Geotimes
Energy & Resources
Coal
and Cremation in Ancient Peru
William E. Brooks
Sidebar:
Pre-Columbian silver mining
After my visit to the adobe-walled archaeological site of Chan Chan, near Trujillo
in northern Peru in the summer of 2000 (Geotimes, August 2003), my guide
asked if I would like to see the metallurgical furnaces used by the Chimú,
ancient residents and master metalsmiths of the region. Chan Chan was the capital
of the Chimú Empire (A.D. 1100-1400) and the largest pre-Columbian city
in the Americas. These furnaces, my guide explained, were where Andean gold, silver
and copper ores were smelted and fabricated into jewelry, masks and plates sought
by the Spaniards. We left the main part of the complex, followed a dusty trail,
and arrived at a site marked by fresh-looking, redbrown, clinker-like debris.
There are
four large burned areas at Chan Chan — one of these, the Tschudi burn,
is approximately 25 by 70 meters and is surrounded by partially eroded adobe
walls that are now approximately 3 meters high. Intrigued by these structures,
I took a soil sample and later analyzed it; oddly, the sample showed no trace
of metals. Thus I began a geochemical quest to understand if these burned areas
were in fact used for ancient metallurgy. My findings thus far have revealed
the possibility of a far more morbid role for these furnaces in ancient Chimú
society.
Interior of the Tschudi burn in northern
Peru shows a research trench cut in the 1970s. Field of view is approximately
20 meters, and the weathered adobe walls, to the right and in the distance,
are approximately 3 meters high. Soil samples at the site show coal use, with
little evidence of metalwork; rather, the soil indicates a potential crematory
nature of the site. Photo courtesy of William Brooks.
Past accounts
American journalist and diplomat George
Squier visited Chan Chan in 1877. In his
book Peru — Incidents of Travel and
Exploration of the Land of the Incas, Squier,
who was not trained in mining or metallurgy,
described these burned areas as
"ancient furnaces with thick walls that
were burned deep with slag of copper and
silver ores." In a very different account,
Colonel La Rosa, a Peruvian advisor to
Squier, said that "this area was filled with
calcined human bones … and this should
be considered as a place of the burning of
the dead." Still, Squier noted that "few
traces were found at the time of my visit"
and that human burning was "a practice of
which I found no traces elsewhere."
Given the quantity of metal objects produced
by Chimú craftsmen, Squier's conclusion
seemed sound. However, in the
1970s, Massachusetts Institute of Technology
(MIT) archaeologists analyzed the "slag" and
showed that it was simply adobe that had
been melted and vessiculated by the
intense heat. That study did not support
Squier's observations; it showed no geochemical
evidence for metal processing or
smelting at the site.
I explained this enigma to a geochemist familiar with ancient mining and smelting
techniques described in Agricola's 1556 classic text De Re Metallica.
The geochemist suggested that a soil traverse across the area would be the best
test of whether or not metals had ever been processed at the site. And so I
decided to return to Chan Chan a year after my first visit, determined to find
any possible geochemical evidence of metallurgy.
The role of coal
My field
research for the U.S. Geological Survey's (USGS) World Coal Quality Inventory
of South America showed that coal is abundant in the Alto Chicama region of
northern Peru, and sea coal is found on the beach near Trujillo. Although "seacoale"
collected from beaches in 12th-century England would eventually lead to widespread
use of coal in the Industrial Revolution, the early users and sellers of this
resource that produced "filthy vapor" were often tortured or executed.
Modern coal mining at the La Victoria mine, Alto Chicama region in northern
Peru. Photo courtesy of William Brooks.
The archaeological literature indicated that ancient people in South America
used coal for mirrors and jewelry and, in North America, ancient people mined
coal and used it to fire pottery. However, despite its abundance, I found only
two obscure references to the use of coal as a fuel in Peru; one indicated that
coal was found near an Inca wind furnace, which implied, but did not necessarily
prove, use of coal as a fuel.
Therefore, geochemistry of the ash horizon
would help determine the original
fuel. Perhaps it was charcoal or other plant
material referred to in the archaeological
literature; or, given the regional availability,
perhaps it was coal.
