Cross folding, migmatization and ore localization along part of the Singhbhum shear zone, south of Tatanagar, Bihar, India

Abstract

Deformation of Precambrian sedimentary and interbedded basic volcanic rocks in the Tatanagar sector of the Singhbhum shear zone gave rise to two major isoclinal structures trending east-southeast-west-northwest, overturned to the southwest, and separated by a shear plane, to a series of cross folds, and to various minor structures in the shear zone rocks. Metamorphism accompanied deformation, and was followed by migmatization which was most intense in depressions marking intersections of the major and cross-fold axes. Mineralization, consisting of an early oxide phase (apatite-magnetite, uranium minerals) and a later sulfide phase (copper), was associated with the migmatization. The ores occur chiefly in rocks of the central zone of culmination, perpaps as a result of differential thermal gradients established by the flow of heated, plastic migmatitic materials toward the low-pressure areas in the flanking depressions. More rapid cooling in the zone of culmination may have facilita