Geology, geochemistry and genesis of the Zankan iron deposit in the West Kunlun Orogen, Xinjiang, China

The Zankan iron deposit (Taxkorgan County, Xinjiang) is a recently discovered large Fe deposit in western China. The deposit is hosted in the Bulunkuole metamorphic complex in the Taxkorgan terrane of the West Kunlun Orogen. The ores are uniquely composed of magnetite, pyrite and anhydrite with variable contents, and show massive, disseminated and banded styles. The ores contain widely varying (Al2O3 + TiO2) (0.28-5.48 wt%), Zr (3.0-83 ppm) and Hf (< 0.2-2 ppm), indicating a terrigenous clastic material input. Detrital contamination is minor, as demonstrated by poor correlations of Y/Ho ratio vs. Zr, Th, Hf and Al2O3 contents, as well as Zr vs. TiO2. The ores contain seawater-like LREE depletion, positive La and Y anomalies, and occasional Eu enrichment, which suggest hydrothermal contributions. In addition, three samples show relatively high REY (604-1254 ppm), negative Eu anomalies (Eu/Eu*(PAAS) = 0.36-0.96) and MREE enrichment (Sm/ Yb-PAAS = 1.25-2.81), suggesting a probable fluvial input and shallow precipitation. The delta S-34 ratios range widely (3.2-32.8%o) and show an alternating and/or mixing source of two end-members. The seawater sulfate may have been an indispensable end-member, and the other end-member may have been the volcanic host rocks in the Bulunkuole Complex, which has likely contributed the ore-forming metals. Integrating evidence from regional geology, ore geology, and geochemistry, we conclude that the Zankan Fe deposit was the result of an Early Cambrian seafloor hydrothermal system.