Two fluid systems in the Lanping basin, Yunnan, China: their interaction and implications for mineralisation.

The Lanping basin is a Late Triassic to Eocene basin filled with terrestrial sediments. The basin is located between the Tibet-Yunnan and Yangtze plates, is controlled by deep-seated faults and contains a number of metallic deposits, including the Jinding Zn-Pb deposit. Fluid inclusion and isotope data indicate that there were two fluid systems operating in the basin, one derived from the mantle and characterised by high CO2 content and relatively low salinities, and the other from within the basin with relatively high salinities and low temperature. The former was probably a major carrier of metals while the latter provided reduced sulphur through the reduction of sulphates. The formation of major base metal deposits requires geologic conditions that favour interaction of the two fluid systems, which lead to precipitation of sulphides in a localised volume.
The Lanping basin is a Late Triassic to Eocene basin filled with terrestrial sediments. The basin is located between the Tibet-Yunnan and Yangtze plates, is controlled by deep-seated faults and contains a number of metallic deposits, including the Jinding Zn-Pb deposit. Fluid inclusion and isotope data indicate that there were two fluid systems operating in the basin, one derived from the mantle and characterised by high CO2 content and relatively low salinities, and the other from within the basin with relatively high salinities and low temperature. The former was probably a major carrier of metals while the latter provided reduced sulphur through the reduction of sulphates. The formation of major base metal deposits requires geologic conditions that favour interaction of the two fluid systems, which lead to precipitation of sulphides in a localised volume.