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

P. S. N. Murthy ¹, K. Krishna Reddy ¹

Affiliations
1 National Mineral Development Corporation, Donimalai Township, 583118, Bellary District, IN

Abstract

Confirmed stromatolites from a limestone band from Sandur greenstone belt of Karnataka Craton are reported for the first time. The stromatolites are oval to elliptical in shape in gently dipping bedding plane and conical in cross section. Indirect radiometric age data indicates the rocks in which the structures occur are 2900 m.y. old. The discovery of stromatolites demonstrates that biological processes were operative in the early Archaean basins of the Karnataka Craton.

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P. S. N. Murthy ¹, A. K. Chatterji ², K. Kameswara Rao ³

Affiliations
1 N. M. D. C. Limited, Donimalai Township, Bellary District 583118, IN
2 C.P.O. N.M.D.C. Limited, 'Pioneer House' 6-3-653, Somajiguda, Hyderabad 500004, IN
3 Andhra University, Waltair 530003, IN

Abstract

Folds belonging to two generations are identified which have been named as early and late structures. It is possible that the early structures may include folds of two different generations, the more compressed (F_1A) and less compressed (F_1B). The late structures are referred to as (F₂).

The F_1A folds show parallel isogon pattern, while F_1B folds have weakly converging isogon pattern, suggesting their flexural nature. The late generation folds F₂ have bands with convergent isogons alternating with divergent isogons. The isogons' analyses did not reveal any systematic difference in competency between hematite and chert. Gaps between two layers with similar curvature, however, are filled by hematite, suggesting that hematite was less competent compared to chert.

t_α (t_α/t_o) measurements were carried out on different layers of all folds. The observations are; (1) the layers in F_1A folds predominantly belong to class 3 or 1C (2) the F_1B fold layers belong to class 1A, 1C and 3, (3) the F₂ folds predominantly belong to class 1A though other classes are also present. The F_1A are most flattened and F₂ are least compressed. The fold geometry is very complex, as the same layer falls under different classes of folds at different values. Apart from the complexity of folding, this may be partly due to the original feature of banding.

Presence of disharmonic folds and variation of wave length with thickness of layers suggest that the folds were initiated by buckling. The F_1A folds underwent considerable flattening subsequently due to compresssion.

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P. S. N. Murthy ¹, A. K. Chattterjee ¹

Affiliations
1 N.M.D.C.L.t d., 10-3-311/A, Masab Tank, Hyderabad-500 028, IN

Abstract

Donimalai area is located in the SE portion of the Sandur Schist belt of Precambrian age. There are 6 ore deposits comprising 9 ore bodies having more than 150 million tonnes of high grade hematite ore in Donimalai area.

Banded Iron Formation (BIF) is the host rock for the iron ore deposits. Basaltic rocks, shales with tuff, dolerite and quartz veins are other important litho-units in this area. Principaly the BIF consists of alternative bands of iron oxides and chert belonging to oxide facies.

Hard laminated ore, medium hard laminated ore, soft laminated ore, friable powdery ore and blue dust are the major ore types with minor occurences of lateritic/limonitic ore and shally ore.

Leaching of silica has resulted in the origin of friable ore and blue dust. Leaching of silica followed by enrichment of iron oxide by the circulating solutions has given rise to hard laminated ore, medium hard laminated ore and soft laminated ore depending upon the degree of enrichment. Shaly ore occurs at the contact of deposit 1 with shale. It is formed due to the enrichment of shale by iron-rich solutions, Original material of shale has been replaced followed by enrichment of iron oxide giving rise to shaly ore.

Laterite ore/laterite occurs parallel to the surface of the ground with a thickness varying between 2-10 meters. They also occur along steeply dipping fault planes upto depths of 100-150 meters. parallel to the bedding. Geomorphic evolution of planation surface around 1000 mt. R.L. was responsible for the formation of flat surfaced laterites/lateritic ores. Activity of solutions along fault planes parallel to bedding has caused lateritisation/limonitisation at deeper lavels also.

Keywords

Iron Ore, Economic Geology, Donimalai, Kanataka.

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P. S. N. Murthy ¹, A. K. Chaterjee ²

Affiliations
1 C/O V K V Rao, FCA, Dondaparthy, Mandavanpeta, PO Visakhapatnam- 530 016, IN
2 2B-302, Express Apartments, Lakdikapul, PO Hyderabad - 500 004, IN

Abstract

Majority of the Iron ore deposits of the world in general and India in particular have originated due to the secondary enrichment of Banded Iron Formations. It is estimated that Indian as high grade iron ores to the tune of 9 6 billion tonnes. The geostatistical method of calculation of optimum drilling and, is presented, in the context of multivariables and examples are presented for three iron ore deposits. Based on studies on a number secondary enriched hematite iron ore deposits, with respect to many variables, in different iron ore belts in India, an optimum drilling grid of 50-60 m is suggested. Taking an average insitu bulk density of 3 3 tonnes/m³, the quantum of drilling works out to be 120-85 in per million tonnes of iron ore.

The quantum of drilling, indicates the necessary but not the sufficient condition. An example of specifications of the ore from buyers and improvement of quality in the mineral dressing plant are presented. For deciding the grid at local level, the data of blast holes which are drilled at a closer interval, can be used. It is stressed that always geology has to be taken into account, and if necessary a few inclined holes ate to be drilled. A few adits are also suggested for the sake of completeness of exploration. It is suggested that the approach should be comprehensive rather than viewing the problem in parts.

Keywords

Iron Ore Deposits, Optimum Drilling Grid, Exploratory Parameters Geostatistical Methods, Geological Blases.

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P. S. N. Murthy ¹

Affiliations
1 Mandavanpeta, Dondaparthy, PO Visakhapatnam - 530 003, IN

Abstract

This article brings out conceptual errors in some of the models of ore reserve estimation, suggested by Patterson (1959), Popoff (1966) and Peters (1987) with proofs wherever necessary and suggests the needed corrections Popoff, from the mistaken logic, gave the impression that angular bisectors divide the obtuse angle triangle into three areas of different shape but equal in size He further assumed that the intersection of angular bisectors is the centre of gravity. He assumed the manner of dividing the triangle by angular bisector is the rule of gravity. In reality the rule of gravity and centre of gravity refer to median way of dividing the triangle Popoff equated in centre with centroid which iS true only in the case equilateral triangles.

There is a conceptual error m respect of formation of polygonal blocks around sample points by construction of angular bisectors enunciated by Patterson (1959). Though claimed to be logical steps, there is faulty logic w H, namely the so called angular bisectors need not form the block always.

Unless these are specifically pointed out by somebody, it is felt that these errors will get transmitted from a teacher to a student and from one book to the other. For example Peters (1987) adopted the models of Patterson (1959) without pointing out the errors and deficiencies.

Keywords

Ore Reserve Calculations, Conceptual Errors, Polygonal Blocks, Random Sampling.

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P. S. N. Murthy ¹

Affiliations
1 46- 18-13, Mandavaripeta Visakhapatnam-530 016, IN

Abstract

No Abstract.

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P. S. N. Murthy

Abstract

No Abstract.

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K. Sreeramachandra Rao , P. S. N. Murthy

Abstract

No Abstract.

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