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Late Carboniferous bauxite is widely developed on the North China Craton (NCC), and is referred to as the "G" layer bauxite. The bauxite ores of the southern NCC are closely related to the tectonic evolution of the NCC and its neighboring North Qinling Belt (NQB) to the south. In this study, based on the geological and mineralogical observations, we used the U–Pb and Hf isotopes of detrital zircons and chemical compositions of detrital rutiles from the Gunziying and Shibanhe bauxite deposits, along the southern margin of the NCC to study the metallogenic process of bauxite ores and their tectonic implications. One and two bauxite ore layers were observed in the Gunziying and Shibanhe bauixte deposits, respectively. The bauxite ore is dominated by diaspore, illite, anatase, kaolinite, pyrite, zircon, and rutile. Analyses of detrital zircons revealed that the largest group (∼432–515 Ma, at a peak age of ∼450 Ma) is spread throughout the Late Carboniferous bauxite deposits, with εHf(t) values of −5.7–21.4, similar to the zircons from the NQB. Similarly, the detrital zircons with peak ages of ∼950 Ma and age clusters at ∼1.1 Ga, ∼1.3 Ga, and ∼1.8 Ga as well as those ranging in age from 635 to 797 Ma, also exhibited εHf(t) values similar to the zircons from the NQB. In addition, the results suggested that 62 (73%) and 75 (88.2%) of detrital rutiles showed metapelitic protoliths and amphibolite/eclogite facies temperatures, respectively, while 23 (27%) and 10 (11.8%) exhibited metamafic protoliths and granulite facies temperatures, respectively. Based on the results above, we propose that the provenance of the bauxite ores on the southern margin of the NCC is primarily from the NQB. The dominant contributors were the Neoproterozoic Kuanping Group and the Meso–Neoproterozoic Qinling Group. The Archean-Proterozoic metamorphic rocks in the paleo-uplifts of the NCC were also likely involved in the bauxite formation. A probable outline of the bauxite-formation process on the southern NCC, former weathered residuals and subsequent deposition, is proposed; and a reasonable interpretation that the NQB was accreted to the NCC in the Late Carboniferous and formed a northward lying slope basin within the NCC, is supported. Image 1 • New constraints on the source of the NCC bauxite ores are proposed. • Mainly material transport from the North Qinling and Kuanping Group. • Bauxitic formation most likely weathered residuals and deposited. • Late Paleozoic Tectonics resulted in the "G" bauxites throughout the NCC. [ABSTRACT FROM AUTHOR]

Above two billion tons of bauxite were formed during the exposure of the North China Craton (NCC) in 445–300 Ma. Mineralogical, geochemical, and isotopic analyses of karstic bauxite deposits in the Sanmenxia area situated within southern NCC were conducted to explore the genetic processes of Carboniferous bauxite. The bauxite contains three layers: a lower Fe-bearing claystone layer, a middle bauxite ore layer, and an upper claystone layer. Fe-bearing claystone is dominated by illite and hematite in the uplift and illite, siderite, and pyrite in the depression. Bauxite ore is composed of diaspore, illite, pyrite, and anatase, and the upper claystone consists of illite, diaspore, and anatase. Distinct pyrite δ34S values (11.7–15.2 and −11.5 to 1.0), illite (87Sr/86Sr) i (0.711917–0.713588 and 0.708000–0.711057) and ε Nd (t) (−12.2 to −11.4 and −11.8 to −9.7) values, and the immobile elemental ratios were obtained between the lower Fe-bearing claystone and upper bauxite ore and claystone. Together with chemistry of detrital rutile, it is denoted the Fe-bearing claystone was formed from the underlying limestone, whereas the bauxite ore and claystone were derived from both igneous rocks along craton margin and regional Precambrian metamorphic rocks. The visible microorganisms and wide development of framboidal pyrite with negative δ34S within the bauxite ore provide evidences of microbial activity during bauxite formation. Bio-leaching process after the deposition of allochthonous source materials caused the downward migration of ions (Al3+, Fe2+, Ti4+, REE3+, etc.). These ions encountered an alkaline and reducing condition in the karstic depression, forming diaspore, pyrite, and anatase and REE enrichment at the bottom of bauxite ore. This large input of raw materials, warm and humid climate, and microorganisms led to large-scale bauxite formation in the NCC during late Carboniferous. • Karstic bauxite in the karstic depressions in the North China Craton belongs to a new type of terrestrial sedimentation. • The ore-forming source materials were mainly derived from igneous and metamorphic rocks along craton margin. • Sufficient source materials, suitable environment, and post-deposition effect jointly led to massive bauxite formation. [ABSTRACT FROM AUTHOR]