Tungsten enrichment processes in peraluminous granites of the Chinese Altai

• To evaluate the processes for W enrichment in peraluminous granites, three representative intrusions in the Chinese Altai were investigated. • Both magmatic and hydrothermal processes can promote W enrichment in granites, but hydrothermal alteration by F-rich fluid is more effective than fractional crystallization. • Re-melting of a mica-rich igneous protolith can lead to pronounced W enrichment in the resultant granites. To evaluate the processes facilitating the W enrichment in peraluminous granites, three peraluminous granitic intrusions in the Chinese Altai have been investigated. The Yilaike pluton and Tielieke batholith are dominated by biotite granite with subordinate muscovite granite, while the Shangkelan pluton is of A-type granite characteristics and comprised mainly of muscovite granite and topaz-albite granite. The Yilaike pluton, Tielieke batholith and Shangkelan pluton were generated in Late Ordovician (444–447 Ma), Early Devonian (402–406 Ma) and Late Triassic (204 Ma), respectively and possess high-K calc-alkaline and peraluminous composition as well as low oxygen fugacity. All the intrusions underwent fractional crystallization and hydrothermal processes of various extents, and the Shangkelan pluton, among others, is the most striking in hydrothermal alteration. The Yilaike and Tielieke granites have similar εNd (t) (−4.9 to + 0.3 and −2.4 to + 0.7, respectively) and whole-rock δ 18 O (+11.6 to + 15.3 ‰ and + 10.4 to + 13.2 ‰, respectively) values, consistent with an origin of the Early Paleozoic metasedimentary rocks in the Chinese Altai. The Shangkelan granites possess incompatible element ratios and trace element variation trends different from those of the Yilaike and Tielieke granites, and their relatively radiogenic εNd (t) (−0.1 to + 0.4) values, low δ 18 O (+10.1 to + 12.0 ‰) ratios and F-rich muscovite indicate that the Shangkelan granites were probably formed by partial melting of a biotite-rich igneous protolith. The biotite granite of the Yilaike pluton and Tielieke batholith contains low W (0.8–1.2 ppm) equivalent to that of the Early Paleozoic metasedimentary rocks, suggesting a limited efficiency for W transport from the source into partial melts. A pronounced rise of W content in the Yilaike and Tielieke granites (up to 11 and 35 ppm, respectively) occurred during the evolution towards muscovite granite, indicating the contribution of magmatic and hydrothermal processes. The Mesozoic Shangkelan pluton contains the highest W (up to 235 ppm) among these intrusions. The most striking W enrichment occurred in a pseudo-greisen stage characterized by formation of F-rich Li muscovite, which reflects the effect of hydrothermal alteration. Meanwhile, the lowest W concentration (ca. 8 ppm) of the Shangkelan pluton is remarkably higher than that of the Early Paleozoic metasedimentary rocks, implying a relatively high initial W content in its igneous protolith that probably formed in previous crustal reworking. The study demonstrates that repetitively melting of an immature crustal source can significantly increase the W abundance in the resultant peraluminous granites.