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

B. C. Raymahashay ¹, P. R. Bhavana ¹, K. S. Rao ¹, V. K. Mehta ¹

Affiliations
1 Department of Civil Engineering, Indian Institute of Technology, Kanpur 208016, IN

Abstract

The lateritic soils developed over Precambrian crystalline rocks near Calicut have relatively high Cation Exchange Capacity. At the same time, the soils are highly efficient for phosphate uptake. Both of these properties are traced to the presence of halloysite of intermediate hydration in the soils. Experimental results have been interpreted in terms of the structure of soil minerals.

Full Text

     

Y. M. K. Chandra Chowdary ¹, K. S. Rao ¹

Affiliations
1 Geological Survey of India, Hyderabad, IN

Abstract

No Abstract.

Full Text

   

P. Satyanarayana Murty ¹, K. S. Rao ¹

Affiliations
1 Department of Geology, Andhra University, Waltair 530003, IN

Abstract

Textural parameters, viz., mean, standard deviation, skewness and kurtosis and CM patterns in respect of 150 offshore sediments from the continental shelf off Visakhapatnam enabled delineation of two distinct sedimentary facies, one in the northern sector (Visakhapatnam - Bheemunipatnam) and the other in the southern sector (Visakbapatnam - Pudimadaka). The sedimentary facies in northern sector includes sands (from coast up to 37 m) followed offshore by silty sands (up to 50 m), sandy silt (up to 70 m) and silts (up to 80 m) and that in the southern sector, sands (up to 30 m), silty sands (between 30 - 40m and 50 - 80 m) followed offshore by sandy silts (between 40 - 50 m). There is a progressive seaward fining of sediments in the southern sector, whereas in the northern sector the fining is towards both sea and land. Fining of sediments with depth, a feature common to open shelves, is attributed to wave action. Distribution of medium sand zone in the northern sector between 15 to 40 m along the coast has been considered to be the result of dumping of dredged out material from the nearby port area. A major part of the study area is floored by poorly-sorted sediments. Skewness values of the sediments in the southern sector increase uniformly with depth whereas they show more complex pattern in the northern sector. Leptokurtic sediments bordering the coast in the northern sector indicate removal of fines through wave and current activity. CM diagram indicates the prevalence of low to moderate current activity in the south and highly turbulent zones in the north.

Full Text

     

A. K. Chatterjee ¹, K. S. Rao ¹

Affiliations
1 National Mineral Development Corporation Ltd., Hyderabad-500 028, IN

Abstract

The alkaline ultrabasic diatreme at Majhgawan has an idealised geological setting being intruded into the platformal Kaimur sandstones of the Lower Vindhyan Supergroup (1400-1100 Ma) overlying cratonic Bundelkhand granite basement (2550 Ma) which is a typical archon as per Janse (1992). Recent Rb/Sr age data indicate 1042 Ma (Smith 1992) and 1067 Ma (Anil Kurnar and Gopalan 1992) for the Majhgawan pipe. The pipe with surface dimension of 500 × 320 m is a carrot shaped body reminiscent of a typical kimberlite with minimal erosion. The pipe rock has been classified as lamproite by Scott Smith (1989, 1992a) who has termed it as olivine lamproitic lapilli tuff of crater facies. High TiO₂(4-6%), less abundance of typical heavy indicator minerals (HIM) like group-10 pyrope garnet and ilmenite and overall petrological characters of the pipe strongly reflect lamproite nature. High amounts of certain minor elements such as Ba (3000 ppm), Sr (1000 ppm) and REE (high La, U/Th ratio) also indicate its lamproitic character.

On the other hand the typical carrot shape of the plug, almost concentric distribution of diamonds, mode of presence of mantle-derived xenocrysts, overall chemistry with high MgO(25%) low K₂O(1%) and fair amounts of Cr and Ni are highly characteristic of kimberlitic nature. Broad petrographic characters coupled with abundance of xenocrysts and occurrence of country rock xenoliths and geochemical charecteristics suggest it is in several aspects typical kirmberlite rather than lamproite. The garnet population with fair amount of harzburgitic pyrope and larger share of lherzolitic variety indicate characteristics almost intermediate between kimberlite and lamproite.

Irrespective of the nature of the diatreme in any exploration model for search of new primary sources in the area, the spesific nature of HIM of the Majhgawan rock has to be kept in view (i.e.rather less abundance of garnet that too more of group-9 type, predominance of high magnesia spinellchromite, absence of ilmenite etc). The Majhgawan diamonds (42% gem) are predominantly curve faced modified forms indicating signs of resorption.

Keywords

Kimberlite, Lamproite, Diamond, Majhgawan, Panna, Madhya Pradesh.

Full Text

     

Abhijeet Mukherjee ¹, K. S. Rao ¹, D. Bandyopadhyay ¹, Gautam Roy ², A. K. Chatterjee ³

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhawan, Masab Tank, Hyderabad-500028, IN
2 Department of Applied Geochemistry, Osmania University, Hyderabad-500007, IN
3 302-Expresso Apts., Lakdikapool, Hyderabad-500004, IN

Abstract

Geothermometry of the coexisting magnetite-ilmenite (Mt-Ilm) pair from Majhgawan diamondiferous pipe indicates a temperature of 1150°C. The values of fO₂ T and P fall in the equilibria field defined by iron-wustite (IW) and wustite magnetite (WM) indeating depth of sampling of about 155km and pressure of 46kbar.

