STUDIES RELATED TO WILDERNESS 

Mineral Resources of the 

Mount Zirkel Wilderness and 

Northern Park Range Vicinity, 

Jackson and Routt Counties, 

Colorado 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY, 

LOWELL L. PATTEN, U.S. BUREAU OF MINES, and 

JEFFREY J. DANIELS, U.S. GEOLOGICAL SURVEY 

STUDIES RELATED TO WILDERNESS-WILDERNESS AREAS 

U.S. GEOLOGICAL SURVEY BULLETIN 1554 

An evaluation of the mineral resource 

potential of the area 

Includes Davis Peak Roadless Area and 

adjacent wilderness established by P. L. 96-560 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1987 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Library of Congress Cataloging in Publication Data 

Snyder, George L. (George Leonard), 1927-

Mineral resources of the Mount Zirkel Wilderness and northern Park Range vicinity, 

Jackson and Routt Counties, Colorado. 

(Studies related to wilderness-wilderness areas) 

(Geological Survey bulletin ; 1554) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1554 

1. Mines and mineral resources-Colorado--Jackson County. 2. Mines and mineral resources-Colorado-Routt County. 3. Geology-Colorado--Jackson County. 4. GeologyColorado--Routt County. I. Patten, Lowell L. II. Daniels, Jeffrey J. III. Title. IV. 

Series. V. Series: Geological Survey bulletin ; 1554. 

QE75.B9 no. 1554 

[TN24.C6] 

557.3 s [553' .09788' 66] 

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225 

85-600065 
STUDIES RELATED TO WILDERNESS 

WILDERNESS AREAS AND 

STUDY AREAS 

In accordance with the provisions of the Wilderness Act 

(Public Law 88-577, Sept. 3, 1964) and related acts, the U.S. 

Geological Survey and U.S. Bureau of Mines have been conducting mineral surveys of wilderness and primitive areas. 

Studies and reports of all primitive areas have been completed. 

Areas officially designated as "wilderness," "wild," or "canoe" 

when the act was passed were incorporated into the National 

Wilderness Preservation System, and some of them are presently being studied. The act provided that areas under consideration for wilderness designation should be studied for suitability 

for incorporation into the Wilderness System. The mineral 

surveys constitute one aspect of the suitability studies. This 

report discusses the results of a mineral survey of some national 

forest lands in the Mount Zirkel Wilderness and northern Park 

Range vicinity, Colorado, that are being considered for wilderness designation, and of an equal amount of surrounding land 

that has not been considered for wilderness designation. Since 

the initial writing additional wilderness adjacent to the original 

Mount Zirkel Wilderness has been established by Public Law 

96-560, Dec. 22, 1980, and the adjacent Davis Peak Roadless 

Area was classified as further planning during the Roadless 

Area Review and Evaluation (RARE II) by the Forest Service, 

January 1979. Both are shown on the index map figure of this 

report but are not otherwise referred to herein; the area of each 

is completely covered by the geologic, geochemical, and 

geophysical studies contained in this report. 

CONTENTS 

[Letters indicate chapters] 

Summary ................. . 

Introduction .......... . 

Geologic investigations by others . . . . . . . . . . . . . . . . . . . ..... . 

Present studies and acknowledgments . . . . . . . . . . ......... . 

(A) Geological appraisal, by George L. Snyder ....................... . 

(B) Mine appraisal, by Lowell L. Patten ............................ . 

(C) Evaluation of surface metallic and nonmetallic resource potential, 

by George L. Snyder .................................. . 

(D) Geophysical appraisal, by Jeffrey J. Daniels ...................... . 

Summary evaluation of mineral resource potential, by George L. Snyder .. . 

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

ILLUSTRATIONS 

[Plates are in pocket; figures 4-106 listed in "Contents" of chapters] 

PLATE 1. Geologic and aeromagnetic map of Mount Zirkel Wilderness 

and vicinity, Jackson and Routt Counties, Colorado. 

2. Geochemical sample locality map of Mount Zirkel Wilderness 

and vicinity, Jackson and Routt Counties, Colorado. 

Page 

2 

6 

7 

13 

57 

109 

215 

222 

228 

Page 

FIGURE 1. Index map showing areas surveyed by U.S. Geological Survey 4 

2. Photograph of Mount Zirkel and Sawtooth Range . . . . . . 8 

3. Photograph of Gilpin Lake to Big Agnes Mountain . . . . . 10 

107-109. Maps showing: 

107. Location of anomalously high rock elements . . . . 223 

108. Location of anomalously high stream-sediment 

elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 

109. Surface and subsurface mineral-resource potential 226 

v 

STUDIES RELATED TO WILDERNESS-WILDERNESS AREAS 

MINERAL RESOURCES OF THE 

MOUNT ZIRKEL WILDERNESS AND 

NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY, 

LOWELL L. PATTEN, U.S. BUREAU OF MINES, and 

JEFFREY J. DANIELS, U.S. GEOLOGICAL SURVEY1 

SUMMARY 

A mineral resource survey of the Mount Zirkel Wilderness and adjacent area (971 

km2 or 375 mi2) and its surroundings was made by the U.S. Geological Survey and U.S. 

Bureau of Mines during the summers of 1965-73. The area studied, 2,458 km2 or 945 

mi2, lies in the northern Park Range along the Continental Divide between Steamboat 

Springs and Walden, Colorado, immediately south of the Colorado-Wyoming State line. 

Almost all of this wilderness area is underlain by Precambrian rocks, mainly amphibolitic 

to felsic high-grade metavolcanic rocks with minor interlayered metashale and marble 

that have been intruded by bodies of syntectonic gabbro, quartz monzonite, quartz diorite 

and peridotite, and posttectonic quartz monzonite and granite. All the Precambrian 

rocks were cut by northeast-trending, largely left-lateral mylonite shear zones. The adjacent area is underlain largely by the same crystalline rocks, although significant 

Mesozoic and Miocene sedimentary rocks flank both sides of the range. Additional postCretaceous compressional faults and post-Miocene tensional faults offset the younger 

sediments; some of these follow the Precambrian zones of weakness, and some are at 

a large angle to them. 

The mineral resource potential of the area was evaluated by geologic studies including 

geologic mapping, by detailed examination of rocks and mining claims, by geochemical 

and geophysical surveys, and by analysis of the derived data. A total of 3,352 samples 

were collected and studied by petrographic and chemical methods. Known surface 

deposits of fluorspar veins, base- and precious-metal sulfide veins and manto deposits, 

1

Present address (19871 Department of Geology and Mineralogy, Ohio State University, Columbus, OH 43210. 

1 
2 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

and uranium-thorium veins have been explored or mined, and may be economically productive in the future, chiefly near the fringes of the adjacent area Several areas at the 

surface in the centrally located Gilpin district (figs. 3, 14, 70) have anomalous concentrations of copper, lead, zinc, gold, silver, tin, and mercury and have low to moderate 

mineral resource potential. Stream-sediment geochemical data indicate that surface ore 

zones in rugged topography with rapid erosive dispersal of elements (like that of the 

lower Greenville mine) are unlikely to have escaped detection. However, some small blind 

veins (like those at the Elkhorn mine), or surface ores in gentle topography with slow 

erosive dispersal of elements (like the upper Greenville mine) could have escaped 

geochemical detection. No large high-grade metal deposits are present at the surface 

in the Mount Zirkel Wilderness or vicinity, but several geologic environments are present that are favorable for the subsurface occurrence of certain types of mineral deposits, 

some of which may be of substantial value. These include base-metal sulfides along three 

belts across the wilderness area, fluorspar within the Mount Ethel pluton in the wilderness area, uranium, mercury, and molybdenum deposits associated with possible 'Thrtiary plutons buried beneath the wilderness area, and layered chromium-platinum ores 

under the northwestern part of the adjacent area. An aeromagnetic survey identified 

several positive magnetic anomalies that could indicate mineralization at depth within 

the wilderness area (pl. 1 ). A search for the platinum group elements in numerous small 

surface exposures of ultramafic rock has failed to identify economic deposits, but the 

data indicate some potential. Other commodities investigated have little value because 

of small volume, poor quality, or unfavorable economic factors. There is no potential for 

coal, and only a slight potential for oil and gas, largely in undrilled overthrust areas 

near the western boundary of the adjacent area. Evidence for geothermal resources is 

present only outside the Mount Zirkel Wilderness and adjacent area. 

