Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

Figure 29. Outcrop of epidote calc-silicates overprinting the matrix of
Proterozoic amphibolite agglomerate (Xaa). Epidote calc-silicate (green with
white quartz vein gashes) largely replaces the breccia matrix in the upper half
of image.
fine grained to coarse grained. There is a general tendency for grain size to increase with
increasing complexity of the calc-silicate mineral assemblage. Epidote-rich calc-silicates
tend to be fine grained, epidote-garnet calc-silicates tend to be medium grained, and
clinopyroxene-amphibole-mica-garnet calc-silicates tend to be medium to coarse grained.
Hand sample and thin section studies indicate the more complex calc-silicate
assemblages include the presence of diopside-hedenbergite, black amphibole
(hornblende), green amphibole (tremolite-actinolite), black biotite, chlorite, muscovite,
garnet, epidote, quartz, carbonate, and sphene. Calc-silicate gneisses exhibit some
layering that is of similar scale (inch to feet) as the layering in the amphibolite gneiss.
The amphibolite gneiss locally has disseminated garnet and retrograde biotite in the
vicinity of calc-silicate zones. The calc-silicates are generally non-foliated, but mica-rich
layers are locally strongly foliated and sheared.
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