Petrology, Geochemistry, Provenance, and Alteration of Pennsylvanian-Permian Arkose, Colorado and Utah
Petrology, geochemistry, provenance, and alteration of Pennsylvanian-Permian arkose, Colorado and Utah
PETER C. VAN DE KAMP Cornells Corporation, 1750 Cabernet Lane, St. Helena, California 94574-1604 BERNARD E. LEAKE Department of Geology and Applied Geology, The University of Glasgow, Glasgow, G12 8QQ, United Kingdom
ABSTRACT fluids, apparently in the Tertiary. These flu- Rocks studied (Figs. 1 and 2) include the ids were probably heated by deep-seated Middle Pennsylvanian to Lower Permian Late Paleozoic and modern feldspathic magma adjacent to the Colorado Lineament Fountain Formation in the Front Range clastic sediments of the Colorado Rockies and/or range front faults that served as geo- (Hubert, 1960; Howard, 1966). In the Eagle were derived from dominantly igneous and thermal water conduits toward the surface. Basin, the Middle Pennsylvanian Minturn meta-igneous Precambrian basement rocks. Formation (Mallory, 1972) was studied. In Average composition, expressed as Gazzi- the Paradox Basin, the Middle Pennsylva- DickinsonQFL(quartz-feldspar-lithicfrag- INTRODUCTION nian to Lower Permian Cutler Formation ments) is 36:64:0 in modern stream sands, was examined. Sand samples from streams for the Cutler Formation is 54:46:0, for the Petrographic analysis of clastic sedimen- in the Front, Gore, and Park Ranges and in Minturn Formation is 57:43:0, and for the tary rocks has traditionally proven very use- the Uncompahgre Uplift (Fig. 1) were ana- Fountain Formation is 51:49:0. No major ful for determining their provenance (for ex- lyzed. Because these streams drain the same mafic components are present in the prov- ample, Dickinson, 1985). Because only the basement rocks that acted as sources for the enance as indicated by low Co, Cr, and Ni more stable minerals (mostly quartz, Paleozoic sandstones, these analyses estab- abundances, although higher Fe and Mg feldspars, and micas) are preserved through lish baseline data for this study. abundances in Cutler Formation rocks in- weathering and diagenesis, however, prove- We studied 99 samples of ancient sedi- dicate derivation from somewhat more nance resolution by microscopic methods is mentary rocks and 23 samples of modern mafic provenance than the Fountain and limited. Much of the mafic component of stream sediments. All samples were miner- Minturn Formation rocks. Fountain For- parent rocks to sediments is lost by trans- alogically analyzed in thin section and/or by mation rocks are more altered by predepo- formation to chlorite, clays, Fe-oxides, and X-ray diffraction (Table 1). Many sands and sitional weathering, diagenesis, and Holo- solution. Chemical signatures of mafic com- sandstones were quantitatively analyzed cene weathering than their equivalents in ponents (Mg, Co, Cr, and Ni) are commonly with point counts of 400-700 points by the the Minturn and Cutler Formations. Thus preserved through weathering and diagen- Gazzi-Dickinson method (Dickinson, 1985) plagioclase is albitized and clay altered or esis processes (van de Kamp and Leake, in which grains in plutonic rock fragments absent in the Fountain Formation, whereas 1985). Therefore, analyses of major and are counted as minerals rather than as parts it is abundant and much less altered in the trace element abundances commonly reveal of rock fragments. Most samples were also Minturn and Cutler rocks. Fountain For- details of sediment composition, not seen in chemically analyzed for major and trace el- mation sandstone in the Steamboat Moun- thin sections, that are indicative of mafic ements by X-ray fluorescence and wet meth- tain section lacks remaining detrital plagio- rocks in the provenance. ods using the procedures of Leake and oth- clase but contains authigenic albite as This study developed new, integrated min- ers (1969) and Harvey and others (1973). overgrowths on, and replacement of, de- eralogical and major and trace element geo- Normative mineralogy of the sediments was trital K-feldspar and as pore-filling crys- chemical data for 122 samples of modern computed using the unpublished program tals. In the Eldorado Springs section there and ancient sediments derived from conti- SEDNORM, which is based on earlier pro- is extensive epithermal potassic alteration nental block provenance. Critical analysis of grams developed by Garrels and MacKenzie in the Fountain Formation from the detrital the results yielded significant new insights (1971) and Fenton (1987). assemblage quartz + plagioclase + K-feld- on local and regional provenance variations. spar + biotite + muscovite to the assem- Geochemical data, including cation gains PREVIOUS WORK blage quartz + K-feldspar + authigenic and losses, also permit detailed evaluation adularla + illite/muscovite + kaolinite. K of diagenetic and previously unreported hy- Numerous studies have documented the and Rb have been metasomatically added to drothermal alterations. This approach is stratigraphy (summarized by Mallory, 1972; these rocks with concomitant removal of Ca, particularly useful in the case of the mod- DeVoto, 1980; and Maughan, 1980), miner- Na, Co, Cr, Cu, Ni, Ga, Th, U, Zn, Ba, Ce, erately to intensely altered Fountain alogy, and petrology (Hubert, 1960; Raup, La, and Y during passage of hydrothermal Formation. 1966; Boggs, 1966; Werner, 1974; Mack and
Data Repository item 9448 contains additional material related to this article.
Geological Society of America Bulletin, v. 105, p. 1571-1582, 12 figs., 2 tables, December 1994.
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109°W 102°W — 41°N SAMPLE LOCATIONS Fountain Formation, Front Range 1. Steamboat Mountain 2. Lee Hill Road 3. Eldorado Springs 4. Red Rocks, Morrison 5. Perry Park 6. Manitou Springs Minturn Formation, Eagle Basin 7. Vail Pass West 8. McCoy area Cutler Formation, Paradox Basin 9. Ouray 10. Gateway area 11. Fisher Towers 12. Moab area Modern Sediments
13. Rampart Range PARADOX 14. Georgetown 15. Clear Creek 16. Big Thompson Creek 17. Rocky Mountain Park 18. Park Range 19. Gore Range 37° N 20. West Creek
Figure 1. Index map of Colorado and eastern Utah indicating sampling sites for late Paleozoic sedimentary rocks (filled circles) and modern sands from streams draining basement rocks (filled triangles). Sedimentary basins and mountain ranges are indicated. The shading represents outcrops of Precambrian crystalline basement rocks; these were also approximately the late Paleozoic highland areas. Unshaded areas contain Paleozoic to Cenozoic sedimentary and volcanic rocks in various sedimentary basins.
Suttner, 1977; Walker, 1984; Mack and Ras- played showing significant compositional basement provenance with respect to the cli- mussen, 1984; and Suttner and Dutta, 1986) differences between groups. mates in which they were developed. To of the Pennsylvanian-Permian feldspathic classify ancient sandstone, we assume that nonmarine rocks in Colorado. These studies CLIMATE OF WEATHERING the quartz and feldspar contents are similar established that the late Paleozoic sedi- to those at the time of erosion and deposi- ments, formed in response to contempora- The ratio Q/(Q + F) was used by van de tion of the sediments. This is tenuous be- neous uplift of the ancestral Rocky Moun- Kamp and Helmold (1991) to classify first- cause the Q/(Q + F) may be significantly tains, are alluvial and fluvial facies. cycle modern sands derived from "granitic" changed by postdepositional alteration as In the Wet Mountains south of our study area (Fig. 1), Cullers and Stone (1991) stud- ied the mineralogy and chemistry of al- FRONT RANGE UPLIFT, luvial-fan facies feldspathic Fountain For- PARADOX BASIN EAGLE BASIN DENVER BASIN mation sediments. Their work related sediment composition to provenance with major and rare-earth element analyses.
