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Synmetamorphic uranium mineralization from Tiraun, Graubünden, Switzerland

Published online by Cambridge University Press:  05 July 2018

E. von Pechmann  and
F. Bianconi
E. von Pechmann
Affiliation:
Uranerzbergbau-GmbH, Kölnstr. 367, D-5300 Bonn 1, Germany
F. Bianconi
Affiliation:
Uranerzbergbau-GmbH, Kölnstr. 367, D-5300 Bonn 1, Germany
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Abstract

Petrographic, microscopic, and X-ray investigations of a uranium occurrence near Tiraun, Graubünden, Switzerland, are described. The uranium mineralization occurs in greenschist facies metamorphic rocks of the Tavetsch massif and consists essentially of uraninite of various habits with minor chalcopyrite, linnaeite, millerite, galena, marcasite, pyrite, hematite, magnetite, and skutterudite. The ore structure, characterized by concentrations along foliation planes, boudinage, and rotated (helicitic) textures of uraninite porphyroblasts, is indicative of a synmetamorphic (Alpine) remobilization, recrystallization and enrichment of the ore, which was probably derived from an original ‘protore’ in psephites and psammites (? sandstone-type mineralization) of at least Variscan age. The synmetamorphic emplacement of the ore took place under medium- to high-temperature conditions (approx. 350–400°C), as demonstrated by the lattice constants of the uraninite phases and by the ore paragenesis. Late to postmetamorphic tectonism resulted in a partial remobilization (over cm distances) and redistribution of the ore along veinlets that cut the foliation planes. The characteristics of the ore from Tiraun are similar to those from the synmetamorphic ore from Preit, northern Italy, as described by Cevales (1961).

Type
Research Article
Information
Mineralogical Magazine , Volume 46 , Issue 339 , June 1982 , pp. 173 - 178
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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