Bullion production in imperial China and its significance for sulphide ore smelting world-wide

Gold and silver production was of major importance for almost all ancient societies but has been rarely studied archaeologically. Here we present a reconstruction of a previously undocumented technology used to recover gold, silver and lead at the site of Baojia in Jiangxi province, China dated between the 7th and 13th centuries AD. Smelting a mixture of sulphidic and gossan ores in a relatively low temperature furnace under mildly reducing conditions, the process involved the use of metallic iron to reduce lead sulphide to lead metal, which acted as the collector of the precious metals. An experimental reconstruction provides essential information, demonstrating both the significant influence of sulphur on the silicate slag system, and that iron reduction smelting of lead can be carried out at a relatively low temperature. These new findings are relevant for further studies of lead and precious metal smelting slags world-wide. The technological choices of ancient smelters at this site are then discussed in their specific geographical and social-economic settings. (C) 2015 The Authors. Published by Elsevier Ltd.