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

B. K. Sahu

Abstract

No Abstract.

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B. K. Sahu ¹

Affiliations
1 Indian Institute of Technology, Powai, Bombay, IN

Abstract

No Abstract.

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B. C. Patro ¹, B. K. Sahu ², S. Guru ³

Affiliations
1 Department of Earth Sciences, Sambalpur University, Jyori Vihar, Burla, IN
2 Department of Marine Sciences, Berhumpur University, Bhanj Vihar, Berhumpur, IN
3 G. M. College, Sambalpur, IN

Abstract

Mechanical disintegration of source rocks and selective transport of resulting particles together generate log normally distributed traction, saltation, and suspension sand sub-populations of heavy minerals, ilmenite, zircon, rutile and sillimanite as for quartz. Plots of cumulative weight per cent frequencies in geometric size grades of these heavy mineral sand populations against an arithmetic size grade scale (mm. grade scale with equal class interval) on an arithmetic probability paper gives rise to a more sharply segmented curve than a plot of these frequencies against ∅ scale and hence may be more effective in environmental discrimination. Wadell's shape factor is shown to give satisfactory results in the estimation of equivalent hydraulic sizes of the above heavy minerals from the associated quartz sands in a saltation population. The reported hydraulic inequrvalcncy observed in the case of coarser sand grades of heavy minerals with respect to those of quartz is explained to be due to restricted availability of these sizes rather than to differenual entrainment.

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B. K. Sahu

Abstract

No Abstract.

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B. K. Sahu ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Bombay 400 076, IN

Abstract

No Abstract.

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B. K. Sahu ¹, J. Bagchi ¹

Affiliations
1 Dept of Earth Sciences, IIT, Bombay 400076, IN

Abstract

The irregularly spaced assay values of lead and zinc in different boreholes of Rampura-Agucha Pb-Zn deposit (Rajasthan), have been interpolated at equal intervals of one meter using cubic splines to obtain a constant lag, discrete spatial (time) series. The time series has been used subsequently for stochastic modelling of assay values along the drill holes. Univariate stationary models under the integrated autoregressive moving average scheme - ARIMA (p,d,q) - were established for each assay series along four borehole based on statistical analyses of their auto (acl-) and their partial (pacf) correlation functions. These models can be used for univariate forecasting of assay values at different distances. Among the candidate ARlMA (p,d,q) models, ARLMA (1,1,1)and ARIMA (1,1,0) were found to fit spatial distributions of Zn and Pb, respectiveIy, using the principle of parsimony.

Though linear stochastic models were developed for Rampura - Agucha Pb-Zn deposit, a brief review of the scope and use of non-linear stochastic model for modelling of complex ore mineralisation has also been attempted.

Geochemical interpretation has been carried out on the petrochemical data of the amphibolites interlayered with the footwall and the hanging wall rocks using partial correlation coefficients between various oxides. This has led to comprehensive characterisation of the geochemistry and mineralogy of the amphibolites.

Keywords

Cubic Splines, Time Series, Integrated Autoregressive Moving Average Model [ARIMA (p,d,g)], Auto and Partial Correlations, Parsimony.

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B. K. Sahu ¹

Affiliations
1 Geological Survey of India, Southern Region, Hyderabad - 500 068, IN

Abstract

The Southern Aravalli Fold Belt represents a geologically complex terrain comprising migmatites, gneisses, low-grade metasediments and intrusive granites. Processing and interpretation of the existing aeromagnetic data using modern techniques has helped in understanding the geological complexity of the area. High quality aeromagnetic maps - total intensity, vertical derivative, analytic signal and 3D Euler depth - have been produced from the digitally processed data to augment visualisation and interpretation of the data. Strong east-west to northeast-southwest long strike-length anomalies in the southern part within the gneissic/granitic terrain indicate presence of narrow bands of high-susceptibility (magnetic) materials probably along regional lineaments. The thick sequence (> 1 km) of magnetically transparent sedimentary cover in the Rajgad basin is better visualised in the analytic signal and Euler Depth maps. The sediments in the northern part of the basin are deposited in a grabben formed by a northwest-southeast trending marginal fault in the north and an intrabasinal east-west fault in the south as demonstrated in the Euler 3D map. The Lunavada and Champaner Groups are separated by a shear zone comprising en-echelon shears clearly indicated in the shaded relief and vertical derivative maps. Interpretation of magnetic relief of the aeromagnetic data reveals that the area comprises of five distinct litho-tectonic units. This study demonstrates that the old aeromagnetic data acquired few decades back can provide valuable geological information, if processed using modern techniques.

Keywords

Aeromagnetic Survey, Aravalli Fold Belt, Migmatites, Godhra Granite, Gujarat.

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