Mafic schist and amphibolite

Unit symbol: Pzyms
Age range Devonian or older Paleozoic (541 to 358.9 Ma)
Lithology: Metamorphic
Group name: Gneiss, amphibolite, schist, quartzite, and marble (Yukon-Tanana crystalline complex)
“Green, quartz-chlorite-carbonate schist, commonly having abundant plagioclase porphyroblasts. Associated with amphibolitic schist and minor marble, quartzite, and pelitic schist. Thought to represent metamorphosed mafic pyroclastic rocks interbedded with schists of unit |<yqs” in the Circle quadrangle (Wilson and others, 1998; see also Foster and others, 1983). In the south-central Circle and adjacent Big Delta quadrangle unit varies from greenish-gray actinolitic greenschist to dark green, fine- to coarse-grained, schistose amphibolite of unit |<yqm, which is interlayered or interlaminated with muscovite-feldspar-quartz felsite (Smith and others, 1994). In the southeast Big Delta quadrangle, unit is similarly composed of dark-green, fine- to medium-grained, strongly foliated, hornblende-biotite amphibolite gneiss associated with augen gneiss of unit MDag or interlayered with foliated, medium-grained, equigranular calc-silicate schist and, locally, quartzite of unit |ymi (Day and others, 2007). In the southeastern Eagle quadrangle, unit consists of moderately- to nonfoliated, fine- to medium-grained hornblende metagabbro and metadiabase (Werdon and others, 2001).Unit also contains a green and white, medium- to coarse-grained, slightly- to nonfoliated metaigneous rock that has pseudomorphs after clinopyroxene and plagioclase of fine-grained actinolite, chlorite, epidote, clinozoisite, albite, and (or) sphene (Szumigala and others, 2002)

Source map information

Source map Newberry, R.J., Bundtzen, T.K., Clautice, K.H., Combellick, R.A., Douglas, T., Laird, G.M., Liss, S.A., Pinney, D.S., Reifenstuhl, R.R., and Solie, D.N., 1996, Preliminary geologic map of the Fairbanks Mining District, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 96-16, scale 1:63,360.
Symbol Zfa
Unit name Amphibolite, Magnetite-rich biotite schist, quartzose schist, and marble
Description Heterogeneous unit of variably colored, gray to green, fine to coarse grained, garnet hornblende amphibolite, magnetite bearing biotite schist, coarsely crystalline marble, and light gray, mica-rich quartzite or "white schist." Zfa as shown on the geologic map was originally mapped by Robinson and others (1990) as part of both the Chena River and Cleary Sequences. Amphibolites contain prograde hornblende, oligoclase, biotite, and garnet and retrograde chlorite, albite, actinolite, and sphene. Amphibolites contain high Ti02 and exhibit major oxide and trace element signatures typical of tholeiitic, 'within plate' basalt (Pearce and Cann, 1973). Zfa unit appears as linear magnetic anomaly on an aeromagnetic survey (Dighem Surveys and Processing, 1995) due to magnetite content of biotite schist. Hydrothermally altered marble in Fox area juxtaposed against a high angle fault zone contains numerous euhedral tremolite veins. Bleached, light gray muscovite quartzose "white schists" were originally regarded by Robinson and others (1990) as rhyolite tuff or exhalite; major oxide chemistry and trace element data collected during this study do not support this interpretation. Rather, presence of detrital zircons in these "white schists" (Aleinikoff and Nokleberg, 1989) indicate a metasedimentary parentage. Zfa is generally resistant and forms subdued rubble crop throughout map area.
Lithology Metamorphic

Correlated geologic units

Label PzZms
Description Mafic schist
Geologic age Paleozoic to Devonian
Geologic setting Metamorphic, undivided
Lithology Form Importance
Calc-silicate-schist < Schist < Metamorphic Greenschist Major
Amphibole-schist < Schist < Metamorphic Greenschist Indeterminate, major
Marble < Metacarbonate < Metasedimentary < Metamorphic Greenschist Minor
Quartzite < Metaclastic < Metasedimentary < Metamorphic Greenschist Minor
Quartz-feldspar-schist < Schist < Metamorphic Greenschist Minor