Water that has interacted with mineralisation will take on elements from the ore which are then transported with the water producing larger footprints than most solid media samples.
Hydrogeochemistry for exploration
Super Trace Au and Pathfinders
The use of water for mineral exploration in regions with post-mineralization cover has the potential to open large regions with wide-spaced sample spacing. The ability of water to identify Au mineralization has been established by multiple studies (Grimes et al., 1995, Gray et al.,2009). Grimes et al (1995) sampled ground water in the Nevada Getchell Trend from up-flow, over and down flow of mineralization to identify key element associations, together with determining how distal from mineralization anomalism could be identified. They found that waters had a distinct Au anomaly under oxidizing redox conditions, and when waters were reducing the anomalism was of As, Sb and W. Gold concentrations higher than 1ng/L (part per trillion) were found associated with gold mineralization, highlighting the importance of being able to differentiate this low level of Au in water from background. ALS’s new super trace Au method uses a specifically tuned ICP-MS instrumentation to report Au to 0.0002mg/l (0.2 ppt) and selected pathfinders (Ag, As, Co, Pd, Pt, Sb, Tl, and W).
One challenge when measuring Au in water is that it adsorbs to the walls of both plastic and glass containers during even limited transport and storage (Chao et al., 1968). The traditional preservation of water samples with nitric acid (Gray et al., 2011, Leybourne, M.I., 2007) was not intended for Au stabilization and will not prevent this adsorption onto bottle surfaces. An alternative preservation using aqua regia is suggested, or alternatively ALS can offer in-laboratory desorption treatment of water samples prior to Au analyses. This desorption can also be offered for our standard ME-MS14L method where Au is also measured.
<Chao, T.T., Jenne, E.A., and Heppting, L.M., 1968. Preventing of adsorption of trace amounts of gold by containers. Geological Survey Professional Paper 600-D. pp. 16-19
Gray, D.J., Noble, R.R.P., and Reid, N., 2009. Hydrogeochemical mapping of Northeast Yilgarn Groundwater. CSIRO Report P2009/1612.
Gray, D., Noble, R., and Gill, A., 2011, Field guide for mineral exploration using hydrogeochemical analysis. CSIRO Earth Science and Resource Engineering.
Grimes, D.J., Ficklin, W.H., Meier, A.L. and McHugh, J.B.,1995, Anomalous gold, antimony, arsenic, and tungsten in ground water and alluvium around disseminated gold deposits along the Getchell Trend, Humboldt County, Nevada. Journal of Geochemical Exploration, v. 52., p351-371.
Leybourne, M.I., 2007, Aqueous geochemistry in mineral exploration, in Goodfellow, W.D., editor, Mineral Deposits of Canada: A Synthesis of Major Deposit- Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, pp.1007-1033.