Back to Chan Chan
I obtained permission to sample at the
Tschudi burn from the Instituto Nacional
de Cultura, the organization that oversees
field archaeological research in Peru, and
returned to the site in summer 2001.
The 1970s MIT archaeology team had
exposed the stratigraphy of the Tschudi
burn in a research trench. In-place river
gravels formed the lowest unit or floor of
the burned structure; next, a 15- to 20-centimeter,
fully combusted, pink to gray ash
horizon; and, finally, 30 to 40 centimeters
of blocky, lava-like, scoriaceous adobe that
graded horizontally into the partially melted
and scorched adobe walls.
Using a plastic trowel, I took eight soil
samples at 10-meter intervals across the
Tschudi burn — four samples from within
the burned area and four samples from
outside the burned area to provide background
data — from depths of 20 to 30
centimeters. I sieved them in the field
using plastic to eliminate the risk of sample
contamination; if copper or other metals
were present in the soil samples, it would
be apparent in the analytical data.
I sent ash samples to USGS laboratories
and the soil samples to a Nevada exploration
geochemistry lab for analysis.
Geochemical data on the ash from the
Tschudi burn indicated high (approximately
50 percent) silicon dioxide (SiO2),
low calcium oxide (CaO) and high zirconium
(Zr) content. I compared these data
to recent data from ashed Peruvian coal
samples in the USGS World Coal Quality
Inventory of South America database.
That comparison indicated that the fuel
used at the Tschudi burn was coal — the
first geochemical evidence for the use of
coal as a fuel in the pre-Columbian archaeological
record of Peru. In contrast, charcoal
or plant ash typically has low (approximately
5 to 6 percent) SiO2, high CaO and
low Zr content.
The soil geochemistry confirmed what
the MIT archaeologists had already published:
There was no anomalous copper or
other metal content in the soils either from
the exterior or the interior of the structure.
Physical evidence had again shown that
the Tschudi burn had no metal signature
and therefore had not been used for metallurgy
at any time in the past.
But the soil geochemistry held more
information. Calcium, phosphorus and
sulfur content of the samples was low outside
of the burned area and high within the
burned area. Colonel La Rosa had
described "calcined human bones" —
could the high calcium and phosphorus
content indicated in the soil data be related
to "burning of the dead"? I contacted
archaeological colleagues and the
Cremation Association of North America
for answers.
Making the link
Researching the history of coal and cremation, I learned that coal was used
for fire 70,000 years ago in France and that the oldest-known cremation took
place 50,000 years ago in Australia. Bronze Age tribes in Wales used coal for
funeral pyres 3,000 years ago; coal was used for cremation at the first U.S.
crematorium in Washington, Pa., in 1876; and the poet Robert Service wrote about
coal as the fuel in his 1908 Yukon tale "The Cremation of Sam McGee."
But while cremation was an acknowledged worldwide custom, it was not a pre-Columbian
mortuary practice, according to my archaeology colleagues. There were rare examples
of secondary cremations where bones of the deceased had been burned, but there
was no evidence for cremation as a primary mortuary procedure in pre-Columbian
Peru.
Pre-Columbian mortuary customs in
the region are quite interesting. For example,
the elite were wrapped in elegant textiles
with gold, feathers and ornaments for
the afterlife, while the poor were given
simple burials with no objects for use in the
afterlife. Criminals, however, were buried
alive, and the bodies of some prisoners left
to decompose on the surface show signs of
intentional mutilation.
At Chan Chan, archaeologists described
Chimú multiple burials and vaults with 13
female skeletons "stacked like cordwood;"
they estimated that as many as 300 may be
buried at other sites. Perhaps the Tschudi
burn was a mass cremation intended to
destroy the bodies and thereby deny an
afterlife to the victims.
