Evaluation of the "quartz-eye" hypothesis

Abstract

Deformed rocks containing are common in mining areas and a correct interpretation of the origin of the quartz eyes is important for evaluating models for ore genesis, especially volcanogenic models. Reexamination of the literature provides little or no support for the hypothesis that large, embayed quartz grains (quartz eyes) that resemble phenocrysts and that occur in fine-grained, generally foliated aggregates are porphyroblasts. Quartz phenocrysts in deformed volcanic or volcaniclastic rocks can remain undeformed, even though the surrounding fine-grained matrix has undergone extensive deformation and recrystallization. Therefore, most, if not all, quartz eyes should be interpreted as residual phenocrysts.