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Selenium (Se) is an essential trace element for humans and animals, and an excess of or deficiency in Se is harmful to health. Research on the selenium enrichment zone began in the late 1970s in Shuang'an, Ziyang, southern Shaanxi Province. Naore village is only one selenosis area in Shuang'an, Ziyang, China. Different scholars have conducted systematic studies on the occurrence of selenium, its organic geochemistry and biomarkers, and its content and enrichment patterns in this area. This study applied the TIMA (TESCAN integrated mineral analyzer) for the first time to conduct detailed mineralogical work. The minerals included quartz, carbonate minerals (calcite and dolomite), feldspar (plagioclase, albite, and orthoclase), biotite and muscovite, clay minerals (chlorite and kaolinite), hematite, pyrite, and accessory minerals (almandine, olivine, zircon, and apatite) in Naore village, Ziyang, Shaanxi Province. The ATi index (100 × apatite/(apatite + tourmaline)) is used to determine the source of heavy minerals and the degree of heavy minerals' weathering. The content POS (100 × (pyroxene + olivine + spinel)/transparent heavy mineral) of olivine, pyroxene, and spinel in heavy minerals can reflect the contribution of basic and ultrabasic rocks in the source area. The ATi and POS indexes for the heavy minerals in the research area were 91.83~99.96 and 0.01~18.75, respectively, reflecting the abundance of volcanic rock material in their source. In addition, the migration, transformation, bioavailability, and toxicity of selenium in the environment are closely related to its species. The species of selenium in various selenium-rich areas (Naore, Wamiao, and Guanquan) mainly include unusable residues and organic forms, followed by humic-acid-bound selenium. The proportions of water-soluble, exchangeable, and carbonate-bound selenium are relatively small, and the proportion of Fe-Mn oxide-bound selenium is the lowest. [ABSTRACT FROM AUTHOR]

Apatite-rich rocks from marine phosphorites, alkaline igneous complexes, and iron-oxide copper gold (IOCG) deposits commonly contain elevated but sub-economic contents of rare earth elements (REE). In this study, we selected fluorapatite from the Paleoproterozoic Yinachang IOCG deposit in Southwest China to evaluate the mechanisms of REE remobilization, transportation and precipitation during fluorapatite alteration. Four texturally and compositionally distinct types of fluorapatite were identified. Ap1, related to mantle-derived magmatic-hydrothermal fluid from dolerite intrusions, contains the highest (REE + Y) content (> 1 wt%). Ap2 was directly deposited from a magmatic-hydrothermal fluid related to Cu mineralization, rich in Cl and S but poor in REE + Y. Pervasive REE-rich mineral inclusions and micro-pores in the altered domains from Ap1 and Ap3-1 indicate that extensive metasomatic alteration occurred via a coupled dissolution-reprecipitation process, which was related to a late oxidizing hydrothermal fluid. After the end of the dissolution-reprecipitation process, Ap3-2 formed through regrowth of Ap3-1. Ap4 in late monazite-sulfide veins has extremely high positive Eu anomalies (24-32) and the highest Eu contents, which are related to a late reduced hydrothermal fluid. This study demonstrates that the geochemical and textural features of altered fluorapatite from the Yinachang IOCG deposit were controlled by both a sorption processes and the oxidation states of the hydrothermal fluids. The most salient feature in the Yinachang deposit is that REE remobilization associated with the alteration of fluorapatite by Neoproterozoic hydrothermal fluids is not strictly localized in extent, and REE in fluorapatite can also be transported in distance and precipitate as REE-rich minerals in independent mineralized veins., Author(s): Bing Xiao [sup.1] [sup.2], Yuanming Pan [sup.3], Hao Song [sup.4], Wenlei Song [sup.5], Yu Zhang [sup.6], Huayong Chen [sup.1] [sup.2] Author Affiliations: (1) grid.9227.e, 0000000119573309, Key Laboratory of Mineralogy [...]

Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world's market, while its origin is still unclear because of the complicated and diverse REE ore mineralogy and texture. Thescanning electron mircroscopy SEM)-based automated mineralogy allows for the numeric assessment of rocks and ores' compositional and textural properties. Here, we use TIMA (TESCAN Integrated Mineral Analyzer) to quantitatively characterize REE ore mineralogy from the deep drill core within the H8 unit ("dolomite marble") to better understand the deposit. The mineral composition, occurrence, and Ce elemental deportment of the borehole ores at different depths (i.e., 1107 m, 1246 m, 1406 m, 1546 m, and 1682 m) were obtained. The results show that the main types of ores in the investigated samples can be divided into banded REE-Fe ores, banded REE ores, disseminated REE-Fe ores, and veined REE ores. REE and gangue minerals vary significantly in abundance and occurrence. Monazite-(Ce) and bastnäsite-(Ce) are the primary REE host minerals, and both contribute the most to the REE budget. Other REE minerals, such as parisite-(Ce)/synchysite-(Ce), cerite-(Ce), huanghoite-(Ce)/cebaite-(Ce), and aeschynite-(Ce), are significant contributors. The gangue minerals generally include fluorite, barite, magnetite, pyrite, quartz, magnesio-arfvedsonite, and minerals of the biotite and apatite groups, among others. Combined with the newly published mineral-scale chronological and isotopic geochemical analyses, it is reasonable to conclude that the later hydrothermal fluids remobilized and redistributed the original Mesoproterozoic carbonatitic REE minerals and formed a high variable ore mineral assemblage. Furthermore, it is demonstrated that the mineralogical study using TIMA can provide accurate and reliable mineralogy data for the comprehensive interpretation of the complex REE ores, and extend our understanding of the deposit. [ABSTRACT FROM AUTHOR]

