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Liang, Z.; Ji, D.; Zhang, X.; Lingyun, W.; Zhang, T.; Li, S.; Yong, J.; Luo, J.; Liu, Y., and Zeng, J., 2023. Carboniferous oceanic basin sediment-gravity flows in the margin of the Junggar Basin, NW China: Characterisation and implications for hydrocarbon potential and evolution pacing. Journal of Coastal Research, 39(5), 890–906. Charlotte (North Carolina), ISSN 0749-0208. Several Carboniferous deep-marine-sandstone reservoirs have recently been discovered in the Junggar Basin, NW China. These reservoir sandstones were deposited by sediment-gravity flows that occurred on the continental slope of the Junggar Basin, and they have high hydrocarbon exploration potential. In this study, careful observations and petrological and geochemical analyses of samples from outcrop sections of Carboniferous rocks from the Junggar Basin were conducted to establish the deep-marine sedimentary characteristics, depositional environments, and mechanism of these gravity-flow deposits, as well as a sedimentary model for their occurrence. The deep-marine, gravity-flow deposit types include those of turbidity currents, debris flows, and slumps. The debris-flow deposits can be divided into pebbly debris-flow deposits and sandy debris-flow deposits. Results allow the relationship between the type and nature of gravity flows and ocean basin evolution to be established. During the early Carboniferous, the ocean basin had sufficient space to accommodate incoming sediment, and the sediment transport distance was long. The gravity-flow sediments of this period are dominated by sandy debris-flow deposits and turbidity-flow deposits characterised by thin individual layers but thick accumulations of multiple deposits. With continuous narrowing of the oceanic basin during the late Carboniferous, the basin had a smaller accommodation space. The main types of gravity-flow deposition during this period were pebbly and sandy debris flows, with rare thin turbidity-flow deposits. These deposits were coarser grained than their early Carboniferous equivalents, and their cumulative thicknesses were smaller. The results of the study provide insights into the prediction of deep-marine reservoir sandstones and the distribution of hydrocarbons in the Junggar Basin. [ABSTRACT FROM AUTHOR]

[Display omitted] (a) μ-XRF mapping and Nb content distribution maps of dolomite-type Nb-REE-(Fe) ore, displaying the representative magmatic Nb mineralization; (b) μ-XRF mapping and Nb content distribution maps of fluorite-type (banded) Fe-REE-Nb ore, showing the typical hydrothermal Nb mineralization; (c) back-scattered-electron images of different kinds of niobium-bearing minerals in Bayan Obo Fe-REE-Nb deposits; (d) niobium-bearing mineral compositions (Wt %) of various Fe-REE-Nb ores in Bayan Obo deposit. • The Bayan Obo Fe-REE-Nb deposit contains huge amount of niobium resources. • Niobium occurrence and typical mineral compositions of different types of Fe-REE-Nb ores are determined. • Hydrothermal process plays an important role in controlling the migration and mineralization of niobium. The Bayan Obo Fe-REE-Nb deposit is the largest rare earth deposit in the world, which also contains huge amounts of niobium resources, hosting 83% of industrial reserves in China. The previous researches focused on the REE mineralogy, mineralization age and REE source, whereas only a few studies paid attention to the genesis of Nb mineralization. The REE and Nb might present systematic mineralization difference as the degree of REE and Nb mineralization is distinct in different types of ores in host dolomite. Many complicated factors such as low grade, fine-grained dissemination and complex mineral composition are the main obstacles to hinder the effective utilization of Nb. In this study, a variety of niobium-bearing minerals have been identified, including aeschynite, fergusonite, columbite, pyrochlore, fersmite, baotite, and ilmenorutile. The distribution regularity of niobium in various types of ores in the giant Bayan Obo Fe-REE-Nb deposit is asserted. In massive Nb-REE-Fe ore and dolomite-type Nb-REE-(Fe) ore, niobium-bearing minerals are represented by columbite, while niobium mineralization in aegirine-type Nb-REE-Fe ore is characterized by pyrochlore and aeschynite. The major niobium-bearing mineral in the riebeckite -type Nb-REE-(Fe) ore and fluorite-type (banded) Nb-REE-Fe ore is aeschynite, and major niobium-bearing mineral in biotite-type Nb-REE-Fe ore and diopside-type niobium ore is fergusonite. The μ-XRF results and SEM observations display that columbite contains dolomite, magnetite and monazite inclusions and show obvious genetic links with apatite. Columbite, apatite and magnetite in massive Fe-REE-Nb ore and dolomite-type Nb-REE-(Fe) ore occur at same mineral generation, both having magmatic origins. Pyrochlore from aegirine-type Fe-REE-Nb ore also showsclose genetic relationship with apatite, which is formed by fractional crystallization during the magmatic stage of carbonatite. Aeschynite in fluorite-type (banded) Fe-REE-Nb ore, riebeckite-type Nb-REE-(Fe) ore, and fergusonite in biotite-type Fe-REE-Nb ore and diopside-type niobium ore are large in grain size and have hydrothermal origins. Moreover, intensive Nb mineralization in a series of ores related to fluoritization and alkali-metasomatism demonstrates the critical role of hydrothermal process in niobium enrichment in the Bayan Obo deposit. Fluid-rock interaction leads to the generation of alteration minerals, such as fluorite, biotite and aegirine, and contributes to a slash of K, Na and/or F in hydrothermal fluids, facilitating precipitation of niobium-bearing minerals. By using scanning electron microscope (SEM), X-ray energy dispersive analysis (EDS), Micro-XRF spectral analysis (μ-XRF) and TESCAN Intergrated Mineral Analysis (TIMA), detailed mineralogical study on niobium occurrence and typical niobium mineral compositions in various types of Fe-REE-Nb ores was conducted to provide an important reference for mineral processing and niobium prospecting and give a deeper understanding of the niobium anomalous enrichment mechanism of the Bayan Obo Fe-REE-Nb deposit. [ABSTRACT FROM AUTHOR]