Zhang and Tao (1986) recognized two stages of Hercynian granite rocks; biotite ages show the early stage of 311-306 Ma and the later stage of 258-234 Ma. The alkali amphibole in the fenitized contact zone of this carbonatite gave an 40Ar/39Ar plateau age of 1.28 Ga (Ren Yingchen, oral commun., 1993). In addition to the widespread occurrence of Hercynian biotite granites and granodiorites in the Bayan Obo region, evidence for the Hercynian regional metamorphism is based on 40Ar/39Ar single-grain total-fusion analyses of biotite from H9 biotite schist, which was reset and yielded ages ranging from 309.8+-5.8 to 297.1+-5.2 Ma. China has be mining rare earth metals for more than fifty years, without any regulations for safety. The monazite of sample 7B30-20 has about equal concentrations of La2O3 (13.60 wt. percent) of ferroan dolomite from H8 dolostone marble of Bayan Obo. International Journal of Applied Ceramic Technology 12 (S1), 41-48. Euhedral martite and martitized magnetite are apparently the oldest Fe ore minerals in ores hosted by dolostone marble. Approximately 75 m3 (2,600 cu ft) of acidic wastewater, plus about a ton of radioactive waste residue are also produced.[4]. The least metamorphosed parts of the H9 unit are black shales that contain detrital quartz and illite, whereas the more intensely metamorphosed H9 shales now are biotite and albitized biotite schists, which are much more dominant in the mine region than the relatively unmetamorphosed shales. percent) and high Fe content due to the presence of late-stage magnetite. Figure 18. The dominant REE mineral is bastnaesite, but lesser amounts of cebaite also are present. 4. 4; Wang, 1985) that took place at the northern edge of the North China Platform or craton. Get this image in a variety of framing options at Photos.com. percent) is appreciably higher than that of 7B31-1A (18.27 wt. Sie ist die wichtigste Fund- und Förderstätte der Welt für Seltene-Erden-Metalle (SEE, englisch rare-earth-elements, REE) [1] . East Mine, Bayan Obo deposit, Bayan Obo, Bayan Obo … Table 1. Albite is widespread, especially as a replacement mineral in the H9 biotite schist, where albite usually preceded and was replaced by late-stage unmartitized magnetite. Alkali amphibole from sample 8B42 contains 2.82 wt. Economic geology. 24). 33) in the Bayan Obo mine region (Conrad and others, 1991; Chao and others, 1995): Late Proterozoic (about 900 Ma), Silurian to Mississippian (Caledonian, 425-343 Ma), and Pennsylvanian to Triassic (Hercynian, 310-220 Ma). The uppermost H9 unit of the Bayan Obo Group, which is the cap rock of the Bayan Obo orebodies, consists of dark-gray to black shale, slate, biotite schist, and albitized biotite schist. Textural relations indicate that the fine-grained ferroan dolomite in some of the marble was formed by mylonitization or granulation during regional metamorphism. The internal isochrons, in ascending order of 208Pb/204Pb initial ratios, for selected samples are shown in figures 19-22. Seltene Erden - der wichtigste Rohstoff des 21. Monazite from sample 34-24, with an internal isochron mineral age of 532+-3.1 Ma, is the next least radiogenic and has a 208Pb/204Pb initial ratio of 34.89+-0.15. In samples 796-48,277 and 8B7, there is a possibility that the alkali amphibole may have been reset by the replacement and mineralization of late-stage fresh magnetite. Because of the high contents of combined F, Fe, and REE's, inductively coupled plasma-atomic emission spectrometry (ICP-AES) was used for partial analysis of most of the disseminated and banded ores. BaO, SrO, Ce2O3, La2O3, Nd2O3, and Nb2O5 contents of unmineralized and REE-mineralized H8 dolostone marble were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Because of the high contents of combined F, Fe, and REE's in many of the ore types, only partial analyses of ore samples could be obtained by the ICP-AES method, which did not analyze for SiO2, Na2O, CO2, or in most cases, P2O Chemically, these alkali amphiboles are generally slightly richer in FeO than MgO and contain from 1.77 to 3.28 wt. [4], China produced about 81,000 tons of rare-earth metals in 2001; the number jumped to about 120,000 by 2006. All Bayan Obo alkali amphiboles are characteristically low in Al2O3. Some of these ores also contain various amounts of fluorite. Reserves are estimated at more than 40 million tons of REE minerals grading at 3–5.4% REE (70% of world's known REE reserves), 1 million tons of Nb2O5 and 470 million tons of iron. Chao, This page was last edited on 22 November 2020, at 19:54. percent) of high-REE, low-Fe, and low-F banded ores of Bayan Obo. Due to the scarcity of water in the north, the heavy industry, urban, military, and supporting agricultural bases are located in Baotou City, in the south. Hydrothermal replacement of marble by fluorite is observed from initial interstitial replacement to the development of bands of fluorite in the host rocks (fig. REE minerals were discovered in 1936, and Nb-bearing ores in the late 1950s. A minimum age of the H8 marble also is indicated by the 40Ar/39Ar