INTRODUCTION 

The Mount Zirkel Wilderness and adjacent area covers about 970 

km2 (375 mi2) of rugged terrain astride the Continental Divide in 

Jackson and Routt Counties, Colo. (295 km2 or 114 mi2 in the Mount 

Zirkel Wilderness). 2 Geochemical, geophysical, and geological surveys 

have covered more than twice the area of the Mount Zirkel Wilderness 

and adjacent area (fig. 1); the surveyed area lies entirely within Routt 

National Forest. Mean annual precipitation ranges from 30 em (12 in.) 

at lower levels to four times this on the highest mountains; most 

moisture falls in the form of snow, and snowfields persist all summer 

in the high cirques. (For illustration see figs. 9, 16.) Westward drainage 

flows into the Little Snake-Elk-Yampa River system, and northward 

and eastward drainage is part of the Encampment-North Platte River 

system. Runoff is profuse, especially in the spring; the average Park 

Range stream has an average discharge of more than an acre-foot of 

water per day for each square mile of its drainage area (Todd, 1970, 

p. 139, 140, 167). 

2

For this report, most original measurements were made in inches, pounds, or U.S. customary units and converted 

to equivalent metric units. The precision of the original measurement or statement as well as of the conversion varies 

and can best be judged from the context. Elevations taken from topographic maps printed in feet are given first 

in the map unit, and those numbers are then shown converted to meters. 
SUMMARY AND INTRODUCTION 3 

Scenery in the Mount Zirkel Wilderness is spectacular, especially 

in the vicinity of Big Agnes Mountain and Mount Zirkel in the north 

(fig. 2) and Mount Ethel and The Dome in the south (Snyder, 1978, 

figs. 4, 5B). Streams and (former) glaciers have carved deep canyons 

in Precambrian crystalline rocks; rapids and small waterfalls are prominent along many streams. Some of the tarn, cirque, and paternoster 

lakes are among the most beautiful anywhere (fig. 3). Total relief is 

nearly 1,525 m (5,000 ft), ranging from an altitude of less than 7,200 

ft (from topographic map; 2,200 m) along Big Creek in the southwest 

to 12,180 ft (3,712 m) on Mount Zirkel; most of the major peaks rise 

above 11,400 ft (3,475 m). The barren high ridges expose varicolored 

resistant Precambrian schist, gneiss, and granofels. Timberline lies 

at an average of 10,500 ft (3,200 m), but can vary 210 m (700 ft) up 

or down from this average. Ribbon forests-stable linear stands of 

evergreens with parallel intervening meadows (fig. 15)-are extensive 

near timberline especially in the vicinity of Buffalo Pass (Buckner, 

1977). An extensive spruce-fir-lodgepole pine-aspen forest blankets 

most of the intermediate slopes; valleys and lower slopes are locally 

swampy or choked with brush. Numerous species of wild game share 

the forests and meadows in summer with grazing livestock and camping people. 

Access to the Mount Zirkel Wilderness and adjacent area is by 

numerous all-vehicle roads. Popular ingress points are Buffalo Pass, 

Strawberry Park, numerous points along the Elk River and its 

tributaries (especially Slavonia at the end of the Elk River road), Big 

Red Park, the Encampment River, Big Creek Lakes, Lone Pine Creek, 

Norris Creek, and Little Grizzly Creek. More than 140 U.S. Forest 

Service camp units were available in established campgrounds in 1976 

along the border of the area; in addition, numerous State-supported 

(for example, near Steamboat Lake) or informal campsites are available 

along the area margins. Movement within the area is necessarily on 

foot or horseback along the well-established trail system, or overland, 

except for a very few four-wheel-drive roads. One of these, the historic 

Ellis Trail, the earliest stage and wagon route between Columbine and 

Hog Park, Wyo., via Big Red Park, winds across the Continental 

Divide and along the South Fork Hog Park Creek in the northwest 

corner of the area. Another four-wheel-drive road crosses the summit 

of Farwell Mountain between North Fork Elk River and Twin Mountain. Vehicular traffic has been prohibited in recent years along two 

former jeep roads-up West Fork Encampment River and from Buffalo Pass to Luna Lake. 

A variety of maps and aerial photographs covers the area. Part of 

the U.S. Army's 1:1,000,000 Cheyenne sheet (NK13) covers the area 

with planimetry and 500-m contours. Likewise, part of the U.S. 
4 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

!Hahns 

. Peak o 

!(village) 

10 

25 KILOMETERS 

15 MILES 

EXPLANATION 

Mount Zirkel Wilderness 

Adjacent area 

Area of geochemical survey 

------ Western boundary of aeromagnetic survey-Entire area to 

right of line was surveyed 

- ·-·- Western boundary of geological 

survey-Entire area to right of 

line was surveyed 
SUMMARY AND INTRODUCTION 

41°00' 

107° 106°30' 

