Facies Variations of Felsic Volcanic Rocks around Mundiyawas-Khera Copper Deposit, Alwar Basin, North Delhi Fold Belt, Western India

Felsic volcanic rocks of rhyolite to dacite composition, hosting copper mineralization, are exposed near Mundiyawas-Khera area within the Alwar basin of Proterozoic North Delhi Fold Belt. Distinct variations in grain size, mineralogical composition, texture, sulfide mineral associations, structure, and outcrop patterns of the felsic volcanic rocks are observed in the field. In this study, litho-facies analysis of felsic volcanic rocks around Mundiyawas-Khera copper deposit has been attempted for the first time to understand their spatial distributions and bearing on copper mineralization. Signatures of five distinct facies variations in felsic volcanic rocks are recorded based on the field and laboratory studies. These facies variations recorded in the study area are (a) vitrophyric felsic volcanics; (b) fine grained felsitic fiamme bearing tuff; (c) fiamme-bearing welded ash flow tuff; (d) poorly welded ash flow tuff; and (e) volcanic ash. Presence of glass shards in the study area indicates phreatomagmatic eruptions in an aqueous to sub-aqueous environment. Occurrences of massive sulfide associated with the felsic volcanic unit can also correlate with well-known volcanic hosted massive sulfide (VHMS) deposit and is taken as an additional evidence of felsic volcanic rock occurrences at a submarine environment.