Sunflower structure of pyrite in Lignite of Western Kachchh, Gujarat (India): Insights on its origin and mechanism

Abstract Textural analysis of pyrite has been carried out in the lignites of Kachchh Basin to decipher its micro-morphological character. The study entails the intermediate stage and authigenic sunflower structured pyrite. The origin, characteristics, shape and distribution of pyrite within Tertiary lignites has been comprehensively explored through petrography, ultimate analysis and scanning electron microscopy (FE-SEM). Along with the sunflower structure, the study has also revealed the presence of variouspyrite-textures of such as pyrite-framboids, massive type of pyrite, discrete-pyrite, fissure and cavity filling pyrite, disseminated pyrite gains, euhedral pyrite and subhedral pyrite of which the dominating one is framboidal pyrite. Wide variation in the size of framboidal pyrite (6 µm – 11 µm) indicates epigenetic process of its formation and the deposition of lignite in a suboxic/ dysoxic environment. The presence of high sulfur concentration in lignite is further suggestive of a marine origin. The initial study indicates that the lignite in western Kachchh is not significantly agreeable to beneficiation, whether through physical or biological method and also prone to spontaneous combustion that leads to environmental issues. In addition, close association of pyrite with macerals also sheds light on the influence and active participation of organic matter in the pyrite formation.