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The Late Permian coal measures in eastern Yunnan, western Guizhou, and central Guangxi are significantly enriched in critical metals that could serve as important supplements to conventional critical metal deposits in China. This study collected previous geochronological and geochemical data from the Late Permian coal measures to evaluate the distribution characteristics and enrichment factors of critical metals. Moreover, metallogenic models for critical metals were also developed. The results showed that Late Permian coal measures in Yunnan, Guizhou, and Guangxi provinces exhibited abnormal enrichment in Nb, Zr, and rare earth elements (REY, or REE if Y is excluded). The Emeishan mafic rocks and intermediate-felsic volcanic ash from the Truong Son orogenic belt underwent chemical weathering, with Nb and Zr selectively preserved in situ in the form of heavy minerals (e.g., rutile, zircon, and anatase), which subsequently led to the enrichment of Nb and Zr in bauxite and Al-claystone at the bottom of the Late Permian coal measures. Intermediate-felsic volcanic ash from the Emeishan large igneous province (ELIP) and the Truong Son orogenic belt supplied Nb, Zr, and REY for the middle and upper parts of the Late Permian coal measures. The intermediate-felsic mineral material of the coal measures in the intermediate zone, outer zone, and outside zone of ELIP are derived mainly from the ELIP, the mixture from ELIP and the Truong Son orogenic belt, and the Truong Son orogenic belts, respectively. Nb, Zr, and REY were leached by acidic aqueous solutions and from the parting and roof into underlying coal seams, where they deposited as authigenic minerals or adsorbed ions on organic matter during early coalification. [ABSTRACT FROM AUTHOR]

Research on the mineralogical and geochemical characteristics of altered end-Guadalupian basaltic volcanoclastic rocks can increase the understanding of the alteration history of the overlying stratabound Nb(Ta)-Zr(Hf)-REY-Ga mineralization in the Late Permian coal-bearing sequences. In this paper, based on petrographic observations in addition to XRD, XRF, and ICP-MS analyses, we present and discuss in detail the relationships between primary and secondary minerals and outline the distribution of major and trace element chemistry in the middle/Late Permian basaltic volcaniclastics from the ELIP's zone, western Guizhou, southwest China. The primary clastic suite consists of plagioclase-group minerals, clinopyroxenes, feldspathoids, spinels, and basaltic glasses. Fragments of mafic and, less commonly, felsic and alkaline volcanic rocks are minor components of the studied samples. The alteration products are represented by various chlorite-group minerals (including abundant chamosite), quartz, calcite, albite, analcime, barite, and pyrite, along with relatively minor amounts of titanite, sanidine, magnetite, rutile, and copiapite. The mineralogical and geochemical characteristics of the studied volcaniclastics provide strong evidence correlating them with the high-Ti basalt group, widely distributed within the inner Emeishan large igneous province (ELIP) and coeval rift zone of the middle and outer ELIP. After deposition, the volcaniclastics reacted with complex solutions including heated meteoric waters and were periodically infiltrated by seawater and ascending hydrothermal fluids. As a result, the primary volcanic rocks partly lost alkalis, titanium, silica, and most of the trace elements. These elements, especially the incompatible elements, were probably enriched in the overlying tuffaceous and coal-bearing sequences in the middle and outer ELIP. • Primary and secondary minerals of Emeishan basaltic volcaniclastics were presented. • The volcaniclastics reacted with complex solutions from various sources. • The primary volcanic partly lost alkalis, Ti, Si, and most of the trace elements. • The lost elements were probably enriched in the overlying sediments. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Danping bauxite is rich in critical metals such as Li, Ga, Zr, Sc, and REE. • There are significant differences in the enrichment characteristics of each critical metal. • Leaching and later adsorption of Li+ on clay minerals are critical to Li enrichment. • REE were enriched through pre-enrichment, re-enrichment and precipitation processes. Critical metals are indispensable for the global scientific and economic development, and their shortage has drawn attention to critical metal exploration in bauxite-related rocks. Bauxite deposits, especially karst-type ones, are usually enriched in critical metals like Li and REE (rare-earth elements La-Lu and Y). In this study, we analyzed the bauxite ore-bearing rocks at Danping (Guizhou, SW China) with a combination of XRF, ICP-MS, XRD, and SEM-EDS techniques, with the aims to investigate the distribution characteristics and enrichment mechanisms of the critical metals (e.g., Li, Ga, Zr, Sc, and REE). The bauxite ore layer at Danping is unconformably contacted with the underlying Huanglong Formation (Fm.) limestone or the Hanjiadian Fm. mudstone/shale, and the overlying Qixia Fm. limestone or Liangshan Fm. carbonaceous shale. Lithium is mainly enriched in the top and bottom of the bauxitic clay strata (abbrev. OBC and UBC, respectively). Gallium is enriched in all the bauxite layers, OBC and UBC. Zirconium is moderately enriched in the bauxite layer, whilst Sc is more enriched in the UBC and its nearby wallrocks (e.g., compact bauxite). REE are locally enriched in/around the basement, with the total REE content of the bauxite ore host being 