Hydrogeochemical mineral exploration in deeply weathered terrains: An example from Mumbwa, Zambia.

Locating mineral deposits in areas of thick or transported overburden is notoriously difficult. Post-mineral cover is prevalent in many parts of the globe and has led to prospective geological sequences being missed by traditional methods of exploration. Hydrogeochemistry is particularly applicable for the exploration of Iron Oxide Copper Gold (IOCG) deposits because, when compared to larger porphyry or sediment-hosted systems, IOCG deposits tend to be smaller and high-grade with a limited lateral footprint to intersect with grid-drilling; groundwater interactions and ion dispersion tend to produce a much larger anomaly target than regolith geochemistry alone and require fewer samples. As a case study, we examine the hydrogeochemistry of the Kitumba IOCG deposit, located in the Mumbwa district of west-central Zambia. We present physicochemical data (Eh, pH, TDS, conductivity), major and trace element concentrations, and isotopic compositions (δ98Mo, 87Sr/86Sr, and δ65Cu) from groundwaters interacting with the Kitumba deposit and surrounding prospects. A hydrogeochemical footprint of As, Mo, Fe, Mn, and Zn is dispersed from the deposit. Groundwater 87Sr/86Sr values (0.708832 to 0.731807) reflect the mixing in varying proportions of waters that have interacted with distinct lithological endmembers in the Mumbwa area, corresponding to a complicated tectonic and metamorphic history. We report fractionation of 1.34 to 1.60‰ (∆65Cugroundwater - chalcopyrite) between proximal groundwater and primary chalcopyrite, which we postulate may be related to the oxidative dissolution of primary sulfide minerals. The δ98Mo3134 values of groundwaters proximal to known ore bodies are isotopically distinct (-1.08 ± 0.18‰ 2SE to 0.64 ± 0.08‰ 2 SE) from background aquifers (2.08 ± 0.12‰ 2SE). The trace element and isotopic hydrogeochemical patterns described in this study document water-rock and water-deposit interactions and demonstrate the potential of non-traditional stable isotopes to be employed in district-scale reduction of exploration ground and vectoring towards undisturbed ore deposits similar to Kitumba.

Mineral status of soils and forage in the Mole National Park, Ghana and implications for wildlife nutrition.

Geochemical mapping of soils and selected plant species has been carried out in the Mole National Park, Ghana. The distribution of the essential nutrients: cobalt, copper and manganese is largely controlled by bedrock geology, while the geochemical dispersion of Ca, I, Fe, Mg, Mo, P, K, Se, Na and Zn has been modified by soil and hydromorphic processes. From selective extraction experiments, Fe, Mn and Co are found to be largely fixed in the soil mineral fraction. Larger proportions of Cu, I, Mo, Se and Zn are EDTA extractable and have a high chelation potential.Cobalt, Cu and Mn were preferentially concentrated in grass species while molybdenum and selenium are concentrated in browse plants. Copper uptake is antagonistic to Fe, Mo and Zn accumulation in all plant and grass samples. Similarly, Se and Mn appear antagonistic and Fe uptake is antagonistic to Co, Cu, Mn, Mo and Zn.The low concentration of P points to a potential dietary deficiency of this element throughout the park. Cobalt deficiency may also occur due to a love extractability of these elements in the soils and low concentration in plants. However, the lack of data on the elemental requirements of wildlife allows only tentative conclusions to be drawn.