Vertical ionic migration: mechanisms, soil anomalies, and sampling depth for mineral exploration

Abstract

Field studies, in particular mobile metal ion analysis of soil samples taken over mineralization, suggest that subtle geochemical anomalies exist above mineral deposits which are demonstrably covered by allochthonous material such as glacial till. Empirical observations suggest that the anomalies are preferentially located 10 to 25 cm below the soil interface, comprise elements contained in ore, and are located directly above the mineralizing source. Laboratory experiments suggest that capillary rise and evaporation play an important part in determining the position of emplacement of ions in the soil profile: in nature, root-zone transpiration also plays a part in solute deposition/adsorption within the evapo-transpiration zone. The effects of downward-percolating water after rainfall events, as well as the upward force of capillary rise, are considered in a model which explains many of the features of ion emplacement in soils. Laboratory modelling also suggests that convection, perhaps due to the heat produced by oxidation of the deposit, may in some cases provide a mechanism for rapid ascension of ions beneath the water table.

Recognition of geochemical footprints of mineral systems in the regolith at regional to continental scales

“…Note that the formation of carbonate in the regolith occurs under oxidising and alkaline conditions and can be biomediated (McQueen, Hill, & Foster, 1999;Reith et al, 2011;Schmidt Mumm, & Reith, 2004). The precious/transition metals association is likely a signature of ore-related elements having moved through the alluvial/colluvial sediments post-deposition (Anand et al, 2016;Mann, Birrell, Fedikow, & Souza, 2005) and is generally consistent with the regolith signature of mineralisation including porphyry-associated deposits such as Cadia-Ridgeway and Northparkes (McQueen, 2005). In conclusion, it appears that PC1 dominantly reflects weathering (both dissolution/bleaching as revealed by the REEs, and neoformation of regolith carbonate), with an intriguing addition of metals possibly reflecting mineralisation.…”

Catchment-based gold prospectivity analysis combining geochemical, geophysical and geological data across northern Australia

“…Accordingly the MMI response can be subdued after significant rain and flooding, but can also reform relatively quickly (Mann et al 2005). Thus the system investigated geochemically here is a fairly dynamic one, especially in the region of interest where rainfall is seasonal (typical dry and wet seasons in winter and summer respectively).…”

Répartition des anomalies pédogéochimiques en relation avec un indice polymétallique et une ligne à haute tension à courant continu, secteur de la rivière Pontax, Baie-James /

“…L'anomalie en Zn analysée par PYRO-MS est représentée par la courbe bleue, les résultats de PS au-dessus du profil d'échantillonnage correspondent à la courbe rose et la topographie est illustrée par le trait noir . 61 L'intérêt pour la pédogéochimie d'exploration s'est développé suite à la découverte de plusieurs anomalies de sols au-dessus de minéralisations enfouies sous une couverture de dépôts meubles (Alekseev et al, 1996;Antropova et al, 1992;Cameron et al, 2004;Goldberg, 1998a;Govett and Pwa, 1981;Mann et al, 2005). Par contre, les processus à l'origine de la formation de ces anomalies et la façon d'interpréter ces dernières sont encore mal compris.…”