Volcano-Meta-Sedimentary origin of Ghutrigaon Chromite Quartzite/Chromite Fuchsite Quartzite from the Southern fringe of Singhbhum Craton, Eastern India

Abstract:

The chromite mineralisation in an Archaean supracrustal sequence from the southern fringe of Singhbhum Craton/Rengali Province, around Ghutrigaon, Eastern India exhibit a dissimilar mode of occurrence as compared to well-known chromite deposits of mafic-ultramafic origin. The Ghutrigaon chromite quartzite/fuchsite quartzite occurs within a low-grade metamorphosed volcano-sedimentary rocks of the Iron Ore Group (IOG). The ore body has a sedimentary parentage, having its precursor to be of siliceous mud with appreciable amount of Cr and subordinate amount of Zn, Mn, Ni, Co and V. It has originated from a sub-marine exhalative source and is precipitated in an oxidizing mixed hydrothermal-marine environment at low temperature. The chromite quartzite constituted of well-developed alternate colour bands of quartz and chromite which is an indicative of alternate precipitation according to different Eh and pH condition. Accessories such as fuchsite, muscovite, chromephyllite, chromeceladonite, chromechalcedony, rutile and zircon are commonly found. Presence of current bedding and fibrous broom-stick structure suggests its precipitation in a shallow marine exhalative environment.

Microchemical results of Ghutrigaon chromite plotted in different binary [Mg^#/Cr₂O₃, Mg^#/Cr^#, Mg^#//Fe^3+/Cr³⁺+Al³⁺+Fe³⁺, Fe²⁺/Mg²⁺+Fe²⁺//Cr^#, Mg^#//Fe²⁺/Fe^T] and triangular diagrams [Cr-Al-Fe & Cr-Mg-Fe] show distinctly different domains way apart from Stratiform-Alpine type complex and spinel xenoliths. The spinel composition show very low Mg-number (0.01-0.06) which is an indicative of depositional environment to be a marginal basin with high river discharge and thus of low salinity. Paucity in high Cr-number (0.69-0.79) is in contrast to micro composition of other major chromite bodies in India. Partitioning between chromite and quartz, their recrystallisation, grain enlargement, band development, redistribution of Cr, elevated value in trace elements gradually took place at different stages of deposition followed by metamorphism. The volcaniclast added to the Si-Cr protolith has given rise to different Al-Silicate minerals during metamorphism. Thus, foregoing observations unequivocally lead to surmise that Ghutrigaon Chromite Quartzite is of volcano-meta-sedimentary origin.