Combined In Situ Chemical and Sr Isotopic Compositions and U–Pb Ages of the Mushgai Khudag Alkaline Complex: Implications of Immiscibility, Fractionation, and Alteration

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F41601670%3A_____%2F21%3AN0000009" target="_blank" >RIV/41601670:_____/21:N0000009 - isvavai.cz</a>

Alternative codes found

RIV/00216305:26620/21:PU143826

Result on the web

<a href="https://www.mdpi.com/2075-163X/11/5/450" target="_blank" >https://www.mdpi.com/2075-163X/11/5/450</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.3390/min11050450" target="_blank" >10.3390/min11050450</a>

Result language

angličtina

Original language name

Combined In Situ Chemical and Sr Isotopic Compositions and U–Pb Ages of the Mushgai Khudag Alkaline Complex: Implications of Immiscibility, Fractionation, and Alteration

Original language description

The Mushgai Khudag complex consists of numerous silicate volcanic-plutonic rocks including melanephelinites, theralites, trachytes, shonkinites, and syenites and also hosts numerous dykes and stocks of magnetite-apatite-enriched rocks and carbonatites. It hosts the second largest REE–Fe–P–F–Sr–Ba deposit in Mongolia, with REE mineralization associated with magnetite-apatiteenriched rocks and carbonatites. The bulk rock REE content of these two rock types varies from 21,929 to 70,852 ppm, which is much higher than that of syenites (716  241 ppm). Among these, the altered magnetite-apatite-enriched rocks are characterized by the greatest level of REE enrichment (58,036  13,313 ppm). Magmatic apatite from magnetite-apatite-enriched rocks is commonly euhedral with purple luminescence, and altered apatite displays variable purple to blue luminescence and shows fissures and hollows with deposition of fine-grained monazite aggregates. Most magmaticapatite within syenite is prismatic and displays oscillatory zoning with variable purple to yellow luminescence. Both magmatic and altered apatite from magnetite-apatite-enriched rocks were dated using in situ U–Pb dating and found to have ages of 139.7  2.6 and 138.0  1.3 Ma, respectively, which supports the presence of late Mesozoic alkaline magmatism. In situ 87Sr/86Sr ratios obtained for all types of apatite and calcite within carbonatite show limited variation (0.70572–0.70648), which indicates derivation from a common mantle source. All apatite displays steeply fractionated chondrite-normalized REE trends with significant LREE enrichment (46,066  71,391 ppm) and high (La/Yb)N ratios ranging from 72.7 to 256. REE contents and (La/Yb)N values are highly variable among different apatite groups, even within the same apatite grains. The variable REE contents and patterns recorded by magmatic apatite from the core to the rim can be explained by the occurrence of melt differentiation and accompanying fractional crystallization. The Y/Ho ratios of altered apatite deviate from the chondritic values, which reflects alteration by hydrothermal fluids. Altered apatite contains a high level of REE (63,912  31,785 ppm), which are coupled with increased sulfur and/or silica contents, suggesting that sulfate contributes to the mobility and incorporation of REEs into apatite during alteration. Moreover, altered apatite is characterized by higher Zr/Hf, Nb/Ta, and (La/Yb)N ratios (179  48, 19.4  10.3, 241  40, respectively) and a lack of negative Eu anomalies compared with magmatic apatite. The distinct chemical features combined with consistent Sr isotopes and ages for magmatic and altered apatite suggest that pervasive hydrothermal alterations at Mushgai Khudag are most probably being induced by carbonatite-evolved fluids almost simultaneously after the alkaline magmatism.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10505 - Geology

Project

<a href="/en/project/GX19-29124X" target="_blank" >GX19-29124X: EVOLUTION AND POST-EMPLACEMENT HISTORY OF CARBONATITES: IMPLICATIONS FOR THE MOBILITY AND CONCENTRATION OF CRITICAL METALS</a><br>

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2021

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Minerals

ISSN

2075-163X

e-ISSN

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Volume of the periodical

11

Issue of the periodical within the volume

5 - 23 April 2021

Country of publishing house

CH - SWITZERLAND

Number of pages

21

Pages from-to

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UT code for WoS article

000662455900001

EID of the result in the Scopus database

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