ages of alkali amphiboles occurring along foliation planes in the marble, which in spite of varying degrees of argon loss indicated by age spectrum and total fusion analyses (fig. Two different billets of each banded ore sample to be analyzed, each approximately 2-3 cm wide, 4-6 cm long, and 0.5 mm thick, were cut across the banded structure. percent total RE2O3 (tables 6-9). Photomicrograph of a doubly polished thin section (sample 796-48,449) of marble showing relict dolomite grains surrounded by fine granular aegirine augite that partially replaced dolomite. The Bayan Obo Mine produced 55,300 tons of RE 2 O 3 in 2005, accounting for 47% of the total rare earth production of China and 45% of that of the world (Hedrick, 2006). Partial analyses of the chemical compositions of two fractions of a high-grade REE-disseminated ore sample, 7B30-33 (7B30-33A and 7B30-33B, table 6), each having significant amounts of relict host carbonate, show contents of RE2O3 of 19.56 and 13.23 wt. Effect of existence form of La3+ on the properties of the Bayan Obo Mine tailing glass ceramics. Hercynian regional metamorphism also accounts for the isoclinal and chevron folds that are widespread in the H9 biotite schists with limestone boudinage. These two samples were collected more than 50 m apart, about 130 m above the footwall of the East Orebody (fig. The biotite in biotite and albitized-biotite schists of the H9 lithologic unit has been reset and has 40Ar/39Ar single-crystal total-fusion ages ranging from 309.8+-5.8 Ma to 297.1+-5.2 Ma. Figure 23. Typically, Bayan Obo hand specimens show a variety of colors that are characteristic of some of the most abundant minerals. percent. A small swarm of 11 calcitic carbonatite dikes, mostly 1-2 m wide and up to 150 m long, cut across an anticlinal structure in the Archean Wutai granitic gneisses and migmatites, approximately 1.5 km northeast of the mine area. The total RE2O3 and P2O5 contents of sample 7B34-16 are 0.08 wt. Bayan Obo Mine, which belongs to BIS, is located in the north of Baotou City, approximately 150 km from the urban area of Baotou. Thin sections also show mortar texture wherein granulated fine-grained quartz occurs between large quartz grains. Seite 2623 der Diskussion 'Das große Ganze - was Politik, Zentralbanken, Trends, Medien und Gesellschaft mit Aktien, Rohstoffen' vom 25.01.2015 im w:o-Forum 'Börse - Allgemein'. The bastnaesite of this generation is also characterized by low U, Th, and Pb concentrations, as well as a low initial 208Pb/20 Evidence for the earliest episodes of granular hematite mineralization is found in sample 8B35-2, where fine-grained hematite with associated Nb-rutile replaced monazite with an age of 474+-4.5 Ma (table 14), and therefore crystallized after that date. Most of the rare earths processed by Baotou are extracted in Bayan Obo, a mining district in the Gobi desert 120km north of the city. Alkali amphibole from sample 8B42 has a K-Ar age of 442+-11 Ma, determined by the Tianjin laboratory. Jahrhunderts Wie Sie als Anleger vom Boom profitieren Wie Sie als Anleger nachhaltig profitieren One type of amphibole occurs as fine- to medium-grained prismatic magnesio-arfvedsonite crystals (7B34-1P) and the other as extremely fine grained asbestiform magnesio-riebeckite crystals (7B34-1F). 4 One of these samples has a delta18O value of 13.9 and a d13C value of -9.27. 6), and rounded detrital apatite grains are present in the coarser grained marble (fig. The MgO and FeO contents of both the coarse-grained ferroan dolomite and the fine-grained dolomite are variable, ranging from 13.78 to 19.54 wt. In sample 34-24, magnetite is not present; hence, resetting of the alkali amphibole age by late-stage magnetite-precipitating hydrothermal solutions is unlikely. For this reason, episodes of REE mineralization as a whole are well established, whereas episodes of Fe and Nb mineralization are not. Additional, but minor, occurrences of Fe minerals are very fine grained disseminated magnetite with rims of hematite, rare wormy textures in hematitic ores, and goethite in weathered Fe-oxide ores. Partial chemical analyses of monazite-hematite-apatite banded ores are also shown in table 6. Radiometric ages of minerals in sample 796-48,277: A, Internal isochron showing mineral age of the monazite (4328.5 Ma), which replaced the host limestone marble and occurs as abundant inclusions in alkali amphibole; B, 40Ar/39Ar plateau showing age (343.13.0 Ma) of the coexisting alkali amphibole that replaced the monazite. Chao and others (1993) determined that remobilization of monazite was unlikely because any metal-transporting acid hydrothermal solutions entering along microfractures and grain boundaries within the carbonate host rock would tend to dissolve and remove the carbonate host, become neutralized, and precipitate the metals and other mineral components from such solutions. The uppermost lithologic unit, H9, 340-350 m thick, consists of a sequence of interbedded gray to black shale, slate, and biotite schist that conformably overlies the H8 unit. To a very minor