Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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Table 1. Whole-rock chemical analyses of select igneous rocks from the Maysville quadrangle, Colorado. Sample locations are given in Appendix 1. [Commercial analyses by ALS-Chemex, Sparks, Nevada (Certificate RE05113617). XRF analyses.] ___________________________________________________________________________________________ Trp Dike Tnfg Tqlp Dike Tmpp Tqm Ta Dike Ta Dike SiO 2 75.82 76.05 58.53 61.68 57.42 54.01 60.91 Al 2 O 3 13.71 12.62 16.23 16.92 16.27 15.04 15.06 1 Fe 2 O 3 0.73 0.58 7.49 5.93 8.14 8.02 5.47 CaO 0.30 0.31 4.57 3.36 5.57 3.88 3.18 MgO 0.03 0.04 3.33 2.33 2.77 5.02 2.83 Na 2 O 4.32 3.76 3.60 3.59 2.83 3.12 4.10 K 2 O 4.41 4.40 3.26 3.28 2.86 4.01 3.17 Cr 2 O 3 0.01
One age determination on the rhyolite porphyry dikes in the Mount Antero region was reported by Limbach (1975). A K-Ar whole rock age determination of 25.4 +/- 1 Ma for a rhyolite porphyry dike in Chalk Creek was recalculated (Shannon, 1988) by using revised constants from Dalrymple (1979) as 26.1 +/- 1 Ma. Table 1 gives a whole rock chemical analysis (sample 05-542) of the main northeast-trending rhyolite porphyry dike. The analysis indicates an alkali rhyolite composition (De la Roche and others, 1980) with a very high SiO 2 content (75.82 percent), and high Na 2 O content (4.32 percent) and K 2 0 content (4.41 percent). This analysis is very similar to a sample of rhyolite porphyry dike from the Buena Vista West quadrangle (McCalpin and Shannon, 2005) except for slightly higher Al 2 O 3 and Na 2 O contents. The chemistry of the rhyolite porphyry dike is also very similar to the North Fork leucogranite (sample 05-575A, table 1). Tcf California leucogranite-rhyolite dikes (early Oligocene) – These porphyritic, fine-grained, biotite granite-rhyolite dikes (Tcf) are white to light gray and have variable texture with generally moderate phenocryst content and aplitic groundmass with a 0.1 to 0.5 mm grain size. In general, the phenocrysts tend to be less euhedral and the groundmass is coarser in the fine-grained granite-rhyolite dikes (Tcf) in comparison to the rhyolite porphyry dikes (Trp). The distinction between phenocrysts and groundmass is also less clear than in the rhyolite porphyry, because of the coarser and variably textured groundmass. The overall phenocryst content varies from about 20 to 40 percent with 8 to 15 percent quartz (1 to 3 mm), 7 to 12 percent alkali feldspar (1 to 3 mm), 5 to 12 percent plagioclase (1 to 2 mm), 2-4 percent biotite-muscovite (0.5 to 2.0 mm), 1 to 3 percent orangeish garnet (0.2 to 2.0 mm), and 0.5 to 2 percent magnetite. Two dikes of porphyritic, fine-grained, biotite granite-rhyolite (Tcf) are mapped in the northeast corner of the Maysville quadrangle (plate 1). In addition, numerous 1 to 5 ft thick dikes are present in the area around the summit of Mount Shavano and are especially abundant around the California leucogranite intrusion (Tcm) in Squaw Creek. One dike occurs as a 4,000 ft long, arcuate, northeast-trending dike crossing the ridge just north of the summit of Mount Shavano; the dike extends for another 2,500 ft into the southwest corner of the Mount Antero quadrangle. The dike is 8 to 20 ft thick and strikes 79
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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
Page 27 and 28: Shannon, 2005). Widmann and others
Page 29 and 30: the Upper Arkansas graben (fig. 5)
Page 31 and 32: 15-minute quadrangle, which is adja
Page 33 and 34: etween the northern and southern se
Page 35 and 36: on U.S. Forest Service color aerial
Page 37 and 38: We use fractional map units on the
Page 39 and 40: Qpt Pinedale till, undivided (late
Page 41 and 42: weathered, but Mount Princeton quar
Page 43 and 44: stratified, matrix-supported, bould
Page 45 and 46: as rockfalls, rock avalanches, rock
Page 47 and 48: stream-channel deposits of all pere
Page 49 and 50: Figure 10. View west up South Arkan
Page 51 and 52: Figure 11. View west up South Arkan
Page 53 and 54: valley near the eastern map boundar
Page 55 and 56: lithologies are variable and depend
Page 57 and 58: Arkansas River in parts of Redman C
Page 59 and 60: angular to subangular. Deposits gen
Page 61 and 62: elations, age constraints from foss
Page 63 and 64: elated to the inferred Squaw Creek
Page 65 and 66: Figure 14. Crude bedding in coarse
Page 67 and 68: microcline, and muscovite. The latt
Page 69 and 70: Volcanic Ash Figure 17. View of eas
Page 71 and 72: Figure 18. Close-up view of intense
Page 73 and 74: The western zone of brecciated Pale
Page 75 and 76: Tr Rhyolite dikes (early to late Ol
Page 77: as the overall N47°E trend of the
Page 81 and 82: 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
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typically expressed by intermittent
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The field relations and characteris
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the north side of all three segment
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eplaced by muscovite. The western m
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sillimanite-quartz-muscovite that a
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sillimanite gneiss (Xmsg) and the m
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Figure 35. Outcrop of Proterozoic h
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samples) indicates they are compose
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Xal Lineated amphibolite (Early Pro
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of the Proterozoic metamorphic rock
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that the present structural configu
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elated to rotation of domain blocks
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sometimes terminate at a cross stru
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limestone that is exposed in a wind
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quadrangle are intimately associate
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of the quadrangle. The north-northw
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quartz monzonite ring dikes (Tma).
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that truncates the Upper Arkansas g
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as at the mouth of Squaw Creek. How
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adjacent to the southwestern edge o
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graben and the Upper Arkansas Valle
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GEOLOGIC HAZARDS Potential geologic
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In addition, older landslides may h
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sparse vegetation. One such area is
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Table 7. Historical (pre-instrument
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4262272N. ECONOMIC GEOLOGY Currentl
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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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