Geology, experimental in situ leaching and site remediation of the Dinnyeberki uranium ore deposit

Abstract

The Dinnyeberki uranium ore deposit is located west of Dinnyeberki, at a depth range of 25.8–40.8 m below the surface, and at 100–115 m above sea level (N 46°05´ 36.46˝ E 17°56´47.20˝). It is in the 0.5–3.5 m-thick, coarse-grained
sedimentary rocks along with the high organic matter content of the Szászvár Formation. Its horizontal extent is 50×70 m. The underlying rocks of the Szászvár Formation are the Palaeozoic basement (Mórágy Granite, Korpád Sandstone,
Gyűrűfű Rhyolite, Cserdi Sandstone) and the Middle Miocene (Karpathian) Tar Dacitic Tuff. It is overlain by the Upper Pannonian (s.l.) Somló Formation. On the top of the bed sequence there is loess and re-deposited loess.
The immediate over- and underlying beds of the mineralization are poor aquifers (10–8 m/s). The original water content of the mineralized horizon is 5% its average porosity is 15–20%, and its permeability 1–10 mD. Its average
effective coefficient of permeability is 3.5×10–7 m/s. The lead isotopic age of the mineralization is 20 million years, with additional enrichment through mobilisation 11–15 million years ago. When discovered, 90% of the uranium was mobile
and in an oxidised (U6+) state. The ore reserve is 18,000 kg U. The equilibrium conditions of the mineralization were changed by the experimental in situ leaching. In the mineralized section of the Dinnyeberki Db–3 well (drilled in 1982)
the RaUeq/U equilibrium ratio varied randomly between 0.76 and 1.5. In the lower mineralized section of the Db-46 well drilled in 2008 this parameter was 0.39, while in its upper mineralized section the ratio has shifted towards a radium
surplus, even reaching a value of 1.89. According to the Dahlkamp classification, the mineralization belongs to sandstonetype deposits within these the Chinle subtype has developed in a basal channel environment.
The Mecsek Ore Mining Company launched experimental in situ leaching to exploit the uranium in the middle of the 1980s. The production was stopped in 1989. The environmental status assessment started in 1995. The solution retained in the deposit was strongly acidic (pHmin = 2.8), with highly dissolved uranium (Umax = 42 mg/l) and sulphate (SO4 2–max = 16,255 mg/l. The remediation with clean water washing-out was started in 1999 and lasted three years.