Temperatures of formation of pegmatites of Nellore mica-belt, Andhra Pradesh, India

Babu, V. R. R. M.

doi:10.2113/gsecongeo.64.1.66

Cited by 6 publications

(4 citation statements)

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“…Maurice (1982) suggested that kasolite is dimorphous with uranophane and beta-uranophane due to the complete replacement of Ca by Pb during the high degree of oxidation condition. Babu (1969) applied several geothermometers to the pegmatite of India and reported temperature of 700 o C for the pegmatitic magma with descending temperature of 670 o to 500 o C for biotite, 600 o to 300 o C for feldspars, 500 o to 435 o C for muscovite, 500 o to 400 o C for milky quartz and 300 o C for clear quartz in the core.…”

Section: Mineralogymentioning

confidence: 99%

Environmental radioactivity of pegmatites associating younger granite of Ras Baroud area, Central Eastern Desert, Egypt.

2020

The Egyptian Journal of Environmental Change

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Ras Baroud pluton is one of the well exposed granitic batholiths in the Central Eastern Desert of Egypt. The granites occure as isolated plutons of high relief circular and semicircular outlines. They are cut by zoned pegmatites and dikes of different types. The pegmatites are found as lenticular pockets and sheet-like bodies along the southern periphery of Ras Baroud pluton. The zonal sequence of the pegmatites is formed of an outer blocky feldspar zone. The intermediate mica zone (muscovite and/or biotite) and an inner zone of massive quartz might present in some pockets and absent in others. In some pegmatite pockets, the intermediate zone of mica occurs with some distinct dark alteration parts that record the highest radioactivity levels. The geochemical studies revealed that these pegmatites are attributed to low temperature late differentiated magmatic fluids enriched in volatiles.Field radiometric survey was used to evaluate the suitability of mineral resources at the different pegmatite zones to industrial use. The environmental radioactive parameters showed that the radioactivity of all four zones of the pegmatites is higher than the safety limit which indicate hazardous effects on human lives if used as indore building and/or ornamental stones. Also, the uranium migration rates and directions showed that uranium migrates from the radioactive altered zone which has the higher uranium content towards the other three pegmatite zones (outer, intermediate and inner zones).From a paragenetic point of view, zones in pegmatite are developed from the wall inward within a restricted pegmatitic stage. In the early stage, zoned pegmatites of simple mineralogy are produced. In the later stage, residual fluids rich in soda, silica, alumina and significant quantities of Nb, Ta, U, Th and F travel along fractures, react with the previously formed pegmatitic minerals forming new minerals of replacement origin.The zoned pegmatites host U-minerals (betafite and kasolite) as well as Nb-Ta mineral (columbite) as invisible disseminations in the intermediate alteration zone, that confines their formation in a temperature range between 300 and 500 o C. The hydrothermal activity and the alteration processes are responsible for the deposition of the uranium minerals.

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Section: Mineralogymentioning

confidence: 99%

Environmental radioactivity of pegmatites associating younger granite of Ras Baroud area, Central Eastern Desert, Egypt.

2020

The Egyptian Journal of Environmental Change

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“…Datta 1973), mineral and chemical composition (e.g. Babu 1969), mode of development (e.g. Soman & Nair 1986, Singh & Sharma 1997; and mineral paragenesis and rare met al mineralization (e.g.…”

Section: Structural Classificationmentioning

confidence: 99%

“…The extensive belts of pegmatites in India of Precambrian age are those of the three mica-producing fields of Bihar, Rajasthan and Nellore (Babu 1969, Bhola 1971, Datta 1973. The Bastar-Koraput belt of Madhya Pradesh and Orissa is well known for its rare met al (Sn, Ta, Be and Li) bearing minerals, such as cassiterite, columbite, tantalite, beryl, lepidolite, amblygonite, etc.…”

Section: Introductionmentioning

confidence: 99%

Granitic Pegmatites of Koradi-Kolar Sector, Nagpur District, Central India: Field, Petrographic and Mineralogical Features

