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Acanthite (Ag₂S) as an indicator of late-stage silver mineralization in the Zawar Pb-Zn system, Rajasthan, India: Insights from Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) microtextural studies.

Sima Gorai, Bulusu Sreenivas and T. Vijaya Kumar.

The Journal of Indian Geophysical Union. 2026; 30(2)

https://doi.org/10.71122/JIGU.30(2)2026.0015 

This study investigates the occurrence, microtextural features, and chemical composition of acanthite (Ag₂S) in the Zawar deposit, Rajasthan, to better understand silver mineralization in this carbonate hosted Mississippi Valley Type (MVT) system. Acanthite is a low-temperature monoclinic silver sulfide mineral that represents the stable form of Ag₂S under hydrothermal conditions. Silver, traditionally treated as a by-product of Pb-Zn extraction, occurs as late-stage acanthite forming veins and star-shaped aggregates along micro fractures within earlier pyrite. SEM observations show these crystals are confined to structurally controlled openings. EDS analysis confirms dominant Ag and S with minor Fe and Ca. These features indicate precipitation from low-temperature basinal brines during the waning stages of hydrothermal activity.

Fig: (a) SEM image of acanthite (Aca) vein within the fracture zone of pyrite (Py), (b) EDS image; Silver concentration map of the vein .

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