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Developments in Earth system research have led to widespread interest in multi‐sphere interactions that may have controlled bauxite formation. Although karst bauxite ores are abundant in the Tethyan Metallogenic Domain (TMD), their genesis and distribution are not yet fully understood. This study utilizes the Random Forest (RF) model to analyze geochemical data sets compiled from three bauxite provinces in the Tethys, including the Mediterranean, Central Asian, and Chinese provinces. Meaningful variables among the provenance, paleolatitude and tectonic setting that affected the formation of the bauxite deposits are identified. The Logistic Regression model is used to verify the importance of various factors. Our study shows that when RF model achieves the best classifier performance, TiO2 is the variable that has the greatest impact on the model. TiO2 content is the highest in the Central Asian Province. The high TiO2 content in bauxites indicates a provenance of magmatic origine associated with the Subduction Provenance Zone. Bauxites with TiO2 content similar to that of the continental basement are derived from siliciclastic and carbonate rocks, identified as the Orogenic Provenance Zone. This study illustrates a novel link between geochemical compositions (TiO2 content) of bauxites, provenance and regional tectonic setting. Plain Language Summary: Abundant bauxite deposits formed in the Tethyan Metallogenic Domain are of great importance to bauxite research. However, previous studies generally focus on local bauxite occurrences formed over certain geologic time. A comprehensive understanding of the genesis and characteristics of bauxite deposits is hence essential. In this study, Machine learning methods (Random Forest and Logistic Regression) are applied to improve the understanding of Tethyan bauxite formation. Our research reveals that the TiO2 content in Tethyan bauxites is related to their provenance. The enrichment of TiO2 in bauxite deposits points to magmatic rock provenance that underwent subduction. Bauxites with a TiO2 content similar to that of continental basement are derived from siliciclastic and carbonate rocks exposed on orogenic belts. As such, this investigation elucidates a previously unexplored association between the geochemical characteristics (TiO2 content) of bauxite deposits, their provenance, and the regional tectonic context. Key Points: Two Provenance Zones in the Tethys Domain are proposed: Subduction Provenance Zone and Orogenic Provenance ZoneHigh TiO2 content in bauxites resulted from magmatic rocks of the Subduction Provenance ZoneTi in bauxites has the potential for tracing provenance and associated tectonic settings [ABSTRACT FROM AUTHOR]

The Lower Carboniferous Jiujialu Formation bauxite deposits of northern Guizhou Province, China, are a Kazakhstan subtype of karst bauxite deposits. The provenance of the Jiujialu Formation has long been debated, with uncertainty about the formation of the bauxite deposits. Here we report new geochemical data that indicate the affinity between the Lower-Middle Ordovician clastic rocks and argillaceous dolostones and the overlying Carboniferous bauxite deposits, all of which are characterized by high Al2O3, K2O, and ΣREE contents, flat post-Archean Australian shale (PAAS)-normalized REE patterns, and uniform immobile element ratios (TiO2/Al2O3, Nb/TiO2, and Zr/TiO2). Their similar detrital zircon age distributions further indicate the link between the bauxite deposits and the clastic rocks and argillaceous dolostones. Zircon age spectra of clastic rocks of the Lower Silurian Hanchiatien Formation in northern Guizhou match those of the bauxite deposits, with a maximum age peak at ∼980 Ma and other secondary age peaks, suggesting these clastic rocks may represent the provenance of the bauxite deposits. The youngest detrital zircons (∼445 Ma) occur only in the bauxite deposits and are probably sourced from K-bentonite beds of the Ordovician-Silurian transition. Our analyses indicate that the source materials of the bauxite deposits in the Jiujialu Formation are of mixed provenance: Lower-Middle Ordovician aluminosilicate rocks and argillaceous dolostones of the underlying strata, and Lower Silurian clastic rocks and K-bentonite from adjacent areas. A comparison of Early Carboniferous bauxitic provenances in northern and central Guizhou indicates that paleotopography was the major factor controlling the provenance of these bauxite deposits. [ABSTRACT FROM AUTHOR]