.f-~ .f-~ \,'tit ~ ~~~ ~ I ~~~~'\, ~ ~~ ~ ~Oj~ \~Oj~ ~~ '\ ~~'tit~ ~~ 

ef' ~~~ ,§ ~ '\ ~ ~ ~ '*~ COWDREY 

.f-~ 1956 

~~~ ~$ t 

/Ojro"- ~S~'I, ~~~~ ~~~ ~'tit'\ ~~ \ ~'\ \,~ ~ ~y,'t!t 

~ ~~~ t ~'tit# ~'~Ojro"- ~'tit~\\ \ "" '\ 

~ ~\Oj<t!i 

WAlDEN 

1955 

~'J- ~~ ~~~ \,'tit ~ ~ ~~~ro .¢- ro"- ~~Oj~ ~~~ ~~ ,<:S "\ '\ <:,~ {'5 ~ 

40030' 

---------.., 

0 Walden 

\ 

v ·U' 

"-9. 

ov 

I 

COLORADO {<- 40 1 

I 

I \ L_ _____________ J 

FIGURE 1 (above and facing page).-Index map of Mount Zirkel Wilderness and adjacent area, showing areas surveyed for this report and U.S. 

Geological Survey topographic maps. Heavy solid line, outline of Mount 

Zirkel Wilderness; heavy long-dash line, wilderness established by P.L. 

96-560; heavy short-dash line, Davis Peak roadless area. 

5 
6 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Geological Survey 1:250,000 Craig sheet covers the area with 

planimetry and 200-ft contours; that part of the map has been enlarged 

to 1:125,000 and serves as the base for the geologic map (pl. 1). A U.S. 

Forest Service planimetric map of the Routt National Forest, showing drainages and trails, is available at a scale of 1:126,720. U.S. 

Geological Survey 7 1/2-minute quadrangle topographic and forestoverprint maps, at a scale of 1:24,000 and with 20- or 40-ft contours, 

cover the area (fig. 1); a composite of 17 of these maps, reduced to 

1:48,000, serves as the base for the sample map (pl. 2). Along the east 

side of the area, the 7 1/2-minute quadrangles have been seriesconverted into 15-minute, 1:62,500 quadrangles. U.S. Forest Service 

aerial photographs, scale 1:20,000, taken during flights in 1957, cover 

the area. In addition, the entire range is covered by satellite photography, and selected portions are covered by detailed photography at 

various scales. 

GEOLOGIC INVESTIGATIONS BY OTHERS 

Most previous geologic investigations in and adjacent to the Mount 

Zirkel Wilderness have been limited in scope, but the history of investigations stretches back to the reconnaissance geologic exploration 

of the Colorado 'Territory in the last half of the nineteenth century. 

In fact, the earliest petrographic studies of the crystalline rocks were 

of the granite on Mount Ethel and the hornblende gneisses of Mount 

Zirkel and the upper Encampment drainage by Ferdinand Zirkel, for 

whom Mount Zirkel is named (King, 1878, p. 37 -40). Turn-of-thecentury geologic-economic interest focused on the coal beds on either 

side of the Park Range (R. C. Hills, 1893; Hewett, 1889; Parsons and 

Liddell, 1903; Fenneman and Gale, 1906; Gale, 1909, 1910; Ball and 

Stebinger, 1910; Beekly, 1915), the nodular copper-bearing schists at 

Pearl (Read, 1903; Spencer, 1903b), the copper deposits of the Encampment district, Wyoming (Spencer, 1903a, 1904), the Hahns Peak gold 

field (Gale, 1906; George and Crawford, 1909), and the Rabbit Ears 

region (Grout and others, 1913). Anticlines of western Routt County, 

some productive of oil and gas, have been summarized by Crawford, 

Wilson, and Perini (1920); the easternmost mapped anticline, the 'Ihlll, 

extends into the extreme southwestern part of the present map area 

(Crawford and others, 1920, pl. 1). Geological publications concerned 

with the northern Park Range abated between 1920 and the early 

1950's, with the exception of Atwood's (1937) glaciological and 

Christensen's (1942) 'Tertiary igneous studies. 

More modern geological studies adjacent to the Park Range began 

with Steven's thorough coverage of the Northgate fluorspar district 

east of the area (Steven, 1954, 1956, 1957, 1960). The geology and 
SUMMARY AND INTRODUCTION 7 

mineral fuels of a large area west of Steamboat Springs were reviewed 

by Bass, Eby, and Campbell (1955). Mesozoic and Tertiary 

stratigraphy and structures along the east side of the range were mapped by Hail (1965, 1968). Buffler (1967) reviewed the distribution and 

origin of the Browns Park Formation throughout the region. The 

Hahns Peak-Farwell Mountain area has been the subject of recent 

detailed studies (Segerstrom and Kirby, 1969; Segerstrom and Young, 

1972; Young and Segerstrom, 1973). Numerous university theses have 

covered smaller areas, generally about 50 square miles per thesis, 

throughout the northern Park Range and Sierra Madre (Ritzma, 1949; 

Welsh, 1951; Rollins, 1952; Wakefield, 1952; Walters, 1953; Barnwell, 

1955; de la Montagne, 1955; Hunter, 1955; Murphy, 1958; Short, 1958; 

McConnell, 1960; Wied, 1960; Scott, 1961; Kucera, 1962; Merry, 1963; 

Walton, 1963; Ferris, 1964; Fenton, 1965; Lackey, 1965; De Nault, 

1967; Hill, 1969; Ebbett, 1970; Huang, 1970; Miller, 1971; Ridgely, 

1971; and Graff, 1973). The geology and geochemistry of the Sierra 

Madre of Wyoming have recently been summarized by Houston, 

Schuster, and Ebbett (1975), Divis (1975, 1976), Houston and Ebbett 

(1977), Graff (1978), and Houston, Karlstrom, and Graff (1979). Several 

aspects of the regional geologic, stratigraphic, or tectonic setting of 

the northern Park Range area or the sedimentary basins on either side 

of it are covered in numerous recent reports (Oriel, 1954; T. G. Larson, 1955; Osterwald and Dean, 1958, 1961; Tweto and Sims, 1963; 

Tweto, 1968, 1975a, b, 1976a, b, 1977a, b, c; Barclay, 1968; Behrendt 

and Popenoe, 1969; Behrendt and others, 1969; Izett and others, 1971; 

Izett and Barclay, 1973; Izett, 1975; E. E. Larson and others, 1975; 

Blackstone, 1977; Hedge and others, 1977; Madden, 1977a, b; Park, 

1977; Wellborn, 1977; Warner, 1978; and Snyder, 1977a, b, c, 1978, 

1980a, b, c, 1984). Landslides on the Craig 1 o X 2 o quadrangle have 

been mapped by Colton and others (1975), and other surficial deposits 

are currently being studied by R. F. Madole (1982, and written 

commun., 1976). 

PRESENT STUDIES AND ACKNOWLEDGMENTS 

The purpose of this study was to appraise the mineral resource 

potential of the Mount Zirkel Wilderness and vicinity. The report is 

a cooperative effort of the U.S. Geological Survey and the U.S. Bureau 

of Mines. The USGS (U.S. Geological Survey) fieldwork included 

geologic mapping and sample collecting and took place from 1965 

through 1967 and from 1970 through 1973 (pl. 1). The fieldwork was 

supervised by G. L. Snyder, working with Warren Hamilton in part 

of the 1965 field season; Fredric Hoffman, 1966; R. L. Bonewitz, 1967; 

P. W. Schmidt, 1970 and 1972; and Paul Graff, 1971 and 1972. The 
8 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Big AgQeS 

FIGURE 2.-View south to Mount Zirkel and west to Sawtooth Range and North Fork 

brian interlayered quartz monzonite, pegmatite, felsic gneiss, amphibolite, and pelitic 

area was mapped geologically via foot traverses (with one-quarter-mile 

or closer spacing). The resulting geologic maps are available in two 

sheets (Snyder, 1977a, b, 1980a, b), at a scale of 1:48,000, and the 

geology and aeromagnetics of the entire area are summarized in 

simplified form on plate 1 at 1:125,000. 

The USBM (U.S. Bureau of Mines) work consisted mainly of a 

records search of Routt and Jackson Counties (including records of 

Larimer County before 1909, when Jackson County was formed from 

Larimer) for mining locations, and a field investigation of mining 

claims, prospect workings, and mineral deposits. These county records 

contain many mining location notices recorded since the 1870's within 

and near the subject area, and many of the claims are shown in the 

illustrations of this report. H. C. Meeves and R. A. Beach assisted with 

the records search. Assistance received from personnel of the U.S. 

Forest Service and the Jackson, Larimer, and Routt County Clerks' 

Offices was most helpful. Fieldwork was done by L. L. Patten with 

the assistance of R. A. Beach, R. J. J urt, 0. D. Staman, and D. D. 

Keill during 1971 and 1972. The U.S. Bureau of Land Management 

provided records of oil and gas leasing and patented mining claims. 

In the course of these investigations 3,352 samples were collected, 

3,240 by the USGS, and 112 by the USBM. Analyses of most USGS 

samples are available in Snyder and others ( 1981 ); analyses of most 

USBM samples are available in tables 2, 3, and 4 of this report. Of 

the USGS samples, 1,255 are stream sediments, which have been 

analyzed by atomic absorption methods for silver, gold, copper, lead, 
