Bronze Age source of tin discovered

A University researcher has found, for the first time, a local Bronze Age source of tin in the Middle East, a discovery that shows that tin -- the metal that makes the alloy bronze possible -- was not entirely imported from regions outside the area, as archaeologists had previously thought.

Aslihan Yener, Assistant Professor in the Oriental Institute, believes a mine and an ancient mining village she found in the Central Taurus Mountains in Turkey demonstrate that tin mining was a well-developed industry in that area as long ago as 2870 B.C., at the dawn of the Bronze Age.

The site of the mine, Kestel, is about 60 miles north of Tarsus. Yener's work at the mine and at nearby Goltepe, an ancient miners' village, provides new insights into the development of the tin industry. Perhaps most important is her discovery that tin can be smelted in crucibles at relatively low temperatures, a finding that may change established theories about economic and metallurgical developments in the Bronze Age Mediterranean world.

"By closing a significant gap in our understanding of metal production, our research has become central to interpretive efforts aimed at understanding the use of metals in urban areas," she said.

The Bronze Age, which began about 3000 B.C., was a time of great economic expansion throughout the Middle East. During this time, great city-states such as Troy rose in Anatolia (modern Turkey) and empires developed in Mesopotamia.

"Tin's economic role in the metal technology of the time is perhaps akin to that of oil in industry today. It was the most important additive to the then high-tech metal of its age -- bronze," Yener said.

Bronze is an alloy made by combining copper with as much as 5 to 10 percent tin. Because it is more easily cast in molds and harder than copper, bronze replaced copper in the production of tools, weapons and ornamental objects. The Bronze Age lasted until 1100 B.C., when iron became the most important metal in manufacturing.

Despite the importance of bronze and the role tin played in its production, scholars have long believed that tin was not readily available in the Middle East. Later cuneiform texts on clay tablets speak of sources to the distant east, and researchers have believed that perhaps Afghanistan was the only likely location of tin mines. Yener's discovery shows that tin came from local as well as imported sources.

Yener's work is part of a study begun in 1980 to identify sources of metals used in the production of weapons and other objects in the ancient Near East. Yener, an American of Turkish descent, began the work as a member of the faculty of Bosporus University in Istanbul.

"I had not set out to find tin," she said. "When I was being trained as an archaeologist, the standard view was that tin did not come from Turkey but from elsewhere during the Bronze Age."

As part of her exploration of potential mining sites in Turkey, Yener and her colleagues found the Kestel mine. When they began excavating there, they found low-grade tin ore, the remains of richer deposits that had been mined out.

The underground mining system at Kestel measures more than two miles, Yener said. The mining shafts are about two feet in diameter -- too narrow for most adults, providing evidence that the metal was mined by children. Yener and her colleagues have also recovered a burial site inside the mine with the skeletons of a number of 12- to 15-year-old miners, a finding that Yener said supports the view that children were the miners at the site.

"By examining the skeletons further, we will be able to determine if they died of mining-related illness or injury," she said.

The mining was done with stone tools and fire, according to Yener. Miners would light fires by the ore veins, thus making it easier to batter away the ore. The mine probably produced about 5,000 tons of ore during its 1,000 years of operation.

Although the researchers had found tin ore at Kestel early in the excavation, some skeptics thought that there was not enough tin to prove that the mine was actually a tin mine. Working last summer with tin experts from Cornwall in southwestern England, an area famous for its tin deposits, Yener discovered industrial debris, including one ton of tin-slagged crucibles with 30 percent tin content, at the mining village of Goltepe. The discovery provided clues about how the tin was smelted and established beyond doubt that tin-metal had been produced and was the motivation for the mining and smelting industry there.

In recreating the production process, the researchers deduced that the process began with washing the ore, much the way panners in the early American West recovered gold. The ore was ground and then smelted in covered crucibles, into which workers blew air through reeds. Droplets of tin became encased in molten slag, which was ground out, rewashed and resmelted in a labor-intensive process. The intensive use of stone tools to crush ore and slag to release tin globules provides an explanation for the more than 50,000 stone tools -- an unparalleled collection of such materials -- found at the site, Yener said.

"Already we know that the industry had become just that -- a fully developed industry with specialization of work. It had gone beyond the craft stages that characterize production done for local purposes only," she said.

Radiocarbon dating showed that Goltepe was occupied from 3290 B.C. to 1840 B.C. It developed over several phases and began as a community of pit-houses built into the soft sedimentary bedrock. Later, a walled community developed.

Several hundred people probably lived on the site. "It is unclear whether the food used by the community came in as trade or if some form of agriculture took place," Yener said. Terraces on mountain slopes suggest that some crops may have been raised there.

"We want to learn what the division of labor was -- if men and children performed the mining and smelting while other children and women engaged in grinding, metallurgy and in agriculture, for instance," she said.

Yener, a leader in the expanding field of isotope research, hopes further work may also connect metal produced in the Goltepe region with artifacts found elsewhere in the Middle East. Since mining sites produce metals with characteristic isotopes, she is able to determine the origins of the metals used in particular artifacts.

-- William Harms