g. opalization of sediments). Such alteration and deposits are indicators of past hydrothermal activity. Though surface activity has ceased in many areas, relict geothermal features may indicate the presence of a still active geothermal system below the surface.

Relict Geothermal Feature Description
Hydrothermally Deposited Rock Hydrothermally deposited rock includes rocks and minerals that have precipitated from past geothermal fluid discharges at the Earth's surface.
Silica Deposition Includes silica sinter and chalcedony deposits typically encountered around modern neutral chloride hot spring discharges.
Carbonate Deposition Includes travertine and massive carbonate deposits typically associated with modern chloride-rich alkaline hot spring discharges and/or microbial activity.
Alunite Alunite is a potassium sulfate mineral that forms in acid-vapor dominated hydrothermal systems. It is commonly encountered as an alteration mineral in high sulfidation epithermal gold deposits formed from acid-sulfate solutions and in areas with past fumarolic activity.
Other Hydrothermal Deposits User-specified field for unlisted hydrothermally deposited rock and mineral products.
Hydrothermally Altered Rock Hydrothermal alteration refers to rocks that have been altered from their original composition through water-rock interactions with a geothermal fluid. Different types of hydrothermal alteration are often indicative of the composition of the causative fluid, and are typically described via stable alteration mineral assemblages that have replaced preexisting minerals in a rock. Hydrothermal alteration may also refer to the selective removal of minerals by a fluid, as in the case of acid leaching.
Silicification Silicification refers to the addition of silica to a rock by a hydrothermal fluid. Silicification is often visually non-distinct, but results in hardening of the rock that is readily detectable using a scratcher tool.
Argillic-Advanced Argillic Alteration Argillic and Advanced Argillic alteration are shallow types of alteration encountrered in a variety of different types of hydrothermal systems. Argillic alteration forms at lower temperatures and primarily consists of kaolinite + montmorillonite clay minerals. Advanced Argillic alteration forms at higher temperatures and lower pH conditions (e.g. the acid-steam condensate zone of a hydrothermal system). It consists primarily of kaolinite + dickite clay minerals at lower temperatures and pyrophyllite + andalusite minerals at temperatures > 300°C. Advanced Argillic alteration may also be associated with alunite.
Zeolitic Alteration Zeolite minerals, including mordenite and clinoptilolite, have been identified in a number of caldera systems. These and other zeolite minerals are regionally extensive, and their formation is associated with late stage degassing of magmatic fluids and mixing with meteoric water.
Leach Capping Often associated with deposition of alunite and bordered by halos of Advanced Argillic Alteration. Leach Cappings are zones of acid leaching in which all components of a rock have been removed except for silica. Such zones are typically encountered near the surface at the zone of principle hydrothermal upflow, where volatile gases condense into shallow groundwater to produce acidic solutions.
Other Hydrothermal Alteration Products User-specified field for unlisted hydrothermal alteration products.

These values are part of Category:Relict Geothermal Features, and are used for the Property:RelictGeoFeatures.