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

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, 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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