MINERALOGY AND PETROGRAPHY
QFL (quartz-feldspar-lithic) plots of modern sand and ancient sandstone (Fig. 3A) indicate continental block prove- nance (Dickinson, 1985) for these sedi- ments. The small proportion of lithic frag- ments, largely metamorphic schist, is shown by the low L, or lithic, content of these rocks. In Figure 3B, a QPK (quartz-plagioclase- Figure 2. Correlation section for the Pennsylvanian-Permian sedimentary rocks of the K-feldspar) plot, the proportions of feldspar Denver, Eagle, and Paradox basins. Adapted from chart by Pearl (1980). The units sampled and quartz for the same samples are dis- for this study are indicated by heavy vertical bars.
1572 Geological Society of America Bulletin, December 1994
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Paleozoic sedimentaiy rocks
Formation: Modem sediments Fountain Minturn Cutler
Steamboat Location: Front Range Rampart Rg. Park Range Gore Range Uncompahgre Eldorado Mountain Lee Hill Road Others McCoy Paradox
Location no. on 14-17 13 18 19 20 3 1 2 4-6 8 9-12 Figure 1 Number of samples 10 6 7 4 2 2 5 3 5 4 7 5 3 2 5 8 12
Grain size* f-vc vf-vc vf-vc f-vc vf-vc vf-vc siltstone- m-c siltstone- m-vc sitatone- m-vc siltstone- f-c siltstone- f-vc sittstone- Detrital grain shapest a-sr a-sa a-sr a-sa a-sr a-sr shale a-sr shale a-sr shale a-sr shale a-sa shale a-sr shale Sorting? p-m p-m p-m p-m p-m p-m m m-p p-m m m-p
Quartz 34.6 34.0 29.9 29.0 28.7 38.1 33.0 45.4 72.0 61.5 61.8 41.6 17.5 37.3 27.0 38.8 32.4 Plagioclase 22.5 24.9 39.5 39.3 39.0 0.0 0.0 13.5 9.9 4.1 3.0 9.0 4.5 20.2 7.9 22.3 9.0 Plagioclase, An% 10-45 10-38 <10 <10 <10 K-feldspar 25.6 35.9 12.0 16.5 7.9 49.2 45.9 13.7 6.6 22.5 7.2 34.1 15.6 4.6 2.7 12.8 3.9 Authigenic adularia 6.8 0.9 1.1 Biotite 4.7 2.2 9.0 7.6 12.2 8.0 1.4 1.4 14.6 4.1 Muscovite 1.2 X* 0.4 0.5 0.2 1.9 5.2 1.5 1.2 3.4 1.2 Amphibole X 1.0 5.0 5.0 7.7 Chlorite 0.2 0.4 0.2 0.3 Clays 0.1 2.0 2.1 2.1 3.8 14.1 4.0 9.5 6.0 23.2 8.1 56.0 10.9 57.6 10.0 36.5 Carbonate 0.1 3.4 0.2 4.4 3.4 2.0 7.9 12.8 Fe-oxides X 7.0 1.7 2.0 X 4.6 X 6.5 2.8 1.3 5.4 Opaque minerals X 0.8 2.1 0.8 1.3 0.2 3.7 1.0 0.4 3.9 1.1 Epidote X X 0.2 0.4 0.7 X 0.4 Sphene X X 0.1 X 0.2 0.1 X X X 0.1 Apatite X X X 0.2 X X Zircon X X 0.1 0.3 X 0.1 0.1 X Garnet X 0.2 X Tourmaline 0.1 X Rock fragments: Shale 0.4 1.5 0.1 Chert 0.2 Granitic X X X X X X X X X X Metamorphic 2.3 0.1 0.4 X X Ma He 0.7 Volcanic 6.6 0.1 X
P/F 0.47 0.41 0.76 0.70 0.83 0.00 0.43 0.20 0.20 0.80 0.60 Q/(Q + F) 0.42 0.36 0.36 0.34 0.38 0.44 0.58 0.69 0.49 0.58 0.53 Q 37.8 35.5 36.4 28.7 38.0 40.5 61.7 69.0 50.3 56.8 53.0 F 52.5 63.5 63.6 71.3 62.0 59.5 37.0 31.0 49.7 40.2 46.8 L 9.7 0.9 0.0 0.0 0.0 0.0 1.2 0.0 0.1 3.0 0.2
'Grain size: vf = very fine; f = fine; m = medium; c = coarse; vc = very coarse. fGrain shape: a = angular; sa = subangular; sr = subrounded. §Sorting: p = poor; m = moderate. #An x indicates presence of mineral in amounts <0.1%.
Oi
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Q Q discussed by Velbel and Skad (1991). For sandstone in which plagioclase was lost to alteration, Q/(Q + F) is high, and determina- o MODERN SANDS FOUNTAIN FORMATION tion of paleoclimate by this ¡method is incor- Steamboat Mountain rect. Thus such determinations must be lim- « Lee Hill Road ited to sandstone in which postdepositional • Eldorado Springs alterations of framework minerals are minimal. • Red Rocks • PerryPark The modern Colorado sands, with low RECYCLED OROGEN • Manitou Springs quartz and abundant feldspar, developed MINTURN FORMATION under Pleistocene glacial and subglacial a McCoy conditions and modern semiarid steppe cli- CUTLER FM. mate. Their Q/(Q + F) of 0.28-0.46 is only ° Ouray slightly more quartzose than values of 0.25- Gateway 0.40 for basement source rocks. These sands o Fisher Towers are less quartzose than the Paleozoic sand- ; Moab stone due to less intense weathering in the MAGMATIC ARC provenance and lack of postdepositional / diagenetic and weathering alteration. The Q/(Q + F) values (0.38-0.6) for the least altered Pennsylvanian sandstone samples indicate they were formed in semiarid to A more humid temperate climate conditions. This conclusion agrees with results of pre- Figure 3A. Plot of modal quartz, feldspar, and lithic fragments (QFL) for modern sands vious climatic studies on Paleozoic sand- (left) from streams draining basement crystalline rocks and ancient sandstones (right) stone (Mack and Suttner, 1977; Walker, analyzed by point counts. 1978; Mack and others, 1979; Suttner, 1984; and Suttner and Dutta, 1986). They in- ferred, from plant fossils, coal, evaporite distributions, and petrographic data, that MODAL MINERALS Q the sediments were deposited in a humid temperate climate during Morrowan time, FOUNTAIN FORMA TION which changed to semiarid climates later. • Steamboat Mountain 0 Lee Hill Road • Eldorado Springs GEOCHEMISTRY OF SEDIMENTS -f Red Rocks AND SEDIMENTARY ROCKS • Perry Park • Manitou Springs MINTURN FORMATION Comparison of average compositions re- a McCoy veals that the modern sand (Table 2, N) and
