Compositions and Sources of Copper-Based Metals from the Middle

Previous technical examination of copper-based metals recovered from
several sites in the Middle Senegal River Valley (MSRV) is expanded to incorporate
lead isotopic ratio analyses. These new data, when combined with
chemical composition evidence, reveal patterns of distribution of copperbased
metals through time in that region. Results indicate that MSRV copper-
based metals were produced in several regions including West Africa,
Spain, Morocco, and possibly Tunisia and other areas. Comparison with
published lead isotopic ratios and compositional data suggest that the Middle
Senegal Valley first received unalloyed copper from West African sources,
probably from Akjoujt or nearby regions of Mauritania, in the first millennium
BC, and these MSRV metals are chemically similar to many “protohistoric”
unalloyed copper objects found throughout Mauritania. In the first
millennium AD, the MSRV was still receiving unalloyed copper from
nearby West African sources, but also was now receiving copper from across
the Sahara. The imported metals also included unalloyed copper, but copper
alloys also were appearing, such as low zinc brasses (<10 wt% Zn) and ternary
alloys of copper, zinc and tin. The brasses appear to share a common
region of origin, possibly Spain or Morocco. Some objects from the region
also appear chemically and isotopically distinct based on artifact type, such
as two similar samples from copper-based metal vessels. These imported
metals appear to have been reaching the MSRV through established trade
networks crossing the Sahara and connecting through sites such as Tegdaoust
and Koumbi Saleh.