Natural Science in Archaeology

7.5 Other Copper Minerals 163
of Anyang, six copper and three tin mines within 200 km, and six additional copper
and tin mines were located within 400 km (Chang 1980). In the analyses of the
earliest Chinese bronzes presented by Barnard (1961), it was lead rather than arsenic
that served as the alloying element. Lead provided the castability desired by
the Chinese metalsmiths. Mei and Shell (1998) summarize the evidence for the
beginning and early use of copper and bronze in Xinjiang Province, China. These
authors also report preliminary results of research at the Nurasay site, the only
Bronze Age copper mining and smelting site in Xinjiang. Of some importance
is the possible smelting of arsenical copper ore. The copper ore at Nurasay is a
sulfide ore. Radiocarbon dates indicate that copper/bronze came into use by 2000
BCE. The authors note that copper artifact and copper deposit distributions match
very closely.
Based on the physical and chemical properties of ore minerals discussed in the
ancient Chinese literature, Wang and Shen (1986) have concluded that thirteen species
of copper-bearing minerals were exploited. These were native copper, three
sulfides (chalcopyrite, chalcocite, and bornite), three sulfosalts (enargite, bournonite,
and tetrahedrite), two sulfates (brochantite and chalcanthite), two oxides (tenorite
and cuprite), and two carbonates (malachite and azurite).
In India signatures of ancient mining and processing of ores are present in almost
all of the slags from Rajastan and Gujarat. The most common slag was produced
during the smelting of copper ores (Grover 2004). Elsewhere in Southeast Asia,
Thailand played a major role in early large-scale copper production. Ban Chiang
has long been a focus of study (e.g., see Higham and Kijngam 1984). Bennett
(1989) has detailed early copper exploitation in central Thailand. She indicates that
both malachite and chrysocolla were the most likely early ores. From the sulfur
content of slag analyses, Bennett surmises that sulfide ores (probably chalcopyrite
or bornite) were also being smelted. To the north in Vietnam, bronze technology
flourished at Dongson (Ha 1980).
In Mesoamerica, copper ore sources exploited during the Late Postclassic Period
(1300–1521 CE) occur in west Mexico (Hosler and Macfarlane 1996). The minerals
mined and smelted included copper carbonates and copper sulfides. Copper alloy
metallurgy came late to sub-Saharan Africa, not much earlier than the introduction
of iron smelting.
As indicated above, Chalcolithic and Early Bronze Age copper-based artifacts
show appreciable amounts of arsenic, tin, antimony, and lead, often greater than
1%. Because of lead’s low melting point (327°C) and the ease of smelting galena
(below 800°C), lead was an easy metal for early metalsmiths to use. Galena deposits
are available throughout the area where metalsmithing originated. The difficulty
is determining whether lead was added deliberately to improve the resulting
alloy or whether lead entered the metal because it was available as a component
in the ore.
Although antimony is present occasionally in some early copper-based metals in
amounts greater than 1% (thereby having an effect on the properties of the metal), it
seems likely that antimony was always an accidental alloying element when it was a
component of the sulfide ores. As an element, antimony was first described in 1450.