CUTLER FM. ^ o Cutler and Minturn sandstone (Table 2, CO & Ouray is <6 E-J) are rather similar. They each contain O <0 0 ^ Gateway , o about 70% Si02 and, overall, have approx- o Fisher Towers oo imately granodioritic compositions, as ex- 0 Moab pected from the makeup of the provenance. MODERN SANDS, Cutler sandstone (Table 2, J) contains less • Rampart Range o Other locations Mg, Na, and total Fe than the modern sand (Table 2, N), indicative of loss of plagioclase K. and mafic minerals in predepositional weathering. Soda (Na O) is more abundant B z (l%->3%) in Cutler sandstone, reflecting Figure 3B. Plot of quartz, plagioclase, and K-feldspar (QPK) for the modern sands and relatively prolific plagioclase compared to ancient sandstones. Modern sands are generally plagioclase rich (P > K); the sands de- the Fountain Formation sandstone. The rived from the K-feldspar-rich Pikes Peak batholith in the Rampart Range are an excep- Cutler Formation sandstone at Fisher Tow- tion. Most of the Minturn and Cutler sandstones are plagioclase rich, although they are ers (Table 2, H) is more sodic than other richer in quartz than the modern sands due to some loss of plagioclase in predepositional rocks studied here, but its Na20 content weathering. Due to greater intensity of predepositional weathering, the Fountain Forma- (2.2%-5.3%) is similar to that in some mod- tion sandstone is plagioclase poor and K-feldspar rich. Thus there is a trend from plagi- ern sand derived from "granitic" rocks in oclase-rich to K-feldspar-rich ancient rocks as alteration increases. The K-feldspar-rich Colorado (Fig. 4). CaO and C02 are high Fountain sandstone at Perry Park with low quartz content is likely from a K-feldspar-rich due to detrital and authigenic cement car- source such as the Pikes Peak batholith. Note also the generally greater quartz for the bonate. High MgO in the Moab area Cutler ancient rocks due to loss of plagioclase, thereby proportionately increasing quartz. samples is in detrital dolomite, apparently
1572 Geological Society of America Bulletin, December 1994
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A* B C D E F G H I J K L M N O P Q R S T U V W
69.32 61.16 61.39 57.28 57.69 56.13 53.50 Si02 82.70 74.97 81.77 76.82 76.28 70.34 65.94 70.38 62.78 67.58 73.77 68.72 68.94 70.27 69.61 73.27 0.59 0.70 0.75 0.94 0.66 0.82 0.66 Ti02 0.16 0.29 0.31 0.39 0.14 0.23 0.48 0.29 0.39 0.33 0.41 0.44 0.4 0.43 0.44 0.32 16.64 20.24 18.86 11.60 15.60 15.44 A1,03 9.27 9.94 9.14 12.19 10.16 11.12 12.59 11.70 10.09 11.27 12.93 13.89 14.28 13.65 12.83 13.08 13.80 5.14 3.95 4.21 7.47 6.32 Fe203 0.36 1.85 2.26 1.41 0.56 1.68 3.57 2.58 2.51 2.45 2.21 3.35 2.21 2.87 1.78 0.62 4.69 5.73 FeO 0.03 0.19 0.17 0.13 0.56 0.21 0.08 0.24 0.38 0.23 0.78 1.02 1.19 0.97 1.65 1.74 0.17 0.41 0.10 1.86 0.55 0.45 0.56 MnO 0.01 0.04 0.02 0.04 0.05 0.07 0.07 0.06 0.10 0.08 0.08 0.06 0.06 0.07 0.06 0.08 0.03 0.04 0.07 0.06 0.09 0.10 0.06 MgO 0.23 1.45 0.76 0.95 1.04 1.23 1.53 1.56 4.37 2.14 0.60 1.33 1.63 1.15 1.73 1.20 0.44 2.11 1.04 3.02 2.91 4.17 5.28 CaO 0.00 2.76 0.24 0.14 3.01 5.59 5.53 3.79 5.58 5.22 1.36 2.25 2.93 2.06 0.52 1.67 0.00 1.88 0.01 1.32 9.67 1.94 3.50 0.60 0.74 0.99 3.76 0.63 Na20 0.00 1.41 0.26 0.46 2.17 1.90 1.87 3.04 1.08 1.92 2.46 3.15 3.70 3.01 0.29 2.92 0.00 0.16 5.46 4.33 2.72 3.74 5.44 K20 7.16 3.22 3.84 4.83 2.53 3.07 2.88 2.16 3.88 3.05 3.68 3.41 2.99 3.44 4.81 2.30 10.34 5.44 P2O5 0.06 0.07 0.08 0.04 0.05 0.06 0.08 0.09 0.10 0.08 0.16 0.18 0.11 0.16 0.15 0.09 0.10 0.15 0.06 0.22 0.17 0.14 0.34 4.10 2.10 4.08 4.15 H2O 0.38 1.39 1.23 2.43 1.55 1.11 3.06 2.11 3.03 2.18 1.00 1.59 1.28 1.37 3.02 1.47 0.65 3.66 5.09 O 0.82 2.17 3.79 2.94 2.22 5.42 3.71 0.45 1.56 0.82 1.14 0.88 1.80 0.28 1.92 0.24 3.97 6.73 1.38 4.00 O co2 0.26 3.07 0.48 o_ K 5.95 2.67 3.19 4.01 2.10 2.55 2.39 1.79 3.22 2.53 3.05 2.83 2.49 2.86 3.99 1.91 8.60 4.52 4.54 3.60 2.26 3.10 4.51 o" Ba 778 405 455 884 1612 713 1051 963 900 877 933 1254 1374 1171 357 326 380 405 677 289 494 598 594 TO Ce 69 77 61 87 24 39 50 39 40 41 64 63 45 61 125 38 81 113 292 124 91 63 98 o' Co N.D.t 4 3 5 3 3 5 7 3 4 0 8 11 6 16 6 3 13 12 22 15 23 17 cn Cr 32 56 77 19 21 25 30 97 44 45 104 48 43 64 73 42 43 71 38 105 68 96 72 o Cu 9 12 11 15 20 11 15 10 10 11 29 11 18 17 33 16 11 41 28 102 25 35 55 o Ga 9 11 10 14 10 13 13 10 9 11 15 18 17 17 20 15 12 23 31 23 15 20 17 5" La 30 32 28 38 10 18 32 12 17 19 29 28 21 27 45 16 31 47 100 60 41 29 32 Ni 3 10 11 9 5 6 12 6 9 8 24 15 18 18 33 15 9 33 16 46 30 46 31 o Pb 32 19 22 33 17 13 19 13 25 17 69 25 19 38 35 27 23 37 40 35 19 20 17 Rb 197 135 130 194 73 85 64 52 74 71 135 103 82 110 232 105 183 271 299 181 100 142 139 Sr 206 50 190 94 187 158 258 199 116 176 238 463 464 395 116 126 347 92 104 132 165 128 167 Th 12 16 9 16 2 3 4 5 8 5 15 11 3 11 20 8 10 24 47 16 10 10 10 U 2 4 2 4 2 2 3 3 3 3 0 4 2 1 6 3 1 6 9 15 3 5 6 Y 14 23 20 37 9 21 22 21 22 21 26 18 16 20 33 20 14 30 113 34 33 33 35 Zn 16 40 36 48 27 38 47 37 35 39 271 56 54 121 105 62 21 108 102 103 88 127 95 CO Zr 96 162 202 264 77 118 233 131 136 148 189 177 170 180 293 128 158 236 447 236 198 161 132 c 0.2 0.4 1.0 0.1 Na20/K20 0 0.4 0.1 0.1 0.9 0.6 0.6 1.4 0.3 0.6 0.7 0.9 1.2 0.9 0.1 1.3 0.0 0.0 0.1
K/Rb 300 199 301 371 295 286 168 Ö o Sedimentary normative minerals o o Quartz 55.2 54.2 65.5 56.3 53.0 45.2 40.0 42.3 39.8 42.7 43.7 35.8 30.4 37.5 50.3 46.4 29.6 39.2 36.7 33.0 37.5 16.7 26.4 3 5.6 a" Albite 0.0 12.0 2.2 4.0 18.6 16.2 16.2 26.5 9.5 16.6 21.0 26.8 31.5 25.7 2.6 24.9 0.0 1.4 5.3 6.5 8.6 33.3 et Anorthite 0.0 0.0 0.0 0.0 0.9 3.4 8.5 3.9 0.0 2.0 2.9 0.1 8.7 2.0 0.0 0.0 0.0 0.0 0.0 0.0 4.4 0.0 0.0 K-feldspar 38.1 8.8 11.1 12.3 7.8 10.8 10.4 6.0 17.2 10.2 12.9 9.3 16.1 11.2 12.5 0.1 54.5 6.3 0.0 0.0 5.8 14.3 15.3 Mg-chlorite 0.0 1.3 1.0 0.6 2.5 3.0 3.8 4.2 8.3 5.2 1.5 3.2 3.9 2.8 2.9 1.6 0.4 3.9 2.1 0.3 7.1 10.5 9.6 Fe-chlorite 0.1 0.4 0.3 0.3 1.1 0.5 0.3 0.5 0.9 0.6 1.5 1.9 2.2 1.9 3.2 3.3 0.4 0.8 0.3 3.6 1.2 1.0 1.2 Muscovite 5.6 14.2 16.1 22.9 10.7 10.3 9.7 8.6 8.9 11.2 12.5 15.0 2.3 12.7 23.9 18.6 9.2 37.1 46.4 36.2 14.4 12.1 25.0 Apatite 0.0 0.2 0.2 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.4 0.4 0.3 0.4 0.4 0.2 0.0 0.4 0.0 0.5 0.4 0.3 0.8 Calcite 0.0 4.8 0.2 0.2 5.0 8.7 6.9 4.5 10.1 8.6 1.0 3.6 1.9 2.6 0.6 2.8 0.0 3.1 0.0 1.9 15.6 3.3 5.7 Magnesite 0.5 1.9 0.7 1.5 0.0 0.0 0.0 0.0 2.3 0.0 0.0 0.0 0.0 0.0 1.3 1.1 0.5 1.2 0.5 6.3 0.0 0.0 3.2 Siderite 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Kaolinite 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.4 6.7 0.0 0.0 0.0 Rutile 0.2 0.3 0.3 0.4 0.1 0.2 0.5 0.3 0.4 0.3 0.4 0.4 0.4 0.4 0.5 0.3 0.6 0.7 0.8 1.0 0.7 0.9 0.7 Hematite 0.4 1.9 2.3 1.4 0.6 1.7 3.7 2.9 2.6 2.5 2.2 3.4 2.2 2.9 1.9 0.6 4.7 6.0 5.4 4.1 4.3 7.8 6.6
