The base-metal mineralization occurs as polymetallic massive sulfide mineralization, mainly pyrite, sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, and locally barite, and as pyrite-chalcopyrite stockworks. Pervasive hydrothermal alteration is dominantly quartz-sericite. Maximum enrichment in gold, bismuth, selenium, and tellurium is at the interface between the stockwork and massive sulfide mineralization styles. Deeper parts of the stockwork zone are characterized by elevated molybdenum and rhenium, whereas the distal parts to the massive sulfide mineralization have high mercury, antimony, zinc, cadmium, arsenic, lead and silver. The metal association and mineral assemblage are typical of volcanic rock-hosted massive sulfides in back-arc volcanic settings.
Uranium-Pb dating on zircon by LA-ICP-MS defines an age of 429 ¡À 3 Ma (2¦Ò) (n = 19) for the dacite sequence. Rhenium-Os isotope data on Mo-rich bulk ore samples define an isochron of 429 ¡À 10 Ma (2¦Ò) (n = 9; MSWD 0.21; initial 187Os/188Os 3.1 ¡À 1.9). Common Os is very low, and the absolute abundances of 187Re and 187Os define a model age of 429 ¡À 4 Ma (n = 9; 95 % confidence). The mid-Silurian dacite sequence and associated massive sulfide mineralization identify a hitherto unknown early rifting and back-arc seafloor spreading event at the northeastern Gondwana margin related to the early evolution of the Paleotethys Ocean.