FRAMBOIDAL-COLLOFORM-RECRYSTALLIZED PYRITE IN VOLCANIC TUFFS OF BARSUAN VALLEY, ORISSA

Abstract

Petrographic studies of pyritiferous tuff forming a part of Precambrian Iron-Ore Volcanics of Bausuan valley, Sundergarh district, Orissa, reveal interesting textural peculiarities of pyrite. The three textural varieties: framboidal, colloform banded and recrystallized appear both in composite association and as independent units in highly carbonatized tuff. In composite association, the framboidal variety constitutes more or less the central part of the globules of colloform banded pyrite (gel pyrite) which in turn is enveloped at the periphery by discontinuous crusts of recrystallized variety. Different intermediate textures of pyrite are described and variations in reflectivity, microhardness, etch behaviour and elemental distribution vis-a-vis the varieties have been discussed. Average Co/Ni ratio along with the textural manifestations of the pyrite attests its sedimentary origin. Different stages of process of formation of textural varieties are also briefly outlined.