SUMMARY AND INTRODUCTION 9 

Elk River from Continental Divide north of Mount Zirkel. Rocks are mainly Precamschist; Mesozoic sediments underlie low meadows between viewer and Hahns Peak. 

August 1970. 

and zinc and by standard semiquantitative spectrographic techniques 

for a suite of 30 elements. The other 1,985 samples are mainly rock 

specimens (a few are soils), most of which were thin sectioned for 

petrographic study. Three hundred fourteen of these are potentially 

mineralized rocks which were analyzed by atomic absorption methods 

for silver, gold, copper, lead, and zinc; by detector for mercury; and 

by standard semiquantitative spectrographic techniques for a suite 

of 30 elements. Atomic absorption analyses of stream sediments or 

potentially mineralized rocks were made by R. B. Carter, J. G. Frisken, 

J. D. Hoffman, E. Martinez, A. L. Meier, J. Mitchell, J. M. Motooka, 

R. M. O'Leary, T. Roemer, Z. Stephenson, R. Tripp, and S. H. Truesdell. 

Mercury detector analyses were made by W. Campbell, J. G. Frisken, 

and J. James. Semiquantitative spectrographic analyses were made 

by R. Babcock, W. D. Crim, G. W. Day, J. H. Domenico, C. Forn, R. 

T. Hopkins, Jr., E. Mosier, J. M. Motooka, and A. L. Sutton, Jr. In 

addition, 32 stream sediments and 22 potentially mineralized rocks 

possessing 20 ppm or greater niobium, were analyzed by delayed 

neutron technique for uranium and thorium by H. T. Millard, Jr., C. 

L. Shields, C. M. Ellis, R. L. Nelms, and C. A. Ramsey. Standard 

chemical analyses have been run on 95 typical crystalline rocks for 

14 major oxides (plus chlorine and fluorine for 26, Cr20 3 and NiO for 

1) by E. L. Brandt, E. Engelman, G. 0. Riddle, and V. C. Smith. 

Ninety-seven ultramafic or related rocks have been analyzed for 

platinum, palladium, and rhodium by L. B. Breeden, W. D. Goss, 

Joseph Haffty, A. W. Haubert, H. G. Neiman, and L. B. Riley. One 
10 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Big Agnes 

Mountain 

FIGURE 3.- View north over Gilpin Lake to Big Agnes Mountain. Quartz diorite of 

Gilpin Lake well exposed in glacially polished whaleback left of lake. Two mine portals labeled, across Gilpin Creek on lower slopes of Big Agnes Mountain. Xgl, quartz 

diorite, and Xgn, felsic gneiss, both of Proterozoic X age. August 1971. 

.. hundred fifty-five of the typical crystalline rocks or the ultramafic 

rocks have been analyzed by standard semiquantitative spectrographic techniques for a suite of 34 elements by L.A. Bradley, L. D. 

Forshey, J. C. Hamilton, B. W. Lanthorn, H. G. Neiman, and G. W. 

Sears, Jr. R.L. Rahill has run colorimetric Cr20 3 analyses on nine of 

the ultramafic rocks; J. G. Crock and G. 0. Riddle have run Na20 2 

fusion-colorimetric Cr 20 3 analyses on four other mafic rocks. Also, 

Wayne Mountjoy has run spectrophotometric Si0 2 and Al20 3 

analyses on two rocks. Eleven hot-spring waters from the Steamboat 

Springs Group were analyzed for lithium by P. R. Barnett in 1950. 

Twenty-five USBM ore samples were analyzed in the USGS 

laboratories by standard semiquantitative spectrographic techniques 

for a suite of 30 elements by J. H. Domenico and R. T. Hopkins, Jr. 

G. H. Allcott, T. M. Billings, H. E. Eichler, S. K. McDanal, R. V. 

Mendes, C. M. McDougal, and L. 0. Wilch assisted with computer 

storage and retrieval of analytical data. 

All analyses of ores and stream sediments prepared by the USGS 

for G. L. Snyder are available on open file (Snyder, 1981). These 

analyses are summarized in tables 5 and 6, and the geographic distribution of the anomalous chemical data is shown on map figures 52-104. 

Semiquantitative spectrographic data for unmineralized crystalline 
SUMMARY AND INTRODUCTION 11 

rocks are presented in table 7. All analyses prepared for the USBM 

are given in tables 2-4. 

In addition, a geochemical survey using 805 soil samples is available 

for a 16 mi2 area centered on Hahns Peak overlapping the northwest 

edge of the area studied (pl. 2; Young and Segerstrom, 1973, fig. 2, 

p. 10, 11). Also, 144 modern chemical analyses of several types are 

available for Tertiary and Precambrian crystalline rocks in 

southwestern North Park (Hail, 1968, table 3, p. 54-55), the Hahns 

Peak area (Segerstrom and Young, 1972, tables 1, 5, 7, p. 10, 11, 38, 

39, 42; Young and Segerstrom, 1973, table 1, p. 14-15), and the Wyoming Sierra Madre (Divis, 1976, tables 1, 3-7, 9; p. 25, 48, 49, 57, 58, 

64, 65, 72, 76, 89). Available radiometric geochronologic data for the 

vicinity of the northern Park Range are reviewed by Segerstrom and 

Young (1972), Divis (1977), and Snyder (1978). 

Many professional colleagues in the USGS and USBM besides those 

specifically mentioned also helped with the field, laboratory, manuscript, or illustration work, and we are deeply grateful for their help. 

Our gratitude is also expressed to the many people outside the USGS 

and USBM who assisted in some way in the preparation of this report. 

Walter Metcalf and Gay Weidenhaft of the U.S. Forest Service located 

the surveyed boundaries of the Mount Zirkel Wilderness and adj acent area on USGS topographic maps (written commun., April1972). 

Richard Dirmeyer, Warren Hartman, Melvin Hitchings, and Parker 

T. Qualls of the U.S. Forest Service were helpful in the field. Joseph 

Gerrans and James Houston of the Colorado Natural Resources 

Department were most cooperative in helping maintain order at one 

campsite repeatedly raided by six bears. The following geologists contributed unselfishly to many geological discussions or educational field 

trips: W. A. Bowes (Steamboat Springs, Colo.), R. T. Buffler 

(Galveston, Texas), A. F. Divis (Lakewood, Colo.), A. B. French, Jr. 

(Houston, Texas), Paul Graff (Casper, Wyo.), J. J. Hill (Colorado State 

University), R. S. Houston (University of Wyoming), E. E. Larson 

(University of Colorado), M. E. McCallum (Colorado State University), and A. E. Miller (Steamboat Springs, Colo.). Robert Perry and 

Alex Paul (Ozark Mahoney Co.) sponsored a private survey of the 

fluorite veins underground at the N orthgate mine. R. , R. Ogilby 

(Minerals Exploration and Development, Ltd.) conducted a tour of 

several then-active fluorite prospects above the Crystal mine. Numerous local residents extended courtesies throughout the field investigations, often without introduction or identification. The following 

residents, whose names are known, were especially helpful: Ray Barrows, Donald Hoelzen, Mary Morgan, the late Gerry Truax, and Forrest Warren of Steamboat Springs, Gary Hayter and Luis N agra of 

Three Forks Ranch, Mr. and Mrs. Ralph Warrick of Big Creek Ranch 
12 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

and Craig, Mr. and Mrs. William Bush, then at Clark, and Melvin J. 

Bradley of Craig. 
Geological Appraisal 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY 

MINERAL RESOURCES OF THE MOUNT ZIRKEL 

WILDERNESS AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

U.S. GEOLOGICAL SURVEY BULLETIN 1554-A 
CONTENTS 

Page 

Geologic setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

Precambrian rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Metavolcanic and other rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Mafic and ultramafic intrusive rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

Old quartz monzonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

Quartz diorite of Gilpin Lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

Young quartz monzonites of the Mount Ethel pluton . . . . . . . . . . . . . . . . . 31 

Precambrian dikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

Paleozoic and Mesozoic sedimentary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 

Permian and 'Iriassic formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

Jurassic formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

Cretaceous formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

Thrtiary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 

Quaternary deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7 

Mineral and geochemical setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Timing of mineralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Interpretation of origin of sulfide deposits . . . . . . . . . . . . . . . . . . . . . . . . . . 53 

