Micro-PIXE and micro-IBIL characterization of lapis lazuli samples from Myanmar mines and implications for provenance study

Abstract

The provenance of raw lapis lazuli used since the Neolithic Age for the realization of carved artefacts can be pivoting for the reconstruction of ancient trade routes. The role of main provider of this material in ancient times is generally attributed to the Badakhshan quarries (Afghanistan), although other deposits could have been exploited as well since antiquity. The systematic multi-technique analysis of lapis lazuli rocks coming from four known source areas (located in present-day Afghanistan, Tajikistan, Siberia and Chile) has led in the last years to the compilation of a protocol for provenance determination. The protocol is based on differences in the physical–chemical properties measured with non-invasive techniques (Ion Beam Analysis (IBA)), making it suitable also for precious ancient artefacts. In this work, 10 new reference samples from the Mogok quarry (Myanmar), previously subjected to a complete petrographic and mineralogical characterization, have been analysed employing mu-PIXE (Proton Induced X-ray Emission) and mu-IBIL (Ion Beam Induced Luminescence) techniques. The subdivision of Myanmar samples into three groups, previously suggested, is corroborated by diopside trace elements concentrations. The results also allow to include Myanmar as a new provenance in the analytical protocol, indicating that provenance markers such as presence/absence of wollastonite, altered pyrites and Sr content are still valid to discriminate also the Myanmar lapis lazuli from Chilean or Siberian ones. New weaker markers (Zn content in diopside, Se and Cu contents in pyrite) are proposed for the discrimination of Myanmar from Afghan or Tajik provenances; however, from the analysis it arose the need of investigating new mineral phases with IBA to find strong markers for a definitive discrimination with samples from Southwest Asia.