Chemical and Cu-isotopic characteristics of native gold from carbonatites and Quaternary deposits of the Guli massif (Maimecha–Kotui province, Russia)

Research subject. Mineral assemblages of native gold from carbonatites and Quaternary deposits of the Guli massif (Maimecha–Kotui province, Russia), which are associated with complex gold–iridium–osmium placer deposits. Aim. To identify mineral assemblages and variations in the chemical and Cu-isotopic composition of native gold from calcite– dolomite carbonatite of the Southern carbonatite stock and Quaternary deposits of the Gule River, draining carbonatites of the Guli massif. Methods. The chemical composition of native gold was studied using a CAMECA SX 100 electron microprobe analyzer. The analytical technique for determining δ⁶⁵Cu included dissolving gold samples in a mixture of HCl and HNO₃, selective chromatographic separation of Cu from solution, followed by determination of the ⁶⁵Cu/⁶³Cu value using a ThermoFisher Neptune Plus MC-ICP mass spectrometer. Results. The analyzed samples are represented by single-phase and polyphase mineral assemblages of native gold within homogeneous and heterogeneous grains, which consist of high-fineness gold, electrum, natural Au–Ag–Cu alloys, tetra-auricupride, and auricupride. The first Cu-isotope data for gold minerals from calcite-dolomite carbonatite of the Guli massif and Quaternary deposits of the Gule River revealed identical, within analytical uncertainty, average δ⁶⁵Cu values (−0.49 ± 0.08‰ (n = 3) and −0.30 ± 0.30‰ (n = 8), respectively). Conclusions. The observed features of the mineral assemblages and the chemical composition of native gold from calcite–dolomite carbonatites show a close similarity to those of placer deposits of the Gule River, located near the Southern Carbonatite Stock. Copper isotopic data for both primary and placer gold are consistent within analytical uncertainty, suggesting a common juvenile source. It is proposed that the principal bedrock sources of gold were rocks of the Maimecha–Kotui ijolite–carbonatite complex.

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