Abbreviations: Ap-Apatite; Cc-Calcite; Di-Diopside; Phl-Phlogopite; Mag-Magnetite; Mnz-Monazite; Par-Parisite; Py-Pyrite; PM-phosphate melt. BSE images of the exposed melt inclusions in apatites from Ulgii Khiid carbonatites showing varied assemblage and volume of calcite, diopside, phlogopite, monazite, parisite, magnetite, pyrite daughter mineral phases, as well as a phosphate melt. Hole indicates former fluid and CO 2 phases existed in the open of the inclusions. We proposed that the Ulgii Khiid carbonatite was produced by silicate-carbonate liquid immiscibility processes with subsequent crystal differentiation and phosphate-carbonate immiscibility. The REE, together with P, preferentially incorporated the residual phosphate melt during the immiscible process. The phosphate melt plays a vital role in the REE behavior in carbonatites and associated ore mineralization. • REE-rich minerals and phosphate melts were found within the apatite melt inclusions. • The carbonatite was produced by immiscibility and crystal differentiation processes. • The phosphate melt is efficient for extract REE in the P-rich carbonatite magmas. Carbonatites are abundant in the rare earth elements (REE), and they host the most important REE resources in the world. However, the mechanisms that concentrate these elements during carbonatitic magmatic processes are still poorly constrained. Here, we report the occurrence of apatite-hosted melt inclusions from the Ulgii Khiid carbonatites, Mongolia, and use these to reconstruct the evolution of REE concentrations and patterns in early, primary carbonatite magma. The melt inclusions consist of a varied polycrystalline assemblage of daughter minerals, including calcite, diopside, phlogopite, magnetite, pyrite, monazite, parisite, and a phosphate glass which is remarkably enriched in REE. Heating-quenching experiments show that the homogenization temperatures of the inclusions are above 1200 °C and produce three immiscible liquid phases (i.e., phosphate-, silicate-, and Fe-silicate-melt). The phosphate melt has much higher REE content than the silicate melts. We, therefore, suggest that the melt inclusions trapped a REE-, P- and silicate-enriched carbonate melt produced via carbonate-silicate liquid immiscibility. During this process, both REE and P preferentially incorporated into the carbonate melt. With subsequent crystal fractionation of REE- and P-poor carbonate and silicate minerals, the separated carbonatitic melt becomes P-REE-saturated, forming REE minerals and an immiscible REE-rich phosphate melt. The phosphate melt is highly efficient at concentrating REE during the immiscibility process and plays a crucial role in controlling the REE budget in the P-rich carbonatite magmas. [ABSTRACT FROM AUTHOR]

Preliminary mineralogical and geochemical studies have been carried out on dolomite marble drill cores from the Bayan Obo REE deposit in China. Three types of apatites and four types of monazites have been identified based on textural features: Type 1 apatite occurs as grains with minor monazite (Type 1 monazite) on its border; Type 2 apatite veinlet shows clusters of assemblages with abundant bastnäsite and parisite at the rim; Type 3 apatite has a linear array associated with fluorite and bastnäsite veinlets. Type 2 monazite occurs as clusters intergrowing with parisite and fluorite. Type 3 and 4 monazites occur as polymineralic (fluorite and bastnäsite) and monomineralic veinlets, respectively. These four types of monazites have similar LREE composition but variable Y content (Y 2 O 3 ranging from below determination limits to 0.7 wt%). The three types of apatites also show different REE content and distribution patterns, ranging from high REE abundance (∑REE + Y: 27243–251789 ppm) and strong LREE enrichment [(La/Yb) CN ∼101] in Type 1, less LREE enrichment [(La/Yb) CN ∼8] in Type 2 to relatively low REE abundance (∑REE + Y: 4323–11175 ppm) but high REE fractionation [(La/Yb) CN ∼58] in Type 3. The primary apatite has high Sr (5461–6892 ppm) and REE content, implying a carbonatite origin. The late-stage apatites (Types 2 and 3) show different Sr and REE abundances. Significant differences in their Sr composition (6189 ± 573, 6041 ± 549 and 3492 ± 802 for Types 1–3 samples, respectively) and Y/Ho ratio (20.9 ± 0.11, 19.5 ± 0.17 and 17.4 ± 0.37, respectively) indicate that the three types of apatites may have crystallized from different metasomatic fluids. Multi-stage metasomatism resulted in remobilization and redeposition of primary REE minerals to form the Bayan Obo REE deposit. [ABSTRACT FROM AUTHOR]