The determination of gold in vegetation and its application to specific problems in biogeochemistry : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry in the Dept. of Chemistry and Biochemistry at Massey University

Abstract

Studies were carried out to devise a method for determining nanogram quantities of gold in vegetation. The samples (0.5g) were digested with fuming nitric acid over a water bath. After addition of hydrochloric acid, the gold was extracted into a small volume (1 ml) of methylisobutyl ketone (MIBK). The organic layer was back-extracted with distilled water to remove iron interference and gold in the MIBK was determined by an electro­ thermal atomization technique with graphite furnace atomic absorption spectrometry. The optimum instrumental conditions for drying, ashing and atomization of gold were as follows: drying, 4.5V, 20 secs; ashing 6V, 20 secs; atomization 8V, 4 secs. A furnace cooling time of 50 sec. was allowed to attain high precision of signal heights. Tests on the efficiency of the method developed, showed high precision, good accuracy with the limit of detection of 1 ng/g. Recovery studies on the known amounts of gold added to vegetation, showed an average recovery of 99.4%. On the basis of these results, the method developed and outlined can be used on a routine basis for analysis of vegetation, soils and rocks. Biogeochemical and geochemical studies were carried out at 4 areas having different geological, topographical and climatic conditions. These were: Waihi, New Zealand, Seruwila in Sri Lanka, the Serbomaced­onian massif in Northern Greece, and Yathkyed Lake in Arctic Canada. At each of these study areas, different plant species were collected and analyzed together with the soil for biogeochemical studies. Investigations were carried out to determine whether the concent­ration of gold in plants could be used to predict the concentration of this element in the soil and also whether any other elements present could be used as a pathfinder for gold. The results of biogeochemistry showed good correlation existing between gold in plant and gold in soil provided the gold concentration in the substrate was sufficiently high. Arsenic was found to be a possible pathfinder element for gold, particularly when the latter is present with chalcophile elements.

The range of plant species analyzed in this study suggest that gold uptake is not restricted to any particular plant species or to plants with deep rooting system provided the substrate is auriferous.