Biogeochemical patterns surrounding the Sunny Corner Ag-Pb-Zn and Thackaringa cobaltiferous pyrite deposits: Implications for exploration

Limited studies comparing geochemical patterns in vegetation with those in regolith materials over mineral deposits have been undertaken in arid to semi-arid regions. Biogeochemical responses to base metal mineralisation in two contrasting regolith settings are assessed. The first examined the response of Pinus radiata, Acacia dealbata (green wattle) and Baeckea utilis to areas of contamination and outcropping mineralisation in felsic volcanic units at the historic Sunny Corner Ag-Pb-Zn mine in eastern New South Wales, Australia. The second involved Atriplex vesicaria (bladder saltbush) composition over the deeply weathered, gneiss-hosted cobaltiferous pyrite deposit at Thackaringa in far western NSW. At Sunny Corner, foliage and other organs display elevated concentrations of Pb, Zn and As over mineralisation and the extensive zone of mine tailings. P. radiata needles also exhibit regional variation in the concentration of nutrient elements depending on the underlying lithology. Saltbush at Thackaringa displays elevated Co and Zn above and downslope of outcropping gossans, whereas Mn and Zn values are more elevated along drainage lines. Both A. vesicaria and P. radiata exhibit controls on uptake of Cu, S and other nutrients that is likely to be a mechanism to prevent accumulations reaching toxic levels. For some elements there is weak direct correlation between element concentrations in the plants and adjacent shallow soils, although overall spatial patterns display similarity. Where the distribution of selected species permits sampling at the requisite scale, biogeochemistry offers an alternative and potentially preferable sampling media to regolith, although there are advantages in sampling both media.