Fig 1.
Locations of prehistorically exploited mines in southern Africa.
For location and discussion of these mines, see Bisson [2], Chirikure [10], Evers and van der Berg [5], Friede [11], Hammel et al. [12], Herbert [1], Huffman et al. [13], Killick et al. [14], Mason [15], Miller [16], Miller and Sandelowsky [17], Molyneux and Reinecke [18], Phimster [19], Summers [6], Swan [8], Van Waarden [7]. For a geological legend to the map, see Fig C in the S1 Appendix. (Geological basemap adapted from Thiéblemont et al. [20]).
Fig 2.
“Ia” (rectangular and fishtail) and croisette ingot typology.
Fig 3.
Highlighted archaeological sites, geological districts, and geological mines from the text.
Geological basemap adapted from Thiéblemont et al. [20].
Table 1.
Associated information for each sample.
Further details for each sample are presented in the S2 Appendix.
Table 2.
All values are reported in μg g-1. Detection limits are included in the second row, however these values are reported in μg L-1 of dissolved sample in solution. Thus, all values below detection limits were culled prior to converting the sample data to μg kg-1 (ppb), μg g-1 (ppm), and wt% in the solid sample. <D.L = less than detection limits.
Table 3.
LIA values for samples.
Fig 4.
Produced from fishtail ingots from Kamusongolwa and Luano, the rectangular ingot from Kumadzulo, and the Luano ingot sample from Rademakers et al. [24]. 0.0177 is the 100(1- α)% confidence interval for the 207Pb/204Pb intercept. 0.1283 is the studentised 100(1-α)% confidence interval for u with overdispersion. The gray band around the regression line represents the confidence interval. MSWD is Mean Square of the Weighted Deviates, and gives an indication of the mean distance of points from the line. Isochron calculated using the IsoplotR “three Ratio” option for Pb-Pb isochrons [71].
Fig 5.
LIA data from rectangular and fishtail ingots.
Ingot data is compared to geological ore data from the Central African Copperbelt. The geological data is comprised of ore samples from the Domes Region, Kafue Syncline, Katanga Core, Katanga Copperbelt, Kundelungu Plateau, and Zambian Copperbelt–all of which are genetically related. Ore data in the S3 Appendix from compilation of Killick et al. [59] and data produced by Stephens in 2020.
Fig 6.
Comparison to existing archaeological data.
Ia (rectangular and fishtail) and croisette ingot data from this study compared to ingot data from Rademakers et al. [24] on Ia (rectangular) and croisette ingots from the Upemba Depression. Results from these two projects agree well with one another and clearly illustrate that the Kent Estates HXR ingot was produced from a different geological source.
Fig 7.
Produced from ingots with radiogenic lead isotopic data (206Pb/204Pb > 18.700. 207Pb/204Pb > 15.628). The Kent Estates ingot and ingots matching the Kipushi deposit were excluded from this calculation. 0.0039 is the 100(1- α)% confidence interval for the 207Pb/204Pb intercept. 0.1055 is the studentised 100(1-α)% confidence interval for u with overdispersion. The gray band around the regression line represents the confidence interval. MSWD is the Mean Square of the Weighted Deviates, and gives an indication of the mean distance of points from the line. Isochron calculated using the IsoplotR “three Ratio” option for Pb-Pb isochrons [71].
Fig 8.
LIA data from croisette ingots.
Comparison of HIH and HXR ingot LIA data to geological ore LIA data from the Central African Copperbelt and Magondi belt. Ore data in the S3 Appendix from compilation of Killick et al. [59] and data produced by Stephens in 2020. The Kent Estates HXR ingot clearly diverges from the dominant trend in Copperbelt LIA values and is a better match for the Magondi belt. However, more isotopic measurements of Magondi belt ore samples are needed to better define this trend line, and to investigate whether individual ore deposits within this mining district can be distinguished.
Fig 9.
Highlighted samples from Fig 8.
A zoomed-in perspective of the highlighted box from Fig 8 shows the highly clustered group of HIH and HXR ingot samples which match to LIA data from the Zn-Pb-Cu Kipushi deposit. Note that the scale is drastically different from Fig 8. Included in this plot are one copper casting spill and one fragment of malachite recovered from smelting sites near Kipushi. Present in this narrow window are 30 datapoints from ore samples from the Kipushi deposit, and 9 datapoints from 7 other deposits within the Copperbelt that are closest to the Kipushi cluster. Ore data in the S3 Appendix from compilation of Killick et al. [59] and data produced by Stephens in 2020.
Fig 10.
Logged concentrations of chalcophile (A) and siderophile (B) elements from samples in this paper, Rademakers et al. [24], and Stephens et al. [33]. Ingots are grouped by their determined isotopic provenance, and the experimental “X” ingot is represented by the “Kansanshi” category since we know its specific provenance.
Fig 11.
Map of the inferred provenance conclusion for each rectangular, fishtail, and croisette ingot in this study.
Provenance results indicate that objects travelled significant distances to reach certain destinations and that interactions between the Copperbelt and areas further south can be traced back to the 6th-7th century CE. Geological basemap adapted from Thiéblemont et al. [20].