Fingerprinting of Gold Artefacts fromMapungubwe, Bosutswe and Thulamela

B Grigorova, W Smith, K StiiJpner, and]A Tumilty

Anglo American ResearchLaboratories (Pty) Ltd, PO Box 106, Crown Mines, 2025, South Africa

andDMilJer

ArchaeologyDepartment, University of Cape Town, Private Bag, Rondebosch, 7700

The AARL gold fingerprinting technology has been applied to the analysis of gold artefacts excavated fromthe southern African sites of Mapungubwe, Bosutswe and Thulamela. Information gleaned from this processis relevant to studies conducted into artefact origins and provides increased insight into the history of thisregion with regards to the mining, cultural and trade practices associated with these early communities.

The history of metallurgy and metal ore mmmg insouthern Africa is thought to date back at least 2000years. Prospecting for iron ore and malachite byindigenous farming communities during the 1stmillenium AD, together with gold and tin ore at thestart of the 2nd millenium AD had importanteconomic and social implications. Production of thesemetals to manufacture jewellery, ingots, implementsand a variety of other artefacts led to the establishmentof wealthy intra- and intercontinental trading townssuch as Mapungubwe and Great Zimbabwe. Theexport of iron, copper, gold and tin from southernAfrica via the Indian Ocean trade network in exchangefor glass beads and other luxury goods is evidence ofeconomic contact with North Africa, the Middle East,India and China. Such intercontinental tradingflourished from about AD 800 and is marked by asignificant increase in metal production at the start ofthe 2nd millenium AD. Metal mining and metallurgywere therefore pivotal in urbanisation, socialstructuring and state formation (1, 2).

A series of seventy-six gold artefacts fromMapungubwe, Bosutswe and Thulamela archaeologicalsites kept in the Department of Archaeology,University of Cape Town, were examined using theAARL gold fingerprinting technology (3). This processadopts a qualitative approach utilizing laser ablationinductively coupled plasma spectrometry (LA-ICP­MS) as the means for sample analysis. LA-ICP-MSensures sufficient sensitivity and resolution to allow

(00' Cold Bulletin 1998,31 (3)

detection of major, minor and trace elements from45Sc to 238U. The profiles generated are a function ofsignal intensity and subsequent source discriminationis based on elemental comparisons of sample profileson a presence/absence basis together with differences intheir corresponding lead isotope ratios. The analyseswere conducted with the view to obtaining moreinformation regarding gold composition and itsderivation from single or multiple sources as well astracing possible trade between various sites.

The AARL gold fingerprinting technology isappropriate for the analysis of gold artefacts as it isessentially a non-destructive technique with sufficientsensitivity to investigate the full element range fromlithium through to thorium and uranium. Fingerprintingis currently used to determine the provenance of goldbullion and this analysis provides the first instance of itsuse in the study of gold artefact origins.

The Mapungubwe archaeological site is situatedin South Africa at the confluence of the Limpopoand Sashi Rivers and dates back to the 10th - 13thcenturies AD. Although the manufacture of jewellerypredominated, this early 2nd millenium site shows thefirst appearance of large iron agricultural tools andweapons other than small arrow heads. Mapungubwe,with its evident wealth, is thought to have been one ofthe major towns which dominated the Indian Oceantrade in southern Africa. The gold artefacts (Figure 1),including the famous gold rhinoceros, different typesand sizes of gold beads, spirally wound strips, beaten

99

Figure 1 Cold Artefacts from Mapungubwe

sheets, wire and minute gold tacks, were all excavatedfrom elite burial sites at the top of the Mapungubwe hilland constitute the oldest known gold in South Africa.

Bosutswe, a hill-top site in south-east Botswana,dates from the 8th - 13th centuries AD. A single pieceof gold wire from levels containing Mapungubwe stylepottery was available for the fingerprinting exercise.Investigations were focused on determining whetherMapungubwe was the origin of the gold used toproduce this wire, thus suggesting a possible trade linkbetween these two centres.

