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7/14/2017 by mdc
https://www.nature.com/articles/ncomms3614
Lintern, et al., report that Eucalyptus trees may withdraw Au from mineral deposits and support the use of vegetation (biogeochemical) sampling in mineral exploration, particularly where thick sediments dominate. However, biogeochemistry has not been routinely adopted partly because biotic mechanisms of Au migration are poorly understood. For example, although Au has been previously measured in plant samples, there has been doubt as to whether it was truly absorbed rather than merely adsorbed on the plant surface as aeolian contamination. Here we show the first evidence of particulate Au within natural specimens of living biological tissue (not from laboratory experimentation). This observation conclusively demonstrates active biogeochemical adsorption of Au and provides insight into its behavior in natural samples. The confirmation of biogeochemical adsorption of Au, and of a link with abiotic processes, promotes confidence in an emerging technique that may lead to future exploration success and maintain continuity of supply.

Mineral explorers need to find new ore deposits. New Au discoveries are down by 45% over the last 10 years. Novel exploration techniques are required to find the more difficult deposits hidden beneath sediments. Furthermore, these new techniques need to be underpinned by an improved understanding of mechanisms of metal mobilization that are currently poorly understood. Biogeochemistry for mineral exploration is one such relatively new technique, but defining the boundaries as to when and where it may or may not be effective has been difficult.

One of the major technical problems facing research involving natural samples is that Au concentrations in vegetation are commonly very low (1 to 2 ppb). There is no unequivocal evidence that Au is actually absorbed by plants over mineral deposits and that currently measured Au is not merely a result of dust contamination of samples. Thus explorers are reticent to embrace an important emerging method.

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