Chemistry and the origin of carbonate-rich rocks in the area of Amisk Lake (East), Saskatchewan

CIM Bulletin, Vol. 74, No. 836, 1981

G.R. PARSLOW, B.R. WAITERS and F.H. McDOUGALL, Department of Geology, University of Regina, Regina, Saskatchewan

Carbonate-rich rocks occur at several localities within the Flin Flon volcanic sequence of the eastern Amisk Lake area. The rocks occur in two areas: as a group of small occurrences on islands within Amisk Lake and as two much larger linear belts running parallel to the regional structure east of Amisk Lake. Mineralogically, the rocks consist of talc and Ca-poor ankerite with occasional graphite. Segregation of these minerals and colour variation impart a well-defined planar fabric to the rocks and where the units are fairly continuous (e.g. Mosher Lake), their trend and attitude suggests a concordant relationship to the volcanics. Major and trace analysis of 22 samples confirms the presence of two types, with one type being represented in each of the two areas. Most of the elements studied can be used to characterize the two groups, but three elements in particular give a clear separation: Mg, Al and Ni. Recalculation of the major element analyses, on a water and carbonate-free basis, indicates that one group (large concordant bodies with high MgO, high Ni and low Al2O3) is altered ultrabasic material of peridotitic or dunitic composition. Because no relict igneous material is observed, and the contacts are apparently very sharp, it is possible that the hydration-carbonization process occurred simultaneously with intrusion, .in a closed system. The other group (small occurrences with relatively low MgO, low Ni and high Al2O3) represents alteration of basaltic rocks. Although some analyses suggest the introduction of calcium, as carbonate, along with the volatiles, the major oxides have remained remarkably stable during the alteration process(es).
Keywords: Geology, Geochemistry, Carbonate rocks, Amisk Lake area, Volcanic rocks, Flin Flon sequence, Mineralogy.