BAPI GOSWAMI

Geology

C BHATTACHARYYA

A MANDAL

A RAY

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of the Geological Society of India

The area of investigation at and around Mashak Pahar, Bankura district, West Bengal, India comprises a number of rock types namely: granite gneiss, migmatized quartz tourmaline gneiss, quartz pebble conglomerate, ferruginous quartzite, quartz tourmaline veins (as veins) and graphite schists. Interestingly, the study area lies in the region extending South Purulia Shear Zone (∼Tamar–Porapahar Shear Zone) which marks the boundary between two contrasting tectonic blocks of eastern India, namely, the Chhotanagpur Gneissic Terrane (CGC) to the north and Singhbhum Group of rocks to the south. The rocks of the study area are poly-phasedly deformed by three phases of folding, namely, F1, F2 and F3. All the tourmalines are classified to be of ‘Alkali Group’. Chemistry of tourmalines from migmatized quartz tourmaline gneiss and those from quartz tourmaline veins are in conformity with their relation to (earthquake induced) shear system evolution in this terrain. In general, the compositional evolution of tourmaline during prograde metamorphism (∼400◦–730◦C) has been supported by both petrographic and chemical evidences. Assessment of mineral–chemical data of constituent tourmaline grains clearly suggests compositional variations across zonal boundaries within tourmaline that was controlled by changing metamorphic milieu in this terrane. Field and petrographic evidences clearly indicate activation of earlier and later shears in this region accompanied by infiltration of boron and formation of zoned tourmaline crystals. © Indian Academy of Sciences.

Fulltext

Journal of Earth System Science

Mineral chemistry of tourmaline from Mashak Pahar, South Purulia Shear Zone (SPSZ), eastern Indian shield

The variant rock types of an Alkaline-Carbonatite Complex (ACC) comprising alkali pyroxenite, nepheline syenite, phoscorite, carbonatite, syenitic fenite and glimmerite along with REE and Nb-mineralization are found at different centres along WNW-ESE trending South Purulia Shear Zone (SPSZ) in parts of Singhbhum Crustal Province. The ACC occurs as intrusions within the Mesoproterozoic Singhbhum Group of rocks. Alkali pyroxenite comprises of aegirine augite, magnesiotaramite, magnesiokatophorite as major constituents. Pyrochlore and eucolite are ubiquitous in nepheline syenite. Phoscorite contains fluorapatite, dahllite, collophane, magnetite, hematite, goethite, phlogopite, calcite, sphene, monazite, pyrochlore, chlorite and quartz. Coarse fluorapatite shows overgrowth of secondary apatite (dahllite). Secondary apatite is derived from primary fluorapatite by solution and reprecipitation. The primary fluorapatite released REE to crystallize monazite grains girdling around primary apatite. Carbonatite is composed dominantly of Srcalcite along with dolomite, tetraferriphlogopite, phlogopitic biotite, aegirine augite, richterite, fluorapatite, altered magnetite, sphene and monazite. The minerals comprising of the carbonatite indicate middle stage of carbonatite development. Fenite is mineralogically syenite. Glimmerite contains 50-60% tetraferriphlogopite. An alkali trend in the evolution of amphiboles (magnesiotaramite- magnesiokatophorite-richterite) and chinopyroxenes (aegirine augite, aegirine) during the crystallization of the suite of rocks is noted. Monazite is the source of REE in phoscorite and carbonatite. Fluorapatite has low contents of REE, PbO, ThO2 and UO2. Pyrochlore reflects Nb-mineralization in nepheline syenite and it is enriched in Na2O, CaO, TiO2, PbO and UO2. Pyrochlore containing UO 2 (6.605%) and PbO (0.914%) in nepheline syenite has been chemically dated at 948 ± 24 Ma by EPMA. © 2014 Geological Society of India.

Petrography and mineral chemistry of Alkaline-Carbonatite Complex in Singhbhum Crustal Province, Purulia region, Eastern India

A new occurrence of (syenite-hosted) Vanadium bearing titaniferous magnetite ore body has been reported from Ganjang (26°09'35" N: 93°20' E), Karbi-Anglong, Northeastern India. The magnetite ore bodies have lumpy and sporadic occurrences within the host syenite pluton intrusive into gneissic country rocks. Ore microscopic studies reveal that magnetite is often associated with haematite and ilmenite depicting different textural patterns. Critical consideration of several elemental patterns suggests magmatic differentiation to be main ore-forming process. The ore body is suggested to have been formed as late stage segregation from a differentiating alkaline magma in a fluid enriched milieu. © GEOL. SOC. INDIA.

Journal	Journal of the Geological Society of India
Publisher	-
ISSN	0016-7622
Open Access	No