Abstract:The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Cr… Show more
“…In the Catalao I carbonatite complex, weathered monazite displayed a less steep REE pattern (i.e., lower La/Nd ratio) when compared to those within carbonatite [28]. The detailed chemical compositions of monazite within carbonatite related environments can be found in Supplementary Materials Table S2 [ [11][12][13][14][16][17][18]20,23,24,29,30,34,35,[37][38][39][40][41][42][43].…”
Approximately >50% of global rare earth element (REE) resources are hosted by carbonatite related deposits, of which monazite is one of the most important REE minerals. Monazite dominates more than 30 carbonatite-related REE deposits around the world, including currently exploited mineralization at Bayan Obo and Mount Weld. These deposits are widely distributed across all continents, except Antarctica. Though rare, monazite occurs as the primary mineral in carbonatite, and mostly presents as a secondary mineral that has a strong association with apatite. It can partially or completely replace thin or thick overgrowth apatite, depending on the availability of REE. Other mineral phases that usually crystallize together with monazite include barite, fluorite, xenotime, sulfide, and quartz in a carbonate matrix (e.g., dolomite, calcite). This review of monazite geochemistry within carbonatite-related REE deposits aims to provide information regarding the use of monazite as a geochemical indicator to track the formation history of the REE deposits and also supply additional information for the beneficiation of monazite. The chemical compositions of monazite are highly variable, and Ce-monazite is the dominant solid solution in carbonatite related deposits. Most monazite displays steep fractionation from La to Lu, absent of either Eu or Ce anomalies in the chondrite normalized REE plot. The other significant components are huttonite and cheratite. Some rare sulfur-bearing monazite is also identified with an SO 3 content up to 4 wt %. A 147 Sm/ 144 Nd ratio with an average~0.071 for monazite within carbonatite-related ores is similar to that of their host rocks (~0.065), and is the lowest among all types of REE deposits. Sm/Nd variation of monazite from a single complex reflects the differentiation stage of magma, which decreases from early to late. Based on the differences of Nd and Sr abundances, Nd isotopic composition for monazite can be used to track the magma source, whereas Sr isotopic composition records the signatures of the fluid source. Th-(U)-Pb age determination of the secondary monazite records variable thermal or metasomatic disturbances, and careful geochronological interpretation should be brought forward combined with other lines of evidence. ThO 2 is the most difficult contamination in the beneficiation of monazite, luckily, the ThO 2 content of monazite within carbonatite is generally low (<2 wt %).
“…In the Catalao I carbonatite complex, weathered monazite displayed a less steep REE pattern (i.e., lower La/Nd ratio) when compared to those within carbonatite [28]. The detailed chemical compositions of monazite within carbonatite related environments can be found in Supplementary Materials Table S2 [ [11][12][13][14][16][17][18]20,23,24,29,30,34,35,[37][38][39][40][41][42][43].…”
Approximately >50% of global rare earth element (REE) resources are hosted by carbonatite related deposits, of which monazite is one of the most important REE minerals. Monazite dominates more than 30 carbonatite-related REE deposits around the world, including currently exploited mineralization at Bayan Obo and Mount Weld. These deposits are widely distributed across all continents, except Antarctica. Though rare, monazite occurs as the primary mineral in carbonatite, and mostly presents as a secondary mineral that has a strong association with apatite. It can partially or completely replace thin or thick overgrowth apatite, depending on the availability of REE. Other mineral phases that usually crystallize together with monazite include barite, fluorite, xenotime, sulfide, and quartz in a carbonate matrix (e.g., dolomite, calcite). This review of monazite geochemistry within carbonatite-related REE deposits aims to provide information regarding the use of monazite as a geochemical indicator to track the formation history of the REE deposits and also supply additional information for the beneficiation of monazite. The chemical compositions of monazite are highly variable, and Ce-monazite is the dominant solid solution in carbonatite related deposits. Most monazite displays steep fractionation from La to Lu, absent of either Eu or Ce anomalies in the chondrite normalized REE plot. The other significant components are huttonite and cheratite. Some rare sulfur-bearing monazite is also identified with an SO 3 content up to 4 wt %. A 147 Sm/ 144 Nd ratio with an average~0.071 for monazite within carbonatite-related ores is similar to that of their host rocks (~0.065), and is the lowest among all types of REE deposits. Sm/Nd variation of monazite from a single complex reflects the differentiation stage of magma, which decreases from early to late. Based on the differences of Nd and Sr abundances, Nd isotopic composition for monazite can be used to track the magma source, whereas Sr isotopic composition records the signatures of the fluid source. Th-(U)-Pb age determination of the secondary monazite records variable thermal or metasomatic disturbances, and careful geochronological interpretation should be brought forward combined with other lines of evidence. ThO 2 is the most difficult contamination in the beneficiation of monazite, luckily, the ThO 2 content of monazite within carbonatite is generally low (<2 wt %).
