Evidence for Early Bronze Age tin ore processing

Recent discoveries related to ores from Kestel Mine in the Taurus Mountains of Turkey show how prehistoric miners used the magnetic properties of the black iron oxide to accomplish the difficult separation of cassiterite (tin oxide) from low-grade cassiterite ores. Excavations at the site of Goltepe, dating to the third millenium BC, have yielded hematite ore nodules containing a few percent, or less, of cassiterite and a sequence of processed, ground, and separated minerals. Laboratory experiments showed that reduction at temperatures as low as 700-850 degreesC converted hematite to the black magnetic oxide, which could be much more easily crushed than the hematite ore. On grinding and panning this material, the magnetic oxide clumped together effectively to yield almost complete separation of the cassiterite grains, a separation which, without automatic magnetic clumping, would be extremely difficult to accomplish due to the similar densities of cassiterite and magnetite minerals. The deliberate production of magnetic oxide may explain the shallow crucible bowl furnaces, the vast quantities of stone grinding tools, the large amount of residual magnetite at the site, and the fine particle sizes (which were necessary for the magnetic separation). These findings establish Kestel/Goltepe as a viable cassiterite (ore) production site. (C) 2001 Elsevier Science Inc. All rights reserved.