Petrographic Characterization of Some Precambrian Crystalline Rocks from the Sondre Stromfjord Area, West Greenland

As part of investigations of the nature and characteristics of rocks likely to been countered below the Inland Ice of interior Greenland, four samples collected from bedrock outcrops in the region at the eastern end of Sondre Stromfjord, West Greenland were analyzed petrographically. These represent materials from the Ikertoq gneiss complex, within the Nagssugtoqidian mobile belt, of Precambrian age. Of particular concern were characteristics of these rocks which would be informative as to engineering/technological considerations related to sub-ice drilling and sample retrieval. Principal factors of interest in this context were mineralogical and textural attributes of these samples.

Two of the samples are medium-grained microcline-bearing granites, one is a medium- grained orthoclase-bearing granite, and one is a coarse-grained microcline-bearing granitic rock with decided gneissic characteristics. All exhibit features characteristic of metamorphism and structural deformation subsequent to their original, presumably igneous crystallization.

All possess the qualities of coherent aggregates of the principal constituent rock-forming minerals feldspar(s) and quartz, with attendant mineral component hardnesses of 6-7 on the Mohs scale. Although some degree of intra and, to a lesser degree, intergranular fracturing is evident in each of these outcrop samples, such features are not deemed likely to appreciably affect the behavior of rocks such as these when encountered by the drill beneath significant thicknesses of overlying ice.