Quartzite and pelitic schist

Unit symbol: PzPxyqs
Age range Devonian and older (635 to 358.9 Ma)
Lithology: Metamorphic
Group name: Pelitic schist and quartzite and mafic interbeds (Yukon-Tanana crystalline complex)
Dominantly quartzite, schistose quartzite, and quartz-mica schist; also contains subordinate gritty quartzite, chlorite schist, calc-silicate schist, marble, magnetite-biotite schist, amphibolite, and greenstone. Ranges from amphibolite to upper greenschist facies and locally retrograded to lower greenschist facies (Nokleberg and others, 1992a; Smith and others, 1994). Corresponds, in part, to the Fairbanks schist of Newberry and others (1996) of the Fairbanks mining district and surrounding areas of the southeastern Livengood and northeastern Fairbanks quadrangles (Robinson and others, 1990; Weber and others, 1992; Newberry and others, 1996) as well as a large portion of the Circle quadrangle (Foster and others, 1983). Smaller areas of exposure occur in the southern Big Delta quadrangle (Weber and others, 1978) and in the Eagle quadrangle (Foster, 1976). In the Circle quadrangle and northern Big Delta quadrangle, small exposures of gray or greenish-gray marble and gray to cream-colored dolomitic marble are included in this unit; diopside is present locally, indicating amphibolite facies metamorphism. No age control exists for these carbonate rocks

Source map information

Source map Smith, T.E., Robinson, M.S., Weber, F.R., Waythomas, C.W., and Reifenstuhl, R.R., 1994, Geologic map of the Upper Chena River area, eastern interior Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 115, 1 sheet, scale 1:63,360, pamphlet, 19 p.
Symbol pCcq
Unit name Clinky quartzite
Description Thickness 3,000-10,000 feet. Dominantly thin- to medium-bedded, gray quartzite with lesser bronze- or silvery- weathering pelitic schist and minor marble (pCcm). The proportion of schist in the unit varies both laterally across the area and vertically within the section; uppermost part of the unit has quartzite schist ratio of about 1:1, lower part about 6 or 8: 1. Quartzite typically thin-bedded, banded, gray rocks; a few contain "streaky" chalky-weathering feldspar and sparse gray quartz "eyes." Muscovite and biotite content of quartzite ranges to 10 percent; small red garnets are present locally. Pelitic schist is typically medium- to coarse-grained, garnet- biotite-muscovite quartz schist. Garnet porphyroblasts to one-half inch in diameter form knobby schistosity surfaces. K-feldspar and untwinned plagioclase are minor minerals; tourmaline is a common accessory; chlorite and sericite replace garnet, biotite, and feldspar. Crenulations in two directions, minor folds, crenulation cleavage, and ribbon-textured quartz are ubiquitous structural elements. Quartz veins are rare; aplites and tourmaline-bearing pegmatites are present locally. Bedding in unit is parallel to that in the overlying Chena River sequence.
Lithology Metamorphic

Correlated geologic units

Label PzZyqs
Description Quartzite subunit of quartzite and quartzitic schist
Geologic age Paleozoic to Devonian
Geologic setting Sedimentary, shallow-marine-siliciclastic
Lithology Form Importance
Quartzite < Metaclastic < Metasedimentary < Metamorphic Greenschist Major