•Identification of analyses: (A) Eldorado Springs, average of 6 Fountain Fm. sandstones; (B) Steamboat Mountain, average of 6 Fountain Fm. sandstones; (C) Lee Hill Road, average of 12 Fountain Fm. sandstones; (D) Manitou Springs, average of 7 Fountain Fm. sandstones; (E) McCoy area, average of 9 Minturn Fm. sandstones; (F) Ouray, average of 7 Cutler Fm. sandstones; (G) Gateway, average of 4 Cutler Fm. sandstones; (H) Fisher Towers, average of 4 Cutler Fm. sandstones; (I) Moab area, average of 5 Cutler Fm. sandstones; (J) Cutler Fm., average of 20 sandstones; (K) East Flank, Front Range, average of 10 modern sands; (L) Gore Range, average of 19 modern sands; (M) West Creek, average of 4 modern sands; (N) Colorado Rockies, average of 33 modern sands; (O) Santa Ynez Mtns., California, average Paleogene Sandstone (van de Kamp et al., 1976); (P) Gottero Fm., N. Apennines, Italy, average sandstone, unpublished data of the authors; (Q) Eldorado Springs, average of 6 Fountain Fm. shale-siltstones; (R) Steamboat Mtn., average of 4 Fountain Fm. shale-siltstones; (S) Manitou Springs, average of 4 Fountain Fm. shale-siltstones; (T) McCoy area, average of 3 Minturn Fm. shale-siltstones; (U) Ouray, average of 5 Cutler Fm. shale-siltstones; (V) Fisher Towers, average of 2 Cutler Fm. shale-siltstones; (W) Moab area, average of 2 Cutler Fm. shale-siltstones. tN.D. = no data.
L/l
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O MODERN SANDS ble 2\ K), the Gore Range ¡and West Creek sand averages (Table 2, L, M) are poorer in FOUNTAIN FORMATION ® sandstone Si, Al, and Na and richer! in Fe and Mg. • siltstone and shale Normative minerals (Table! 2, K-M) reflect FOUNTAIN FORMATION, Eldorado Springs these differences as greater! quartz with less 0 sandstone plagioclase and mafic minerals (as chlorite) 0 siltstone and shale in the eastern samples. All modern sands MINTURN and CUTLER FORMATIONS were derived under similar climatic condi- % Na20 0 sandstone tions, so a real difference in provenance * siltstone and shale composition is indicated. Thus the Front Range area is a somewhat more felsic prov- enance than the areas west of the Front Range. The ancient sandstone units, consid- ered in the same fashion, have similar pro- vincial compositional characteristics. In the % K20 Fountain Formation sandstone (Table 2,
Figure 4. Na20 plotted against K20 showing distributions of these alkalies in the modern A-D), Si and K abundances are higher, and (shaded area) and ancient sediments. Cutler and Minturn sandstones contain generally Fe, Mg, and Na are generally lower than in
similar abundances as the modern sands, whereas Na20 is much diminished in the Foun- the Minturn and Cutler rocks. The higher tain Formation sandstone due to apparent greater predepositional weathering of Fountain Fe and Mg indicate more mafic provenance detritus, subsequent diagenesis and weathering, and loss of plagioclase in potash meta- for the Minturn and Cutler Formations.
somatism. High K20 (>6%) represents K-metasomatised rocks. Abundances of Si, Al, Na, and K are more difficult to evaluate in terms of provenance because they have been affected by weath- derived from older Paleozoic carbonate the known distribution of rock types in both ering prior to deposition and by diagenetic rocks. The trace element abundances in the the Front Range and the Uncompahgre Up- and hydrothermal alterations. The more in- modern and ancient sands are also charac- lift, that is, dominantly felsic gneisses and teristic of granodioritic rocks. Noteworthy is quartz diorite to granitic plutonic types and the absence of high abundances of Co (>10 paucity of ultramafic rocks (Tweto, 1977). 'GSA Data Repository item 9448, Tables 3, 4, ppm), Cr (>200 ppm), and Ni (>50 ppm), Provincial compositional differences in 5, and 6 (mineralogy and chemical analyses of which would be indicative of ultramafic modern stream sands and Pennsylvanian and Per- the modern sands reflect similar variations mian sandstones), is available on request from rocks in the provenance (van de Kamp and in the ancient rocks. Compared to the east Documents Secretary, GSA, P.O. Box 9140, Boul- Leake, 1985). These observations agree with flank of the Front Range sand average (Ta- der, CO 80301.
FOUNTAIN FORMATION » Steamboat Mountain & 0 Lee Hill Road 50- A • Eldorado Springs i> MINTURN FORMATION 40- + Red Rocks * Vail Pass West • Perry Park a McCoy 30- + Manitou Springs NÌ (ppm) CUTLER FORMATION MINTURN FORMATION 20 « Ouray 60-1 A McCoy ^ Gateway CUTLER FORMATION 10- o Fisher Towers * 50 n Moab « Ouray A a ^ Gateway 40 o Fisher Towers Ni (ppm) 0 Moab e- * 30 0 40- FOUNTAIN FORMATION % Steamboat Mountain 20 « » * 30" * Lee Hill Road 0 % • NÌ (ppm) * • • 0 • • • Eldorado Springs «is» * • 20- 10 0 -f Red Rocks O \ Ù 10" • Perry Park 0 t Manitou Springs 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 20 30 total Fe203% al-alk B
Figure 5. A. Nickel plotted against total iron as Fe203 showing the correlation of these parameters indicative of Ni in Fe-bearing minerals. B. Nickel plotted against al-alk showing the gross similarity of these variables in the modern sands and Minturn and Cutler rocks.
