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R. C. Sinha ¹, N. C. Ghose ¹

Affiliations
1 Department of Geology, Patna University, Patna, IN

Abstract

The present studies deal with the nature of the chemical changes induced in a suite of Archaean metasediments of varying lithologies during the emplacement of a granitic pluton. On the basis of a large number of analyses of the affected and unaffected rocks it has been shown that the nature and magnitude of the chemical changes have been primarily governed by the original composition of the respective zones, while the other factors have played only a secondary role. It has been suggested that the idea of 'basic front' is out of place in the context of granitization and that it refers to an altogether different process. Similarly it has been shown that the process of granitization, truly speaking, is very restricted in its application and that it is not correct to ascribe such processes as metamorphic differentiation, feldspathization and alkali metasomatism to it.

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N. C. Ghose ¹

Affiliations
1 Department of Geology, Patna University, Patna, IN

Abstract

No Abstract.

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C. B. Sharma ¹, N. C. Ghose ²

Affiliations
1 Public Health Institute, Patna 800004, IN
2 Department of Geology, Patna University, Patna 800005, IN

Abstract

The present study reveals that chemical pollution around Patna in the river Ganga (av. B.O.D. 2.3 ppm) is rather insignificant. but the bacteriological pollution is alarmingly high (av. 904/ml of most probable number, MPN, count) within 10 metres of the right bank. The higher MPN count of drain water (av. 6.2 × 10⁶/ml) is drastically reduced to seven thousand times within a distance of 500 metres in the downstream. High regenerating capacity of Ganga has been ascribed to be due to the higher concentration of sbortlived isotope of radium in comparison to that of its tributaries, viz., Son and Gandak.

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N. C. Ghose ¹, D. Mukherjee ², N. Chatterjee ³

Affiliations
1 G/608, Raheja Residency, Koramangala, Bangalore - 560 034, IN
2 Department of Geology, Patna University, Patna - 800 005, IN
3 Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, Massachusetts 02139, IN

Abstract

The Chotanagpur gneiss-Granulite complex (CGGC)-a mobile belt north of the Archaean Singhbhum cratonic nucleus and contiguous orogenic belt with the Singhbhum Proterozoic basin, is a vast tract of high-Grade rocks and gneisses with enclaves of granulite and metasedimentary rocks, and intrusive granites of Proterozoic age. Pervasive intrusions of mantle-Derived rocks of varied composition ranging from mafic-Ultramafic, sodic-Ultrapotassic alkaline rocks, massif anorthosite to younger tholentic basalts (Rajmahal) and dolerite at different geological periods ranging from Late Paleoproterozoic to Early Tertiary, give evidence of an active mantle in the prolonged history of evolution of this mobile belt. The present study is limited to metamorphosed mafic-Ultramafic rocks at the eastern sector of CGGC. The mafic-Ultramafic suite is represented by amphibolite, basic granulite and hornblendite. Compositions of the primary amphibole in these rocks range from hornblende to pargasitic hornblende, and plagioclase from An₄₀ to An₅₉. Positive correlation of Mg# between clinopyroxene and hornblende, and clinopyroxene and orthopyroxene, indicating that the Fe-Mg exchange K_D is constant between the ferromagnesian minerals, and the rocks to have attained equilibrium conditions of metamorphism. Calculated post-Peak metamorphic equilibrium pressures and temperatures are 3 8-5 4 kb and 643- 781°C, similar to conditions in the surrounding country rocks.

Chemically, the metabasic rocks studied are associated with the Bengal anorthosite massif at Saltora and have been grouped into low-Ti and high-Ti tholeiites. The former shows similarity with transitional basalts derived from T-MORB, while the latter is rich in incompatible elements and shows affinity with basalts derived from E-MORB or from recycled mantle fed by subducted oceanic crust. The nepheline normative ultramafic rock is the most depleted in incompatible elements and shows similarity in trace element contents with MORB. All these rocks show variable crustal contamination. Nevertheless, the bulk chemical compositions of the low-Ti rocks preserve evidence of low-Pressure fractional crystallisation involving olivine, plagioclase and clinopyroxene. The intra-cratonic Mesoproterozoic bi-Modal (tholeiitic-alkaline) magmatism in CGGC is analogous to Phanerozoic magma generation(Rajmahal tholentes-Ultrapotassic mafic-Ultramafic intrusions in the Gondwana basins) in a rift setting (Damodar graben /Shield margin faults) accompanied with crustal thinning. The trace element geochemistry of mafic-Ultramafic rocks gives evidence of plume-Generated magmatism in the Eastern Indian Shield margin during Mesoproterozoic time, which is correlatable with the global thermal event in the Precambrian shields.

