Highly differentiated felsic granites linked to Mo mineralization in the East Kunlun Orogenic Belt, NW China: Constrains from geochemistry, and Sr-Nd-Hf isotopes of the Duolongqiarou porphyry Mo deposit

Abstract

The Mo deposits in the Kunlun-Qinling-Dabie orogen are mainly associated with porphyry or porphyry-skarn mineralisation in a collision or post-collision setting. However, collision-type Mo deposits that are related to granite and mineralization produced in magmatic systems remain poorly constrained. To better define the genetic relationship between the intrusions and Mo mineralization in collision setting, the geochronology, geochemistry, and Sr-Nd-Hf isotopes of the granodiorite and monzogranite in Duolongqiarou Mo deposit, East Kunlun Orogenic Belt (EKOB), NW China, are presented. Zircon U-Pb dating shows granodiorite and monzogranite ages of 237.6 ± 1.5 Ma and 236.8 ± 1.8 Ma, respectively, which is consistent with the molybdenite Re-Os weighted mean model age of 235.9 ± 1.4 Ma. This suggests that the granitic magma related to Mo mineralization at the Duolongqiarou formed during the Triassic (ca. 236 Ma). The ore-bearing monzogranites with high SiO2 contents (76.84–77.92 wt%) are peraluminous high-K calc-alkalic rocks, while the ore-barren granodiorites with low SiO2 contents (66.89–69.90 wt%) are metaluminous Na-rich calc-alkalic rocks. Both are enriched in large ion lithophile elements and light rare earth elements but depleted in high-field strength elements, which is characteristic of I-type granites. Ore-bearing and barren granites have similar εNd(t), εHf(t), and TDM2 age, indicating a similar magma source derived from partial melting of ancient Mesoproterozoic lower crustal components with involvement of mantle materials. The amphiboles of monzogranite show higher values of calculated pressures (average 122 MPa) and melt H2O content (average 5.7 wt%) than granodiorites, suggesting that monzogranites and granodiorites crystallized at different depths of the same magma chamber. Ore-bearing monzogranites show much lower contents of transition metals (e.g., Sc, V, and Cr), negative Eu anomalies (δEu = 0.32–0.46), and higher differentiation index values (94.52–96.92) compared to barren granodiorites. This suggests that high differentiation and fractionation promote Mo metal enrichment during magmatic evolution and subsequent formation of the magmatic-hydrothermal Duolongqiarou Mo deposit. The Duolongqiarou Mo deposit was formed in a collisional setting in response to the slab break-off of the EKOB Paleo-Tethys ocean. The results of this study combined with published data suggest that at least two generations of Mo polymetallic metallogenic events were observed in the Paleo-Tethys of the EKOB. This is very helpful to target porphyry Mo mineralization and guide regional exploration.