Bauxite deposits at the base of the Upper Permian Heshan Formation in the Youjiang Basin, South China, contain zircons with dominant age peaks at 263–262 Ma. During the Middle to Late Permian, the Youjiang Basin consisted of a number of isolated and attached carbonate platforms separated by inter-platform troughs. The bauxite deposits are limited to the isolated carbonate platform facies and are not present on attached carbonate platforms and inter-platform troughs. Discriminant plots based on the trace element composition of the zircons indicate a combination of within-plate/anorogenic and arc-related/orogenic sources. Geochemical and isotopic data suggest that the metallogenic materials of the bauxite deposit came from felsic volcanic rocks of the Emeishan Large Igneous Provence (ELIP) in South China and from the Truong Son volcanic arc located between the South China and Indochina cratons. The northwestern and southeastern parts of the Youjiang Basin received larger amounts of ELIP detritus and volcanic arc detritus, respectively. Coarser siliciclastic material in proximal attached carbonate platform and inter-platform trough settings was delivered by rivers, but finer siliciclastics that accumulated on distally located carbonate platforms in isolated deep-water areas was probably transported by wind. [ABSTRACT FROM AUTHOR]

Abstract: The rare earth element (REE) behavior and the related Ce anomalies of two profiles in bauxite of the Xinmo Syncline from Wuchuan–Zheng'an–Daozhen (WZD) area (Northern Guizhou, China) have been studied. The bauxite has diaspore as its main ore mineral, with lesser amounts of boehmite. Clay minerals, including kaolinite, chlorite, illite and smectite, are a minor mineral constituent. Furthermore, a significant Ce-bearing mineral parisite (Ce2Ca(CO3)3F2) is found near the bottom of the profiles. The bauxites have flat HREE (Er–Lu) shape relative to NASC, with variable weak depletion to weak enrichment patterns of LREE (La–Nd) and MREE (Sm–Ho) across the profiles. Strong positive Ce-anomalies (normalized to NASC) are also noticeable in the uppermost part of the profiles. Mass balance calculations suggest that an obvious fractionation exists among different REE and LREE are more mobile than HREE during the leaching process. In addition, the samples collected along a vertical profile show that a downward increase for the REE concentration and a remarkable enrichment of REE are found at the basement of the bauxite deposits. A similar downward increase trend is also observed in the values of LaN/YbN and GdN/YbN. The above characteristics show that the REE losses caused by leaching decreased gradually from the top to the bottom of the profile. The higher mobility of LREE in the profile might be due to differences in the stabilities of the original REE-bearing minerals during leaching process. The REE enrichment at the basement of bauxite deposits is attributed to the increase of pH around the parent rock as well as the presence of mineral ligands during bauxitization. The value of [Ce/Ce*]NASC decreased downwards, and increased again near the bottom of the profile. The positive Ce-anomaly in the uppermost part of the profile has been attributed to the redox change of Ce3+ to Ce4+ and the consequent precipitation of cerianite (CeO2). A decrease in the oxidation state downwards causes the decrease of the value of [Ce/Ce*]NASC. The formation of parisite near the bottom of the profile leads up to the increase in the value of [Ce/Ce*]NASC again. The precipitation of parisite may occur via reactions between the fluoride complexes (CeF2+ or CeCO3F0) and Ca2+ and HCO3 −. [Copyright &y& Elsevier]

Geomorphology is an important control on the formation of bauxite. However, geomorphological research on bauxite deposit formation is usually hampered by the lack of systematic detailed data collection. This study focuses on the Wuchuan–Zheng'an–Daozheng (Wu–Zheng–Dao) area of northern Guizhou Province, South China, an area containing bauxite deposits of the Dazhuyuan Formation. These deposits formed during the early Permian in a period associated with the peak timing of the late Paleozoic Ice Age (LPIA). This study used data from 329 drillcores within the Dazhuyuan mining district (DMD) to generate high-precision geomorphological reconstructions for the period of bauxite formation. This includes a series of contour maps showing the total thickness of the bauxite deposit, ore grades, the thickness of Lower (bauxitic claystone) and Upper (bauxite ore) members of the bauxite formation, and the