Hydrothermal quartz as archive for the injection of pulsed magmatic fluids and tellurium-gold mineralization of the Kochbulak epithermal deposit, Tien Shan, Uzbekistan

Abstract Quartz with micro-scale growth zoning (i.e., zoned quartz) is commonly found in epithermal gold ± tellurium deposits, and its variable mineralogical, textural and geochemical characteristics contain critical information on the ore-forming processes. This study provides a rare case of integrated mineralogical, fluid inclusion, in-situ trace element and oxygen isotope studies on zoned hydrothermal quartz that is unequivocally linked to precipitation of tellurides and gold from the Kochbulak epithermal deposit in Tien Shan of eastern Uzbekistan. Detailed scanning electron microscope (SEM) and cathodoluminescence (CL) imaging have identified six generations of growth zones from the inner core to the outer rim (e.g., Qz-1, Qz-2, Qz-3, Qz-4, Qz-5 and Qz-6) in zoned quartz grains from the main gold-tellurides mineralization stage. Among these, the Qz-6 hosts abundant telluride inclusions (e.g., hessite and altaite). The homogenization temperatures (Th) of fluid inclusions from the tellurides-bearing quartz rim (Qz-6; mean Th of 319°C) are higher than those in the quartz core (Qz-1; mean Th of 292°C). These zoned quartz grains show significant trace element heterogeneity during crystallization, e.g., Al (67.0–2918.7 ppm), Li (3.8–146.0 ppm), Ge (0.1–2.5 ppm), and Ti (0.1–4.0 ppm). These compositional fluctuations exhibit systematic covariation with in-situ oxygen isotopes measured by secondary ion mass spectrometry (SIMS) across the six quartz generations (e.g., δ18OVSMOW = 14.4–5.1‰). Specifically, coupled abrupt positive δ18OVSMOW shifts (from Qz-1 to Qz-2 and from Qz-5 to Qz-6) and trace element composition (e.g., Li, Al and Ge) variations in the zoned quartz reveals two intermittent pulses of high-temperature, acidic magmatic fluids injection. Abundant altaite and hessite inclusions observed in Qz-6 not only link ore precipitation to specific zones but also suggest metal-rich magmatic fluid influx triggered tellurium-gold mineralization at Kochbulak.

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