Abstract

In connection with the intensive wartime exploitation of domestic mica deposits, the Geological Survey has been engaged in a comprehensive investigation of New England mica pegmatites. More than 200 pegmatites have been mapped and studied in detail and some hundreds of others have been given brief examination. The opportunity for pegmatite study has been unprecedented, and much new information on the characteristics of pegmatites has been obtained. Geologic analysis of pegmatites has helped to clarify the relationships between mica distribution and structural features and has led to a classification of mica deposits into basic types, of which five are especially important: wall-zone, intermediate-zone, pod, fracture-controlled, and disseminated. In some pegmatites, designated complex deposits, combinations of two or more of the basic types have been found. The different types are described and illustrated and their relative economic importance is shown by production figures. Analyses show clearly that certain types of deposits are far more productive than others and are far more likely to sustain profitable mining operations. Applications of current studies to mica mining, prospecting, and exploration are discussed.

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