No abstract

The Saima deposit is a newly discovered niobium deposit which is located in the eastern of Liaoning Province, NE China. Its mineralization age and geochemical characteristics are firstly reported in this study. The Nb orebodies are hosted by the grey-brown to grass-green aegirine nepheline syenite. Detailed petrographical studies show that the syenite consists of orthoclase (~50%), nepheline (~30%), biotite (~15%) and minor arfvedsonite (~3%) and aegirine (~2%), with weak hydrothermal alteration dominated by silicification. In situ LA-ICP-MS zircon U-Pb dating indicates that the aegirine nepheline syenite was emplaced in the Late Triassic (229.5 ± 2.2 Ma), which is spatially, temporally and genetically related to Nb mineralization. These aegirine nepheline syenites have SiO 2 contents in the range of 55.86-63.80 wt. %, low TiO 2 contents of 0.36-0.64 wt. %, P 2 O 5 contents of 0.04-0.11 wt. % and Al 2 O 3 contents of more than 15 wt. %. They are characterized by relatively high (K 2 O + Na 2 O) values of 9.72-15.51 wt. %, K 2 O/Na 2 O ratios of 2.42-3.64 wt. % and Rittmann indexes (σ = [ω(K 2 O + Na 2 O)] 2 /[ω(SiO 2 − 43)]) of 6.84-17.10, belonging to the high-K peralkaline, metaluminous type. These syenites are enriched in large ion lithophile elements (LILEs, e.g., Cs, Rb and Ba) and light rare earth elements (LREEs) and relatively depleted in high field strength elements (HFSEs, e.g., Nb, Zr and Ti) and heavy rare earth elements (HREEs), with transitional elements showing an obvious W-shaped distribution pattern. Based on these geochronological and geochemical features, we propose that the ore-forming intrusion associated with the Nb mineralization was formed under post-collision continental-rift setting, which is consistent with the tectonic regime of post-collision between the North China Craton and Paleo-Asian oceanic plate during the age in Ma for Indosinian . Intensive magmatic and metallogenic events resulted from partial melting of lithospheric mantle occurred during the post-collisional rifting, resulting in the development of large-scale Cu-Mo mineralization and rare earth deposits in the eastern part of Liaoning Province.

Central Jilin is tectonically subordinate to the Lesser Xing'an Range–Zhangguangcai Range polymetallic metallogenic belt, an important region for Cu–Mo prospecting in NE China. Dozens of large‐scale molybdenum deposits, including Fu'anbu, Chang'anbu, Jide, and Dashihe, have been recently discovered in Central Jilin, whereas porphyry Cu or Cu–Mo deposits have not been found to date. One such example of an intracontinental porphyry Cu–Mo deposit is the Chang'anbu Cu–Mo deposit in Shulan, Jilin Province, hosted in early Yanshanian rocks. Here in this contribution, we described detailed geology based on our field observation and conducted a comparative study on the metallogenic epoch and the ore‐forming sources of the Chang'anbu Cu–Mo deposit by using zircon U–Pb dating and H–O–S–Pb stable isotopes. We propose that the Chang'anbu deposit is rare in the Lesser Xing'an Range–Zhangguangcail Range metallogenic belt and differs from other porphyry deposits that consist solely of Mo, indicating a unique mechanism of metallogenesis. Zircon U–Pb ages indicate emplacement of a granite pluton which is the main metallogenetic rock body during the Early Jurassic (182.10 ± 1.20 Ma). The pluton is spatially and temporally associated with Cu–Mo mineralization and led to large‐scale porphyry Cu–Mo mineralization during the early Yanshanian. Sulphur, Pb, H, and O isotope data suggest that magma generated by subduction of the Paleo‐Pacific oceanic crust was the main ore‐forming source of this deposit (206Pb/204Pb = 18.046–18.734; Pb207/Pb204 = 15.502–15.655; δ34S = 0.3–2‰; δDV–SMOW = −102.2–93.4‰; δ18OV–SMOW = 9.1–11.6‰). The Chang'anbu porphyry Cu–Mo deposit is representative of large‐scale polymetallic metallogenic events in Central Jilin that resulted from magmatism related to crust and mantle melting during the early Yanshanian.

Many data have been reported from the Early Palaeozoic subduction complex belt and accretionary arc to the south of the Solonker‐Xar Moron‐Changchun‐Yanji Suture (SXCYS) zone. However, as the suture is covered to the east by the Mesozoic–Cenozoic Songliao Basin, there have yet been no related reports about the Early Palaeozoic igneous rocks in this area. The authors discovered an Early Palaeozoic granitoid intrusion in the Fangjiatun area, northern Liaoning, and performed petrologic, geochemical, zircon U–Pb dating and Hf isotopic analyses on it. Zircon SHRIMP U–Pb dating results show that the intrusion formed at 437–432 Ma, that is, in the late stage of the Early Silurian. Petrogeochemical analysis indicates that the intrusion records 63.14%–66.45% SiO2, with Na2O/K2O ratios of 1.01–6.12 and magnesian index (Mg#) values of 32.42–40.82. The REEs show a certain degree of LREE/HREE fractionation and slightly lower ΣREE contents. The trace elements are relatively enriched in Rb, Ba, Th, K, and Sr (large‐ion lithophile elements [LILEs]) and depleted in Nb, Ta, P, and Ti (high‐field‐strength elements [HFSEs]), displaying continental magmatic arc characteristics. The rocks have high Sr mass fractions, low Y and Yb mass fractions, and high Sr/Y ratios, which are consistent with the geochemical signatures of typical adakites. Zircon Hf isotopic analyses indicate that their εHf(t) values range from 0.29–6.56, reflecting the relatively depleted signatures of the source area. Based on its occurrence location and emplacement time, the intrusion is interpreted to have been produced by tectonic thermal events during the subduction of the Palaeo‐Asian oceanic crust beneath the northern margin of the North China Craton (NCC), thus reflecting the existence of an Early Palaeozoic continental marginal accretionary arc in the eastern segment of the NCC along the south of the SXCYS and provide new evidence for the tectonic evolution of the northern margin of the NCC in the Early Palaeozoic.