gems, beryl, emerald, Kazakhstan, Delbegetey, inclusions, gemology, provenance, origin determination, fluid inclusions, oxygen isotopes

The aim of this study is to provide the first detailed mineralogical and fluid-inclusion description of emeralds from the Delbegetey deposit (Kazakhstan). The characteristic features of Delbegetey emeralds are established: they show dissolution figures on crystal faces, a bluish colour with distinct colour zoning; their refractive indices are ω = 1.566–1.570 and ε = 1.558–1.562, while the specific gravity is 2.65 ± 0.005—relatively low for natural emeralds; they contain only trace amounts of common impurities (Fe, Mg, Na, etc.) and are coloured by Cr and V. Fluid inclusions of all types are strongly vapour-rich, and primary inclusions homogenize to liquid at 395–420 °C. The lattice oxygen-isotope composition (δ¹⁸O SMOW = 11.3 ‰) places the deposit within the range typical of other granite-related emerald occurrences. Emerald crystallization occurred in a low-density (0.40–0.55 g cm⁻³) aqueous fluid composed of (mol %) 75.6–97.4 H₂O, 0.0–18.4 CO₂, 0.0–0.9 CH₄, with a salinity of 4.06–9.65 wt % NaCl equiv. Isochore calculations indicate formation pressures of 570–1240 bar.