• journal_title：The Canadian Mineralogist
• Contributor：Jiří Zachariáš ; Jiří Adamović ; Patrik Konečný
• Publisher：Mineralogical Association of Canada
• Date：2008-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.46.5.1159
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：46
• issue：5
• firstpage：1159
• section：Articles

Trace-element variations in uraninite were employed to decipher its chemical age and to evaluate the As-rich nature of fluids during its formation at Jeníkov, Teplice area, in the central part of the Cenozoic Ohře Graben, Bohemian Massif, Czech Republic. Cretaceous sandstones of the graben fill show two distinctive stages of young mineralization (less than 18 Ma), most probably related to topography-driven flow of epithermal fluid along the northwestern boundary-fault of the graben (the Krušné hory Fault). The older stage is dominated by pervasive precipitation of silica accompanied by pyrite, sphalerite, galena, uraninite and kaolinite, whereas the younger stage is represented by barite with pyrite inclusions and fluorite. The uraninite formed together with microcrystalline quartz (Qtz–4) at the end of the first stage. Uraninite of subgroup A shows high As/Pb values (14.6–69.9), higher Ca (1.02–1.99 wt.%), lower Ti (0.27–0.44 wt.%), and other trace elements compatible with the structure of uraninite. Uraninite of subgroup B shows low As/Pb values (2.5–8.4), lower Ca (0.39–0.90 wt.%), higher Ti (0.43–8.94 wt.%), and the presence of elements incompatible with the structure (Ti, Fe). A significant correlation between As and Pb was found in both subgroups. The calculated apparent radiometric age of the uraninite samples shows a broad dispersal, suggesting the presence of common lead, which was corrected using the correlation between the contents of As and Pb_tot (Pb_common + Pb_radiogenic). This procedure allowed us to assign an age of uraninite formation of about 0.5 Ma (± 0.6 Ma), which fits the geological data, and to demonstrate its formation during a single episode of mineralization. An approximately five-fold increase in As content of the fluid phase during uraninite and pyrite formation can be inferred from the correlation between the intragroup As/Pb values and the observed intragrain As^max/As^min values in the associated arsenian pyrite. If amounts of common lead are introduced into uraninite in conjunction with another conservative element, a correlation between the conservative element and total lead can be used to decipher the age of the mineralization and to track element variations in the parent fluid phase.