Monazite from mountain to ocean: a case study from Trolognaro (Fort-Dauphin), Madagascar

Montel, Jean Marc; Razafimahatratra, Dieudonné; Ralison, Bruno; Parseval, Philippe de; Michel, Thilo; Randranja, Roger

doi:10.1127/0935-1221/2011/0023-2149

Cited by 23 publications

(12 citation statements)

References 31 publications

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“…Trivalent cations may substitute directly for the Ln 3+ host cation in the crystal lattice. In contrast, the accommodation of actinides with higher oxidation states requires coupled substitution with a mono‐ or divalent charge‐compensating cation . Additionally, a direct incorporation mechanism, based on the replacement of four Ln 3+ by three An 4+ and the simultaneous generation of a vacancy, was also reported in imperfect structures .…”

Section: Introductionmentioning

confidence: 99%

Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

Xiao

Lösch

Huittinen

et al. 2018

Chemistry A European J

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In this study, the effect of host cations on the local structure around the dopant site of materials from the xenotime family is systematically studied on the molecular level. A series of six Eu -doped xenotime-type single crystals (Tb, Y, Ho, Er, Yb, and LuPO ) have been grown and spectroscopically analyzed by using polarization-dependent laser-induced luminescence spectroscopy (p-TRLFS). Our results demonstrate that the structural disorder changes in a non-linear manner with a structural break between Yb and Lu . Despite adopting identical crystal structures, the solid solutions of these materials vary significantly, and differ from monazite solid solutions. Similar Eu incorporation behavior with a strongly distorted dopant site is found for the early members of the xenotime family, whereas LuPO with the largest host versus dopant radii mismatch is anomalous in that it contains the most symmetrical lattice site. This goes along with a significantly stronger crystal field, indicating a shorter Eu-O bond length, as well as a strong vibronic coupling to external translational lattice vibrations. The p-TRLFS analysis confirms the breakdown of the crystallographic site symmetry from D to C in YPO , whereas a small distortion of the crystallographic site in LuPO results in an S point symmetry for the Eu cation. The lattice with the smallest cation host site is no longer sufficiently flexible to make room for Eu and instead "forces" the guest ion to occupy a less distorted Lu site.

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Section: Introductionmentioning

confidence: 99%

Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

Xiao

Lösch

Huittinen

et al. 2018

Chemistry A European J

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“…Standardization was carried out using periclase (Mg), wollastonite (Ca and Si), pyrophanite (Mn and Ti), corundum (Al), hematite (Fe), barite (Ba), albite (Na), sanidine (K), chromite (Cr), zircon (Hf and Zr), graftonite (P), UO2 (U), ThO2 (Th), Pb2P2O7 (Pb), Nb metal (metal), and Ta metal (Ta). The standards used for the REE and yttrium are the orthophosphate of each element (nPO4, where n is a given REE) and the lines analyzed were Lalpha for La, Ce, Sm, Er, Yb, and Y, and Lbeta for Pr, Nd, Gd, and Dy (more details in Montel et al, 2011). Peak and background positions were carefully selected after detailed wavelength dispersive spectroscopy scanning.…”

Section: Methodsmentioning

confidence: 99%

The Origin of Skarn-Hosted Rare-Metal Mineralization in the Ambohimirahavavy Alkaline Complex, Madagascar