Keywords

Mafic-Ultramafics, Mesoproterozoic, Intra Cratonic Magmatism, Mantle Plume, Chotanagpur Gneiss-Granulite Complex, Eastern India.

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N. C. Ghose ¹, Kabita Das ², Dipankar Saha ³

Affiliations
1 Department of Geology, Patna University, Patna - 800 005, IN
2 Department of Chemistry, Ram Mohan Roy Seminary, Patna - 800 004, IN
3 Central Ground Water Board, Jai Prakash Bhawan, Dak Bungalow, Patna - 800 001, IN

Abstract

The vast tract in Gandak basin in north Bihar is known iodine deficient area and the population is prone to dreaded and endemic disease like goiter. The present study provides an in-depth account of the iodine content of the Gandak basin in terms of spatial and seasonal variation in both soil and water system in one of the most fertile and thickly populated part of Mid-Ganga basin. In surface water, iodine content ranges from 1.56 ug/1 to 5.52 jjg/1, while in groundwater which is the only source for drinking, it varies from 2.1 ug/1 to 4.56 ug/1. In addition to iodine, pH, dissolved oxygen, Ca, Mg and CI of water were also analyzed. Only pH is found to have good correlation with iodine. In soil, the iodine content ranges between 3.65 ug/gm to 12.59 (ig/gm. Seasonwise, there is considerable variation in iodine content both in surface and groundwater. During monsoon it reduces considerably in surface water due to dilution and in groundwater it reduces owing to heavy recharge of the aquifer system through infiltration. In soil, there is no definite pattern in seasonal variation in iodine content. Spatially iodine decreases towards south in both groundwater and river water. In major part of the study area, the iodine content is deficient and ranges between 3 and 4 ug/1. The cause of low iodine is attributed to repeated floods and erosion of top soil which is the main source of iodine to the groundwater system.

Keywords

Iodine, Groundwater, Surface Water, Soil, Gandak Basin, Bihar.

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N. C. Ghose ¹

Affiliations
1 G/608, Spruce, Raheja Residency, Koramangala, 3rd Block, Bangalore 560 034, IN

Abstract

Occurrence of native gold and gold-silver alloy formed in high-temperature olivine gabbro of a layered cumulate body is reported 2 km northwest of Sutsu. It lies close to a major fault in the central part of Late Cretaceous-Eocene Naga Hills ophiolite (NHO). The amphibole-bearing olivine gabbro is composed of serpentine (MgO-28.91), anorthite (An93), clinopyroxene (En46Fs8Wo46), edenite (Mg# 76), magnesiohornblende (Mg# 78), accessory minerals, viz., chlorite (Mg# 75), epidote, sulphides (chalcopyrite and millerite) and gold. The formation of noble metals in olivine gabbro is related to partitioning of Au into intercumulus sulphides and silicates in magma and their deposition along grain boundaries and fractures. It was carried out by hydrothermal fluids by transportation and concentration of immiscible sulphide phases, and depositing these in suitable locales during final stages of crystallization. Gold mineralization in layered gabbros of cumulate bodies opens a new avenue towards primary source of precious metals in NHO. Alternative secondary source of precious metals in NHO, e.g. (i) basal conglomerate of cover sediments derived from ophiolite (Jopi or Pokhphur Formation), and (ii) placers of arterial Tizu River in Nagaland, may be considered as favourable repository.

Keywords

Anorthite, Gold–Silver Alloy, Layered Olivine Gabbro, Ophiolite, Native Gold.

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N. C. Ghose ¹, S. K. Chakraborty ¹

Affiliations
1 Department of Geology, Patna University, Patna, IN

Abstract

Composition of biotites from the pelitic schists and granitic rocks of McCluskieganj indicate that the former is rich in magnesium and the latter in iron; their Mg-Fe content is controlled by the composition of the respective host rock. The study of biotite of granitic rocks suggests that oxygen fugacites which prevailed during crystallization closely followed the QFM buffer. Positive correlation of Na between the co-existing K-feldspar and biotite in the granitic rocks, indicates that equilibrium conditions had reached during crystallization of these minerals. Experimental results of a porphyritic granite show that the rock was formed at the 'minimum melt' condition (655°C at PH₂0 = 4 kb).

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