Metallogenic mechanism of the Tianbaoshan Pb-Zn deposit, Sichuan

The Tianbaoshan Pb-Zn deposit in Sichuan Province, exhibiting open-space-filling and/or replacement textures, occurs as being of vein style in the Sinian (Late Proterozoic) carbonate rocks, and is simple in ore composition. A systematic study of lead isotope and rare-earth elements reveals that the ore-forming materials were derived from multiple sources. The ultimate source of the sulfur in all stages is seawater sulfate but the reducing mechanisms are different. The carbon was derived from marine carbonate and organic matter. The ore-forming fluid, meteoric in origin, belongs to a Ca2+ -Mg2+ -Cl- -HCO3- type of weak acidic to alkalic solutions with a salinity of about 5 wt % NaCl. The ore was formed at the depth of about 1 km from 150 to 250°C during the main stage of ore deposition. The heated meteoric water, after extracting ore materials from wall rocks, evolved into ore-forming solution with a low salinity, in which metals were transported as chloride complexes such as PbCl, ZnCl and ZnCl. The metal-bearing solution moved upward along deep faults to low-pressure zones, where the metal ions reacted with reduced sulfur and were precipitated as sulfide minerals. The textures of the minerals were controlled by the rate at which the reduced sulfur was supplied.