Abstract
AbstractThe Annaberg-Buchholz district is a classic occurrence of hydrothermal five-element (U-Ag-Bi-Co-Ni-As) veins in the Erzgebirge (Germany) with an historic production of ~8,700 metric tons (t) Co ore, 496 t U ore, and 26.9 t Ag. Multiple mineralization stages are recognized in polyphase veins hosted by Proterozoic paragneiss. Fluorite-barite-Pb-Zn mineralization occurs across the entire vertical profile of the district, whereas U and five-element stages are restricted to the upper 400 m below surface, coinciding with a graphite-rich gneiss lithology.Here, we present field and petrographic observations, electron probe microanalysis and fluid inclusion data, as well as thermodynamic calculations to characterize five-element and fluorite-barite-Pb-Zn associations, and to constrain the origin of the vertical zoning in the Annaberg-Buchholz district. Microthermometric analyses of fluid inclusions related to the fluorite-barite-Pb-Zn stage yield homogenization temperatures between 78° and 140°C and salinities between 21.9 and 27.7 equiv wt % (NaCl-CaCl2). A correlation of fluid inclusion Na/ (Na + Ca) ratios with salinity suggests fluid mixing as a likely precipitation mechanism and relates ore formation tentatively to regional tectonics of the Mesozoic opening of the Atlantic.Thermodynamic calculations indicate that U is more sensitive to reduction than As, predicting that arsenide minerals are precipitated more distally relative to uraninite upon reduction along the fluid-flow path. This implies that the observed vertical zoning is not a primary feature but is the result of hydrothermal remobilization. The observations made in the Annaberg-Buchholz district have general importance to the understanding of U-rich five-element mineralization and may be relevant for exploration targeting in unconformity-related U deposits.
Highlights
The Annaberg-Buchholz district is located in the central part of the Variscan Erzgebirge/Krušné Hory metallogenic province and is among Jáchymov (Ondruš et al, 2003a, b, c), SchlemaAlberoda (Hiller and Schuppan, 2008), and Schneeberg (Lipp and Flach, 2003) one of the classic localities for five-element (Ag-Bi-Co-Ni-As) and associated U vein-type mineralization
The ore petrographic description focuses on the native metalarsenide stage with native metal, arsenide, and Ag-Bi-(As)-S substages that are the predominant assemblages in the investigated samples (Table 1; Figs. 3D-F, 4A-D)
The native metal-arsenide veins in the Annaberg-Buchholz district show many typical characteristics, including mineral assemblages, textures, and fluid inclusion systematics that have been reported of native metal-arsenide veins, elsewhere
Summary
The Annaberg-Buchholz district is located in the central part of the Variscan Erzgebirge/Krušné Hory metallogenic province and is among Jáchymov (Ondruš et al, 2003a, b, c), SchlemaAlberoda (Hiller and Schuppan, 2008), and Schneeberg (Lipp and Flach, 2003) one of the classic localities for five-element (Ag-Bi-Co-Ni-As) and associated U vein-type mineralization. Five-element veins refer to a globally occurring mineralogically distinct style of mineralization characterized by native elements, which are enclosed by a succession of Co-Ni-Fe arsenides with carbonates most commonly occurring as major gangue minerals (Kissin, 1992; Markl et al, 2016; Burisch et al, 2017). According to their distinct mineralogical features, five-element veins are referred to as native metal-arsenide veins in this contribution.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
