Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

Figure 30. Outcrop of Proterozoic quartzite (Xq) representing lenses of metachert().
Note abundant hematitic slickensides related to deformation.
Quartzite-metachert is interlayered with amphibolite gneiss (Xag) at one locality
about 300 ft west of the western quadrangle boundary, on the north side of the North
Fork. The quartzite is interlayered with amphibolite gneiss in the northern part of a 2,500-
ft long roof pendant preserved in the roof zone of the North Fork leucogranite intrusion.
The southern part of the roof pendant consisting of Xgd/Xgdh and Xag extends into the
Maysville quadrangle. The about 85-ft thick zone of interlayered amphibolite gneiss and
quartzite includes at least three beds of quartzite up to about 7 ft thick. The amphibolite
gneiss is oriented about N56° to 62°W with steep dips (85° to 90°) to the northeast. Faint
bedding () laminations in the quartzite are oriented N58°W with an 87° southwest dip
subparallel to the amphibolite gneiss. The distribution and association of the quartzite
beds suggest that at least three and probably four or more different horizons of quartzites
are present in the Proterozoic sequence. Some of the quartzite beds are associated with
mafic-rich amphibolite gneiss (Xag) and calc-silicate gneiss (Xcs) and some are
associated with muscovite-cordierite schist (Xmc) and muscovite felsic schist (Xmfs).
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