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 SiO2 contents in the range of 55.86–63.80 wt. %, low TiO2 contents of 0.36–0.64 wt. %, P2O5 contents of 0.04–0.11 wt. % and Al2O3 contents of more than 15 wt. %. They are characterized by relatively high (K2O + Na2O) values of 9.72–15.51 wt. %, K2O/Na2O ratios of 2.42–3.64 wt. % and Rittmann indexes (σ = [ω(K2O + Na2O)]2/[ω(SiO2 − 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 (257–205 Ma). 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.
Highlights
China’s reserves of rare earth metals account for up to 87% of the world total, while the reserves of niobium metals are relatively scarce, which only account for 18.19% of the world [1]
Few Nb and Ta deposits had been discovered in NE China, which was attributed to the restricted prospecting and research at present
Numerous rare earth deposits associated with alkali rocks represented by Ba’erzhe have been recently discovered in NE China [3] and rare metals such as Nb and Ta occurred in alkaline intrusive rocks have received extensive attention
Summary
China’s reserves of rare earth metals account for up to 87% of the world total, while the reserves of niobium metals are relatively scarce, which only account for 18.19% of the world [1]. Geological survey in recent years have shown that most of the niobium (Nb) and tantalum (Ta) deposits are distributed in south China, such as Hunan, Guangdong, Shanxi and Jiangxi Province in which host. Minor similar deposits have been sporadically discovered in the Panzhihua-Xichang district, northern Xinjiang and Inner Mongolia [2]. Few Nb and Ta deposits had been discovered in NE China, which was attributed to the restricted prospecting and research at present. Numerous rare earth deposits associated with alkali rocks represented by Ba’erzhe (inner Mongolia province) have been recently discovered in NE China [3] and rare metals such as Nb and Ta occurred in alkaline intrusive rocks have received extensive attention. The Saima deposit, an niobium deposit with medium-scale prospecting potentials, is located about
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