Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. K. Som ¹, A. K. Bhattacharya ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, IN

Abstract

Recent weathering of Panchpatmali bauxite-bearing terrain, Koraput district, Orissa has been discussed in terms of groundwater geochemistry. pH and Eh are in favour of Fe (OHh development, whereas Na⁺ : Ca²⁺ vs. HCO₃ : SiO₂, HCO₃ : SiO₂ vs. ppm HCO) and pH -pNa, 2pH -pCa, pK-pH vs. -log [H₄ Si0₄] are all in favour of kaolinite development with a minor amount of gibbsite. These observations have been confirmed by X.R.D., I.R., and S.E.M. of the recent weathered samples of the area. The condition of development of these mineral phases with respect to C0₂ has  also been discussed.

Keywords

Ground Water Geochemistry, Weathering, Bauxite, Koraput, Orissa.

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S. K. Som ¹, A. K. Bhattacharya ²

Affiliations
1 Geological Survey of India, Unit: VIII : Nayapalli, Bhubaneswar - 751 012, IN
2 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN

Abstract

Mineralogy of bauxite profile, after khondalite parentage, at Panchpatmdi area, Koraput district, Orissa is studied by XRD, JR, DTA and Optical/electron microscopy. XRD shows thedominance of kaolinite in saprolite, whereas IR and DTA results confirm its presence in the entire profile. All the above studies confirm the strongly disordered nature of kaolinite. Gibbsite, geothite, hematite, diaspore and allophane are present in the entire profile with the intermittent occurrence of boehrnite, anatase, and futile. Microscopic investigation reveals poIycyclic crystalisation of gibbsite and ultimately resilicated to kaolinitevia dlophane. Transformation of alurninious parent minerals to gibbsite is direct without the intermediate kaolinite stage. Evidences are presented to show that gibbsites are later transformed to kaolinite due to ground water activities.

Keywords

Bauxite, Mineralogy, Panchpatmali, Orissa.

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S. K. Som ¹, R. Joshi ², P. K. Roy ², M. M. Mukherjee ²

Affiliations
1 Geological Survey of India, Opn.WB-S-A&N, 4, Chowringhee Lane, Calcutta 16, IN
2 Geological Survey of India, Unit:8, Nayapalli, Bhubaneswar 12, IN

Abstract

Sukinda ultramafic field of Jajpur district, Orissa is capped by thick lateritic duricrust. Two generations of laterite are inferred in the studied area. The older laterite (in situ) is capped by transported laterite (younger). The entire area is divided into two subareas (A₁ and A₂) Physiographically, three terraces are identified in A₁ area, of which, the oldest one (T₃) comprises of insitu lateritic hard crust. The other two terraces (T₂ and T₁) are made up of valley fill deposits, which are later lateritised. The area A₂ shows the lateral continuity of T₃ terrace of A₁ area along with valley fill deposit of T₁ terrace and the absence of T₂ terrace. Drainage analysis show the A₁ area is structurally more disturbed than A₂ area. Correlation of geomorphological evolution and lateritisation indicates three stages of development in the A₁ area. Lateritisation was initiated on a comparatively flat ground (T₃ terrace) and subsequent destabilisation of the area developed the younger terraces (T₂ and T₁) with the modification of older laterite profile.

Keywords

Geomorphology, Laterite, Morphometric Evolution, Sukinda, Orissa.

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S. K. Som ¹, R. Joshi ², G. Neogi ², M. M. Mukherjee ²

Affiliations
1 Geological Survey of India, Opn. WB-S-A&N, 4, Chowringhee Lane, Calcutta 700 016, IN
2 Geological Survey of India, Opn. Orissa, Unit: 8; Nayapalli, Bhubaneswar 751012, IN

Abstract

The geochemistry of groundwater over Sukinda ultrabasic - basic rocks, Orissa, covering an areat extent of about 50 km², has been investigated to understand the hydrogeology of the area. The dominant geochemical processes were interpreted from geochemical data and mass balance calculations. The entire study area contains two broad lithounits comprising ultrabasic rock at the centre and metabasics at eastern and western flanks, with a general groundwater flow pattern from east to west. The groundwater in the area is fresh, meteoric in origin with high Na, Kover metabasics as well as the northern part of the ultrabasic rock, and high Mg, HCO₃^- and TDS over the remaining ultrabasic rock. Mineral solubility study of Mg^- phases present in the system shows that the present day geochemical conditions are not suitable for Mg²⁺ precipitation and most likely, serpentine is the dominant Mg²⁺ contributer in the system. Mass balance calculations based on mixing ratio along the E-W flow path show that K and to some extent Na behave conservatively in the evolution of groundwater. The conservative mixing model presented here evaluates the formation of secondary mineral phases along the flow path.

