Abstract

Sills in Cambrian sandstone at two localities provide complementary evidence for the magmatic origin of keratophyres near St. Nicolas. The thickest sill has one facies whose solids at the time it was half or somewhat more crystallized had the composition of a hornblende laugenite. The rest magma at this stage gave rise to stellate and trachytoid keratophyre characterized by chlorite and checker-board albite with some quartz. At the other locality magma approximately of the composition of the stellate keratophyre was emplaced as sills up to 4 ft (1.2 m) thick and gave rise to medium-grained keratophyre with, along the selvages or within the sills, a fine-grained variety with chlorite and nodules, up to 1 in. (2.5 cm) diameter, of plagioclase. Illite or its precursor was secreted from the sills and was replaced by a network of veins with cores of quartz and spheroids of plagioclase, of chlorite, and of carbonate.

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