Abstract:

The Lower Cretaceous in southern Tibet mainly consists of the submarine fan system, which is widely developed in Jiangzi Basin. Near the Shalagang antimony deposit, which is the biggest in southern Tibet, a segment of the submarine fan was silicified.According to the mineralogy and geochemistry features, the silicified mudstones and limestones were identified Besides the quartz, the albite was found in the silicified mudstones, but the silicified limestones contain only calcite without albite.The geochemical data show that the silicified mudstones contain relatively high content in Al₂O₃ and Na₂O，and reveal high value of ΣREE and distinctly δ(Eu) anomaly.These features indicate that the elements of the silicified mudstones are mainly derived from the source rocks. For the silicified limestones, the contents of the trace elements are related to the silicification, and four groups are identified to reveal the mobility of the trace elements.The values of ΣREE and LREE/ HREE are increasing with the growing of the silicification intensity.With these geological and geochemical features, it can be inferred that the fluids, which led to the silicification processes, are characterized by mid-low temperature, rich in SiO₂ and alkali material and metal elements.It is suggested that these SiO₂-rich fluids have close associations with the genesis of the antimony mineralization in this area.

Key words: Tibet, silicification, albite, trace element mobility, REE, antimony mineralization