Keywords

Geochemistry, Groundwater, Mass Balance Calculation, Sukinda, Orissa.

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S. K. Som ¹

Affiliations
1 Earthquake Geology Division, Geological Survey of India, Eastern Region, DK Block, Sector-II, Salt Lake City, Kolkata-700091, IN

Abstract

Celsium bearing aplitic pegmatites ot Chhotanagpur Gneissic complcx Purulia district. West Bengal show enrichment in U and Th through at least one phase of lanthanide actinide rich hydrothermal activity. Monazite group of minerals with Th and REE are hosted by the aplitic pegmatites with varying texture and composition. Monazite(Ce) occurs as inclusions within quartz and feldspar with evolutionary trcnd from huttonitic monazite at core to monazite (Ce) at rim Ce/Sm ratio varies from 8 11 to 25 67 representing a wider evolutionary trend of the melt from which monazite crystallized. Principal component analysis shows different subsitution phenomenon in monazite. Chemical variations indicate the huttonitic monazite to be a primitive component which was transformed to monazite (Ce) by interaction with LREE P-rich fluid.

Keywords

Aplitic Pegmatite, Cesium REE, Cheralite, Monazite, Chhotanagpur, Gneissic complex, Belamu Purulia, District West Bengal.

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S. K. Som ¹, P. Jana ¹, U. Bhattacharya ², Sandeep Bardhan ¹, S. R. Basir ³, A. K. Ghosh Roy ¹

Affiliations
1 Earthquake Geology Division, Geological Survey of India, Eastern Region, DK-Block, Sector-II, Salt Lake City, Kolkata - 700 095, IN
2 Earthquake Geology Division, Map Division, Geological Survey of India, Eastern Region, DK-Block, Sector-II, Salt Lake City, Kolkata - 700 095, IN
3 Earthquake Geology Division, TC-1 Division, Geological Survey of India, Eastern Region, DK-Block, Sector-II, Salt Lake City, Kolkata - 700 095, IN

Abstract

A moderate earthquake struck the Sikkim Himalaya on Tuesday, February 14, 2006 at 6.25 am. The earthquake was felt in North Bengal, Sikkim,nepal and Bhutan. Macroseismic survey was carried out for the accessible regions of Sikkim and the northern portion of West Bengal to assesses the intensity of ground motion, the damage caused by the earthquake and also to ascertain the possible source and its orientation.

The survey results show that the MSK (Medvedev-Sponheuer-Karnik) intensity varies between III to VII. The maximum intensity is found in Gangtok-Deorali-Tadonga areas, which are far from the instrumental epicenters identified by USGS and IMD. Statistical procedure has been adopted for numerical weighted intensity calculation to quantify the MSK intensity and for deducing the isoseismal lines more logically. Separate macroseismc epicenter is calculated from the high MSK- intensity sites, which falls in between Deoralt and Tadong. The probable orientation of the source (fault) is found to be E-W that passes through Makha village, north of Gangtok area. The damages to constructions on the terraces is much less than those constructed on other topographic forms, like slopes, ridges and low zones. Within the most damaged Gangtok-Deorail Tadong areas, most of the buildings are located along the ridge top or along the ridge axis.

Keywords

Earthquake, Macroseismic Survey, Sikkim.

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S. K. Som ¹, K. C. Bandyopadhyay ², R. K. Prasad ³

Affiliations
1 Earthquake Geology Division, Eastern Region, DK-Block, Sector-11, Salt lake City, Kolkata - 700 091, IN
2 H R D Division, 27, J L Neheru Road, Kolkata - 700 016, IN
3 Ranchi Institute, Ranchi Centre, 433 A, Road No 5 , Ashoknagar, Ranchi - 834 002, IN

Abstract

The cesium bearing aplite and pegmatite in the southern slope of Belamu hill occur in association with calc-Silicate and granite gneiss country rocks of Chhotanagpur Gneissic Complex (CGC). The hydrothermal units are highly peraluminous and tectonically disturbed in which, cesium is mainly incorporated within pollucite and Li-Muscovite Rb/Sr shows sympathetic relationship with cesium having a strong correlation towards the higher end for both aplite and pegmatite. Cesium resource evaluation by ground survey and shallow drilling has been done for aplite and pegmatite. Reserves and grades established for both aplite and pegmatite have shown concoidance with the statistical laws of distribution, suggestive of productive output.

