Geochemistry and protolith restoration of the metamorphic rocks from the Sansegou Pb-Zn mining district in Dulan, Qinghai

The examination of petrology and geochemistry of the metamorphic rocks from the Sansegou Pb-Zn mining district in Dulan, Qinghai has mirrored that the protolith of the Jinshuikou Group mesometamorphic to hypometamorphic rock series are assembled by a succession of volcanic-dominated volcanic-sedimentary associations containing volcanic rocks, volcanic rocks intercalated with sedimentary rocks, and sedimentary rocks. The volcanic rocks consist of crystal tuff, lithic tuff, breccia tuff and tuffaceous sandstone, indicating the calc-alkaline rock series. The sedimentary rocks are made up of marl. The tectonic setting of the volcanic rocks should belong to the active continental margin, and eruption depths range between 120 and 250 km, with an average of 180 km. The metamorphic rocks are characterized by SiO₂ contents ranging from 59.32 to 79.43%, Al₂O₃ contents from 12.21 to 16.8%, σ values from 0.18 to 2.64, AR values from 1.53 to 3.54, TiO₂ contents from 0.08 to 0.88%, ΣREE (not including Y) from 92.44 to 337.33, LREE from 81.10 to 305.48, and HREE from 9.59 to 55.65. The LREE and HREE are highly differentiated, and the HREE are heavily depleted. The REE distribution patterns display right-leaning curves. δEu values vary between 0.2 and 1.04, whereas δCe values vary between 0.81 and 0.86.