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

Pankaj K. Srivastava ¹, Sukhchain ¹

Affiliations
1 Department of Geology, University of Jammu, Jammu - 180 006, IN

Abstract

The composition of micas from Degana granite show significant chemical variation and trioctahedral nature. High Al₂O₃, and FeO content and a very distinctive depletion in MgO characterize the biotite whereas zinnwaldite has comparatively lower FeO and MgO. The biotites plot in the field of lithian-siderophyllite. The trioctahedral micas show high positive correlation between Si and Li and between Fe and Al^iv. and negative correlation between Si and Al^iv and Si and (Fe²⁺), suggesting that the coupled substitution Li^vi+Si^iv=(Fe²⁺"+Al^iv was operative during their evolution. The analysis of the micas show chemical continuity, suggcsting their continuous evolution from biotite to zinnwaldite composition. Late to post magmatic process for formation of zinnwaldite is favoured.

Keywords

Biotite, Zinnwaldite, Granite, Degana.

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Sukhchain ¹, Pankaj K. Srivastava ¹

Affiliations
1 Department of Geology, University of Jammu, Jammu - 180 006, IN

Abstract

Perthites are important disequilibrium textures found in the topaz bearing Degana Granites. Out of the two types of the perthites in the Degana Granite, the Fine-Grained stringlet type perthite is found in the unaltered portion while the dominant coarser type replacement perthite is present in the potassic alteration zones. In the present communication, a schematic model for the progressive evolution of perthite texture in the potassic alteration zone of the Degana Granite is proposed.

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