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An Investigation of the Trace Element Compositions of Gold
from the Zimbabwe and South Africa : Implications for tracing
the source of archeological gold
Robert Netshitungulwana 1 , M. Tredoux 2 , L. Jacobson 3
1. Council for Geoscience, South Africa, robertn@geoscience.org.za
2. University of Free State, South Africa, mtredoux@ufs.ac.za
3. McGregor Museum, South Africa, jake@museumsnc.co.za
ABSTRACT
The early Bantu farmers who settled in southern Africa were involved in trading and metal technology, and the
history of mining for metals like iron, copper, tin and gold in southern Africa spans at least the past 2000 years.
The main aim of the research was to test the viability of using gold chemistry to compare the composition of gold
ores in South Africa and Zimbabwe with those of the archaeological gold artefacts in Thulamela, Mapungubwe,
Bosutswe and Great Zimbabwe. Samples from Archaean greenstone belt in South Africa and Zimbabwe, as well as
samples from ores associated with the Witwatersrand Supergroup, were used in the study.
Trace element signatures were determined by laser ablation inductively coupled plasma mass spectrometry (LA-
ICP-MS), a technique whereby low concentration (down to low ppb levels) can be detected. In addition, Ag
concentrations (wt. %) were determined using scanning electron microprobe, so that Ag could be used as an
internal standard during the LA-ICP-MS runs to give semi-quantitative data. The most commonly occurring
isotopes in gold, namely, 56 Fe, 59 Co, 60 Ni 63 Cu, 66 Zn, 75 As, 188 Os, 105 Pd, 195 Pt, 202 Hg, 107,109 Ag, and 204, 206,207,208 Pb
and 209 Bi, were used to construct the signatures, using their intensities in the mass spectra in counts per second
(cps). Isotopic ratios were used to compare the gold ores with the gold artefacts.
The results show some variations in the signatures of gold from the greenstone belts and the Witwatersrand Basin.
The 107 Ag and 202 Hg cps in gold from the Witwatersrand Basin are high compared to the greenstone belts. These
differences have implications for the various models of gold deposition in these environments, pointing to different
geochemical histories. Multivariate correspondence analysis plots for the major gold deposits show the wide group
of the Barberton samples with little or no distinctive characteristics compared to the Zimbabwean gold samples.
The Witwatersrand gold plot differently to the Barberton greenstone belt but closely related to the Zimbabwean
greenstone belts. The ratio plot of 56 Fe (10 5 )/ 107 Ag versus 202 Hg (10 5 )/ 107 Ag shows that archaelogical gold artefacts
differ completely from the natural gold, indicating that the gold could not merely have been gold-worked, as has
been suggested. This suggests that gold from any one archaeological site could not be related to any particular or
even regional source. The problem could be associated with the possibility of mixing of gold from multiple
sources, recycling, contamination in melting, and trade in items.
KEYWORDS: Archaeology, Gold, Trace element analysis, Southern Africa, Zimbabwe
Netshitungulwana Robert. 1 received his Bachelor of Science (Honours) (BSc.H) degree
in Geology from the University of Venda, South Africa in 2003. He is currently doing his MSc.
Degree at the University of Free State, South Africa, with research interest geared towards
“trace elements geochemistry in southern African gold and artefacts”. He has done
geochemical fieldwork, compiling geochemical maps and data interpretation in South Africa
and internationally with Council for Geoscience, South Africa.
. 1 Department of Geology, University of Free State -Bloemfontein , SA
Email: robertn@geoscience.org.za / Mobile +27 73 339 9917
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