Types of pegmatites in the Archean at Grand Canyon, Arizona
Granite pegmatites are abundantly developed in the Archean terrane in the Grand Canyon district. They are associated with the youngest Archean granites and appear to be later than the regional deformation. Simple composition is the rule, and complex varieties except for traces of boron facies, are almost unknown. Three types are recognized: the most abundant is similar to the common quartz-microcline pegmatites and is definitely intrusive into a series of meta-sediments and metabasites. A second type has developed by replacement, "pegmatization," processes. A third and very unusual type owes its origin to a late stage development of microcline within a quartz vein or quartz dike. The second and third types are only recognizable as such when the processes to which they owe their origin have stopped somewhat short of complete development. It is possible that many of what are regarded as Type I pegmatites may really be of Type II or Type III.