1572 Geological Society of America Bulletin, December 1994
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FOUNTAIN FORMATION Ce, La, Th, and Zr are generally less X Steamboat Mountain abundant in the Cutler and Minturn Forma- 0 Lee Hill Road tions than in the Fountain Formation. Cu, • Eldorado Springs Pb, and Zn are similar in all the units, indi- Red Rocks Perry Park cating no significant provincial differences Manitou Springs or mineralization. As the averages (Table 2, MINTURN FORMATION Q-W) show, the trace metals are commonly A McCoy more concentrated in the finer-grained CUTLER FM. rocks in clays and heavy minerals. Zr and Y & Ouray are correlated (Fig. 6), indicating substitu- Gateway tion of Y in the zircon lattice. However, Ce Fisher Towers Moab and La do not correlate strongly with Zr; they are probably located in clays and micas. Clays correlate well with al-alk (Fig. 7). Exceptional to the general trend are the cat- ion-rich adularia-rich rocks that have low al- alk, because clays are absent or make up a small proportion of the rock. These charac-
teristics are also evident in the plot of KzO against al-alk (Fig. 8A). Fountain Formation sandstone (Table 2, Y (ppm) A-D) and shale and siltstone (Table 2, Q-S) Figure 6. Plot of Zr and Y showing a good correlation indicative of their presence together tend to be richer in silica and potassium and in zircon. poorer in many major and trace cations than the Cutler and Minturn sandstone (Table 2, tense weathering, postulated by Suttner and Thus the Ni vs. al-alk plot has rather similar F-J), shale and siltstone (Table 2, T-W), Dutta (1986) for the lower Fountain For- values for modern sands and the Minturn and the modern sands (Table 2, K-N). Al- mation detritus, removed more plagioclase and Cutler Formations but demonstrates a though the composition of modern sands and mafic silicates than the drier climate in marked shift to higher al-alk in the more may not be identical to that of the Paleozoic which Minturn-Cutler detritus developed. altered Fountain rocks (Fig. 5B). Cr, in con- sandstone prior to burial and diagenesis, Hydrothermal alteration in some Fountain trast to Ni, does not correlate with total iron, they make a reasonable basis for compari- Formation rocks markedly changed their Mg, or al-alk. Chromium is probably distrib- son. Minturn and Cutler rocks have appar- chemistry through leaching and potassic uted among micas, clays, and oxides. ently had little chemical compositional metasomatism. Notwithstanding these com- plications, the least-altered Fountain For- MUSCOVITE mation sandstones at Manitou Springs and CHLORITE ILLITE SMECTITE KAOLINITE Perry Park reflect less mafic provenance 100 than the Cutler Formation sandstone. This 90- is indicated by Si, Al, Fe, and Mg contents as well as normative quartz, plagioclase, and 80- FOUNTAIN FORMATION chlorite (Table 2). The Minturn Formation to < 70 * Steamboat Mountain o sandstone is also from a less mafic, more 0 Lee Hill Road siliceous provenance than the Cutler For- 60- • Eldorado Springs mation rocks. -f Red Rocks 50- • Perry Park Ni correlates with total Fe in these sedi- + Manitou Springs ments (Fig. 5A), indicating its presence in 40- MINTURN FORMATION iron oxides, including magnetite, ilmenite, IS A a Vail Pass West 30- hematite, and secondary oxides derived v.* A McCoy CUTLER FORMATION from mafic silicates. Modern sands contain 20 ® Ouray amphibole, biotite, and opaque minerals in ti Gateway which Fe, Mg, and Ni are concentrated. The 10- o Fisher Towers QUARTZ 0 Moab ^ ancient sediments lack amphibole and con- ALBITE tain variably altered biotite and secondary K-FELDSPAR 10 20 30 40 50 60 70 80 90 100 chlorite, clays, and red-brown iron oxides, al-alk reflecting postdepositional alteration and Figure 7. Relation of al-alk with clay species for shale and siltstone analyzed by X-ray oxidation. Fe, Mg, and Ni contents are sim- diffraction. Kaolinite and smectite, with low cation abundances, have high al-alk, whereas ilar in the modern and ancient sediments cation-rich illite, muscovite, biotite, and chlorites have much lower al-alk. This plot of total (Table 2), but Niggli al-alk (Niggli, 1954) is clay abundance against al-alk for shale and siltstone yields a trend from the origin toward higher in the ancient rocks, particularly the the dominant clay type, illite-muscovite in this case, in agreement with the X-ray diffraction Fountain Formation, due to clay alteration. analyses.
Geological Society of America Bulletin, December 1994 1577
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o MODERN SANDS FOUNTAIN FORMATION © sandstone • siltstone and shale 16 K-Feldspar FOUNTAIN FORMATION, Eldorado Springs 0 sandstone
P siltstone and shale Figure 8A. Plot of K20 against al-alk showing MINTURN and CUTLER FORMATIONS distribution of these parameters for modern sands a sandstone 12 and the similar Minturn and Cutler sandstones; • siltstone and shale siltstone and shale plot on a trend toward higher al-alk and K 0 and toward illite approximately Muscovite 2 along the quartz + albite/illite-muscovite tie line. Both Fountain Formation shale and the clay and Field of Smectite and lllite sericite-altered sandstone follow a similar trend % K2O with the important exception of the highly altered, potash metasomatised rocks that trend to low al-
alk and high K20 as plagioclase is destroyed and replaced by adularia. Clay data are from Weaver and Pollard (1973) and Newman (1987).
Quartz Albite Kaolinite 10 20 30 40 50 60 70 80 90 100 al-alk
K-Feldspar o Modern Sands Fountain Formation ® sandstone
-o • siltstone and shale c toward low Na20 + CaO levels as plagioclase is lost. The highly altered and metasomatised sediments in the Fountain Formation plot at high levels of K20 with little or no Na20 + CaO. S E® B. - Loss of Plagioclase Carbonate-rich 12 16 B % Na2 O + CaO change since deposition compared to the ished plagioclase caused by pre- and post- although NazO is diminished due to low pla- Fountain Formation rocks. depositional weathering and solution and gioclase content in the Moab samples with The relative similarity of quartz and feld- trend to very high K-feldspar due to authi- average NazO of 1.08% (Figs. 3B and 9C). spar abundances in the basement rocks and genic adularia and K-feldspar overgrowths, The most extreme compositional changes modern sands and the general plagioclase- particularly at Eldorado Springs. Relative to are in the Eldorado Springs rocks in which rich character of the modern and ancient modern sand with average NazO = 3.01% CaO and NaaO are absent (Table 2, A, Q; sediments derived from the calc-alkaline (Fig. 4), the Minturn (average Na20 = Figs. 4 and 8B) because there is no plagio- provenance are illustrated in Figure 9. The 2.17%) and Cutler (average NazO = 1.92%) clase. The original deposits at this site prob- Fountain rocks are notable for their dimin- sandstones have fairly similar alkali contents ably contained considerable plagioclase be- 1572 Geological Society of America Bulletin, December 1994 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/12/1571/3381889/i0016-7606-106-12-1571.pdf by guest on 01 October 2021 PENNSYLVANIAN-PERMIAN ARKOSE, COLORADO AND UTAH cause it is abundant in the provenance and SEDNORM MINERALS in contemporaneous deposits along strike Q and downdip (Walker, 1984). If it is assumed that the original Fountain Formation sand- MODERN STREAM SANDS stone at Eldorado Springs was similar to the modern sands and the Minturn and Cutler rocks, then the amount of enrichment of re- sidual cations may be calculated after the removed cations are subtracted from the modern sand average. This yields a sand with 83% Si02 and 4.1% K20. The silica content is similar to that found in the Eldo- rado Springs rocks; therefore, the higher sil- ica is the result of proportionate increase due to removal of other cations. The pro- portionate increase of K20 is insufficient