Calcrete groundwater

Table 1. Hydrogeochemistry of representative groundwater analysis, Calcrete Uranium...

Fig. 2. Matrix plot for key groundwater parameters, calcrete-hosted carnotite deposits, Namibia.

Geochemical Controls The speciation of uranium and vanadium has been determined for groundwaters from the calcrete-hosted carnotite deposits. These were completed in Geochemists Workbench v.7 using in-... 

The correlation to calcrete-gypcrete deposits is that saline groundwater may mobilize uranium both laterally and vertically through cyclic diffusion and pumping in a similar, abet on a smaller scale. This may occur in response to... 

Field measurements in sedimentary fluvial-type calcrete deposits also suggest that present-day groundwater in these areas may also display potential to both dissolve and precipitate uranium in the near surface. Chemical dilatancy and evaporation-driven diffusion that promote de-complexing, diffusion, and reprecipitation mechanisms are seen to play integral parts in the continued chemical reworking and modification of these calcrete-hosted carnotite deposits. 

Where uranium and vanadium concentrations are in pg/L and potassium and bi-carbonate are in mg/L. Where the CSI is equal to zero then groundwater chemistry and carnotite saturation are in equilibrium and the mineral has the potential to be present. The assessment of groundwater chemistry in the vicinity of calcrete-hosted carnotite deposits indicates that a wide geochemical halo exists and that this halo can be identified during exploration. In Australia direct analysis of groundwater and the CSI have been demonstrated as suitable methods for exploration. In Namibia, in reality although the approach may be useful for... 

Phosphorus-rich sedimentary rocks (limestones, mudstones, siltstones) Groundwater from porous rock or from karst features (limestone, dolomite and calcrete) Mainly arid F, U, Rn Irrigated agriculture Mo, Pb... 

All Groundwater from fractured bedrock, alluvial aquifers or calcrete Arid N03- high concentrations may occur where there are leguminous plants (e.g, Acacia species), and widespread termite activity ... 

Calcrete uranium Yeelirrie, Australia Discharge end of shallow groundwater flow system Dissolution from source rock, transport, and precipitation due to evaporation and decomplexation... 

Figure 2.1 Settings for calcrete development. In fluvial settings pedogenic calcretes can develop on floodplains and terraces, whereas groundwater calcretes may form in channel deposits or around the capillary fringe and upper part of the phreatic zone in more permeable parts of the floodplain. In alluvial fans paired calcretes may develop on the fans, with hydromorphic calcretes near discharge zones.

A common feature in some landscapes is inverted relief, usually of only a few metres, caused by the groundwater calcrete zones becoming exhumed and being more resistant to erosion than surrounding sediments (Reeves, 1983 Kaemmerer and Revel, 1991 Mann and Horowitz, 1979 Maizels, 1990). Groundwater calcretes act as cap rocks in some basins (Kaemmerer and Revel, 1991 Nash and Smith, 1998). 

Figure 2.9 Characteristics of groundwater calcretes. (A) Generalised macroscopic features based on various sources. Some workers, such as Carlisle (1980), identify two zones in the massive phreatic unit an upper earthy zone with remnant soil and alluvium, and a lower, dense porcellaneous zone with abundant cracks and cavities. Phreatophytic plants may also produce features such as rhizocretions and laminar rhi-zolite crusts (Seminiukand Meagher, 1981). (B) Generalised model for the evolution of groundwaters and their precipitates in semi-arid to arid alluvial systems based on Arakel (1986).

Figure 2.10 Geometries of groundwater calcretes and dolocretes. Linear, ribbon-like valley calcretes are known from the late Cenozoic of central and Western Australia, and the late Triassic of the Paris Basin (see text). Lacustrine groundwater calcretes or dolocretes forming halo-like masses are known from the Danian of Provence (see text). Alluvial fans are associated with sheet-like bodies, and are known from the Plio-Pleistocene of Oman and the Palomas Basin (New Mexico), and the Paleocene of the Lisbon and Sado basins (see text).

Mann, A.W. Horwitz, R.C. (1979) Groundwater calcrete deposits in Australia some observations from Western Australia. Journal of the Geological Society of Australia 26, 293-303. 

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