et al. 2015

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The Cenozoic Ambohimirahavavy alkaline complex in Madagascar consists of several syenitic to granitic intrusions (24.2 ± 0.6 Ma) the largest of which, the Ampasibitika intrusion, is characterized by the presence in its outer flanks of late peralkaline granitic dikes intruding mudstone and limestone of the Isalo Group. A network of dikelets and veinlets propagates from these dikes, intruding along bedding or obliquely to bedding. At the contact between the dikes and dikelets and a limestone, a reaction zone enriched in rare metals, dominated by calc-silicate minerals such diopside and andradite-grossular, forms a rare example of skarn resulting from peralkaline igneous activity.Much of the rare-metal mineralization (REE, Zr, Nb, Th, Sn, and Ti) occurs as secondary phases in the dikelets and skarn. In the dikelets and endoskarn, high field strength element (HFSE)-rich phases consist mainly of zircon, bastnäsite-(Ce), and Ca-REE-, and Ca-HFSE-rich phases in pseudomorphs after aegirine-augite. In the exoskarn, the main HFSE-rich phases are bastnäsite-(Ce), zircon, pyrochlore, Nb-rich titanite, and an unidentified F-rich Ca-zirconosilicate finely disseminated in a matrix composed of calcite, diopside, andradite, phlogopite, quartz, fluorite, and fluorapatite. The secondary zircon is characterized by a low Zr content and by the presence of REE, Ca, Al, and Fe.Three types of primary fluid inclusions were observed in dikelets and skarn in quartz, calcite, and diopside: (1) liquid-rich inclusions (L-V) (20 to 40 vol % vapor) occur in all three minerals and homogenize to liquid;(2) vapor-rich inclusions (V) (>90 vol % vapor) occur in diopside and quartz, and homogenize to vapor; and (3) halite-bearing L-V inclusions (L-V-H) occur in diopside and quartz, and homogenize either by disappearance of the vapor bubble or by halite dissolution. The L-V inclusions have low to intermediate salinity and homogenize at temperatures ranging from 200° to 380°C. The V inclusions have low salinity and homogenize at higher temperature (350°-395°C). The L-V-H inclusions mainly contain NaCl (35-45 wt % NaCl equiv), and homogenize by three modes, namely, bubble disappearance (mode A), halite dissolution (mode B), and simultaneous bubble and halite disappearance (mode C); the homogenization temperatures range from 260° to 380°C. We propose a model in which rare metals were transported by a Cl − , F − and HFSE-rich orthomagmatic fluid exsolved at 400° to 450°C and about 20 MPa. At these conditions, the fluid was in the two-phase region and vapor dominated. The rare metals were deposited as a result of the interaction of this fluid with limestone and mixing with an external fluid. This interaction/mixing buffered the orthomagmatic fluid to higher pH and lower temperature, resulting in the destabilization of REE-chloride complexes and deposition of fluorocarbonate minerals in the limestone; Zr and Nb, which were likely transported as hydroxyl-fluoride complexes, precipitated as zircon and pyrochlore due to deposition of fluorite and a consequent d...

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“…1C) [10]. They are generally in translucent, shiny resinous with its color ranging from light yellow to brown (honey color) and even black, sometimes also reddish or greenish reflections [11]. From the optical point of view, the crystals are strongly birefringent.…”

Section: Mineralogical Characteristicsmentioning

confidence: 99%

Petrostructural Signature of the Monazite of Andoharano Ambatofinanadrahana, Madagascar

Razafimahatratra¹,

Andriamamonjy²

2018

JMSE-A

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The monazite deposit at Andoharano is 7 km NE of Ambatofinandrahana. It is in the form of filons of hydrothermal chalcedony origin both with monazite and barite, which intersects the small syenitic post-tectonic massif, aged 550 to 510 Ma. The syenite is part of the Ambalavao-Kiangara-Maevaranomagmatic suite located in the Itremo sub-domain. The mineralized filon's length is approximately 100 meters with an average thickness of 2 to 5 meters, direction N75 and a subvertical dip. It is characterized by the mineralogical association of monazite, chalcedony, barite, quartz and magnetite. Two deformation phases affect the emplacement of the deposit. The first phase corresponds to the crystallization of the automorphic monazites, while the second phase affects the filon which leads to the fracturing of the first through silicification and which leads to the formation of the small xenomorphic monazite crystals. The monazite appears as brownish spots scattered in the rocks. It is rich in ceric earth (32% to 33%) and low in thorium. It constitutes ceric earth ore in the region.

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Monazite from mountain to ocean: a case study from Trolognaro (Fort-Dauphin), Madagascar

Cited by 23 publications

References 31 publications

Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

The Origin of Skarn-Hosted Rare-Metal Mineralization in the Ambohimirahavavy Alkaline Complex, Madagascar

Petrostructural Signature of the Monazite of Andoharano Ambatofinanadrahana, Madagascar

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Monazite from mountain to ocean: a case study from Trolognaro (Fort-Dauphin), Madagascar

Cited by 23 publications

References 31 publications

Local Structural Effects of Eu3+ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

Local Structural Effects of Eu3+ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

The Origin of Skarn-Hosted Rare-Metal Mineralization in the Ambohimirahavavy Alkaline Complex, Madagascar

Petrostructural Signature of the Monazite of Andoharano Ambatofinanadrahana, Madagascar

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Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations

Local Structural Effects of Eu³⁺ Incorporation into Xenotime‐type Solid Solutions with Different Host Cations