Natural Science in Archaeology

160 7 Metals and Related Minerals and Ores
Copper ores developed at the base of gossans were called by the German name
fahlerze (pale ore), and now are commonly called fahl ores. In some environments,
lead/silver ores are also found at the base of gossans, often accompanied by the
mineral jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ]. An example of this is at Lavrion in Greece, but
there are other occurrences in France, Germany, Spain (see Williams 1950), and the
Czech Republic. Pre-Roman mining at Rio Tinto, Spain, extracted silver and copper.
The silver ores were jarositic in composition because they came from gossans.
It is likely that the earliest copper smelting was conducted well below the melting
temperature of copper (1083°C). A variety of scenarios may be proposed to account
for the initial discovery that copper metal can be separated from nonmetallic-looking
minerals such as malachite and azurite. For example, bright green malachite or
bright blue azurite might have been applied as decoration on the surface of pottery
by Chalcolithic artisans. If the pottery was then fired in a reducing atmosphere, copper
beads would have formed. Malachite and azurite, which are carbonate minerals,
begin to decompose below 400°C, and early pottery was fired at temperatures above
600°C. Once ancient metallurgists learned how to smelt the more difficult copper
sulfide ores, perhaps soon after 2000 BCE in the eastern Mediterranean, they turned
to the much more abundant copper iron sulfide, chalcopyrite. The technology for
smelting copper sulfide minerals probably had a profound effect on economics and
trade relationships in the early phases of the Bronze Age. Oxide zone copper deposits,
which undoubtedly provided the first raw material for copper smelting, are not
normally as rich or as extensive as sulfide zone copper deposits. As the Bronze Age
developed, oxide zone deposits were depleted, and sulfide copper, available beneath
the oxide zone and in regions where erosion exposed primary copper ores, would
have been the only secure source for copper.
The earliest copper “alloys” contain appreciable quantities of arsenic and lead,
sometimes nickel or antimony, and occasionally silver, bismuth, or tin. A primary
question is whether the arsenic, lead, and tin were added deliberately or were the
result of impure raw materials. If the early arsenical coppers were deliberate, then
what prompted the initial effort(s) to smelt “mixed” ores? Was it random experimentation
with metallic-looking stones, or was it the result of perceptive understanding
of the smelting products of naturally complex ores? Zwicker et al. (1980)
point out that arsenic in a copper ore can be dissolved in the copper during smelting.
The Sican culture, 700–1400 CE, introduced bronze metallurgy in northern Peru
with their extensive production of arsenical copper (Shimada and Griffin 1994).
For most of the region from Europe and the Mediterranean throughout the Near
East to the Indian subcontinent, the first copper alloys were predominantly arsenic
bronzes containing more than 1% arsenic. The name arsenic comes from the Greek
word for strong because of its potent chemical properties. In the British Bronze
Age the earliest bronzes were made with arsenic (McKerrell and Tylecote 1972).
Renfrew (1967) states that tin bronze is rare in the Greek Aegean Early Bronze
Age. In Crete in EB I–II, arsenic was more common than tin as an alloying element
(Branigan 1974). In central Italy, excavations near a number of copper deposits
about 20 km south of Sienna have revealed an Etruscan bronze metallurgy of the
seventh and sixth centuries BCE (Warden et al. 1982).