Keywords

Geothermometry, Geobarometry, Fe-Ti-Oxides, Majhgawan Pipe.

Full Text

     

Abhijeet Mukherjee ¹, K. S. Rao ¹, A. K. Chatterjee ²

Affiliations
1 National Mineral Development Corporation Limited, Khanij Bhawan, Castle Hills, Masab Tank, Hyderabad-500028, IN
2 302, Expresso Apts., Lakdika Pool, Hyderabad-500004, IN

Abstract

The phlogopite megacrysts of Majhgawan diatreme have been grouped into two groups and from the inspection of the chemical analysis of micas their origin are discussed.

Full Text

   

Abhijeet Mukherjee ¹, K. S. Rao ¹, D. Bandyopadhyay ¹, Gautam Roy ²

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhavan, Masab Tank, Hyderabad - 500 028, IN
2 Applied Geochemistry Department, Osmania University, Hyderabad - 500 007, IN

Abstract

The compositional trends in ilmenites from Majhgawan indicates slightly increased values of -log f02 i.e., 9.2. The divariant plots of Fe₂O₃ vs MgO and Cr₂O₃ vs MgO indicate resorption of most diamonds. The rounded-dedecahendra from indicates a preservation percentage of 65-70. The wine-red garnets from diamondiferous pipe are moderately subcalcic. The CaO vs Cr₂O₃ plot shows that they fall very close to the 85 percent Gurney line indicating emplacement at the craton margin having moderate diamond content. Geothermobarometry based on the co-existing pyropeknorringite and spinel geothermobarometer for the diamondiferous pipe yielded an equilibration temperature and pressure of 1160°C and 47 KbaT.

Keywords

Economic Geology, Diamond. Geochemistry, Madhya Pradesh.

Full Text

     

P. K. Raman ¹, K. S. Rao ², K. Soman ³

Affiliations
1 Flat # 202, 'Narmisam 'Srinagar Colony PO Hyderabad - 500 073, IN
2 Flat # 401, Srinilaya Estate Ameerpet, Srinagar Colony P O Hyderabad - 500 073, IN
3 Centre for Earth Science Studies Thiruvananthapuram, IN

Abstract

No Abstract.

Full Text

   

P. K. Raman ¹, K. S. Rao ¹

Affiliations
1 Hyderabad, IN

Abstract

No Abstract.

Full Text

   

P. K. Ramam ¹, K. S. Rao

Affiliations
1 Plot-22, Flat #202, Naimisain Srinagar Colony P. O. Hyderabad - 500 073, IN

Abstract

No Abstract.

Full Text

   

Abhijeet Mukherjee ¹, K. S. Rao ¹, E. V. S. S. K. Babu ², Gautam Roy ³

Affiliations
1 National Mineral Development Corporation Ltd., Khanij Bhawan, Masab Tank, Hyderabad - 500 028, IN
2 Department of Earth Sciences. University of Cambridge, Cambridge CB2 3EQ, GB
3 Applied Geochemistry Department, Osmania University, Hyderabad - 500 007, IN

Abstract

Geological Survey of India had recently discovered Wajrakarur pipe-10 and spinels from this pipe were analysed. Q-cluster analysis of these spinels based on Cr₂O_3, Al₂O_3, TiO₂ and MgO contents indicate the presence of S1, S3, S4, S5 and S10 groups. S1 group spinels are supposed to be cogenetic with diamond i.e., stable in the mantle within the P-T regime under which diamonds are known experimentally to form. The Cr/(Cr+Al) vs Fe/(Fe+Mg) plot also show that a few spinels are from the field of diamond inclusion chromites. This study suggests probable diamondiferous nature of the Anumpalle pipe.

Keywords

Geochemistry, Mineral Chemistry, Kimberlites, Diamond, Spinel, Andhra Pradesh.

Full Text

     

Abhijeet Mukherjee ¹, K. S. Rao ¹, Gautam Roy ², E. V. S. S. K. Babu ³

Affiliations
1 Natl. Min. Dev. Corp. Ltd., Khanij Bhawan, Masab Tank, Hyderabad - 500 028, IN
2 Applied Geochemistry Department, Osmania University, Hyderabad-500 007, IN
3 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, GB

Abstract

Based on the Q-Cluster analysis of 536 garnet grains, the garnets of Majhgawan are classified as Group 1, Group 2, Group 9, Group 10 and Group 11. Group 10 garnets have very high MgO (21.2%) and moderate to high Cr₂O₃ (9.5%), combined with low CaO. MgO shows negative correlation with CaO and FeO and this cluster contains a large number of garnet inclusions in diamonds. The major element chemistry of these garnets confirm that they are moderately subcalcic and have high Crcontent with a well-defined Ca-Cr trend. Around twenty percent of garnets show harzburgitic trend indicating low to moderate grade of the pipe. Nickel thermometry has indicated a well-defined geotherm between 1150° - 1400°C and corresponds approximately to a slightly elevated 42 m W/m² conductive model. Garnets with temperature > 1150°C probably were derived from diamond stability field. Based on Ni-thennometry (using only lower cut-off) omega value is calculated (<30) which suggests an average grade upto 15 ctpht for Majhgawan pipe.

Keywords

Cluster Analysis, Geothermometry, Garnet, Diamond, Madhya Pradesh.

Full Text