to attain the level of 7.2% K20 observed in the Eldorado Springs rocks, however. There- fore, KzO must have been added by meta- somatic processes from an outside source. Similarly, in the shale and siltstone at Eldo- FOUNTAIN FORMA TION rado Springs, many cations (Al, Fe, Mn, Mg, x Steamboat Mountain Ca, and Na) are in low abundance relative to 0 Lee Hill Road similar rocks in the Steamboat Mountain • Eldorado Springs and Manitou Springs sections. By removal • Red Rocks of these cations (—13% by weight), Si0 in- • Perry Park 2 t Manitou Springs creases proportionately from 61% to 70% and K20 from 5.4% to 6.2%; the actual K20 is 10.3%, implying metasomatic addition. Normative minerals in lutite (Table 2) indi- cate high K-feldspar and low mica in the Eldorado Springs average shale and silt- stone. This agrees with the abundant K-feldspar found by X-ray diffraction anal- ysis. Thus the layer silicate abundance (and al-alk) in the K-enriched rocks is low, with MINTURN AND CUTLER much of the K in authigenic K-feldspar, as FORMATIONS adularia and K-feldspar overgrowths on de- a McCoy trital microcline and orthoclase. Ouray >s. Gateway o Fisher Towers The plots of Al203-Na20-K20 (Fig. 10) 0 Moab show the effects of alteration as soda is de- pleted and the rocks are enriched in K20. Examples of the epithermal potassic alter- ation in the Bodie, California, intermediate composition volcanic rocks (O'Neil and oth- ers, 1973) and the Fountain Formation show similar trends which suggest similar process- es were operative in both cases. Rubidium correlates well with the K- bearing minerals (K-feldspar + micas + Figure 9. Plots of normative quartz, plagioclase, and K-feldspar (QPK) for modern sands clays) and reaches highest concentrations in (A) and ancient sediments (B and C). The modern sands and Minturn and Cutler rocks the highly altered potassium-rich Eldorado are generally plagioclase rich, whereas the Fountain rocks, particularly those with potassic Springs rocks (Fig. 11). Strontium, com- alteration, are K-feldspar rich. Least-altered Fountain Formation rocks (B) indicate the monly substituting for Ca in plagioclase, has detritus was originally plagioclase rich. Note the relatively abundant plagioclase in auto- relatively low abundance in the Fountain genic albite-bearing Steamboat Mountain rocks (B). These compositional trends, derived Formation sandstone (Fig. 12) due to low from rock chemistry, mimic those for modal data in Figure 3B. plagioclase content. Trace metals Co, Cr, Cu, Ga, Ni, Th, U, and Zn plus Ba, Ce, La, and Y are much less abundant in the Eldo- rado Springs lutite relative to the Fountain Geological Society of America Bulletin, December 1994 1577 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/12/1571/3381889/i0016-7606-106-12-1571.pdf by guest on 01 October 2021 VAN DE KAMP AND LEAKE FOUNTAIN FORMATION (1984). Normative plagioclase in Fountain MINTURN FORMATION Formation sandstone is albite in all cases. * Steamboat Mountain a McCoy K-feldspars in the Fountain Formation 0 Lee Hill Road CUTLER FORMATION commonly have significant syntaxial over- • Eldorado Springs AloOo & Ouray growths. Authigenic adularia is common + Red Rocks 2 3 ^ Gateway in the samples from Eldorado Springs and • Perry Park o Fisher Towers Lee Hill Road where resistant "flatirons" + Manitou Springs ^ Moab consisting of this hard, tightly cemented, highly altered sandstone form striking to- pography near Boulder, Colorado. West of the Front Range, Minturn and Cutler sandstones contain abundant partly albi- tized plagioclase (An0_40) comparable to the normative plagioclase (An0_35). In chemical and normative mineral composi- K-feldspar tions, the Cutler and Minturn are compa- Unaltered rable to other arkoses (Table 2, J and E, O Volcanic rocks and P). The similarities and differences among provenance, modern sands, and various an- Albite cient sandstones are displayed in a QPK diagram (Fig. 9). By alteration of plagioclase to clays and metasomatic addition of K20, the Fountain Formation sandstone and silt- stone at Eldorado Springs and Lee Hill Road are considerably enriched in K-feldspar. The alteration observed in the Figure 10. Plot of Al203-Na20-K20 with original detrital compositions represented Fountain Formation, from the vicinity of El- toward the right; increasing alteration shifts compositions to the left. The most intensely dorado Springs north to Lee Hill Road, in- altered rocks plot along the A1203-K20 join with shale and siltstone closer to the A1203 cluding the leaching of metals and addition apex and adularia-rich, plagioclase-free sandstone closer to the ideal K-feldspar point. of potassium to the rocks, is typical of po- Inset to the right (same scale) is for unaltered and altered intermediate composition tassic hydrothermal alteration (O'Neil and volcanic rocks (dots) at Bodie, California, showing the trend to increasing K20 as hydro- others, 1973; Rose and Burt, 1979), com- thermal potassic alteration becomes more intense. mon in hot springs systems. The model for epithermal alteration and ore deposition de- Formation at other localities. Total clays in those now exposed in the Colorado Rockies. veloped by Buchanan (1981) and modified the Eldorado Springs lutite range from Basement rocks of approximately grano- by Hayba and others (1985) implies that <1% to 29%. This is much less than in other dioritic composition are most common, and adularia was deposited by potassium-rich localities where clays constitute 14% to modern sands derived from them reflect this geothermal waters in a boiling zone proba- 74%, commonly >30%, of the fine-grained composition. Those on the east flank of the bly at 150-350 m depth and 150-250 °C. rocks. Thus many elements that are con- Front Range are less mafic than those west Modern analogues are geothermal occur- tained in clays or adsorbed on them are in of the Front Range. Modern sands, like rences in the Great Basin, such as Roosevelt low abundance at Eldorado Springs com- their ancient counterparts, contain abun- Hot Springs, Utah, and Dixie Valley, Ne- pared to Fountain Formation lutite at other dant plagioclase and K-feldspar in variable vada. In such systems, the alteration and localities. proportions. The Paleozoic sandstones, af- high heating is confined to a restricted, per- meable zone adjacent to faults carrying hot In hydrothermally altered rocks, Ag, As, ter accounting for weathering and diage- fluid apparently heated by magma at depth. Sb, and Hg are commonly in high abun- netic alterations, are grossly similar to the Thus it is unlikely that the Fountain Forma- dance due to deposition from hot fluids (van modern sands; the Fountain and Minturn tion in the subsurface, at some distance east de Kamp and others, 1994). Our results for Formations were derived from more felsic of the Front Range, is similarly altered. This the Eldorado Springs rocks show that Sb val- provenance than the Cutler Formation. In is actually the case as shown by Walker ues are >1 ppm in some of the altered rocks, modern sands, plagioclase is generally fresh (1984), who found albitized K-feldspar in whereas abundances of <1 ppm are normal to slightly altered and has compositions in deeply buried (3 km) Fountain Formation in unaltered clastic sediments. Ag, As, and the range of An0_40 approximately; similar sandstone. Hg values are not anomalous in these rocks. to the normative plagioclase compositions of An0_33. Mineralization by migrating basin- DISCUSSION Plagioclase in Fountain Formation sand- derived brines provides an alternative expla- stone is diagenetic albite. Texturally, some nation for the potassium metasomatism. In Colorado and eastern Utah, late Pale- of the albite is similar to the albitized K- Such fluids, expelled from compacting sedi- ozoic sediments were derived from Precam- feldspar in subsurface Fountain Forma- ments in the Denver Basin, may be compa- brian crystalline