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

M. N. Praveen ¹, Biswajit Ghosh ¹, H. S. Shrivastava ¹, M. L. Dora ², L. D. Gaikwad ¹

Affiliations
1 Geological Survey of India, E-5 Arera Colony, Bhopal - 462 016, IN
2 Geological Survey of India, Seminary Hills, Nagpur - 440 006, IN

Abstract

Sulphide mineralisation and syn-Volcanic hydrothermal alteration in the Betul Belt is associated with submarine bimodal volcanism. Felsic volcaniclastics form the favourable host rocks in most areas. Alteration zones have been metamorphosed to middle to upper-Amphibolite facies giving rise to various metamorphic mineral assemblages. Based on metal ratios, mineralisation can be classified into Zn-Cu and Zn-Pb-Cu types. The difference between the two types might be related to the composition of the footwall volcanics. Zn-Cu types are in close proximity to mafic volcanics towards their footwall side whereas, Zn-Pb-Cu types occur in areas dominated by felsic volcanics with little mafic volcanics towards the footwall. The sub-Parallel sheet like nature of the ore bodies and strata-Bound alteration might be related to the permeable nature of the host volcaniclastics.

Keywords

Sulphide Mineralisation, Classification, Hydrothermal Alteration, Subsea-Floor Replacement, Betul Belt, Central India.

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M. N. Praveen ¹, Biswajit Ghosh ¹

Affiliations
1 Geological Survey of India, E-5 Arera Colony, Bhopal-462 016, IN

Abstract

Multiple origin of gahnite of different generations and their relationship with other coexisting minerals like garnet, biotite, chlorite and sphalerite were studied in metamorphosed synvolcanic hydrothemally altered rock associated with base metal mineralisation from the Proterozoic Bhuyari prospect, Betul Belt, Central India. The present assemblages appear to be the result of overprinting of arnphibolite grade metamorphism on primary hydrothermal alteration products. Gahnite is found in a quartz + biotite + muscovite + pLagioclase + gahnite + garnet + chlorite assemblage. Petrographic evidence with supporting mineral composition data suggests the presence of two generations of gahnite. The first generation gahni te is found surrounding sphalerite grains and may be the product of desulphidation of primary sphalerite involving first generation garnet. Second generation gahnite show petrographic evidence of transformation from biotite and might be the result of overstepping of the zinc saturation limit of biotite during alteration to chlorite. The Bhuyari area was subjected to one prograde event followed by a retrograde metamorphic event and mineral paragenesis is in conformity with the metamorphic hlstory.

Keywords

Gahnite, Zn-Pb-Cu deposit, Hydrothermal alteration, Betul Belt, Madhya Pradesh.

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Biswajit Ghosh ¹, M. N. Praveen ², H. S. Shrivastava ²

Affiliations
1 Geological Survey of India, E-5 Arera Colony, Bhopal - 462 016
2 Geological Survey of India, E-5 Arera Colony, Bhopal - 462 016, IN

Abstract

Gahnite Chemistry from metamorphosed Zn-Pb-Cu sulphide occurrences of Betul Belt, Central India has been presented here. Gahnites of this Belt are suggested to be a product of desulphidation of sphalerite during metamorphism. Although the very presence of zincian spinels in rocks may appear to constitute an exploration guide for metamorphosed massive sulphide (MMS) deposits, spinels that are likely to be spatially associated with sulphides appear to have characteristic Zn-rich, Mg-poor compositions.

Keywords

Gahnite Chemistry, Zn-Pb-Cu-Deposits, Genetic Implications, Betul Belt, Central India.

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