distribution of different types of bauxite ore. These maps indicate that thicker deposits of bauxite are concentrated in deep depressions, whereas no bauxite is found in highly elevated erosional regions. High-grade bauxite ores, including clastic, oolitic, and porous types of mineralization, are located within depressions or in gently sloping areas, whereas low-grade bauxite deposits, including massive bauxite and bauxitic claystone mineralization, are located at the bottom of depressions or are present as thin units within uplifted areas. The geochemistry of the drillcore samples from the study area indicates that leaching is the main control on bauxite ore quality in the study area. Finally, a low groundwater table and water-permeable underlying units provide good drainage, which also contributes to the generation of high-grade bauxite ores. • Geomorphological reconstruction in the Dazhuyuan Mining District, South China • Leaching process rebuilding based on geochemical profiles • Formation model for the early Permian bauxite deposit of the Dazhuyuan Formation [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Carboniferous bauxite deposits in the SW South China Craton were formed in karstic depressions. • Formation processes of Early Carboniferous bauxite deposit were reconstructed. • Paleosalinity proxies indicate that bauxite deposits formed in the alternant freshwater and seawater environments. The Carboniferous karstic bauxite-bearing rock series within the Jiujialu Formation were widely distributed in central Guizhou, South China, with a prominent enrichment of ferrous clay materials at the lower part and fluctuations of Al contents at the upper part of those deposits. Yet, the evolution, distribution and formation mechanism of those bauxite ore-bearing rock series require further investigation. We used thickness data from ∼ 800 drillcores in central Guizhou to generate a high-precision paleo-geomorphological reconstruction of the study area, which reveals a series of karstic depressions from Southwest to the Northeast on a coastal karstic plain. Based on a typical drillcore of ZK47-12 located at a karstic depression, a relatively complete depositional records of bauxite deposits in the Jiujialu Formation have been yielded. The study bauxite deposit contains the lower Fe-rich layer and upper Al-rich layer. Within Al-rich deposits, bauxite ore comprises Al-bearing minerals including diaspore, boehmtie, with slight amounts of Fe-bearing and clay minerals, while bauxitic claystone yields higher contents of clay minerals. And Fe-rich layers comprise Fe-bearing minerals (mainly for chamosite). Geochemistry of the drillcore samples and mass changes reveal strong losses of most mobile elements, relative enrichment of Al within the bauxite ores and enrichment of some trace elements and REEs within claystones, caused by leaching process. Mineralogical and geochemical cycles within the upper Al-rich layer directly link with variations of the groundwater table (GWT) during the bauxitization in central Guizhou. The B content and B/Ga ratios indicate that the Jiujialu Formation in central Guizhou contains variations of paleosalinity, this evidence further supports that the fluctuations of GWT may cause by the Early Carboniferous sea-level changes. Our new data indicate that multiple factors control the formation of the Carboniferous bauxite deposits in central Guizhou. Paleo-geomorphological features of a series of karstic depressions upon the underlying carbonate rocks providing deposition space, tropical climate near the paleo-equator contributing to the weathering process, frequent fluctuation of groundwater table enhancing or releasing the intensity of leaching process, glacio-eustatic cycles promoting karstification and driving the fluctuations of GWT, and input of seawater influencing the intensity of leaching process during bauxitization. [ABSTRACT FROM AUTHOR]