14 
GEOLOGICAL APPRAISAL 15 

ILLUSTRATIONS 

Page 

FIGURE 4. Geologic index maps of region and study area . . . . . . . . . . . . 20 

TABLE 

5-11. Photographs: 

5. Precambrian layered metasedimentary rocks from northern Park Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

6. Precambrian pod-rocks of various origins . . . . . . . . . . . 26 

7. Precambrian lit-par-lit rocks in Sawtooth Range . . . . . 32 

8. Big Agnes Mountain massif . . . . . . . . . . . . . . . . . . . . . . 33 

9. Interlayered Precambrian rocks near head of Gilpin Creek 33 

10. Textures and structures of intrusive igneous rocks . . . 34 

11. Quartz monzonite contact on southeast ridge of Buck 

Mountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

12. Map showing location of Precambrian dikes . . . . . . . . . . . . . . 37 

13-19. Photographs: 

13. Mount Zirkel and Red Dirt Pass . . . . . . . . . . . . . . . . . . 39 

14. Summit plateau of Flattop Mountain . . . . . . . . . . . . . . 41 

15. Vertical layered amphibolite truncated by summit plane 

of Flattop Mountain . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

16. Mount Zirkel and Frying Pan Basin . . . . . . . . . . . . . . . 42 

17. Active rock glaciers on east side of Mount Zirkel . . . . 46 

18. Steeply dipping fault plane crossing Hinman Creek . . 49 

19. Bedded silt, ash-rich beds, and silicic intrusive porphyry 

of Sand Mountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 

TABLE 

Page 

1. Ages of selected mineralizations in the northern Park Range 52 

MINERAL RESOURCES OF THE MOUNT ZIRKEL WILDERNESS 

AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

GEOLOGICAL APPRAISAL 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY 

GEOLOGIC SETTING 

The oldest rocks of the northern Park Range were formed in Precambrian time off the shore of a yet older continent to the north and have 

been added to by continent-building or affected by continentshattering forces several times since that ancient origin. Some younger 

deposits or structures were controlled by, or appear to be related to, 

the oldest Precambrian rocks and stuctures; others are unrelated, or 

are not presently known to be related, to the rocks and structures of 

earlier Colorado history. Ironically, the old erosion-resistant Precambrian rocks that guarantee the presence of a mountain range of great 

scenic beauty are the ones that also guarantee maximum time and 

opportunity for the development of mineral resources useful to man. 

The oldest Precambrian rocks of southern Wyoming are 2.6 b.y. (billion 

years) old (Hills and others, 1968; Divis, 1977; Hills and Houston, 1979) 

in contrast to the oldest Precambrian rocks of northern Colorado which 

are 1.8 b.y. old (Peterman and Hedge, 1967; Peterman and others, 

1968; Snyder, 1977a, 1978, 1980a). Isotopic evidence indicates that 

the Colorado rocks overlie new oceanic crust rather than older continental rocks (C. E. Hedge, Z. E. Peterman, R. F. Zartman, oral communs., 1967-77), so the boundary in southern Wyoming between these 

two provinces must represent the remains of the southern margin 

of an old continent. The Precambrian rocks discussed in this report 

17 
18 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

include the younger Precambrian metavolcanics or metasediments 

deposited at the margin of this older northern continental mass, and 

the even younger rocks that intrude or overlie them. The general trend 

of Precambrian fold, fault, and intrusive structures south of this 

boundary is parallel to it, showing that this continental boundary has 

had a major effect in orienting subsequent Precambrian tectonic 

events. It is now the site of a major shear zone that trends northeast 

across the Medicine Bow Mountains and east across the Sierra Madre 

of southern Wyoming (fig. 4). Another major northeast-trending shear 

zone cuts the 1.4- to 1.8-b.y.-old rocks between Soda Creek and North 

Fork Fish Creek northeast of Steamboat Springs in the southern part 

of the mapped area (fig. 4; Snyder, 1978, fig. 2). Some shearing must 

have taken place after 1.4 b.y. ago because it affects rocks and structures of this age (Snyder, 1978). Possibly 19 km (12 mi) or more of 

left lateral offset has taken place along some of the shear zones 

(Snyder, 1978). 

The available geologic record shows that uppermost Paleozoic and 

Mesozoic rocks (750-3,000 m, or 2,500-10,000 ft, of strata) were 

deposited next on top of the sheared, folded, and metamorphosed 

Precambrian rocks. This deposition was interrupted by repeated 

uplifts, as indicated by the near-source pebbles and boulders of 

Precambrian lithologies in nearly all the sedimentary deposits nearest 

the mountains. Folding and faulting intensified near the end of the 

Cretaceous Period and continued during deposition of sedimentary 

rocks of Paleocene and Eocene age (as much as 1,000 m, or 3,400 ft). 

In additio11 to reactivation of older faults (for example, fig. 18), the 

range was broken along north to northwest directions into several major fault blocks that today preserve partial Mesozoic sections within 

downfaulted or overridden parts of the range. Displacement along 

these faults of the Laramide orogeny (Cretaceous to Eocene age) must 

have been from a few thousand to several thousand meters, partly 

in a compressional regime, and partly tensional, at the extreme northernmost wedge-out of the Rio Grande rift zone (Tweto, 1977 c). Deposition was also substantial in the Miocene (300 m or more), and this was 

followed by minor (as much as 300 m) normal faulting of diverse orientations. Late Miocene intrusives and contemporaneous faults cut the 

Miocene sediments along the west margins of the mapped area. 

Pleistocene glaciers sculptured the mountain highlands and canyons 

and left thick morainal deposits near their margins and extensive 

fluvial gravel terraces beyond their margins. Stream erosion and 

deposition and minor landsliding continue to this day. 
GEOLOGICAL APPRAISAL 19 

PRECAMBRIAN ROCKS 

The most widespread rocks of the Mount Zirkel Wilderness and adjacent area are Precambrian crystalline rocks. They fall into four main 

types in terms of volumetric importance and into three main groups 

in order of age. More than 90 percent of the exposed mountain ledges 

are mafic to felsic metavolcanics, intrusive igneous gabbros, or two 

types of quartz monzonites (Snyder, 1978). In addition, there are lesser 

amounts of layered metasedimentary rocks of several types (fig. 5) and 

ultramafic or intermediate intrusive rocks. Nearly all the Precambrian 

crystallines are medium to coarse grained, locally porphyritic, porphyroblastic, or augen-containing. Most rocks are resistant to erosion, 

forming ledges, cliffs, rapids, aretes, or roches moutonnees. Colors range 

from light to dark in shades of gray, green, and pink. Metamorphic 

grade is high: amphibolite or higher, with pyroxene or sillimanite widely 

distributed as grade-indicator minerals. Extensive metamorphic recrystallization and shearing have eliminated all primary structures from 

most rocks, but rare exposures of preserved intersertal or coronitic 

structure in former mafic magmatic rocks and graded beds or crossbedding in former sediments testify that primary structures were once 

widespread. Generally oligomictic pod-rocks (fig. 6) containing pods, 

lenses or inclusions from 3 mm to 15 em (1/8 in. to 6 in.) in diameter 

are common; they consist either of felsic pods in a mafic matrix or the 

reverse, and they owe their origins to a variety of causes. Some were 

definitely caused by sedimentary processes (such as calc-silicate concretionlike structures in layered gneisses; for example, fig. 6A), some 

by igneous extrusion or intrusion (such as agglomerates or contact 

breccias; for example, fig. 6B), and some by metamorphic differentiation (such as sillimanite-quartz-muscovite faserkiesel; for example, fig. 

6C); some are without discernible genetic clues. Some fine-grained rocks 

near faults-mylonites-are the result of mechanical milling of originally coarser grained rocks after the peak of metamorphic crystallization. 

METAVOLCANIC AND OTHER ROCKS 

Most of the northern Park Range is underlain by the oldest Precambrian rocks, mainly medium grained mafic to felsic metavolcanics with 

