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

Shabbir Hussain ¹, S. Raju ², B. Dayal ², Fareeduddin ¹

Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur, IN
2 Geological Survey of India, Aliganj, Lucknow, IN

Abstract

The concordantly emplaced polyphase granite suite exposed in the Champawat area of Pithoragarh district of Uttar Pradesh represents a part of the southernmost granitoid belt of Himalayan region. In the field it can be divided into four successive mappable phases, viz. biotite granite, grey granite, leucogranite and microgranite. Mineralogically the biotite granite and grey granite are classified as "granodiorite" while the leucogranite and microgranite are classified as "granite". All these varieties of granite show xenoliths of country rocks. Champawat granite suite is a well differentiated, polyphase, calc-alkaline, peraluminous, S-type granitoid batholith that ranges in composition from granite to granodiorite- adamellite and trondhjemite. It is interpreted to be the product of anatexis of supracrustals at middle to lower crustal levels. The geochemical discriminant diagrams of the Champawat granite suite suggest that it is an orogenic granite showing characters of continental collision environment.

Keywords

Igneous Petrology. Granite, Champawat, Himalayas, Uttar Pradesh.

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J. K. Pati ¹, S. Raju ¹, V. D. Mamgain ¹, Ravi Shanker ¹

Affiliations
1 Geological Survey of India (NR), Aliganj, Lucknow-226 024, IN

Abstract

Geological mapping in parts of Bundelkhand Granitoid Complex (BGC) reveals a number of E-W trending shear zones marked by mylonites. Synkinematic fluid activity along these shear zones is conspicuous. Anomalous gold values in the range of 5 and 1000 ppb in BGC is recorded against a background value of l to 2 ppb in most Precambrian granitoids.

Keywords

Economic Geology, Gold, Granites, Precambrian, Bundelkhand, Central India.

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Santosh Kumar ¹, S. Raju ², Manjari Pathak ¹, Abhishek Pandey ³

Affiliations
1 Department of Geology, Kumaun University, Nainital - 263 002, IN
2 Geological Survey of India, Dimapur - 797 112, IN
3 Rolta Academy, MIDC, Marol, Andheri East, Mumbai - 400 093, IN

Abstract

Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (∼2600-2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG) , grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10^-3 SI with an average of 6.35×10^-3 SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10^-3 SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10^-3 SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10^-3 SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10^-3 SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31-10.22×10^-3 SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10^-3 SI) and pink (av. MS=6.72×10^-3 SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.

Keywords

Magnetic Susceptibility, Magnetite Series, Ilmenite Series, Granitoids, Bundelkhand Massif, Central India.

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