Abstract

Pegmatites genetically related to the Mount Morrison gneiss and migmatite, the Boulder Creek granite and granite gneiss, a quartz diorite, the Pikes Peak granite, and the Silver Plume and Mount Olympus granites invaded the Denver Mountain Parks area, particularly the Idaho Springs and Swandyke formations in the order named, probably in late Precambrian times.

The development of the five granitic rocks was accompanied by thousands of pegmatites in the form of dikes, sills and irregular bodies. Field studies indicate that the pegmatites of each granite surge are distinctive. The characteristics that distinguish one granite from another are reflected, to a limited extent, in the pegmatites genetically related to each granite cycle.

Relatively few pegmatites are complex. Some appear to have been subjected to more than one pegmatization. Some dikes, initiated as simple primary pegmatites in the earlier granite cycles, were replaced and enriched during one or more of the succeeding periods. Fault and shear zones served as thoroughfares for repeated mineralization of pegmatite bodies that partially filled them.

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