smaller amounts of intercalated marine metasedimentary rocks, such 

as marbles. The rocks interpreted as metavolcanics are prominently 

to faintly layered pink, gray, or green gneisses of sillimanite grade, 

about 50 percent mafic and 50 percent felsic, but including rocks of 
20 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

4P 

GRANITE 

- JJ9 ~MOUNTAINS 

~~ 

A 

~:..~ ----... ~ ~~ -- ~- ~ 

20 40 

20 

60 80 

40 

0 Cheyenne 

WYOMING 

-COLORADO --

0 Fort Collins 

DENVER 

100 KILOMETERS 

60 MILES 

FIGURE 4 (above and next three pages).-Geologic index maps of Precambrian rocks. 

A, southern Wyoming and northern Colorado. 
GEOLOGICAL APPRAISAL 

EXPLANATION FOR MAP A 

1.4-b.y. Laramie Anorthosite 

Lower Proterozoic Libby Creek 

Group 

Lower Proterozoic Deep Lake Group 1 .4- to1.8-b.y. rocks south 

2.6-b.y. rocks north of Mullen 

Creek-Nash Fork shear zone 

Contact 

of Mullen Creek-Nash Fork 

shear zone 

Fault-Dotted where inferred 

21 

PRECAMBRIAN 

a wide spectrum of compositions (figs. 5A and 5B). Also included but 

not described here are numerous bodies of pegmatite too small to show 

on plate 1. 

The typical mafic metavolcanic rock is amphibolite consisting chiefly 

of subequal amounts of hornblende and calcic plagioclase with regionally important concentrations of biotite, garnet, or epidote. Amphibolites grade into mafic amphibolites with decreasing plagioclase or into 

hornblende gneisses with increasing plagioclase, biotite, and quartz. 

Amphibolites may be massive and unstructured, probably representing lava flows and near-surface intrusives, or they may be minutely 

layered, probably representing water-deposited basaltic ash (figs. 5A, 

15). Layered amphibolites in many places are interlayered with, or contain inclusions or pods of, calc-silicate rock consisting of plagioclase, 

aluminous epidote, diopside, scapolite, calcite, and other minerals. The 

interlayered rocks may represent sediments from two sources, perhaps 

basaltic ash in a carbonate-secreting or carbonate-depositing environment; some interlayered rocks can be observed to grade laterally into 

pure calc-silicate rocks and eventually marbles. Some pod-rocks may 

be due to sedimentary processes with tectonic overprinting (fig. 6A), 

but exposures just across the Wyoming State line of amphibolite 

pillows with recrystallized carbonate mud in their interstices suggest 

that some similar Colorado pod-rocks without preserved primary 

structures may also have had a mixed igneous-sedimentary origin. 

The typical felsic metavolcanic rock is feldspar-quartz-biotite gneiss 

with sodic plagioclase and minor potassium feldspar. This rock grades 
22 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

10 15 20 25 MILES 

10 20 30 40 KILOMETERS 
GEOLOGICAL APPRAISAL 

DIAGRAMMATIC CROSS SECTION FOR MAP B 

., > v' 

a~~ NE G~ss~o ./: : " >, '," • > 

AND PERIDOTITE ~ ~ . ~ < <' c 

z 

<( 

a: 

al 

~ 

<( 

u 

w 

a: 

a.. 

FIGURE 4 (continued).-Geologic maps of Precambrian 

rocks. B, northern Park Range. 1.4 b.y. quartz monzonite 

phases of the Mount Ethel pluton are coarse grained 

(diagonal line pattern from top left to bottom right), 

medium grained (coarse stipple), and fine grained (diagonal 

line pattern from top right to bottom left). Light line, contact; heavy line, fault (dotted where inferred). 

23 

with increasing hornblende into hornblende gneiss and with marked 

increase of biotite, or biotite with minor hornblende, into several 

varieties of mafic schist. There are also, in the more felsic terrains, 

important regional concentrations of garnet, muscovite, magnetite, 

and quartz-muscovite-sillimanite pods (fig. 6C). The felsic pod-rocks 

grade into massive quartz monzonites with increasing groundmass 

potassium feldspar and with a decreasing number of pods, and into 

pelitic schists with increasing groundmass and decreasing size of pods. 

The magnetite-rich alaskites have a characteristic streaky appearance. 
24 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 5 (above and facing page).-Precambrian layered metasedimentary rocks of various types from northern Park Range. A, Subtly but distinctly layered amphibolite from 

7,360-ft elevation (from topographic map; 2,243 m). U.S. Highway 40 cut, south of Steamboat Springs. Probably originally water deposited basaltic ash. B, Tightly folded and 

sheared migmatitic felsic gneiss and biotite gneiss from north of 10,136-ft (3,089-m) 

saddle on Buffalo Pass road southwest of Buffalo Pass. Possibly originally water deposited ash of intermediate composition. C, Isoclinal folds in layered biotite-muscovitequartz-garnet-sillimanite pelitic schist, originally a shale, from 10,300-ft (3,140-m) elevation south of summit of peak between Soda Creek and South Fork Soda Creek. 
GEOLOGICAL APPRAISAL 25 
26 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 
GEOLOGICAL APPRAISAL 27 

FIGURE 6 (above and facing page).-Precambrian pod-rocks of various origins. A, 

Vertical surface exposure in pod-rock of mixed origin. Light calc-silicate pods in 

dark amphibolite matrix, probably originated with deposition of basaltic ash in a 

carbonate-depositing environment followed later by concretionary sedimentary or 

diagenetic processes, which preserved species distinction, and tectonic stretching, 

which produced vertical lineation. Rocks of this type are common in the northern 

Park Range, but details of the structure are seldom this well exposed because of 

lichen cover on pitted weathering surfaces. These pod-rocks can grade over short 

distances into pure amphibolite in one direction or pure calc-silicate rocks or 

marbles in another direction. From 10,200 ft altitude on south end of ridge east 

of Hogan Creek (Snyder, 1977c, 1980c). Aluminum map holder at base of photo 

is 20 em (8 in.) wide. B, Pod-rock formed by brecciation near contact of igneous 

intrusion. Amphibolite wall-rock inclusions in quartz monzonite from 9,900-ft 

(3,018-m) elevation on south end of Black Mountain northwest of West Fork 

Lake. C, Pod-rock believed to have been formed by mineral segregation during 

metamorphism. Oriented pods of quartz-sillimanite-muscovite rock in a granitic 

matrix. Rock may have been emplaced originally as a peraluminous extrusive, 

perhaps contaminated by shale fragments. From crest of Independence Mountain 

northwest of Sugar Loaf. 
28 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

The various types of felsic gneiss may represent compositional 

variants of several types of silicic extrusives, perhaps in some cases 

with an admixed arkosic or pelitic detrital component, but the 

rocks themselves lack primary structures or textures. However, 

the compositions are appropriate for a variety of silicic ashes or 

welded tuffs from dacites to alkali rhyolites. The great local 

thicknesses of particular compositional variants are suggestive of the 

great local thicknesses of silicic welded tuffs found in many modern 

calderas, although later tectonism and total metamorphic recrystallization have obscured any traces of bounding caldera faults that may 

have existed. 

The commonest recognizable metasediment intercalated in the 

metavolcanic sequences is medium-grained aluminous schist or metapelite or metashale, several belts of which are continuously mappable 

across the range (pl. 1; fig. 5C). These rocks vary markedly from belt 

to belt, but all belts have this in common: their rocks contain 

aluminous minerals recrystallized from former detrital clays. Minerals 

present are mainly micas (especially muscovite), sillimanite, sodic 

plagioclase, potassium feldspar at higher grades, and almandine 

garnet; rarely present are staurolite, tourmaline, cordierite, chloritoid, 

or andalusite. Sillimanite occurs either as euhedral crystals or fibrolite 

pods, either of which may be retrogressively altered to pseudomorphs 

of pinite or sericite. Quartz is ubiquitous. The more aluminous, 

schistose, or micaceous rocks are inter layered in many places with less 

aluminous, more granular, or gneissic layers. Some metapelite belts 

contain minor but distinctive pods of mafic rocks of unusual composition, for example, garnet amphibolites or biotite-actinolite schist. 

Although top and bottom criteria are only rarely preserved, the contrasting compositions of adjacent layers are more suggestive of several 

