Discovery of andesite tuffs with graphite from the Vaigat Formation of south central Nûgssuaq: stratigraphical implications

Abstract

During helicopter reconnaissance in 1987, one of us (P. U.-M.) found patches of poorly exposed tuffaceous rocks within the Vaigat Formation on the west side of Ilugigsoq valley north of Auvfarssuaq (fig. 1). Subsequent investigation under the microscope revealed that the tuft consists of graphite-rich andesite very similar to the most abundant tuft type described from the Abraham Member of the Agatdal Formation by Pedersen (1978). The discovery of the new locality with this rare rock type led to a helicopter-based reconnaissance in the Ilugigsoq and Qilakitsoq valteys in the summer of 1988 by two of us (A. K. P. & L. M. L.) in order to trace this possibie marker horizon and put it into a stratigraphical context. Similar tufts were found at two localities described below. Graphite andesites are known from other localities on Nûgssuaq and Disko, and notes on these are also given below.