Abstract The late Paleozoic Era was an interval of major tectonic and climatic changes, including formation of the supercontinent Pangea and the ~60-Myr-long Late Paleozoic Ice Age (LPIA). Although bauxite formation declined globally from the Carboniferous to the Permian in conjunction with global cooling, it was an interval of widespread bauxite formation in China. In South China, (1) the Jiujialu Formation bauxite deposits in central and northern Guizhou (Zunyi area) are of early-middle Visean age; (2) the Dazhuyaun Formation bauxite deposits in northern Guizhou (Wuchuan–Zheng'an–Daozheng area) to southern Chongqing (Nanchuan area) and southeastern Guizhou (Fuquan–Kaili area) are of Late Pennsylvanian–Early Permian age; and (3) the Heshan Formation bauxite deposits in western Guangxi to Yunnan are of Middle–Late Permian age. In North China, the Benxi Formation bauxite deposits are of Late Mississippian–Middle Pennsylvanian age. The contrasting trends in bauxite metallogenesis between China and the rest of the world imply different climatic patterns in the eastern Tethys (high annual humidity with seasonal dryness) and Pangea (aridification). This hypothesis is further supported by differences in the chemical index of alteration, or CIA (>80 in the eastern Tethys vs. ~50 in western Pangea), and in paleotemperatures (mean annual temperature, or MAT = ~20 °C in the eastern Tethys vs. ~4 °C in western Pangea) determined from Permo-Carboniferous siliciclastic deposits. Permo-Carboniferous bauxite deposits in South China formed in coastal plain and coastal karstic depression environments, in which the position of the groundwater table was related to sea-level changes. During the late Paleozoic, high-frequency eustatic fluctuations caused by waxing and waning of Gondwana icesheets controlled sedimentation in these coastal depositional systems, leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose- and phreatic-type bauxite formation. The results of the present study show that, during interglacial stages, lateritization resulted from high p CO 2 , high sea-level and groundwater-table elevations, low precipitation, and limited vegetation cover, whereas during glacial stages, bauxitization of these ferralitic weathering products was promoted by low p CO 2 , low sea-level and groundwater-table elevations, high precipitation, and more extensive vegetation cover. Thus, a unique combination of geographic, climatic, and eustatic factors accounted for widespread formation of bauxite in South China during the LPIA. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Lower Carboniferous Jiujialu Fm at Zunyi, northern Guizhou, contains 110 m of Kazakhstan-subtype karst bauxite deposits. • Alternating bauxite ore and bauxitic claystone layers having different petrological, mineralogical and geochemical compositions. • A total of seven cycles developed in response to fluctuating groundwater table levels, controlled by LPIA glacio-eustasy. Abstract The Lower Carboniferous Jiujialu Formation bauxite deposits at Zunyi, northern Guizhou are distinguished by their great thickness (to 110 m) and cyclic alternation of bauxite ore and bauxitic claystone layers. These features are typical of the Kazakhstan subtype of karst bauxite deposits, although the genesis of this type of deposit is poorly understood. Here, we undertook a petrological, mineralogical, and geochemical study of the Zunyi deposit in drillcore ZK5600 to gain insights into its formation history. The Zunyi profile contains seven bauxite cycles, as recorded by petrological, mineralogical and geochemical features, indicating a multistage formation history. Each cycle is composed of a lower bauxitic claystone layer and an upper bauxite ore layer. The bauxite ore is characterized by high Al 2 O 3 , high Al-mineral (diaspore), and low SiO 2 content. Positive Ce anomalies, high CIA values (>90), and strong depletion of major elements indicate that the bauxite ore formed through intense chemical weathering and leaching in a well-drained soil environment. The bauxitic claystone is characterized by relatively lower Al 2 O 3 and higher SiO 2 and clay mineral (mostly illite) content. This lithology exhibits both negative and positive Ce anomalies, moderate CIA values (70–80), and enrichment of some elements (e.g., Fe, K), indicating formation through moderate chemical weathering in a poorly drained soil environment. Secular variations in chemical weathering intensity and soil drainage conditions were linked to regional hydrologic changes. During the early Carboniferous, the Zunyi area was located in a karstified coastal upland setting, and its hydrologic system was affected by glacio-eustatic fluctuations. High groundwater table elevations during eustatic highstands led to formation of bauxitic claystone layers, whereas low groundwater table elevations during eustatic lowstands led to formation of bauxite ore layers. [ABSTRACT FROM AUTHOR]