individual sedimentary beds than of isoclinal fold repetition of a single 

stratum (despite the fact that isoclinal folds abound on all scales: fig. 

5B, 5C). 

The most unusual mapped metasedimentary rocks or mixed 

metavolcanic-metasedimentary rocks occur mainly near Willow Creek 

or on Farwell Mountain and consist of clean quartzites and dirty 

metaconglomerates and meta-agglomerates, respectively. The quartzites contain minor muscovite and hematite. They must have been more 

resistant to shearing than most rocks because they commonly preserve 

primary crossbedding, which clearly indicates that the quartzite body 

north of Willow Creek is an overturned syncline. The Farwell Mountain 

body is a complex mixture of unusual rocks including gray to gray-green 

polymictic conglomerate (generally with biotitic matrices), oligomictic 

agglomerate (generally with hornblendic matrices), and oligomictic 

pisolitic rocks containing peasized feldspar-quartz-muscovite pods 
GEOLOGICAL APPRAISAL 29 

of uncertain origin, some possibly due to metamorphic segregation, 

some possibly due to metamorphism of nonelastic primary structures, 

such as amygdules or pumice clots. 

The age of the felsic gneisses, and therefore of all intercalated 

metavolcanic and metasedimentary rocks, is greater than 1.78 b.y., 

possibly as old as 1.9 b.y. or Proterozoic X. Some felsic gneisses have 

contributed to Rb-Sr (rubidium-strontium) whole-rock isochrons, or 

their accessory zircon has been dated by uranium-thorium-lead 

methods, but some current dating attempts need to be carefully 

qualified. Unlayered or thickly layered gray felsic gneisses along the 

east margin of the northern Park Range could be extrusives of compositions ranging from dacite to alkali rhyolite. Three, from Lone Pine 

Creek to Newcomb Creek, form a Rb-Sr whole-rock isochron, suggesting an age of 1.69 b.y. (Hedge, in Snyder, 1978). Another gneiss, 

north of Line Creek, possesses zircons giving highly discordant U-ThPb ages that are difficult to interpret but are at least 1.58 b.y. (C. E. 

Hedge, written commun., November 1976). Both these ages must be 

minima, as the rocks are cut by a gabbro that yields a U-Th-Ph date 

of 1.78 b.y. (Hedge, in Snyder, 1980a, 1977a) and by quartz monzonites 

that yield Rb-Sr dates of 1.65-1.70 b.y. (Hedge, in Segerstrom and 

Young, 1972, p. 16) and 1.80 b.y. (Hedge, in Snyder, 1978). Additionally, felsic gneisses in the adjacent Sierra Madre of Wyoming continuous 

with these are dated by Rb-Sr at 1.88 b.y. (Divis, 1976, p. 56; 1977, 

p. 98), but this age is controlled by a single pegmatitic phase. A nearby gneiss in the Sierra Madre contains discordant zircons, giving a 

minimum age by 207Pb/206Pb of 1.73 b.y. (Divis, 1976, p. 56, 60). 

MAFIC AND ULTRAMAFIC INTRUSIVE ROCKS 

Dark medium-grained gabbro, olivine gabbro, and peridotite are 

associated in an intrusive body of batholithic dimensions-the gabbro of Elkhorn Mountain-in the northwestern part of the area and 

in numerous smaller bodies. These rocks normally weather to distinctive chocolate-brown soils containing equidimensional gabbro 

boulders. Most samples contain subequal amounts of calcic plagioclase 

and mafic minerals including clinopyroxene, hornblende, and biotite, 

singly or in various mixtures, invariably occurring in a uniform, 

unlayered, diabasic or homogeneous rock. Typical rocks in the large 

gabbro body of Elkhorn Mountain are hornblende-clinopyroxenebiotite gabbro, hornblende-biotite gabbro, hornblende gabbro, and porphyritic feldspar amphibolite; rare dark diorite is exposed at Three 

Forks. Hornblendic and anorthositic gabbros are prominent on Farwell 

Mountain. 
30 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Olivine gabbro occurs in a single pluton within the gabbro of Elkhorn 

Mountain between South Fork Hog Park Creek and the Sierra Madre 

Continental Divide, where it is associated with small peridotite masses 

and is rarely cut by dikes of olivine-free gabbro of Elkhorn Mountain. 

This distinctively different rock contains corona structures in which 

orthopyroxene, clinopyroxene, pargasitic amphibole, and spinel are 

arranged in concentric shells around olivine grains. 

Ultramafic peridotite masses occur either within the gabbro of 

Elkhorn Mountain or as separate isolated intrusive bodies as much 

as 2.5 km (1.5 mi) long. These rocks are everywhere black or dark olive 

gray but may weather to a bright-red soil. They include amphibole 

peridotite of various types including dunite, wehrlite, harzburgite, and 

also hornblendite, many containing some spinel and chromite. 

Pargasitic amphibole occurs in peridotite, either as large poikilitic 

crystals containing olivine and pyroxene inclusions or as kelyphytic 

rims around olivine with the amphibole partly alone and partly in complex symplectic intergrowths with spinel. 

The gabbro of Elkhorn Mountain is believed to be a composite mafic 

body intruded in several inhomogeneous batches that carried along 

solid rafts of peridotite derived from its mantle source area (Snyder, 

1984). It is asymmetrically zoned from diorite along the north and 

south (but not east) margins to predominant gabbro in the center and 

along the east margin. Olivine and hypersthene are most common in 

the most mafic central and eastern rocks, and biotite the least common, but many different mineral mixtures occur. Although the gabbro of Elkhorn Mountain is more altered and less magmatically layered 

than gabbros in the Lake Owens and Mullen Creek Mafic Complexes 

in Wyoming's Medicine Bow Mountains (McCallum, 1968; Houston 

and others, 1968), it is similar in age and aeromagnetic signature to 

these bodies. Lake Owens and Mullen Creek are believed to be layered 

funnel-shaped intrusives. Intrusives of this type elsewhere in the world 

contain layered chromium-platinum ores at depth, and this should be 

considered a possibility here, even though surface evidence of such 

in any of the bodies is minimal or lacking. 

That the gabbro of Elkhorn Mountain is older than the quartz monzonite of Seven Lakes is well shown by numerous dikes of quartz monzonite cutting gabbro and by numerous swarms of lozengelike gabbro 

inclusions in quartz monzonite near some contacts. Zircons separated 

by Robert Sperandio from a dark diabasic andesine-clinopyroxenebiotite-magnetite diorite phase of the gabbro of Elkhorn Mountain 

near Three Forks of the Little Snake River have a highly concordant 

U-Th-Pb age (C. E. Hedge, written commun., November 1976; analyst 

Margarita Gallego); the 207Pbf2°6Pb age, usually the best approximation to the true age, is reported as 1.78 b.y., Proterozoic X. 
GEOLOGICAL APPRAISAL 31 

OLD QUARTZ MONZONITE 

Red to gray medium;. to coarse-grained massive to augen-gneissic 

biotite granite, quartz monzonite, and granodiorite occur in numerous 

discordant tabular, lensoid, or irregular bodies in two main beltsone about 12 km (7.5 mi) wide extending in a broad curve from the 

northeast corner of the mapped area, south of Seven Lakes, to the 

northwest corner of the mapped area; the other about 1.6 km (1 mi) 

wide passing through Buffalo Pass near the south margin of the area. 

Individual bodies of the quartz monzonite of Seven Lakes or Buffalo 

Pass range in size from small dikes to large plutons; contacts range 

from sharp (figs. 9, lOB, 11) to diffuse. Structure and texture are 

variable and include: (1) medium grained and equigranular; (2) coarse 

potassium feldspar augen gneiss; (3) sheared flaser gneiss; (4) finegrained equigranular leucogranite; (5) complex lit-par-lit zones with 

pegmatite (figs. 7, 9). Weathering forms vary from resistant ledges, 

roches moutonnees and monadnocks to less resistant smooth uplands 

(fig. 8) and eroded badlands. In places near the borders of the plutons, 

the quartz monzonite is choked with inclusions of country rock (fig. 

6B), and assimilation of some more mafic inclusions leads to the more 

mafic granodioritic plutonic phases in these border areas. The plutons 

were dated at 1.65-1.80 b.y. with Rb-Sr whole-rock techniques by C. E. 

Hedge (in Segerstrom and Young, 1972, p. 16; Snyder, 1978, p. 17, 

18) or Proterozoic X. 

QUARTZ DIORITE OF GILPIN LAKE 

Medium-grained equigranular speckled gray biotite-hornblende 

