Petrography and geochemistry of uranium mineralised Precambrian granitic-pegmatitic rocks of Mawlait, West Khasi Hills district, Meghalaya

Sen, Joydip; Ranganath, N.; Rathaiah, Y.V.; Sen, D. B.; Kak, S. N.

doi:10.1007/s12594-009-0168-8

Cited by 4 publications

(3 citation statements)

References 12 publications

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“…Alexandre & Kyser 2005;Deditius et al 2007). Analogous primary magmatic inclusions of uraninite in garnet have been locally described from peraluminous granites (Petrík & Konečný 2009) and granitic pegmatites (Sen et al 2009;Lima et al 2012). On the contrary, the anhedral uraninite inclusions in zircon are probably products of subsolidus degradation of the metamict host mineral.…”

Section: Mineral Compositionmentioning

confidence: 85%

Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

Uher¹,

Janák²,

Konečný³

et al. 2014

Geologica Carpathica

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Abstract:The granitic pegmatite dike intruded the Cretaceous UHP rocks at Visole, near Slovenska Bistrica, in the Pohorje Mountains (Slovenia). The rock consists mainly of K-feldspar, albite and quartz, subordinate muscovite and biotite, while the accessory minerals include spessartine-almandine, zircon, ferrocolumbite, fluorapatite, monazite-(Ce), uraninite, and magnetite. Compositions of garnet (Sps [48][49] Alm [45][46] Grs +And 3-4 Prp 1.5-2 ), metamict zircon with 3.5 to 7.8 wt. % HfO 2 [atom. 100Hf/(Hf + Zr) = 3.3-7.7] and ferrocolumbite [atom. Mn/(Mn + Fe) = 0.27-0.43, Ta/(Ta + Nb) = 0.03-0.46] indicate a relatively low to medium degree of magmatic fractionation, characteristic of the muscovite -rare-element class or beryl-columbite subtype of the rare-element class pegmatites. Monazite-(Ce) reveals elevated Th and U contents ( ≤ 11 wt. % ThO 2 , ≤ 5 wt. % UO 2 ). The monazite-garnet geothermometer shows a possible precipitation temperature of ~495 ± 30 °C at P~4 to 5 kbar. Chemical U-Th-Pb dating of the monazite yielded a Miocene age (17.2 ± 1.8 Ma), whereas uraninite gave a younger (~14 Ma) age. These ages are comtemporaneous with the main crystallization and emplacement of the Pohorje pluton and adjacent volcanic rocks (20 to 15 Ma), providing the first documented evidence of Neogene granitic pegmatites in the Eastern Alps. Consequently, the Visole pegmatite belongs to the youngest rare-element granitic pegmatite populations in Europe, together with the Paleogene pegmatite occurrences along the Periadriatic (Insubric) Fault System in the Alps and in the Rhodope Massif, as well as the Late Miocene to Pliocene pegmatites in the Tuscany magmatic province (mainly on the Island of Elba).

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Section: Mineral Compositionmentioning

confidence: 85%

Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

Uher¹,

Janák²,

Konečný³

et al. 2014

Geologica Carpathica

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“…The amount of uranium ranges from 1.60 to 3.10 ppm, while that of thorium ranges from 5.30 to 37.50 ppm. As a result, the samples that are currently analysed are distinguished by having different U and Th enrichment similar to that of Sen et al (2009). An in-depth analysis of the Th/U ratio, which ranges from 1.70 to 19.70, reveals that there is a significantly greater abundance of Th than U in the pelitic granulites, which points to the presence of considerable thorium mineralization in the study area.…”

Section: C Trace Element Characteristicsmentioning

confidence: 93%

“Geochronology and geochemistry of pelitic granulite from the South Delhi Terrane of the Aravalli Delhi Mobile Belt, NW India: implications for petrogenesis and geodynamic model”