[Display omitted] • New zircon U-Pb age and Hf isotope data from bauxite deposits in Adria and Sardinia, Italy. • Bauxite deposits in Sardinia show a parental affinity of Variscan metasedimentary basement. • Bauxite deposits in Adria were mainly supplied from coeval volcanic materials. • Diversity of provenances in bauxite deposits may cause differences in geochemical composition. Bauxite deposits in Italy mainly distribute in Sardinia and Adria regions within Cretaceous carbonate sequences. Parental affinity of Italian bauxite deposits has long been a controversial problem. At least four potential sources have been proposed: (1) Cretaceous debris and autochthonous marlstones; (2) alluvial sheets from the weathered Variscan basement; (3) weathering materials from North Africa and (4) Cretaceous bimodal volcanism in the Dinaric and Carpatho-Balkan orogenic belts. In this study, a total of 374 detrital zircon U-Pb ages and 86 Hf isotope values have been acquired from Cretaceous bauxites of Sardinia and Adria regions. Combining with the published geochemical data, provenances of Cretaceous bauxite deposits in Sardinia and Adria regions have been discussed. In bauxite deposits of Sardinia, dominant Early Paleozoic aged zircon grains (main age peaks at 291 – 295 Ma, 454 – 465 Ma, and 582 – 639 Ma) and their various Hf isotope compositions (εHf(t) = +9.61 to −5.66) indicate a parental affinity of Variscan metasedimentary basement. As a contrast, bauxite deposits in Adria show abundant Jurassic – Cretaceous (93 – 178 Ma) zircon grains with negative εHf(t) values (-13.75 to −4.61), demonstrating significant supply from coeval volcanic materials. Cretaceous bauxite samples from Sardinia and Adria shed light on paleogeographic restoration and tectonic evolution of Alpine Tethys. Began in Early Cretaceous, Sardinia was affected by uplift due to the subduction between Ligurian oceanic crust and the Iberia plate. The Mesozoic carbonate sequence were eroded and the underlying Variscan basement was exposed in the area from Sardinia to the Massif Meridional, provided weathering materials for bauxitization. Late Cretaceous witnessed the further NNE-trending subduction of the Adria Plate to the West Vardar oceanic plate, where calcalkaline igneous rocks and volcanic ashes from Dinarides supplied windborne weathering materials to carbonate platforms in Adria. Particularly, provenance difference between the bauxite of central-southern Apennine and Sardinian reveals that the hosting carbonate sequence in Apennine was not located on the Sardinia shelf before the Cenozoic tectonism in the south Mediterranean realm. Diversity of provenances in bauxite deposits from Sardinia and Adria may cause differences in geochemical composition and further influence qualities of bauxite ore in two regions. [ABSTRACT FROM AUTHOR]

Two types of bauxite deposits have been discovered in the Fusui area, Guangxi Province, South China. The original Permian bauxite occurs on the unconformity between the Middle Permian Maokou Formation and the Upper Permian Heshan Formation. The Salento-type (or karstic accumulational) bauxite is composed of the Quaternary incompact sediments that transformed from the original Permian bauxite. Samples were collected from two drilling cores and two profiles in study area, and field observations and mineralogical and geochemical analyses are integrated to reconstruct the metallogenic process from the original Permian bauxite to the Quaternary Salento-type bauxite. In the Permian lateritization and bauxitization, alkali metals and alkali earth metals are preferentially dissolved and removed from the parent rocks due to the intense chemical weathering; other major elements from the original profile are also depleted, as shown by the mass-change calculation result. Elements with a low mobility (e.g., Ti, Zr, Cr, Nb and V) are positively correlated with Al. When the bauxite deposit is affected by the modern groundwater system in the near-surface environment, the elements in the deposit display varied mobility due to the leaching intensity and the drainage conditions. After the bauxite ore horizons are exposed in the surface environment, impurities (primarily Fe and Si) are removed from the profiles, and Al is enriched; the clay minerals (kaolinite and chlorite) in the ores convert into aluminum minerals (boehmite and diaspore). When the exposed original bauxite orebodies break down and accumulate as bauxite gravel in the modern karstic depressions, the Salento-type bauxite deposits appear, and the ore quality is further improved. The intensity of the leaching process and the drainage conditions are the most important factors that control the ore quality during the ore-forming process that converts the original bauxite into the Salento-type bauxite. [ABSTRACT FROM AUTHOR]