Natural Science in Archaeology

144 7 Metals and Related Minerals and Ores
A broad understanding of the geologic processes that concentrate these elements
to the degree necessary for an ore deposit is of great value in understanding the context
in which early humans utilized raw materials. Scattered throughout this book
are short descriptions of geologic processes that form ore deposits, placers, and the
rocks suitable for providing products useful for mankind.
Although gold was always found in the native state, other metals such as copper,
lead, zinc, silver, arsenic, mercury, and cobalt were primarily concentrated in
sulfide deposits. Oxidation later converted many of these metal sulfides to oxides,
oxyhydroxides, carbonates, and sulfates.
The complex picture of the early smelting of lead ores, including the recovery of
silver contained in the lead minerals, remains to be completed. Gale and Stos-Gale
(1981) have argued that, because lead melts at a relatively low temperature (below
800°C), the smelting of galena (PbS) may have occurred early in the Bronze Age.
They suggest that the appearance of quantities of silver artifacts in the fourth millennium
BCE coincides with, or somewhat predates, the evidence for the start of
copper smelting. Their paper includes maps of early metal smelting sites in the
eastern Mediterranean region, Aegean ore deposits, ore deposits on the island of
Siphnos, and the lead mines at Lavrion.
Before the arrival of Europeans in the sixteenth century, the indigenous peoples
of the southwestern United States did not use metal for tools or weapons. However,
in South America, there was a fairly advanced metallurgical alloying of copper,
gold, silver, and even platinum (unknown in Europe). In Mexico and Central America,
copper, gold, and silver were utilized. In the New World, the word “metallurgy”
refers to “Andean metallurgy,” for it is this area alone that developed sophisticated
technologies that later moved north and flourished from Panama to Mexico. The
Andes Mountains contain some of the richest gold, copper, tin, and silver mines in
the world. Unlike the Old World focus on copper, metallurgy in Andean societies
focused on gold, beginning in the middle of the second millennium BCE.
Metal ore smelting normally requires the use of a flux to lower the melting point
(extraction temperature) of the ore mineral or the fluidity of the slag. The slags
formed in primitive copper and iron ore smelting consisted largely of fayalite (an
olivine) with the composition Fe 2 SiO 4 , which has a melting point of 1170°C. Limestone
found at ancient smelting sites cannot have been used as the flux, because the
lime would not lower the melting point or fluidity of a fayalite slag.
Analyses of ice cores present another method of assessing metal production in
antiquity. Atmospheric pollution from lead and copper production over the past
4000 years is locked in the well-preserved and well-dated ice layers in Greenland
and elsewhere. Ferrari et al. (1999) have reviewed the research of the last 20 years
on this topic and note the ice core evidence for the enhanced production of copper
during the Roman Empire in Europe and the Song Empire in China.
Readers interested in the history of metals will come across references to the
development of niello by many societies around the world. The term niello comes
from the Latin for “black work”. Niello has been considered to be a combination
of sulfur with copper, silver, or lead, heated to form a paste that is pressed into
grooves to present a black contrast to copper or bronze. Recent laboratory analyses