| Abstract: | The focal point of this report is a bibliography of 133 references and an associated topic index — both of which could be useful to geochemists attempting to locate new Au deposits. Fifty of these references originated in the Soviet Union, where most of the initial work on biogeochemical exploration for Au had been done. The 15 topics in the index range from agriculture (Au in crop plants) to silver.As an introduction to the bibliography, we have briefly described some examples of applications and difficulties in using plants. These examples are drawn from the literature and from field experience. Because of the generally low Au concentrations found in plants, the analysis of plant tissue is critical to the successful application of the biogeochemical method of prospecting. Neuron activation analysis is the most widely used method to detect Au in plants, due largely to its sensitivity; levels in the parts per billion range are easily attained. Two general types of sampling media are used in prospecting for Au: humus and living plants. Humus has been widely used in Canada, but the sampling of plants has increased there and elsewhere in recent years. Our use of douglas-fir (Pseudotsuga menziesii) at a Au-bearing stockwork in Idaho is a prime example. A maximum Au concentration of 14 μg/g (ppm) was detected in the wood ash of this coniferous tree, well above the normal concentration of ≈ 0.15 μg/g. Among shrubs that might be useful in Au prospecting, we recommend sagebrush or wormwood (genus Artemisia), because it is extremely responsive to concealed mineralization. It has been used extensively in the Soviet Union and could be used in areas of the western United States where disseminated Au occurrences might be located.Among the problems one may encounter in using plants for Au prospecting are: (1) physiological barriers, by which many plant species simply do not absorb Au at detectable levels; (2) misconceptions of soil-plant correlations; (3) localization of Au in plant tissue; and (4) the variation of Au concentrations due to season. Despite these limitations, biogeochemical techniques can complement or replace other geochemical methods currently used. |