et al. 2023

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An attempt has been made to illustrate the evolution of pelitic granulite from south of the Balaram-Abu road, which lies in the South Delhi Terrane (SDT) of the Aravalli-Delhi Mobile Belt (ADMB), using geochemistry and geochronology. The current work offers a plausible explanation for the protolith of pelitic granulite, nature of the sediments and its provenance. The elemental geochemistry of the pelitic granulites reveals that the protolith is an arkosic to shaley type. The rare earth elements pattern shows that there is a negative Eu anomaly and a small excess of LREE over HREE. This means that the source of sediments probably has the same elements as the upper crust. However, the amounts of Sr, Nd and Pb vary a lot, which shows that the sediments supplied from two different types of sources (felsic and mafic) in different proportions from a Proterozoic terrain. The monazite geochronology indicates that the metamorphic overprint occurred between 797 Ma and 906 Ma. Additionally, the ages correlate to the debris that was formed between the 1188 Ma and 1324 Ma from magmatic/sedimentary sources for pelitic granulite. The present research provides a more in-depth understanding of the evolutionary history of the pelitic granulite that comprises the SDT in the ADMB region during the Proterozoic era.

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“…Thorium content ranges from 32.52 to 85.39 ppm. Thus, the currently investigated granitoids are characterized by distinct uranium and thorium enrichment (Sen et al 2009). Critical examination of Th/U ratios (ranging from 3.22 to 6.77) indicates a relatively higher abundance of thorium over uranium and thereby suggests significant thorium mineralization in the Mylliem pluton.…”

Section: Major and Trace Element Characteristicsmentioning

confidence: 96%

Geochemistry and petrogenesis of Neoproterozoic Mylliem granitoids, Meghalaya Plateau, northeastern India

et al. 2011

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The Mylliem granitoids of the Meghalaya Plateau, northeastern India, represent one of the disharmonic Neoproterozoic igneous plutons, which are intrusive into low-grade Shillong Group of metasediments. Field studies indicate that the Mylliem granitoids cover an area of about 40 km 2 and is characterized by development of variable attitude of primary foliations mostly marked along the margin of the pluton. Xenoliths of both Shillong Group of metasediments and mafic rocks have been found to occur within Mylliem granitoids. Structural study of the primary foliation is suggestive of funnel-shaped intrusion of Mylliem granitoids with no appreciable evidence of shearing. Petrographically, Mylliem granitoids are characterized by pink to white phenocrysts of prismatic microcline/perthite and lath-shaped plagioclase (An 20 -An 29 ). Groundmass material is characterized by quartz, microcline, plagioclase, muscovite and biotite. Sphene and apatite occur as accessory minerals. Petrographically Mylliem granitoids have been discriminated as granite and granodiorite according to IUGS system of classification.Critical evaluation of geochemical data and variation trends of major oxides/trace elements suggests a significant role of fractional crystallization in the evolution of Mylliem pluton. Th/U ratios (3.22-6.77) indicate a relatively higher abundance of Th over U. Chondrite-normalized REE diagram characteristically shows an enriched LREE pattern and prominent negative Eu anomaly (Eu/Eu* = 0.16-0.42) indicating the significant role of plagioclase fractionation from the parent magma. An overall strong REE fractionation pattern has been envisaged for Mylliem granitoids. The strong REE fractionation of the Mylliem granitoids is depicted by (Ce/Yb) N values, which show a range of 1.39 to 1.65. The aluminium saturation index (ASI) (ranging from 1.0 to 1.3), A/CNK ratios (ranging from 1.4 to 2.11) and A/NK ratios (ranging from 1.75 to 2.43) provide evidences for the peraluminous, S-type nature of the Mylliem granitoids. The peraluminous, S-type character is further supported by geochemical parameters such as Fe* and MALI (modified alkali lime index). Normative corundum >1.0 wt.% is suggestive of the S-type nature of Mylliem granitoids. This is indicative of parent melt-extraction from metasedimentary source rocks by partial melting. Distinct geochemical parameters suggest a post-orogenic tectonic environment for the Mylliem granitoids. The peraluminous, calc-alkalic to alkali-calcic, post-orogenic Mylliem granitoids are geochemically correlatable with the post-orogenic Caledonian granitoids of Ireland and Britain.

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Petrography and geochemistry of uranium mineralised Precambrian granitic-pegmatitic rocks of Mawlait, West Khasi Hills district, Meghalaya

Cited by 4 publications

References 12 publications

Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

“Geochronology and geochemistry of pelitic granulite from the South Delhi Terrane of the Aravalli Delhi Mobile Belt, NW India: implications for petrogenesis and geodynamic model”

Geochemistry and petrogenesis of Neoproterozoic Mylliem granitoids, Meghalaya Plateau, northeastern India

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