33.3 to 3082 ppm. In situ analysis indicates that the bauxite-bearing rocks contain REE minerals, including bastnasite and xenotime. Moderate to strong lateritization likely plays a vital role in the different enrichments of critical metals, especially in the bauxite and kaolinitic bauxite zone. Physicochemical conditions of the mineralization are very complex. The Li enrichment may have been closely linked to the clay formation and enrichment, especially during the pre-lateritization and late-leaching stages. REE are mainly enriched in the lateritization stage, and then percolated downward via acidic leaching, where differentiation and re-enrichment occur. When REE migrate to an alkaline environment (caused by Huanglong Fm. limestone), bastnaesite precipitated readily, eventually forming REE-rich claystone and concentrated along the alkaline barrier of carbonate rock. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Danaopo sphalerite are characterized by enrichment of Cd and Ge, which incorporated into sphalerite are possibly controlled by substitutions of Zn2+ ↔ Cd2+ and 4Zn2+ ↔ Ge4+ + 2Fe2+ + □ (vacancy) • The C-O isotopes and REEs of ore-stage calcite indicate that the ore-forming materials have a mixed origin at Danaopo • The Danaopo deposit formed under a low-temperature and low f O2 reductive conditions is best classified as a Mississippi Valley-type deposit The Danaopo Zn-Pb deposit, hosted in algal limestone, is the second largest Zn-Pb deposit (150 Mt ores at an average grade of 3.06% Zn + Pb) in the western Hunan-eastern Guizhou metallogenic belt (WHEGMB). Here we investigate the trace elements of sphalerite and C-O isotopes and rare earth elements (REEs) of calcite in the Danaopo deposit, aiming to present insights into the mineralization potentiality of critical metals and origin of Zn-Pb deposits in the WHEGMB. In-situ trace element reveals the inhomogeneous distribution of critical metals within sphalerite, including Cd (1520 to 11570 ppm), Ge (0.73 to 236 ppm), Ga (0.04 to 26.90 ppm), and Tl (0.01 to 3.62 ppm). Cd and Ge exceed the Chinese comprehensive utilization standard. The LA-ICPMS elemental map and inter-element correlations suggest that Cd and Ge enter sphalerite lattice via the substitution of Zn2+ ↔ Cd2+ and 4Zn2+ ↔ Ge4+ + 2Fe2+ + □ (vacancy), respectively. The δ13C PDB (-3.93 to −0.12‰) values of the ore-stage calcite indicate that the carbon in hydrothermal fluids primarily originates from the dissolution of Cambrian algal limestone. Calculated δ18O fluid (+5.23 to + 9.95‰) values on calcites lies between the oxygen isotopic compositions of the algal limestone (+18.76 to + 23.87‰) and the basinal hot brine (+4 to + 10‰), implying that the oxygen was sourced from a binary mixing of ore-host rocks and basin brine. Besides, the REE distribution pattern of Cal-Ⅰ falls within the field of ore-host rocks. In contrast, Cal-Ⅱ is plotted between the Cambrian ore-host and Proterozoic Banxi Group to Cambrian Niutitang Formation footwall. These findings suggest that REE of Cal-Ⅰ was mainly sourced from country carbonate rocks, while Cal-Ⅱ has mixed REE origins from ore-host rocks and footwall sedimentary and metamorphic basement rocks. Overall, based on detailed deposit geology, sphalerite trace elements, and calcite C-O and REE evidences, this study concludes that the Danaopo is a classic Mississippi Valley-type (MVT) Zn-Pb deposit with a low-temperature and low f O 2 reductive ore-forming fluid. [ABSTRACT FROM AUTHOR]

[Display omitted] • The polymetallic beds are unroofed from the Emeishan alkaline silicic rocks. • Nb minerals and low-T Zr zircons are crystallized by magmatic-hydrothermal processes. • The protracted alkaline magmatism of the Emeishan LIP enriched rare metals. • Silicic rocks are generated by waning volcanism with decreasing crustal assimilation. Nb-Zr-REE-Ga-enriched beds are widely found in the Late Permian clastic sediments in southwestern China and are related to the Emeishan large igneous province (LIP). To determine the provenance of these beds, we analyzed their geochemical and mineralogical compositions, along with zircon U−Pb ages, Hf isotopes, and trace elements. Our data show that these polymetallic beds have high Al 2 O 3 contents, Al 2 O 3 /TiO 2 (e.g., mostly >8) and Th/Sc (e.g., mostly >0.6) ratios, low Fe 2 O 3 , TiO 2 contents, and Ti/Y ratios (e.g., mostly <500). These beds exhibit strong negative Ti, Eu, and Ba anomalies, positive HFSEs (high field strength elements) and REEs (rare earth elements) anomalies in trace element patterns, and show geochemical affinities with the alkaline silicic rocks at the top of the Emeishan lavas. Zircons from the polymetallic beds yield U−Pb ages of 259.2–256.2 Ma and ɛHf(t) values of −10.1 − +13.4, which are consistent with the zircon data of the alkaline rhyolites. These results suggest that the mineralized beds dominantly derived from the waning Emeishan silicic volcanism, whereas the barren samples have mixed basaltic compositions. The primary rutile was associated with low-temperature zircon, and was replaced by Nb-rutile and columbite, which were likely to crystallize from an alkaline magma that experienced hydrothermal process. Additionally, the temporal decreases of zircon Eu/Eu* values and crystallization temperatures indicate that rare metals were enriched during the protracted alkaline magmatism. The zircons from the older samples show higher Th/Nb, U/Yb ratios and more negative ɛHf(t) values than those from the younger samples, suggesting that the eroded source rocks were generated by waning silicic volcanism with decreasing crustal assimilation. [ABSTRACT FROM AUTHOR]