PALEOPROTEROZOIC COAL CREEK QUARTZITE: ORIGIN, AGE, AND STRATIGRAPHIC RELATIONSHIPS, JEFFERSON AND BOULDER COUNTIES, COLORADO

The Coal Creek Quartzite (CCQ) (informal) is an integral component of the Central Front Range Paleoproterozoic accretionary sequence. The quartzite-schist interval is 20-25 square miles in extent and best exposed in Coal Creek Canyon. One of several isolated Proterozoic meta-quartz arenite-schist exposures in Central and Northern Colorado, the CCQ may be correlative to similar sequences in the Yavapai Provence, such as the Del Rio Quartzite, Arizona and Waterloo Quartzite, Wisconsin. Origin and age of the CCQ has been considered pre-Boulder Creek Intrusive and coeval with adjacent mica schists. Recognized by Lakes and Marvine, ca. 1870s, Van Hise, ca. 1892, it was definitively mapped by Wells, et al., ca. 1960s. Wells identified four major quartzite units separated by three schists; total sequence estimated at ~11,200 feet/3400 m thick with schists 0-600 feet/180m thick that merge with the adjacent mica schist. Sequences possibly correlative with the CCQ are reported in the Niwot Ridge-Apache Peak area, and in Big Thompson Canyon near Forks Park. Quartz pebble-filled channels S-SW of the CCQ within the mica schist are thought correlative to and derived from the CCQ.

Alternate interpretations of the CCQ include: 1) remnant of a regional coastline/shoreline trend associated with the arc-backarc; 2) isolated late phase orogenic non-marine braid stream deposits intertonguing with lacustrine shales; or 3) part of a post Boulder Creek Batholith “cover sequence” of regional extent. In our present work, we suggest the CCQ is a set of sequences and parasequences deposited in a backarc setting. Field observations of relationships, features, and contacts between the CCQ and Boulder Creek intrusives confirm interpretation of a pre-Boulder Creek age for the Quartzite.

The CCQ has not yielded precious metals. However, clasts from the CCQ have been identified in Upper Eocene Castle Rock Conglomerate paleoplacers 40 miles S-SE of Coal Creek exposures. Gold within those placers is reported only where clasts of CCQ make up the conglomerate. This suggests an intimate relationship of gold with the quartzite and that the CCQ may have acted as a possible source for that gold.

The Coal Creek Quartzite and Schist sequences will be examined during Field Trip No. 403.