Listwänit

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Listwänit (more rarely Listwaenit ) is a metamorphic rock that has arisen from an ultramafic parent rock through metasomatic transformation . Listwänite were first described by Gustav Rose in 1837 after an occurrence on the Listvenya Gora in the Urals .

Drill core from a fresh Listwanite, base of the Samail ophiolite , Oman
weathered Listwanite, Oman
Listwänite at the base of the Samail ophiolite, Oman

Mineralogical composition

Listwänite mainly consists of carbonate minerals such as dolomite , magnesite and ankerite , frequent secondary parts are quartz and fuchsite . In addition, pyrite and chromite often occur as accessory components ; the latter has been taken over unchanged from the original ultramafic rock. Phlogopite , phengite and incompletely transformed minerals from the parent rock can also occur as additional side effects. When fresh, the rock is usually light to medium gray. The fuchsite gives the rock a green speckled appearance. When weathered, Listwänite change color to reddish-brown or orange-brown rocks due to the oxidation of the iron.

Emergence

The origin of rocks which show the Listwänite are olivine - and pyroxene -rich ultramafic rocks (eg. Peridotite ). When such rocks come into contact with hydrothermal solutions along faults , a chemical conversion process of the silicate minerals begins. These can be converted into carbonates either directly or via the intermediate step of the formation of serpentine if the hydrothermal solutions are rich in carbon dioxide . This can be exemplified as the reaction of serpentine with CO 2 : (Mg, Fe) 3 Si 2 (OH) 4 + 3CO 2 = 3 (Mg, Fe) CO 3 + 2SiO 2 + 2H 2 0 serpentine + carbon dioxide = Breunnerite + Quartz + water During this reaction, the collapse of the silicate minerals releases quartz and water. The CO 2 required for the reaction comes from the earth's mantle .


If reduced sulfur (HS - ) also occurs in the hydrothermal solutions , millerite , gersdorffite , pentlandite and other sulphides can also be formed during the metasomatic conversion process.

distribution

In addition to the type locality in the Urals, Listwänites from Oman , Turkey , Greece , Kazakhstan , the Caucasus , the western Carpathians , the Alps , the Alpine chains of Morocco , Canada ( British Columbia and Quebec ), Tibet and other places have been described. The Listwänite deposits are often associated with larger ophiolite complexes, but are usually only of limited extent themselves. The rock itself does not play a role economically, but the formation of Listwänite can lead to sulphide ore and gold deposits.

literature

  • C. Halls, R. Zhao (1995): Listvenite and related rocks: perspectives on terminology and mineralogy with reference to an occurrence at Cregganbaun, Co. Mayo, Republic of Ireland. Mineralium Deposita 30 (3-4), 303-313.

Individual evidence

  1. ↑ Gustav Rose (1837): Mineralogical-geognostiche trip to the Urals, the Altai and the Caspian Seas . Vol. 1: Journey to the Northern Urals and the Altai. GE Reimer (Verlag der Sandersche Buchhandlung), Berlin, p. 185.
  2. ↑ Manuel D. Menzel, Carlos J. Garrido, Vicente López Sánchez-Vizcaíno, Claudio Marchesia, Károly Hidas, Monica P. Escayola, Antonio Delgado Huertas (2018): Carbonation of mantle peridotite by CO2-rich fluids: the formation of listvenites in the Advocate ophiolite complex (Newfoundland, Canada). Lithographs. DOI: 10.1016 / j.lithos.2018.06.001
  3. ^ Basem Zoheir and Bernd Lehmann (2011): Listvenite-lode association at the Barramiya gold mine, Eastern Desert, Egypt. Ore Geology Reviews 39 (1-2), 101-115