basement rocks similar to tion sandstone described by Walker rable to the Mississippi Valley-type (MVT) 1572 Geological Society of America Bulletin, December 1994 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/12/1571/3381889/i0016-7606-106-12-1571.pdf by guest on 01 October 2021 PENNSYLVANIAN-PERMIAN ARKOSE, COLORADO AND UTAH FOUNTAIN FORMATION 400 * Steamboat Mountain Figure 11. Plot of rubidium against total 0 Lee Hill Road potassium-bearing minerals. Most of the • Eldorado Springs Fountain Formation samples analyzed in + Red Rocks this work follow a trend of400-500 ppm Rb; 300- • Perry Park these contain little or no smectite and may + Manitou Springs be considered to be "saturated" in Rb. • Wet Mountains Fountain Formation samples from the Wet Rb(ppm) Mountains studied by Cullers and Stone MINTURN FORMATION (1991) and the Minturn and Cutler rocks plot toward low Rb abundances because 200 a Vail Pass West A McCoy they contain abundant smectite, which is CUTLER FORMATION "undersaturated" with respect to K and Rb. Empirically, it appears that the "mean" Rb Ouray 400 content of K- and Rb-bearing minerals ^ Gateway (mostly K-feldspar and illite/muscovite) is o Fisher Towers 500-600 ppm in these rocks. 0 Moab 20 30 40 50 60 70 80 90 100 %K-feldspar + micas + clays waters responsible for abundant authigenic widespread along the Fountain Formation bounding faults occurred in the Laramide K-feldspar with crystallization temperatures outcrop. uplift or in the late Tertiary uplift event. It of 100-200 °C in Paleozoic rocks of the Ap- A possible historic outline for alterations may correspond to the intrusive activity and palachian area as described by Hearn and in the Fountain Formation is maximum formation of mineral deposits in the Central others (1987). Although we cannot uniquely burial to about 2000-3500+ m in the west- Colorado Mineral Belt (along the trend of indicate which process yielded the alter- ern Denver Basin by Late Cretaceous the Colorado Lineament or Transcontinen- ations observed, we favor the geothermal (Anderson and Ackman, 1963). Diagenesis tal Arch) in the early Tertiary (Bryant and system because the affected area is limited. proceeded as outlined by Walker (1984) and others, 1975; Warner, 1980) or the mid- If the MVT fluids had altered these rocks, Shultz (1984). It is possible that geothermal/ Tertiary. Another possibility is that the hy- then their effects probably would be more hydrothermal activity adjacent to the range- drothermal alteration occurred at shallow O MODERN SANDS FOUNTAIN FORMATION ® sandstone • siltstone and shale FOUNTAIN FORMATION, Eldorado Springs 1000-t 0 sandstone 0 siltstone and shale MINTURN and CUTLER FORMATIONS h sandstone Figure 12. Sr plotted against KzO com- 800- • siltstone and shale O paring modern sands and ancient sand- O ® stones. High Sr values are in some of the potash metasomatised rocks where Sr may 600- substitute for K in the absence of Ca. No Sr (ppm) correlation of Sr with Ca in carbonate-rich rocks was found, implying there is little Sr 400- in the carbonates. 200- 7 8 10 11 12 13 14 15 % K2O Geological Society of America Bulletin, December 1994 1581 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/12/1571/3381889/i0016-7606-106-12-1571.pdf by guest on 01 October 2021 VAN DE KAMP AND LEAKE burial (<1 km) of the Fountain Formation eral analyses. Jim Gallagher, at the Univer- the Rocky Mountain region: Denver, Colorado, Rocky Mountain Association of Geologists, p. 131-132. sediments in late Paleozoic or early Meso- sity of Glasgow, performed the chemical Maughan, E. K., 1980, Permian and Lower'Triassic geology of Col- orado, in Kent, H. C., and Porter, K. W., eds., Colorado zoic time. At whatever time the hydrother- analyses. Fred Meissner and Robert Beres- geology: Denver, Colorado, Rocky Mountain Association of mal activity occurred, a likely source for the kin offered helpful critical reviews of the man- Geologists, p. 103-110. Meyer, H. J., and McGee, H. W., 1985, Oil and gas fields accom- heat would have been magma adjacent to uscript. Further improvements to the paper panied by geothermal anomalies in Rocky Mountain region: American Association of Petroleum Geologists Bulletin, the deep-seated range front faults that con- were suggested by the GSA Editors. v. 69, p. 933-945. ducted the hot fluids to the surface. Newman, A. C. D., ed., 1987, Chemistry of clays and clay minerals: Mineralogical Society Monograph 6, 480 p. Elliot and others (1991) documented a REFERENCES CITED Niggli, P., 1954, Rocks and mineral deposits: San Francisco, W. H. Freeman and Co., 559 p. major heating event at ca. 60 Ma in the O'Neil, J. R., Silberman, M. L., Fabbi, B. P., and Chesterman, northern Denver Basin when the sedimen- Anderson, G. G., and Ackman, E. J., 1963, Structure of the C. W., 1973, Stable isotope and chemical relations during Denver-Julesburg Basin and surrounding areas, in Geology mineralization in the Bodie Mining District, Mono County, tary rocks were at maximum burial in the of the northern Denver Basin and adjacent uplifts: Denver, California: Economic Geology, v. 68, p. 765-784. Colorado, Rocky Mountain Association of Geologists, Pearl, R. H., 1980, Cojorado stratigraphie nomenclature chart, in Paleocene in the area in and west of Wat- p. 170-175. Kent, H. C., and Porter, K. W., eds., Colorado geology: tenberg Gas Field. Coincidentally, the in- Boggs, S., Jr., 1966, Petrology of Minturn Formation, east-central Denver, Colorado, Rocky Mountain Association of Geolo- Eagle County, Colorado: American Association of Petrole- gists, plate 1. tensely altered Fountain Formation rocks um Geologists Bulletin, v. 50, p. 1399-1422. Raup, O. B., 1966, Clay mineralogy of Pennsylvanian redbeds and Bryant, B., Marvin, R. F., Mehnert, H. H., and Naeser, C. W., associated rocks flanking the Ancestral Front Range of cen- are present in this area, so a common event 1975, Upper Eocene porphyries in the Colorado Mineral tral Colorado: American Association of Petroleum Geolo- of heating and alteration along the Colo- Belt and the history of the west margin of the Front Range gists Bulletin, v. 50, p. 251-268. Uplift: Geological Society of America Abstracts with Pro- Rose, A. W., and Burt, D. M., 1979, Hydrothermal alteration, in rado Lineament is suggested. The present- grams, v. 7, no. 5, p. 591. Barnes, H. L., ed., Geochemistry of hydrothermal ore de- Buchanan, L. J., 1981, Precious metal deposits associated with posits (second edition): New York, John Wiley & Sons, day hot spot at Wattenberg (Meyer and Mc- volcanic environments in the southwest, in Dickinson, p. 173-235. Gee, 1985) is probably also related to the W. R., and Payne, W. D., eds., Relations of tectonics to ore Shultz, A., 1984, Provenance and sedimentology of the Fountain deposits in the Southern Cordillera: Arizona Geological So- Formation near Cañón City, Colorado, in Suttner, L. J., ed., Colorado Lineament. A relation of in- ciety Digest, v. 14, p. 237-262. Sedimentology of the Fountain fan-delta complex near Cullers, R. L. and Stone, J., 1991, Chemical and mineralogical Manitou Springs and Cañón City, Colorado: Rocky Moun- creased temperature gradient in the area of comparison of the Pennsylvanian Fountain Formation, Col- tain Section, Society of Economic Paleontologists and Min- the Colorado Lineament was noted by Sma- orado, U.S.A. (an uplifted continental block) to sedimentary eralogists (SEPM), Guidebook, p. 62-85. rocks from other tectonic environments: Lithos, v. 27, Smagala, T. M., Brown, C. A., and Nydegger, G. L., 1984, Log- gala and others (1984). Heat may have been p. 115-131. derived indicator of thermal maturity, Niobrara Formation, DeVoto, R. H., 1980, Pennsylvanian stratigraphy and history of Denver Basin, Colorado, Nebraska, Wyoming, in Wood- supplied by an intrusion related to others of Colorado, in Kent, H. C., and Porter, K. W., eds., Colorado ward, J., Meissner, F. F., and