The members of the Rosses Granitic Ring Complex have been chemically analyzed. The data are presented as averages with 95 per cent confidence limits for individual elements. A limited amount of crystallization differentiation is demonstrated when the major units—the biotite microgranite sheets, the porphyry dykes, the ring granites and the grey and pink microgranite sheets—are compared with one another. This involves an increase in Si, K, a decrease in Ti, Al, Fe, Mg, Ca and P, but Na (and Mn) remain constant. The ring granites G1-G4 undergo very little differentiation and variations in their composition, except for Si, are ascribed mainly to heterogeneity.

The origin of the magma which gave rise to the complex is due to the palingenesis of the Older Granodiorite under the influence of a Na, K, alumino-silicate influx. This magma was the source of the biotite microgranite sheets and, after differentiation, the granites G1 and G2, together with some of the grey and pink microgranite sheets. After a period of quiescence a second influx produced the similar magma which was the source of the porphyry dykes and, after differentiation, gave rise to the granites G3 and G4, the Newer Granite bosses and the late grey and pink microgranite sheets.