Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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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 134
the north side of all three segments. In contrast, the rocks on the south side of the schist changes from predominantly amphibolite and calc-silicate gneiss (Xag/Xcs) at the west segment to predominantly amphibolite gneiss and biotite felsic gneiss (Xag/Xbfg) at the central segment to predominantly biotite felsic gneiss (Xbfg) at the east segment. These relations suggest the presence of facies variations in metamorphic units that may reflect primary stratigraphic facies variations. The schist is intruded by YXgp dikes and sills that are progressively more abundant to the east. The eastern schist segment is also cut by a short segment of a northeast-trending Tertiary () andesite dike. Figure 32. Photomicrograph of muscovite-cordierite schist showing cluster of cordierite porphyroblasts. Crossed nicols, approx. 1.4 inch across. Xmsg Muscovite-sillimanite gneiss (Early Proterozoic) – The muscovite-sillimanite gneiss is another distinctive Early Proterozoic metamorphic unit that occurs in a triangular-shaped, fault-bounded lithologic-structural domain in the southwest part of the Maysville quadrangle. The domain is about 7,000 ft by 10,000 ft by 13,000 ft and extends off the southern boundary of the quadrangle. It consists of muscovite-sillimanite gneiss 135
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OPEN-FILE REPORT 06-10 Geologic Map
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TABLE OF CONTENTS Introduction…
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mylonitic, augen textures………
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INTRODUCTION LOCATION AND ACCESS Th
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SAWATCH RANGE RIFT-SHOULDER UPLIFT
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of the South Arkansas River (subseq
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EXPLANATION Rio Grande Rift Neogene
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in descriptions of the geologic uni
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During the Early and Middle Paleozo
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Mountains, and White River uplifts
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field are the largest remnants of t
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Figure 5. Detailed geologic-structu
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with the Colorado mineral belt (Boo
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Shannon, 2005). Widmann and others
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the Upper Arkansas graben (fig. 5)
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15-minute quadrangle, which is adja
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etween the northern and southern se
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on U.S. Forest Service color aerial
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We use fractional map units on the
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Qpt Pinedale till, undivided (late
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weathered, but Mount Princeton quar
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stratified, matrix-supported, bould
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as rockfalls, rock avalanches, rock
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stream-channel deposits of all pere
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Figure 10. View west up South Arkan
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Figure 11. View west up South Arkan
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valley near the eastern map boundar
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lithologies are variable and depend
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Arkansas River in parts of Redman C
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angular to subangular. Deposits gen
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elations, age constraints from foss
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elated to the inferred Squaw Creek
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Figure 14. Crude bedding in coarse
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microcline, and muscovite. The latt
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Volcanic Ash Figure 17. View of eas
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Figure 18. Close-up view of intense
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The western zone of brecciated Pale
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Tr Rhyolite dikes (early to late Ol
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as the overall N47°E trend of the
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One age determination on the rhyoli
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northwest-trending fault. Thus, fie
Page 83 and 84: on the North Fork leucogranite intr
Page 85 and 86: A small 400 by 400 foot body of Nor
Page 87 and 88: N12°E, 62°NW (about 6,000 ft sout
Page 89 and 90: The age of the quartz latite porphy
Page 91 and 92: Tma Mount Aetna quartz monzonite po
Page 93 and 94: of the Maysville quadrangle and the
Page 95 and 96: Mount Aetna ring dikes (Tma), one i
Page 97 and 98: the margins of the pluton, includin
Page 99 and 100: Shannon (1988). The average of seve
Page 101 and 102: indicating a granite b composition
Page 103 and 104: analysis by Crawford (1913), two an
Page 105 and 106: locally tanish to pinkish gray. It
Page 107 and 108: quadrangle (tables 1 and 3) were fr
Page 109 and 110: slices of Paleozoic sedimentary roc
Page 111 and 112: south-southwest of Maysville is a 9
Page 113 and 114: There is one additional Paleozoic s
Page 115 and 116: near the southwest margin of the qu
Page 117 and 118: eastern contact of the diorite intr
Page 119 and 120: endoskarn zones. The two widely sep
Page 121 and 122: Xhig) along the southeastern contac
Page 123 and 124: Xgd Granodiorite (Early Proterozoic
Page 125 and 126: Hybrid granodiorite is locally deve
Page 127 and 128: Xcs Calc-silicate gneiss (Early Pro
Page 129 and 130: Many of the calc-silicate gneiss zo
Page 131 and 132: typically expressed by intermittent
Page 133: The field relations and characteris
Page 137 and 138: eplaced by muscovite. The western m
Page 139 and 140: sillimanite-quartz-muscovite that a
Page 141 and 142: sillimanite gneiss (Xmsg) and the m
Page 143 and 144: Figure 35. Outcrop of Proterozoic h
Page 145 and 146: samples) indicates they are compose
Page 147 and 148: Xal Lineated amphibolite (Early Pro
Page 149 and 150: of the Proterozoic metamorphic rock
Page 151 and 152: that the present structural configu
Page 153 and 154: elated to rotation of domain blocks
Page 155 and 156: sometimes terminate at a cross stru
Page 157 and 158: limestone that is exposed in a wind
Page 159 and 160: quadrangle are intimately associate
Page 161 and 162: of the quadrangle. The north-northw
Page 163 and 164: quartz monzonite ring dikes (Tma).
Page 165 and 166: that truncates the Upper Arkansas g
Page 167 and 168: as at the mouth of Squaw Creek. How
Page 169 and 170: adjacent to the southwestern edge o
Page 171 and 172: graben and the Upper Arkansas Valle
Page 173 and 174: GEOLOGIC HAZARDS Potential geologic
Page 175 and 176: In addition, older landslides may h
Page 177 and 178: sparse vegetation. One such area is
Page 179 and 180: Table 7. Historical (pre-instrument
Page 181 and 182: 4262272N. ECONOMIC GEOLOGY Currentl
Page 183 and 184: A number of the larger pegmatite bo
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River placers near Buena Vista (Van
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The small mines and prospects along
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elatively recent (post-1970) explor
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contact of two Quaternary gravels (
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quadrangle. The first area is a clu
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y Sharp (1976) to be a fault slice
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quadrant of the Maysville quadrangl
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the large Paleozoic rock outlier) i
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WATER RESOURCES Water resources on
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water near Maysville is being produ
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to Rudy C. Epis: Colorado School of
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University, M.Sc. thesis, 50 p. Din
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Hutchinson, R.M., and Hedge, C.E.,
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Litsey, L.R., 1958, Stratigraphy an
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County, Colorado, in Berg, R.R., an
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Stark, J.T., and Barnes, F.F., 1935
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Tweto, O., 1987, Rock units of the
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quadrangle, Colorado: U.S. Geologic
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94A 391996 4263422 Prospect YXp;Xbf
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336A 396189 4274961 Prospect Xgdf B
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854 391849 4268852 42 Adit; Geochem
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Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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