Clayton, J. L., eds., Hydro- ca. 60 Ma (Hoblitt and Larson, 1975) in this geology: Denver, Colorado, Rocky Mountain Association of carbon source rocks of the greater Rocky Mountain region: Geologists, p. 71-102. Denver, Colorado, Rocky Mountain Association of Geolo- zone of crustal weakness. Thus an area of Dickinson, W. R., 1985, Interpreting provenance relations from gists, p. 355-363. detrital modes of sandstones, in Zuffa, G. G., ed., Prove- Suttner, L. J., 1984, Climatic influence on Fountain sedimentation increased chemical activity and alteration nance of arenites: Dordrecht, Netherlands, D. Reidel Pub- in the Manitou embayment, in Suttner, L. J., ed., Sedimen- along the Colorado Lineament lies directly lishing Co., p. 333-361. tology of the Fountain fan-delta complex near Manitou Elliot, W. C., Aronson, J. L., Matisoff, G., and Gautier, D. L., 1991, Springs and Cañón City, Colorado: Rocky Mountain Sec- below and downdip from the highly altered Kinetics of the smectite to illite transformation in the Den- tion, Society of Economic Paleontologists and Mineralogists ver Basin: Clay mineral, K-Ar data, and mathematical (SEPM), Guidebook, p. 86-96. Fountain Formation outcrops, and it is a model results: American Association of Petroleum Geolo- Suttner, L. J., and Dutta, P. K., 1986, Alluvial sandstone compo- logical present and ancient source of hot wa- gists Bulletin, v. 75, p. 436-462. sition and paleoclimate, I. Framework mineralogy: Journal Fenton, M. W., 1987, The geochemistry and petrology of selected of Sedimentary Petrology, v. 56, p. 329-345. ter for the observed alterations in the Eldo- lower Paleozoic sedimentary rocks from Victoria, Australia Tweto, O., 1977, Precambrian geology of Colorado, in Kent, H. C., [Ph.D. thesis]: Melbourne, Australia, University of Mel- and Porter, K. W., eds., Colorado geology: Denver, Colo- rado Springs area. bourne, 550 p. rado, Rocky Mountain Association of Geologists, p. 37-46. Garrels, R. M., and MacKenzie, F. T., 1971, Evolution of sedi- van de Kamp, P. C., and Helmold, K. P., 1991, Composition of Rocks of the Minturn and Cutler Forma- mentary rocks: New York, W. W. Norton & Co., 397 p. sediments derived from granitic basement rocks in glacial to Harvey, P. K., Taylor, D. M., Hendry, R. D., and Bancroft, F., humid tropical climates: Geological Society of America Ab- tions had similar provenance but less intense 1973, An accurate fusion method for the analysis of rocks stracts with Programs, v. 23, no. 5, p. A72. weathering conditions in their source areas and chemically related materials by X-ray fluorescence spec- van de Kamp, P. C., and Leake, B. E., 1985, Petrography and trometry: X-ray Spectrometry, v. 2, p. 33-44. geochemistry of feldspathic and mafic sediments of the than the Fountain Formation. They were Hayba, D. O., Bethke, P. M., Heald, P., and Foley, N. K., 1985, northeastern Pacific margin: Transactions of the Royal So- Geologic, mineralogic, and geochemical characteristics of ciety of Edinburgh, v. 76, p. 411-449. not subjected to the hydrothermal alteration volcanic-hosted epithermal precious mineral deposits, in van de Kamp, P. C., Leake, B. E., and Senior, A., 1976, The pe- seen in the Fountain Formation of the Berger, B. R., and Bethke, P. M., eds., Geology and geo- trography and geochemistry of some Californian arkoses chemistry of epithermal systems: Society of Economic Ge- with application to identifying gneisses of metasedimentary northern Front Range outcrops. Rather, the ologists, Reviews in Economic Geology, v. 2, p. 129-168. origin: Journal of Geology, v. 84, p. 195-212. Hearn, P. P., Jr., Sutter, J. F., and Beikin, H. E., 1987, Evidence van de Kamp, P. C., Helmold, K. P., and Leake, B. E., 1994, Minturn and Cutler have had more conven- for late Paleozoic brine migration in Cambrian carbonate Holocene and Paleogene arkoses of the Massif Central, tional burial diagenetic alteration with little rocks of the central and southern Appalachians: Implica- France: Mineralogy, chemistry, provenance, and hydrother- tions for Mississippi Valley-type sulfide mineralization: mal alteration of the type arkose: Journal of Sedimentary removal or addition of nonvolatile chemical Geochimica et Cosmochimica Acta, v. 51, p. 1323-1334. Research, v. A64, p. 17-33. Hoblitt, R., and Larson, E., 1975, Paleomagnetic and geochrono- Velbel, M. A., and Saad, M. K., 1991, Paleoweathering or diagen- components. Modal and normative compo- logic data bearing on the structural evolution of the north- esis as the principal modifier of sandstone framework com- sitions of these rocks are quite similar to eastern margin of the Front Range, Colorado: Geological position? A case study from some Triassic rift-valley red- Society of America Bulletin, v. 86, p. 237-242. beds of eastern North America, in Morton, A. C., Todd, those of modern sediments, and relatively Howard, J. D., 1966, Patterns of sediment dispersal in the Foun- S. P., and Haughton, P. D. W., eds., Developments in sedi- tain Formation of Colorado: Mountain Geologist, v. 3, mentary provenance studies: Geological Society of London unstable detrital plagioclase and biotite are p. 147-153. Special Publication 57, p. 91-99. preserved. Hubert, J. F., 1960, Petrology of the Fountain and Lyons Forma- Walker, T. R., 1978, Paleoclimate interpretation from a petro- tions, Front Range, Colorado: Colorado School of Mines graphic comparison of Holocene sands and the Fountain Quarterly, v. 55, 242 p. Formation (Pennsylvanian) in the Colorado Front Range: A Leake, B. E., Hendry, G. L., Kemp, A., Plant, A. G., Harvey, P. K., discussion: Journal of Sedimentary Petrology, v. 48, ACKNOWLEDGMENTS Wilson, J. R., Coats, J. S., Aucott, J. A., Lunel, T., and p. 1011-1013. Howarth, R. J., 1969, The chemical analysis of rock powders Walker, T. R., 1984, Diagenetic albitization of potassium feldspar by automatic X-ray fluorescence: Chemical Geology, v. 5, in arkosic sandstones: Journal of Sedimentary Petrology, In the field, we benefited greatly from the p. 7-86. v. 54, p. 3-16. Mack, G. H., and Rasmussen, K. A., 1984, Alluvial-fan sedimen- Warner, L. A., 1980, The Colorado lineament, in Kent, H. C., and guidance and experience of Ted Walker and tation of the Cutler Formation (Permo-Pennsylvanian) near Porter, K. W., eds., Colorado geology: Denver, Colorado, Gateway, Colorado: Geological Society of America Bulle- Rocky Mountain Association of Geologists, p. 11-21. from his critical discussion in preparation of tin, v. 95, p. 109-116. Weaver, C. E., and Pollard, L. D., 1973, The chemistry of clay this paper. Ken Helmold helped collect sam-' Mack, G. H., and Suttner, L. J., 1977, Paleoclimate interpretation minerals: Amsterdam, Netherlands, Elsevier, 213 p. from a petrographic comparison of Holocene sands and the Werner, W. G., 1974, Petrology of the Cutler Formation (Penn- pies and arranged for the X-ray diffraction Fountain Formation (Pennsylvanian) in the Colorado Front sylvanian-Permian) near Gateway, Colorado, and Fisher Range: Journal of Sedimentary Petrology, v. 47, p. 89-100. Towers, Utah: Journal of Sedimentary Petrology, v. 44, analyses. He also provided the computer Mack, G. H., Suttner, L. J., and Jennings, J. R., 1979, Permo- p. 292-298. program to calculate the sedimentary Pennsylvanian climatic trends in the ancestral Rocky Moun- tains: Four Corners Geological Society Field Conference, norms. Mike Kelton, with ARCO Oil and 9th, Guidebook, p. 7-12. MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 5, 1993 Mallory, W. W., 1972, Pennsylvanian arkose and the ancestral REVISED MANUSCRIPT RECEIVED APRIL 29, 1994 Gas Company, provided excellent clay min- Rocky Mountains, in Mallory, W. W., ed., Geologic atlas of MANUSCRIPT ACCEPTED MAY 5, 1994 Printed in U.S.A. 1572 Geological Society of America Bulletin, December 1994 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/106/12/1571/3381889/i0016-7606-106-12-1571.pdf by guest on 01 October 2021