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

V. K. Nayak ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad 826004, IN

Abstract

No Abstract.

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B. C. Sarkar ¹, V. K. Nayak ¹, P. Srinivas Rao ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad-826 004, IN
2 Mineral Exploration Corporation Limited, Nagpur-440 006, IN

Abstract

The Phosphorite deposit (74°25' to 74°26'E : 22°58' to 23°00'N), Jhabua district, Madhya Pradesh, is one of the productive deposits in India, and has evoked great interest with regard to its phosphogenesis, stromatolite association and resource potential. It is a sedimentary-stromatolite type of deposit within the Precambrian metasediments of the Aravalli Supergroup and represents the southern extension of the well known Jhamarkotra phosphorite deposit of Rajasthan. The geological set-up shows that the phosphorite occurs in two separate host rocks of older carbonate and younger chert sediments. Geological Survey of India (Khan et al. 1979), using conventional cross-section method, estimated the weighted average grade of the Khatamba Blocks from the available 21 intersections in 12 trenches as 28.60% P₂O₅. In the present study, statistical modelling of exploration data of the Khatamba Blocks, using histogram plots, probability diagrams and skewness and kurtosis parameters for 20 intersections reveals a 3-parameter log-normal distribution for accumulation (grade-thickness) and thickness values. The graphical estimate of the average grade from the probability diagrams is 29.59% P₂O₅ and that estimated by computer is 29.40% P₂O₅.

A computer programme ONEPOP.FOR in interactive FORTRAN77 has been developed for statistical modelling of the exploration data. Using this approach the grade. estimated for phosphorite deposit of the Khatamba Blocks shows a marginal increase in the value of average grade of P₂O₅, content as compared to the estimate made by conventional method.

Keywords

Stromatolite, Phosphorite, Economic Geology, Statistical Geology.

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V. K. Nayak ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad-826004, IN

Abstract

Maskelynite recognized in coarse grained shocked basalt fragments in monomiet breccia from the ejecta debris on the eastern side of the LonarImpact Crater, has been investigated. Maskelynite occurs with pyroxenes, opaques and preserves porphyritic texture. Maskelynite laths of various sizes are colourless, clean and show planar features. Its An-content varies from An₆₆ to An₆₉ which closely corresponds to labradorite, is optically isotropic and has an average refractive index 1.560 ± 002. Heating experiments revealed that maskelynite revets to a crystalline state at 800°C. The mechanisms of plagioclase-maskelynite transformation in an impact environment and reversion to plagioclase on heating are discussed.

Keywords

Maskelynite, Impact Crater, Lonar.

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