GWALAN

DALAL

et al. 1999

RBG

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Several bodies of pegmatites have been located within the rocks of Sausar Group (Precambrian) occurring in the Kolar valley, north of Koradi, in Nagpur district of Central India. The XRD and the chemical data have shown that these pegmatites are mostly potassic (K 2 O= 15.58 to 16.31 % and Na 2 O=2.50 to 3.12 %) and are barren of economic mineral deposits. The pegmatites range from a few cm to more than 50 m in width with a maximum extension of about one kilometre. Several mappable pegmatite bodies trend roughly EW and NS, and many good outcrops are encountered in the Kolar Valley and Suradevi Hills. Based on the field and petrographic studies, the pegmatites of this area are characterised in terms of size, shape and mode of emplacement. They are mostly tabular, lenticular, branching and irregular bodies, localised along bedding, foliation, fault planes, tension joints and fold axis. Structurally they can be subdivided into concordant and discordant types on the basis of their relationship with the country rocks. Mineralogically, pegmatites are grouped into (1) Simple Pegmatite, containing quartz, feldspar, biotite, apatite, garnet and (?) monazite, and (2) Complex Pegmatite comprising in addition muscovite, tourmaline and epidote. However, common mineral variation is observed at different places within the same body of pegmatite. In these pegmatites, muscovite, quartz, tourmaline and feldspar seem to have developed mainly in two distinct generations, for example, the muscovite of earlier generation forms tiny "books" while later crystals occur as small disseminated flakes in the groundmass of less coarser quartz. The earlier quartz is strongly deformed, while the later occurs as veins of variable dimensions. The black tourmaline of earlier generation is represented by schorlite and of later origin has been identified as dravite. It may be concluded that these pegmatites were formed by the influx of fluids rich in silica, Al and K that filled the fractures and other planes of weakness (foliation) in the host rocks. The alkali components while migrating towards the wall of the country rocks, crystallised as muscovite and feldspar. In larger pegmatite bodies of Suradevi Hills, the development and concentration of muscovite along their contact with the mica schist is probably due to the migration of Al and K and volatiles towards the border of the intrusion. This crystallization of muscovite in preference to potash-feldspar may be due to the presence of high contents of volatiles.

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“…In India, pegmatites are of Precambrian age and occur in different geological domains [15] [16] [17] and contain rare metal (Sn, Ta, Be and Li) bearing minerals, such as cassiterite, columbite, tantalite, beryl, lepidolite, amblygonite [18] [19] [20], pollucite [21]. These pegmatite belts are localised in metamorphic terrains and are genetically related to various granitic bodies [5] [22] [23] [24].…”

Section: Introductionmentioning

confidence: 99%

Petrological and Geochemical Studies of Lepidolite (LCT Type) and Non-Lepidolite Pegmatite’s from Chakrasila, Dhubri District, Assam, North East India

Meshram¹,

Singh²,

Mishra³

et al. 2021

OJG

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Lepidolite pegmatite occurs as intrusive within biotite gneiss and amphibolite of Assam Meghalaya Gneissic Complex (AMGC) or Precambrian Gneissic Complex in the Dhubri district, Assam. AMGC is the north western extension of the Proterozoic rocks of Meghalaya Plateau or Shillong plateau. In the field it occurs as small to large veins and scattered boulders. Lepidolite pegmatite is later intruded by non lepidolite pegmatite. Pegmatites are medium to coarse grained with quartz and K-feldspar. It also contains lepidolite, which occurs in the form of flakes and clusters varying from pink to purple in colour. Petrography of lepidolite pegmatite reveals lepidolite as major constituents with quartz, K-feldspar and muscovite as minor constituents. XRD analysis reveals lepidolite (muscovite) is major mineral phase with kaliophilite in minor amount. Geochemically, they are calc-alkaline to high calc-alkaline and per-aluminous in nature. On the basis of Alumina Saturation Index (ASI), these pegmatites resemble Lithium-Cesium-Tantalum (LCT) family and compositional affinity with S-type granites of orogenic environments. Trace element compositions (Rb, Sr, Ba) indicate crystal fractionations, variable degrees of fractionation, highly evolved nature of pegmatite's and strongly differentiated granites protoliths as source. The different tectonic discrimination diagrams indicate S-type and I-type melt for pegmatite derivations. Therefore, both the studied pegmatites could be an evolved variety of granitic rocks that originated from the same magma. The REE is relatively low to

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Temperatures of formation of pegmatites of Nellore mica-belt, Andhra Pradesh, India

Cited by 6 publications

References 0 publications

Environmental radioactivity of pegmatites associating younger granite of Ras Baroud area, Central Eastern Desert, Egypt.

Environmental radioactivity of pegmatites associating younger granite of Ras Baroud area, Central Eastern Desert, Egypt.

Granitic Pegmatites of Koradi-Kolar Sector, Nagpur District, Central India: Field, Petrographic and Mineralogical Features

Petrological and Geochemical Studies of Lepidolite (LCT Type) and Non-Lepidolite Pegmatite’s from Chakrasila, Dhubri District, Assam, North East India

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