“…To accommodate this imbalance, Chakhmouradian and Mitchell (1999) suggested the presence of an auxiliary substitution mechanism: Fig. 7.Composition of monazite-(Ce) from Eureka compared with data compiled from other carbonatite complexes (circles; Kukharenko et al ., 1961; Cressey et al ., 1999; Bulakh et al ., 2000; Doroshkevich et al ., 2001; Wall, 2004; Lazareva et al , 2015; Enkhbayar et al ., 2016; Prokopyev et al , 2017; Nikolenko et al , 2018), the Internatsional'naya kimberlite (Chakhmouradian and Mitchell, 1999), and other published occurrences (squares) with SO 3 >1% (Ondrejka et al , 2007; Pršek et al , 2010; Krenn et al ., 2011; Ondrejka et al ., 2016). …”
Section: Discussionmentioning
confidence: 99%
“…A compilation of monazite-(Ce) compositions from different carbonatites was presented by Chen et al (2017). The majority of these data have <1% SO 3 , in addition, published occurrences with monazite-(Ce) containing >1% SO 3 are limited to Nkombwa, Zambia (Wall, 2004); Vuoriyarvi and Seligdar, Russia (Kukharenko et al , 1961; Bulakh, 2000; Prokopyev et al , 2017); and Mushgai Khudag, Mongolia (Enkhbayar et al , 2016; Nikolenko et al , 2018). In all of these occurrences, monazite-(Ce) forms at a late stage in the crystallisation history of the carbonatites.…”
Section: Discussionmentioning
confidence: 99%
“…While rare, the substitution of sulfur into monazite-(Ce) has been described in several localities, predominantly in carbonatites (e.g. Kukharenko et al , 1961; Cressey et al , 1999; Bulakh et al , 2000; Wall, 2004; Enkhbayar et al , 2016; Prokopyev et al , 2017; Nikolenko et al , 2018), but also in kimberlites (Chakhmouradian and Mitchell, 1999), fluid-altered rhyolite (Ondrejka et al , 2007) and in metamorphic rocks (Suzuki and Kato, 2008; Pršek et al , 2010; Krenn et al , 2011; Ondrejka et al , 2016; Laurent et al , 2016). Small amounts of sulfur in monazite-(Ce) and monazite-(La) are also sometimes noted during EPMA radiometric age determination, owing to the close proximity of the S K α line to the Pb M α lines (Jercinovic and Williams, 2005; Suzuki and Kato, 2008), as well as the association of high S contents with increased common Pb (Krenn et al , 2011).…”
Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy data demonstrating that sulfur is accommodated predominantly in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the X-ray photoelectron spectra, however, also indicate that more complex substitution mechanisms incorporating S2– and S4+ are possible. Incorporation of S6+ through clino-anhydrite-type substitution results in an excess of M2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH– for O2–. However, Raman data show no indication of OH–, and instead we suggest charge imbalance is accommodated through F– substituting for O2–. The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements, Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolution–precipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.
“…Detailed mineralogical characterization of the ore was conducted by Enkhbayar et al [14], who found that REEs were mostly associated with fluorapatite and hydroxyapatite. As shown in Figure 2, the apatite grains have hexagonal structures with a layered arrangement of outer crystals grown upon an inner layer of crystals.…”
Section: Mineralogical Characteristics Of the Samplementioning
Abstract:Optimization of the acid leaching process for Mongolian apatite-based ore containing rare-earth elements (REEs) was studied. The ore contained approximately 10% of REEs as total rare earth oxides, and the major impurities were Ca (33% as CaO) and Fe (23% as Fe 2 O 3 ). Fe bearing minerals could be removed by passing the sample through a wet high-intensity magnetic separator before leaching. After magnetic separation, basic leaching tests were conducted to investigate the influence of the acid type and concentration, temperature, and the pH on the REE leaching level and kinetics. Hydrochloric acid was found to be the most effective leaching agent, leaching more than 90% of REEs in an hour. However, the concentrations of Ca ions in the leachate were also high, which would complicate recovery of the REEs. Therefore, to reduce the amount of Ca ions in the leachate, a two-stage leaching procedure was attempted. In stage 1, the sample was preleached using 1.0 M hydrochloric acid to dissolve Ca. In stage 2, the solid residue of stage 1 was leached using 2.0 M hydrochloric acid to dissolve REEs. Consequently, this two-stage leaching significantly reduced the Ca concentration in the final leachate without affecting the leaching levels of REEs.
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