A coal expert at USGS indicated that
the presence of sulfur in the soil data was
especially interesting. If coal were burned,
then the sulfur, available from pyrite in the
coal, should have volatized. However, in
modern power plants, limestone or other
high-calcium materials are added to the
burning coal. The calcium combines chemically
with the liberated sulfur. In a modern
power plant, this reaction is called flue gas
desulphurization and produces synthetic
gypsum. Also, this is environmentally important
because it limits sulfur releases to the
atmosphere that would otherwise contribute
to acid rain. Both the calcium and sulfur content
of the soil samples was high, perhaps
indicating the presence of limestone, shells or
even bone as sources of calcium.
With La Rosa's words about human
bones in mind, I continued down the crematory
path, looking at how temperature
and the duration of the Tschudi burn compared
to the physical conditions at a modern
crematorium. According to lab research
carried out by the MIT archaeologists,
Tschudi burned for 16 to 40 hours at temperatures
greater than 1,300 degrees
Celsius. A modern crematorium operates
for 2 to 3 hours at temperatures of approximately
1,200 degress Celsius. The conditions
of the Tschudi burn, therefore,
exceeded the requirements of a modern
crematorium.
The geochemical evidence — such as
high calcium and phosphorus content of
the soil from human remains and the interrelationship
of calcium burned in the presence
of sulfur from pyrite in the coal — has
led me to believe that the Tschudi burn was
used for cremation. However, collaborative
work between geochemists and archaeologists
is necessary to reach a conclusion.
The excavation skills and recognition of
fragmented, charred human remains, provided
by an archaeologist or physical
anthropologist can determine if La Rosa's
words are eerily true.
Sidebar
Pre-Columbian
silver mining
In the Bolivian Andes, people have been mining and smelting silver for much
longer than previously thought, according to recent research from lake sediments.
For some time, archaeologists have known that the Incans treasured the precious
metal, as did the Spanish colonists after them, but there had been little
evidence that any cultures prior to the Incans had harvested silver.
Geologists Mark Abbott of the University of Pittsburgh and Alexander Wolfe
from the University of Alberta cored Laguna Lobato, a small but deep lake
6 kilometers from the largest silver deposit in the Bolivian tin belt, looking
for evidence of past climate change. What they found surprised them, Abbott
says — evidence of pervasive pre-Incan silver mining.
Abbott and Wolfe's findings are a completely new and unexpected contribution
to the archaeological records of the pre-Incan period, says Marc Bermann,
an archaeologist at the University of Pittsburgh. "Nobody would have
predicted to see silverworking on the scale the lake cores indicated,
because silver is essentially absent from pre-Inca sites in highland Bolivia,"
he says.
The stratigraphic evidence in the cores included layers of metals associated
with smelting, such as lead, antimony, bismuth, silver and tin, at much
higher levels than natural. Pronounced metal-enrichment events coincide
with the late stages of the Tiwanaku Empire (A.D. 1000 to 1200), and with
the Incan period (A.D. 1400 to 1650) and the Spanish Colonial period.
Abbott says the researchers dated samples spanning from 2000 B.C. to
A.D. 1000. They found stable, low concentrations of the metals. Then concentrations
suddenly rose well above background levels, reached a peak around A.D.
1130 to 1150, then decreased during the following period and increased
again with the Incan Empire, Abbott and Wolfe reported in the Sept. 26
Science.
"Metalworking on this scale is a hallmark of highly complex societies,"
Bermann says. These findings are the first evidence that such societies
existed in this area as early as A.D. 1000. "It's very exciting,"
he concludes.
Bermann and Abbott both want to solve the mystery of what happened to
the tremendous amount of silver that was mined once it was produced. "Was
the silver recycled in later cultures, looted or does it remain buried?"
Abbott says.
For now, Bermann will join Abbott and Wolfe in the next trip to the
Andes to search for more lakes that might have preserved similar records
to Laguna Lobato. By studying a series of lakes from the region, they
hope to determine the history of metallurgy across the region.
Megan Sever
|
Brooks is a geologist and mineral
commodity specialist with the U.S. Geological Survey in Reston, Va. He has applied
his knowledge of regional geology to mineral resource use in ancient societies
on archaeological field projects in Belize, Peru and Bolivia. He presented this
interdisciplinary study at Harvard University during the 22nd Annual Northeast
Conference on Andean Archaeology and Ethnohistory, Nov. 1-2, 2003.
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