Source of anomalous gold concentrations in termite nests, Moolart Well, Western Australia: implications for exploration

Abstract

The Moolart Well gold deposit lies in the Duketon Greenstone Belt in the Western Australian Goldfields in an area that has seen nearly 150 years of Au exploration with limited success due to the transported cover masking deposits. Here, the site displays no anomaly indicative of underlying mineralization within surface soils. Termites have the ability to burrow to the subsoil and contribute to the development of soil profiles through bioturbation. This study discusses the use of mounds formed by the termite Tumulitermes tumuli from a site where shallow ferruginised palaeochannel sediments with secondary Au enrichment overlays deeper primary mineralization. A series of samples from termite nests and surrounding soil were sampled along a transect from background areas to over mineralization. Various fractions of these samples were analysed with ICP-MS/AES. Tumulitermes tumuli is able to bring sub-surface mineralized material to the surface from 1 to 4 m depth. Termite mounds over mineralization and soil immediately adjacent to the mounds display an Au anomaly in both <250 and >250 µm fractions. Very high concentrations (>5000 ppb) were found in >2000 µm fractions in nests over mineralization as a result of vertical transport of anomalous pisolitic gravels by termites. These results suggest termite-driven local soil heterogeneity and termite mounds being a consistent geochemical and mineralogical sample medium for the discovery of ore deposits beneath weathered cover and shallow sediments.