Genesis of the sediment-hosted Haerdaban Zn-Pb deposit, Western Tianshan, NW China: Rb-Sr sphalerite and U-Pb zircon geochronological constraints

Haerdaban is a newly discovered Zn-Pb deposit (0.64 Mt at 6.19 wt% Zn and 1.09 wt% Pb) in the Western Tianshan, NW China. Sulfide mineralization mainly occurs as veins, breccias, and semi-massive ores within the dolomitic limestone and calcareous slate. Here we use Rb-Sr sphalerite and SHRIMP U-Pb zircon geochronology to place constraints on the age and formation of the deposit. Rb-Sr dating of sphalerite gives an isochron age of 432 +/- 45 Ma (n = 6; Sr-87/Sr-86(i) = 0.7102 +/- 0.0020), providing a direct age constraint for the main mineralization. SHRIMP U-Pb data for detrital zircon from three samples of host siliceous dolomite have relatively similar age modes with prominent age peaks at 1576 Ma, 1781 Ma, and 1848 Ma, and a smaller peak at 1375 Ma. The maximum depositional age for the host dolomite is constrained at 1099 +/- 21 Ma by the weighted mean age of the four youngest detrital zircons. These results demonstrate that the main mineralization clearly postdates the host sedimentary rocks. Zircons from two diorite samples and one granite sample yield overlapping Pb-206/U-238 ages with a weighted mean of 394.5 +/- 1.5 Ma. This age is slightly younger but within analytical uncertainty of the 432 +/- 45 Ma for the ores, implying a possible temporal relationship between intrusions and main mineralization. The igneous intrusions could provide the heat to drive the hydrothermal system responsible for main-stage mineralization. Haerdaban is interpreted to be a metamorphosed SEDEX Zn-Pb deposit that has been remobilized by subsequent hydrothermal activity.