Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

Figure 31. Subcropping zone of muscovite-cordierite schist (Xmc) with large
porphyroblasts of cordierite (dark brown).
mineralogy (muscovite, sillimanite, cordierite, and tourmaline) suggests a high aluminum
content and shale protolith.
The western muscovite-cordierite schist segment does not crop out, but the
concentrated float pattern suggests it is about 200 to 300 ft thick with a roughly westnorthwest
trend. The eastern half of the central segment is well exposed along a strike
ridge where it is about 500 to 700 ft thick and is oriented N46° to 66°E with moderate
(46° to 78°) to vertical dips to the southeast. The eastern segment has limited outcrop
mostly at low elevation near Willow Creek. Concentrated float suggests it is about 1,100
ft thick. The schist has variable orientations the most reliable of which is N88°E with
vertical dip. Other measured orientations are from outcrops adjacent to the fault zone and
are N6° to 30°E with variable dips (29° and 34°NW and 62°SE).
The three segments of muscovite-cordierite schist get progressively thicker to the
east. The stratigraphic relations with the surrounding gneisses are consistent to the north
with muscovite gneiss (Xmfs) and Berthoud-type granite and pegmatite dikes (YXgp) on
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