Supergene processes and uranium ore formation in the Ronneburg ore field, Germany

Abstract

The Ordovician-Lower Carboniferous sequence of slightly metamorphosed gray carbonate-ter rigenous rocks contains the Silurian black cherty shales enriched in carbon (6-9%), pyrite (6-7%), and ura nium (~30 ppm). The uranium ore is localized at the pinch out of areal and linear zones of the Early Permian supergene (exogenic) oxidation of rocks expressed in reddening (hematitization). U, As, Sb, Cu, Ni, Mo, and Ag have been removed from the oxidized black shales and concentrated in the cementation zone in form of pitchblende and sulfides in wall rock disseminations and veinlets largely hosted in carbonate bearing rocks. In the Late Permian, during deposition of the upper Rotliegende and Zechstein, the fractures in the basement were filled with carbonates and sulfates; uranium was partly redeposited along with enrichment in Pb and Zn. Mesozoic and Cenozoic supergene processes altered uranium ore insignificantly.

Genetic implications of Th/U, Th/K, and U/K ratios for U mineralizations: A case study from El-Missikat and El-Erediya shear zones, Eastern Desert, Egypt

“…The post-magmatic source can be either hydrothermal or supergene solutions. The former can be discriminated from the latter using Th/U ratio whose range ‘‘2.5 > Th/U > 0.1’’ is assigned to the hydrothermal uranium mineralizations [ 17 , 40 , 68 ], while values ≤ 0.1 are associated with supergene enrichment [ 15 , 16 ]. These values, along with the normal ratio, are collectively represented by Th-U variation diagram on which both magmatic and hydrothermal sources are assigned to the anomalous radioactivity of the studied granite at El-Missikat (Fig.…”

Mineral Chemistry and Chronology Investigation of Uraninite in the Jinguanchong Uranium Deposit in Eastern Hunan Province and the Implications for Geological Significance

“…It has two metallogenic ages: 266 ± 42 and 110 ± 5 Ma. 14 , 18 − 21 These examples further highlight the significance of perigranitic uranium deposits in the field of uranium geology.…”

“…Similarly, the Ronneburg mining district (Germany) has yielded 216,000 tons of uranium and is one of the largest uranium mining sites worldwide. It has two metallogenic ages: 266 ± 42 and 110 ± 5 Ma. ,− These examples further highlight the significance of perigranitic uranium deposits in the field of uranium geology.…”

“…The Pribram uranium deposit in the Czech Republic is a typical perigranitic uranium deposit with >68,000 t of U 3 O 8 . The mineralized host rocks belong to Precambrian and Cambrian clastic rock formations, and their metallogenic age is ∼270 Ma. − The Niederchlem–Alberode uranium deposit in Germany has a uranium resource of ∼84,460 t. The ore veins are associated with the subtle thermal metamorphic aureole of the Erzgebirge granitic pluton outer contact zone, and the surrounding rocks comprise black shale and carbonaceous slate. The metallogenic age of this deposit is estimated to be between 318 and 325 Ma .…”