Provenance attribution of lapis lazuli rocks processed at the Bronze age archaeological site of Shahr-i Sokhta (Iran)

In the early 1970s, substantial evidence of lapis lazuli processing was discovered in the archaeological site of Shahr-i Sokhta (Sistan, Iran, about 3200–2300 BCE). 50 years later, the workshop areas of Shahr-i Sokhta are still the only scientifically excavated and extensively published lapis lazuli manufacturing context for the entire ancient Near East and Middle Asia. A substantial amount of lapis lazuli production waste, including chert microliths and debitage, lapis lazuli flakes, semi-processed lumps and unfinished or damaged beads, was discovered in local dumps onto abandoned dwellings. We report the results of the analysis of 16 waste fragments from the described contexts, using microscopic techniques such as optical microscopy, cold-cathodoluminescence imaging and scanning electron microscopy coupled with energy dispersive spectroscopy, and ion beam analyses. The provenance attribution is provided by the use of an established analytical protocol, based on the application of micro-Particle Induced X-ray Emission (μ-PIXE) and micro-Ion Beam Induced Luminescence (μ-IBIL) to single mineral phases inside the rock. Results indicate for more than half of the samples a univocal Badakhshan (Afghanistan) origin, strengthening with robust archaeometric evidence the hypothesis of a primary supply from the Sar-e Sang and neighbouring quarries during the early Bronze Age in Shahr-i Sokhta. The identification of at least one sample not ascribable to Badakhshan, but probably coming from Pamir mountains in South-West Gorno-Badakhshan (Tajikistan), about 130 km North-East of Sar-e Sang, is also discussed, as it supports a preliminary hypothesis of a multi-source network.