Abstract

The Palaeoproterozoic Granites–Tanami Province in Western Australia and the Northern Territory contains numerous significant gold deposits, but recent exploration for additional deposits has been hampered by deep weathering of the basement and extensive Tertiary and Quaternary cover. Biogeochemical exploration has rarely been attempted in this environment, with soil sampling and drilling being the principal exploration methods. This paper outlines the methodology and results of a biogeochemical exploration programme utilizing Triodia pungens (soft spinifex), a perennial, hummock-forming grass, widely found throughout much of arid and semi-arid Australia. The species possesses several attributes which make it suitable for biogeochemical exploration, being ubiquitous in the area, readily harvested and capable of the uptake of trace elements useful in geochemistry. Systematic sampling has been undertaken at 50 m intervals on widely spaced lines over several prospect areas. Collection of large samples from several plants at each sample station is desirable to try to obtain a representative sample. Initial multi-element analytical work utilizing small samples (c. 2.5 g) of dried and shredded vegetation did not allow sufficient resolution of anomalies, with most results for Au and Pt being below detection levels. However, preconcentration by ashing of substantially larger samples (c. 30 g) has allowed anomaly thresholds for those elements to be more readily defined. The species displays extensive geochemical variability for precious metals, pathfinders, base metals and major cations suggesting it offers much promise as a sampling medium. Test sampling traverses across known gold occurrences confirm the effectiveness of the technique in areas of thick cover sequences.

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