Medieval Kirschsteinite-Bearing Iron Slags of the Develi-Yahyali Area (Kayseri), Turkey

Abstract

While continuing our investigation of the geology of copper occurrences in central Anatolia, it was noted that there were a few places in the highlands south of Kayseri, such as Bakirdagi, with the Turkish word for copper (bakir) in their name. However, the search among place names with bakir (dotless i) is complicated by the presence of place names using the similar sounding word bakir (doted i ) meaning virgin or untouched. Enquires with local residents brought to our attention a number of slag sites which we hoped would be for copper. Inspection of these sites revealed that these slags showed no signs of copper alteration and that, when broken open with a rock hammer, showed prills of iron. These slags closely resembled the iron slags that we had previously investigated at Yaprakli in the Cankiri Province north-east of Ankara. As with the slags at Yaprakli, these slags are fully exposed with no sediment cover which would suggest a rather young age. To obtain some idea of their age, charcoal embedded in a selected piece of slag from one of the sites was submitted for AMS radiocarbon dating. The slag which was from Farasaolugu Mevkii, near Yahyali, gave an age of 393 years BP with an expected standard deviation of 39 years. A graph of 14C age versus calibrated calendar age gives an expected primary calendar age of 1470 CE and a secondary calendar age of 1610 CE. The primary age is similar to the average date for the slags at Yaprakli of 1412 CE, and places the slag in early Ottoman times. Most of the sites were similar in size to many of those at Yaprakli, but none were as small nor as large as some of those sites. The individual pieces of slag have the appearance of scoriaceous lava and are 8–10 cm in diameter. The slags, in roughly ‘hand’ size pieces, generally have the texture of a compact ceramic usually with abundant vesicles. While some pieces are glass and some pieces have ropey surfaces, none of the pieces showed any flow banding. Compositionally the iron slags consist mainly of kirschsteinite, calcic fayalite, fayalite, wustite, plagioclase, metallic iron and interstitial glass. Slag samples with high lime contents contain modal wollastonite and calcic-augite. The interstitial glass between the crystalline phases is normative in kalsilite-anorthite-wollastonite-fayalite-quartz. Most of the glasses lie adjacent to but on the silica-rich side of the anorthite-fayalite join, and on both sides of the anorthite-fayalite cotectic. This along with the compositions of the calcic-fayalites suggests that the interstitial glass formed at temperatures in the 1,100–1,200°C range. The glasses of the Develi-Yahyali slags are distinctly richer in iron and lime and lower in silica than those from Yaprakli.