Abstract: The Tyndrum Pb-Zn mineralization occurs as veins and vein breccias in NE-SW trending fractures associated with the Tyndrum-Glen-Fyne fault. The major minerals are quartz, galena, and sphalerite with minor chalcopyrite and baryte. Tetrahedrite (sometimes silver-and cadmium-rich), pyrargyrite, marcasite, and pyrite occur as small inclusions (< 100 µm) in the galena-rich veins. Sphalerite formed early in the depositional sequence, mainly in breccias, with increasing amounts of galena and chalcopyrite deposited in the later vein stages of mineralization. Uraniferous veins post-date the main Pb-Zn mineralization and contain uraninite, calcite, baryte, galena, sphalerite, chalcopyrite, argentite, chalcocite, tetrahedrite, and safflorite.

Fluid inclusion studies reveal that the mineralizing solutions contained c.20 wt. % equivalent NaCl + KCl, had an Na/K ratio of 3 : 1 and were boiling during mineral precipitation.

The Tyndrum fault controlled the upward flow of the hydrothermal solutions and its intersection with fractures in quartzites favoured the siting of the veins. The depositional sequence is explained by an increase in temperature during the mineralizing episode. The uraniferous veins may be a late oxidized stage of the main Pb-Zn mineralization.