@phdthesis{oai:air.repo.nii.ac.jp:00003449,
 author = {NERGUI, SARANGUA},
 month = {Mar},
 note = {The Khaldzan Burgedei peralkaline complex in western Mongolia is an example of extreme enrichment of Zr, Nb, and REEs in A-type granite. The Khaldzan Burgedei was discovered by Kovalenko.V.I in 1984. Preliminary resources calculated (1989-1990) area total of 163.8 Mt resources at ZrO₂ (1.5 wt.%), Nb₂O₅ (0.2 wt.%), Ta₂O₅ (0.01 wt.%), REE₂O₃ (0.3 wt.%) and Y₂O₃ (0.11 wt.%) (Minin et al., 1991). The objectives of this study is to clarify petrology, mineralogy and geochemistry identify rare-metal bearing minerals, and discuss the genesis of HFSE and REEs mineralization based on the samples, which were collected from a drill holes and outcrops in the complex. The study was conducted on the basis of microscopic observations, X-ray diffractometry (XRD), scanning electron microscopy (SEM-EDS), X-ray fluorescence spectrometry (XRF), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), electron probe microanalyser (EPMA), Fluid inclusion microthermometry and Laser Raman Spectra.
 The studied area of the Khaldzan Burgedei complex consists of two main lithologic units of quartz syenite and granite are identified by the result of field and drill core observation. The quartz syenite is dominantly distributed in the study area and they are intruded by granite. A sharp contact between quartz syenite and granite is observed in the outcrops, and sometimes the contact between quartz syenite and granite shows a mingling characteristic. The zone, which has an average width of about 2-5.5m, consists of compositionally and texturally inhomogeneous rocks of syenite and pegmatite.
 The quartz syenite is coarse-grained, mainly consists of K-feldspar, plagioclase, albite, ferrorichterite, arfvedsonite, aegirine-augite, aegirine, and quartz with accessory apatite, rutile, zircon and pyrochlore. The granite is fine-grained, mainly consists of quartz, K-feldspar, albite, arfvedsonite and aegirne with accessory zircon and fersmite. The quartz syenite is occur in the all drill holes and most of drill core basically affected by metasomatism and some interval subsequent hydrothermal alteration with chamosite, nontronite, calcite, fluorite, pyrite, zircon and REE bearing minerals (synchysite, bastnasite, parasite and xenotime). The granite is occur several drill holes and upper part of the granite, in the drill holes becomes quartz rich compared to the lower part. The quartz rich part is related to fractionation. This part is sometimes associated with pegmatites that consist of amphibole, feldspar, and quartz with zircon and fersmite.
 The bulk rock compositions of the drill core show metsomatized and subsequent hydrothermal alteration units, is enriched in Ca, Nb, Zr, and REE, fractionated unit because of high SiO₂ (71.5-79.3 wt%), is enriched in Rb, Ce, Nd, and total REEs. Pegmatite show sharp spikes of Nb and Zr.
 The peralkaline magma evolved from quartz syenite to granite associated with pegmatite. This is supported by similar igneous mineral assemblies and chemical characteristics of the quartz syenite and granite. Differentiated rocks, such as quartz syenites and granites, amphibole evolves from ferrorichterite to arfvedsonite and pyroxene is aegirine-augite to aegirine. This indicates show evolution of the magma changing to from sodic-calcic to more sodic composition during crystallization. The results of EPMA data show were precipitated of mafic minerals more lose Ca in the granite, during the granitic magma evolution and/or especially silica oversaturation.
 The three HFSE and REE enrichment processes (magmatic, metasomatism and hydrothermal) are observed in the Khaldzan Burgedei complex. One is the fractionation of the granitic magma that accumulated HFSE and REEs (especially LREEs) at the top of the granitic stock and associated pegmatites. The fractional crystallization can produce residual magmas that are strongly enriched in the HFSE and REE. The other is the Na metasomatism and subsequent hydrothermal alteration. The Na metasomatism and hydrothermal fluid were enriched in volatiles (CO₂, B, F and Cl) and incompatible elements (HFSE and REE). These volatile elements are helped transported REE carbonates. Effects of the metasomatism primary minerals are replaced by secondary minerals. This replacement indicates that Ca from plagioclase and Ca-bearing mafic minerals (ferrorichterite and aegirine-augite) were the source of Ca for fluorite, calcite and REE-bearing carbonates (synchysite).
 The reactions during the metasmatism are as follow: 
　 3(Na,Ca)(Si,Al)₄O₈(Plagioclase) + Na⁺ + 10H⁺ = 2NaAlSi₃O₈(albite) + 3Ca²⁺ + 10Al³⁺ + 2Na⁺ + 3Si₂O + 5H₂O (1)  
　 Na₂CaFe²⁺₅Si₈O₂₂(OH)₂ (Ferrorichterite) + 1.5Na₂Si₂O₅ + O₂ + Fe³⁺ = 5NaFe³⁺Si₂O₆(Aegirine) + SiO₂ Quartz + Ca²⁺ + Fe²⁺ + 1.5OH⁻ + 0.5H⁺ (2)
　 Ca²⁺ + 2F⁻ = CaF₂ (Fluorite) (3)
　 REEF²⁺ + Ca²⁺ + 2CO₃²⁻ = CaREE(CO₃)₂F (Synchysite) (4)
 After metasomatism, albite altered by sericite and chlorite, and aegirine altered by chlorite. During this alteration, Cl formed from aegirine and this released Cl helped to transport REE. This process is explained by replacement reactions related to acidic alteration. 
 The reactions during the hydrothermal alteration are as follow:
　 4NaFe³⁺Si₂O₆ Aegirine + 2H₂O + 4H⁺ + 2FeCl₂ = Fe₆Si₄O₁₀(OH)₈ Chamosite + 4SiO₂ + 4Na⁺ + 4Cl⁻ (1)
    REECl²⁺ + HF + HCO₃⁻ = REE(CO₃)F Bastnäsite + 2H⁺ + Cl⁻ (2)
Feldspars replaced by smectite (nontronite) and Fe-rich chlorite (chamosite) and hydrothermal minerals formed later than feldspar also includes HFSE and REE bearing minerals. Exsolving fluorine and sodium rich hydrothermal fluids leached HREEs from zircon and transported the host quartz syenite. This hydrothermal fluids reacted (Na metasomatism) with feldspars and Ca-bearing amphibole resulting in the precipitation of fluorite, calcite and HREE rich zircon as well as REE carbonates.
 In summary, we propose a genetic model that the HFSE and REE mineralization of the complex we caused by extreme magmatic fractionation and subsequent Na metasomatism resulted in albitization and fluorite precipitation with extracted Ca²⁺. Destabilized Zr-REE fluoride complexes resulted in zircon and REE minerals precipitation.},
 school = {秋田大学},
 title = {Rare Metal Mineralization of the Khaldzan Burgedei Peralkaline Complex, Western Mongolia},
 year = {2019}
}