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.

Revisiting stigmergy in light of multi-functional, biogenic, termite structures as communication channel

“…Termites have been found to tunnel to depths as great as 70 m, although this is highly variable [162] . Tumulitermes tumuli mounds contain gold particles found at 1 m to 4 m depth [163] , [164] . Deep soil components (clay, fine silts) are better suited to the nest chamber construction for water retention (free water and adsorbed cationic water [30] , [165] ) and require reduced carbon and nitrogen supplements compared to topsoils [123] which are the preferred, less laborious alternative for galleries.…”

How do we distinguish termite stone lines from artefact horizons? A challenge for geoarchaeology in tropical Australia

“…Most biological activity—and translocation of fine sediments—occurs at depths <20 cm (Salvador‐Blanes et al, ), but termite foraging commonly extends to 0.4–1.2 m depth, and is affected by the depth of bedrock and presumably also the water table. Some termite activity has been observed at depths of 2–7 m (Lecomte, ; Stewart, Anand, & Balkau, ), but there are no data on its intensity, and field observations have not identified stone layers at >0.5 m depth. We also assume that stone layers at greater depth will take longer to form than those at <0.3 m depth.…”

Economic and ecological importance of termites: A global review

“…Today, geologists use expensive drilling for these purposes (Stewart & Anand 2014). Termites do not especially choose to bring the gold to their nests; however, soil particles in the underground layers (delivered by the termites from depths of 1-4 m) have a higher gold content and the insects thereby serve involuntarily as artisans (Stewart & Anand 2012).…”