extent, bands of fluorite in banded ores do show slight resorption of early minerals such as REE, Fe oxide, and gangue minerals, but resorption is limited to within the band itself. Figure 9. Fluorite is generally present, as indicated by the 7.18-9.58 wt. A general representation of this development is presented schematically in figure 33. The bastnaesite sample 8B7 (table 14) is characterized by a relatively low La2O3 content (22.92 wt. The most common quartzite-hosted disseminated ore contains extremely fine grained aegirine augite, bastnaesite, and barite, with or without varying amounts of magnetite (sample 9B18-3c). Photomicrograph of a doubly polished thin section of sample 9B15-1L showing a banded ore consisting of monazite-granular hematite-fluorite cut by late-stage, coarse-grained fresh magnetite aggregates. 8). Large block of banded ore consisting of layers of aegirine augite and magnetite. Figure 15. Samples collected in 1987, 1988, and 1990 are numbered with a prefix 7B, 8B, and 9B, respectively, followed by the sample location number. Most monazites with different internal isochron ages, chemical compositions, and initial 208Pb/204Pb ratios were probably brought in at different times and deposited by different hydrothermal solutions. The Bayan Obo mining area is shown in Figure 1. The ores hosted in biotite schist occur only in the hanging wall of the Main Orebody (fig. Although samples having such high REE content are not rare at Bayan Obo, most of the REE ores contain less than 20.0 wt. Bayan Obo and other REE mines in China provided approximately 97% of the global supply The mining in Bayan Obo produces the bulk of the world's rare earths and does so as a by-product of iron ore mining, recycling and implementing a environmental friendly approach termed "Green Mining". The most widespread gangue minerals are alkali amphiboles (predominantly magnesio-arfvedsonite), fluorite, barite, aegirine augite, phlogopite, apatite, albite, and microcline. 19), with an internal isochron mineral age of 431+-2.7 Ma, has the lowest 208Pb/204Pb initial ratio (32.47+-0.17) and is the most primitive, least radiogenic sample. Wirtschaftsgeologie. Very large rare-earth elements (REE) Fe-Nb deposit (Bayan-Obo type), discovered as an iron deposit in 1927. The differences in Fe and REE content between 7B30-28A and 7B30-28B reflect differences in the abundance of Fe versus REE bands in the samples analyzed. Small amounts of porphyroblastic albite biotite schist and biotite-rich minette occur as lenses within this unit. On the basis of textural relations for all these samples of marble-hosted disseminated ore, alkali amphiboles replaced small amounts of monazite, and the amphibole, in turn, was replaced by magnetite. Samples 7B31-1A and 7B31-1B from successive bands of the same hand specimen are similar in composition, but the total RE2O3 content of 7B31-1B (25.06 wt. This finding implies that the Bayan Obo Group may not be of Precambrian age. percent) compared with other dated bastnaesite samples analyzed. Extremely fine grained aegirine augite similarly replaced host dolomite. percent) of disseminated monazite ore in dolostone marble and of monazite-hematite-apatite banded ores of Bayan Obo. percent K2O, and about 2.2-2.5 wt. The bands of granular apatite visible in the corresponding DPTS's are not reflected in the analyses because P2O5 concentrations were not determined. EPMA data on REE content of apatites (table 5) are also in good agreement with data obtained by the SXRF method (Chen and others, 1993). Figure 32. The functional unit of the investigation is therefore “1 kg Nd” and “1 kg Dy”, respectively. Figure 24. The chemical composition of essentially unmineralized dolostone marble (table 3) is an essential parameter for evaluation of a syngenetic versus epigenetic origin of the disseminated REE ores of Bayan Obo. Locally, fluorite is an abundant gangue mineral. percent F. Based on textural evidence and abundance, alkali amphibole of hydrothermal metasomatic origin occurs in marble-hosted disseminated Fe ore samples 8B42; 796-48,252; 796-48,366; 8B7; and 796-48,277. REE-Mineralien wurden 1936 und Niob-tragende Erze Ende der 1950er Jahre entdeckt. Multiple analyses of alkali amphibole subsamples from a vein (sample 7B13C, table 15) have disturbed 40Ar/39Ar spectra, the apparent ages ranging from about 820 to 640 Ma (fig. X-ray diffraction techniques were rarely used because of the difficulty of obtaining pure mineral concentrates from the extremely fine grained ores. B, Retreat of the sea at a later stage, when the Bayan Obo Group was deposited. Indium and gallium specifically are mined from the zinc ores. Figure 22. In fact, about half come from Bayan Obo located in China's Nei Mongol Autonomous Region. These minerals (table 1) consist of both primary and secondary metamorphic minerals of the host rocks and the epigenetic ore and gangue minerals introduced by hydrothermal solutions. Metasomatic alkali amphiboles generally occur in ore hosted by H8 and locally may replace more than 10-50 volume percent of the host rock.