The third archaeological site of interest,Thulamela, is situated in the Kruger National Park

100

near the confluence of the Luvuvhu and LimpopoRivers and dates back to the 14th - 16th centuries AD.Iron, copper, gold (numerous gold beads, a woundgold bangle and melting crucible sherds with adheringgold droplets) and other metal artefacts excavated fromthis area indicated cultural links between theinhabitants of Thulamela, Mapungubwe and GreatZimbabwe (4). Also recovered were glass beads andoriental ceramics which provide evidence thatThulamela was involved in the Indian Ocean tradenetwork.

The artefacts received were all analysed for 130isotopes with representative fingerprint profiles for

(fjS- Cold Bulletin 1998, 31(3)

Mapungubwe, Bosutswe and Thulamela being givenbelow in Figure 2.

The results revealed that all the artefacts containedsimilar levels of silver and copper with elements such asstrontium, bismuth, barium and mercury beingprimarily used for distinguishing gold from the threesources. Profiles for the Mapungubwe artefactsprovided evidence for the existence of two differentsources, Ml and M2, based on the presence or absenceof strontium, mercury, barium, platinum group metals(PCMs) and rare earth elements (REEs). Ml is shownto contain all of these while M2 shows a markedabsence of former three and intermittent presence ofthe PCMs. The fingerprint profile corresponding tothe Thulamela artefacts showed a remarkable similarityto that of Mapungubwe group Ml with the presenceof all the Ml distinguishing elements. The conclusioncould therefore be drawn that both the Mapungubwegroup Ml and Thulamela artefacts originated from thesame gold source. The fingerprint obtained from theBosutswe artefact was unique in containing onlycopper, silver, barium and bismuth and showed no

similarities to the profiles generated for theMapungubwe gold artefacts. However, a moreconclusive evaluation of the origin of gold used in theBosutswe artefact could be made if a greater number ofsamples from this site were fingerprinted. Figure 3 is aflow chart illustrating the process of artefact groupingfrom the three archaeological sites, based on the dataobtained from the AARL gold fingerprintingtechnology.

Calculations of lead isotope ratios for the artefactsfrom Mapungubwe, groups Ml and M2, Bosutsweand Thulamela were carried out and compared to thenatural 206Pb:207Pb ratio. Bosutswe artefacts, having anatural lead isotope profile, once again showed adifference from those excavated from Mapungubwe(M 1 and M2) and Thulamela (Figure 4).

The results have clearly shown that while certainartefacts from Mapungubwe come from one gold source,other come from a different source common to that of theThulamela gold thus suggesting access to the same source.The gold wire from Bosutswe, however, shows no links togold originating from either Mapungubwe or Thulamela.

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Figure 2 Fingerprint profiles ofgold artefacts

(€ii;}' Cold Bulletin 1998,31 (3) 101

ACKNOWLEDGMENTS

exercise provide information regarding both artefactgold sources and intracontinental trading practiceswhich occurred in the early 2nd millenium AD.

We wish to thank the South African National ParksBoard and Pretoria University for access to thesamples.

THULAMELA I'vlAPUNGUIlWE 1l0SUTSWE

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GJStrontium Strontiu m O nlyMercury Mercury BismuthREE', REE', andPGM', PGM ', PG:-1', BariumBarium Bartum

Figure 3 How chart showing artefactgrouping

ABOUT THE AUTHORS60 .--------------------,

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Jim Tumilty is the Managing Director and DaraGrigorova the Manager Research at the AARL. WyattSmith is an integral member of the gold fingerprintingresearch team and performed the analyses and dataassessment studies of the gold artefacts. Dr DuncanMiller is a Chief Research Officer in the ArchaeologyDepartment at the University of Cape Town andsupplied the AARL with both the artefacts and adetailed history of the various excavation sites.Katherine Stulpner is a member of the LA-ICP-MSresearch team and is actively involved in research onthe UV laser system.

Figure 4 Lead isotope profiles REFERENCES

The AARL gold fingerprinting technology has beensuccessful in determining the presence or absence of ahost of elemental isotopes in artefacts from differentarchaeological sites. The results from the fingerprinting

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