Keywords

Cesium, Aplite, Pegmatite, Chhotanagpur Gneissic Complex, Belamu, West Bengal.

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S. K. Som ¹, R. Joshi ²

Affiliations
1 Geological Survey of India, Op. WB-S-A&N, GSI Office Complex, DK-Block, Sector II, Salt Lake City, Kolkata -700 091, IN
2 Geological Survey of India, Op. U.P., Vasundhara, Sector-E, Aligunj, Lucknow - 226 024, IN

Abstract

Weathering of serpentinite from Sukinda area, Orissa is studied from a series of lateritic profiles to understand the behaviour of nickel concentration at different parts of the regolith column. The area shows development of laterite profile of variable thickness. Fresh parent rock (serpentinite) is not exposed. Petro-chemical studies show that Ni is concentrated within nepouite and kerolite in partially altered serpentinite, whereas it is mainly in goethite and partly in Mn- oxides within saprolite horizon and negligible in top in situ laterite. Volumetrically, Ni-substituted goethite is more significant for exploration than Ni-substituted Mn-oxides. In the absence of fresh parent rock, methods such as normalization of chemical elements and calculation of mass balance relations between density and chemical elements are adopted, based on the mean element content of the profile. Application of these methods with studied samples clearly discriminate the residual and supergene behaviour of Ni in laterite column.

Keywords

Chemical Weathering, Laterite, Mass Balance, Ni-Concentration, Sukinda, Orissa.

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S. K. Som ¹, Vijay Shivgotra ¹, Ashim Saha ¹

Affiliations
1 Earthquake Geology Division, Geological Survey of India, Salt Lake City, Kolkata - 700 091, IN

Abstract

Several major earthquakes affected the stable continental Indian peninsular shield in recent past due to the activity of fault movements. This necessitates identifying the active faults in the region for future monitoring. The far field co-seismic and post-seismic effects of recent major earthquakes occurred at Sumatra, 2004, Pakistan, 2007 and Indonesia, 2007 on HYDE and IISc IGS GPS stations were studied by small span GPS analysis. Different type of movement pattern on displacement components ensure the reactivation of existing fault planes signifying an integral relationship between GPS displacement vectors and geological structure of the region.

Keywords

GPS, Active Fault, Earthquake, Peninsular India.

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S. K. Som ¹, K. C. Bandyopadhyay ¹, S. K. Basu ¹, D. K. Santra ¹, R. N. Ghosh ²

Affiliations
1 Geological Survey of India, Op. WB-S-A&N, GSI Office Complex, DK-Block, Sector 11, Salt Lake City, Kolkata -700 091, IN
2 Geological Survey of India, Zorem building, Nongrim Hills, Shillong - 793 003, IN

Abstract

The Li-Cs-Rb bearing Beku pegmatite occurs in a calc-silicate rock enclave within the Proterozoic Chhotanagpur Gneissic Complex (CGC). Its internal structure shows zonation that comprises an outer tourmaline-rich pegmatite and inner rare metal-bearing pegmatite containing spodumene-pollucite-lepidolite. The pegmatite is strongly peraluminous with high SiO₂, low Fe₂O₃(t), CaO, TiO₂, P₂O, and variable Al₂O₃, K₂O and Na₂O. Its Cs/Rb and Li/Rb values increase towards the centre and decrease towards the boundary. K/Rb value increases from pollucite-bearing pegmatite to tourmaline-rich pegmatite, depicting the more evolved nature of the pollucite-bearing pegmatite. Petrography and geochemistry of the Beku pegmatite suggest fractionation from a peraluminous S-type granitic magma. It is synchronous with shear development in the area, under a minimum formational P-T of 4 kbar and 500°C.

Keywords

Rare Metal (Li-Cs-Rb) Pegmatite, Calc Silicate Rock, Proterozoic, Chhotanagpur Gneissic Complex, Beku, West Bengal.

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