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GEOREF RECORD

Clay mineralogy and LA-ICP-MS dating of supergene U-Cu nontronite-bearing mineralization at Nabburg-Woelsendorf, southeastern Germany

Harald G. Dill, Stephan Kaufhold, Berthold Weber and Axel Gerdes
Clay mineralogy and LA-ICP-MS dating of supergene U-Cu nontronite-bearing mineralization at Nabburg-Woelsendorf, southeastern Germany
The Canadian Mineralogist (June 2010) 48 (3): 497-511

Abstract

Nontronite has been reported from a wide range of mineral deposits on the continent and in marine environments, commonly associated with basic igneous rocks, base-metal sulfides, Fe sulfides, Fe-Mn oxide-hydroxides and gold. This smectite-type phyllosilicate forms during the low-temperature alteration of sulfide-bearing parent material. In contrast, nontronite from vein-type fluorite mineralization at Nabburg-Wolsendorf, in southeastern Germany, developed in a sulfur-deficient environment under supergene conditions associated only with uranyl phosphates, mainly uranocircite. It was investigated by XRD, IR spectrometry, XRF, CEC analysis and SEM-EDX. Phyllosilicates and uranium mica are coeval and of Pliocene age. A U-Pb age of 4.0+ or -0.1 Ma was determined using Laser-Ablation--Inductively Coupled Plasma--Mass Spectrometry (LA-ICP-MS). Some younger ages cluster, possibly indicating a multiphase history of crystallization. Both minerals came into existence at temperatures around 30 degrees C when the region underwent pervasive chemical weathering under humid tropical climatic conditions. Uranium was derived from the decomposition of uraninite and coffinite in the veins and from the weathering of U-bearing accessory minerals in the granite, whereas the major elements and barium in uranocircite originated from the alteration of the granitic country-rocks. The vein minerals, e.g., fluorite acted solely as bedrock, but were not involved in this supergene mineralization. Nontronite-uranocircite mineralization can develop in almost all granitic terranes under supergene conditions like those described. The log Al (super 3+) /H (super +3) and log Ca (super 2+) /H (super +2) values are decisive as to whether nontronite, kaolinite or green opal (nontronite plus opal) comes into existence. Both types of supergene alteration minerals, kaolinite and green opal, developed side-by-side with the nontronite-uranocircite mineralization during the Neogene in this area. Uranium-lead dating using the LA-ICP-MS technique serves to constrain the age of this mineralization.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 48
Serial Issue: 3
Title: Clay mineralogy and LA-ICP-MS dating of supergene U-Cu nontronite-bearing mineralization at Nabburg-Woelsendorf, southeastern Germany
Affiliation: Federal Institute for Geosciences and Natural Resources, Hanover, Federal Republic of Germany
Pages: 497-511
Published: 201006
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 13
Accession Number: 2010-080781
Categories: Mineralogy of non-silicatesEconomic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch map
N47°40'00" - N50°34'60", E09°30'00" - E13°45'00"
Secondary Affiliation: Frankfurt University, DEU, Federal Republic of Germany
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201043
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