quartz diorite forms several small homogeneous plutons near Gilpin 

Lake (fig. 3), spanning Hole-in-Wall Canyon (fig. lOA) and along South 

Fork Elk River. The quartz diorites in the northern Park Range have 

never been radiometrically d·ated, but they probably fall in the same 

1.7- to 1.8-b.y. age span (Proterozoic X) as the other old intrusives. 

In the field they can be seen to grade into the old quartz monzonites 

locally, but elsewhere they are also found as angular inclusions both 

in quartz monzonites (fig. lOB) and in some amphibolitic rocks. 

YOUNG QUARTZ MONZONITES 

OF THE MOUNT ETHEL PLUTON 

U nsheared postmetamorphic, largely quartz monzonitic intrusive 

rocks are present in a single large batholith extending from Routt Hot 

Spring northeast under Mount Ethel to Sheep Mountain and beyond. 

Although not shown on plate 1, at least five different lithologic phases 
32 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 7.-Lit-par-lit quartz monzonite and pegmatite interlayered with amphibolite 

and pelitic schist in Sawtooth Range near head of North Fork Elk River. Note angular 

dark-colored amphibolite inclusions in glacially polished light-colored pegmatite ledge 

in foreground. Vertical span from pegmatite ledge to skyline ridge top is more than 

300 m (1,000 ft). 
Big Agnes 

Mountain 

Davis 

Peak 

GEOLOGICAL APPRAISAL 

Blackhall 

Mountain 

Red Elephant 

Mountain 

33 

FIGURE 8.-Big Agnes Mountain massif viewed northeast across Gilpin Creek, 

September 1971. Foreground aretes are formed on vertical interlayered quartz monzonite, pegmatitE:, amphibolite, felsic gneiss, and pelitic schist. (For closeup of lake 

11,050 area, see fig. 9.) Contrast foreground topography with gentler topography from 

Davis Peak to Red Elephant Mountain underlain mainly by quartz monzonite of Seven 

Lakes. Blackball Mountain (on skyline) is in Wyoming. 

FIGURE 9.-Interlayered Precambrian quartz monzonites and pegmatites (light color) 

and amphibolites and pelitic schists (dark color) near lake 11,050 near head of Gilpin 

Creek. August 1971; for snow conditions 2 weeks later, contrast distant view of same 

area in figure 8. 
34 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 10.-Textures and structures of intrusive igneous rocks. A, Pegmatite dike cutting quartz diorite of Gilpin Lake at 8,800-ft elevation (from topographic map; 2,682 m) 

on southwest rim of Hole-in-Wall Canyon. Irregularly parallel walls of pegmatite dike 

suggest dilation of walls during emplacement, but biotite concentrations in pegmatite 

near mafic inclusions and orientation of same inclusion on opposite sides of pegmatite 

(at pencil) prove that replacement of wall rocks was dominant during emplacement. 

B, Light-colored quartz monzonite or granite containing inclusions of dark-colored 

quartz diorite or granodiorite, which themselves contain inclusions of darker colored 

mafic diorite and black amphibolite. From 3-m (10-ft) glacial erratic on ridge top south 

of Fish Creek Reservoir. 
GEOLOGICAL APPRAISAL 35 

FIGURE 11.-Contact between quartz monzonite of Seven Lakes (Xsl) and amphibolite 

wall rocks (Xgn) on southeast ridge of Buck Mountain from south summit of Buck 

Mountain near center of a south-plunging synclinal fold. Light-colored foreground 

boulders are pegmatite that cuts darker colored amphibolite in center of syncline. 

View to southeast. 

of this Mount Ethel pluton were mapped separately and unequivocal 

age relations were determined among them. (For photographs and 

more detailed descriptions see Snyder, 1977b, 1978, 1980b.) The oldest 

phase is a dark-gray medium-grained hornblende-biotite granodiorite 

and diorite found mainly in a 1.6-km (1-mi)-long inclusion in the Gunn 

Creek drainage. The next oldest is a red coarse-grained biotitehornblende quartz monzonite porphyry containing large microcline 

phenocrysts and found in a very irregular 5-km (3-mi)-wide carapace 

around the southwest end of the batholith. The main volume of the 

batholith is occupied by the middle phase-a gray, variable but mainly 

medium grained biotite granite and biotite quartz monzonite. This 

phase was intruded by 3-km (2-mi)-wide and smaller stocks and sheets 

of pink fine-grained binary (two-mica) granite concentrated near the 

middle of the batholith. The youngest phase entirely within the 

batholith is a swarm of pink aplite and leucogranite dikes mainly in 

the western part of the batholith. All phases have knife-blade-sharp 

contacts with each other, contain angular inclusions of older phases, 

and are included in younger phases. The outer contacts of the batholith 

dip steeply outward and are markedly discordant (Snyder, 1978). 
36 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

All batholith phases except the granodiorite and diorite have contributed to a Rb-Sr whole-rock isochron which indicates that the 

batholith was emplaced between 1.37 and 1.4 7 b.y. ago (Hedge, in 

Snyder, 1978) in Proterozoic Y time. 

PRECAMBRIAN DIKES 

Vertical or nearly vertical Precambrian dikes of mafic to silicic composition are present in at least two swarms intruded over perhaps 

500 m.y. (million years) of geologic time (fig. 12). The dikes range in 

width from about 1 em to 30m (100ft). One swarm is blue black, fine 

grained, and of uniform basaltic composition, and trends mainly northeast and north-northeast in the western part of the gabbro of Elkhorn 

Mountain and near the summit of Farwell Mountain. These dikes are 

clearly younger than the gabbro they cut, but they have a complex 

and apparently contradictory transection relationship with the quartz 

monzonite of Seven Lakes (some basalt is younger than some quartz 

monzonite, whereas some quartz monzonite is younger than some 

basalt), perhaps implying two periods of intrusion of one or the other 

lithology or a metamorphic remobilization of one or the other rock. 

Another dike swarm is concentrated within or near the Mount Ethel 

pluton, but several of these dikes are 8 km (5 mi) and one is 24 km 

(15 mi) from the pluton. These dikes are generally porphyritic but are 

diverse in composition with diabases, trachybasalts, trachyandesites, 

quartz latites, and rhyolites represented in profusion. Some dikes are 

at least as old as the middle granite and quartz monzonite unit of the 

Mount Ethel pluton, as they are cut by this unit; other dikes cut the 

granite and quartz monzonite unit of the Mount Ethel pluton (as well 

as other rocks). Some dikes are truncated by, and offset along, the 

Precambrian mylonite shear zones; others were intruded along these 

zones and were themselves partly mylonitized by repeated fault 

movements. Most dikes have altered groundmasses, and whatever 

pyroxene or olivine they originally may have possessed has been completely altered to amphibole. 

PALEOZOIC AND MESOZOIC SEDIMENTARY ROCKS 

Although consolidated Phanerozoic rocks are exposed in only three 

places within the Mount Zirkel Wilderness, there are many exposures 

within the adjacent area, and some evidence of former, more 

widespread existence within the present wilderness area. Mesozoic and 

Paleozoic rocks occupy several downdropped or overthrust blocks 

within the mainly Precambrian range. Because most Mesozoic and 
GEOLOGICAL APPRAISAL 

10 15 20 25 KILOMETERS 

10 15 MILES 

EXPLANATION 

E Tertiary and Mesozoic rocks 

"'- Precambrian dike 

Proterozoic Y quartz monzonites of Mount Ethel pluton 

Proterozoic X gabbro of Elkhorn Mountain 

Remaining Proterozoic X rocks undifferentiated 

37 

FIGURE 12.-Location of Precambrian dikes. Heavy dashed line, approximate wilderness boundary. 
38 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Paleozoic formations contain some easily eroded calcareous shales, they 

tend to weather down to low grassy meadows between higher surrounding Precambrian hills (fig. 2). The three exposures within the Mount 

Zirkel Wilderness boundaries are Chugwater red beds on Red Dirt Pass, 

in the Agnes Creek tributary of the North Fork of the Elk River, and 

on the ridge northwest of Newcomb Park. The Red Dirt Pass locality 

is a tiny fault sliver of red beds atypically preserved in the high mountains (fig. 13) (Beekly, 1915, p. 24-26). Near the red bed remnant at 

Red Dirt Pass, the flat summit planes of Flattop Mountain (figs. 14, 

15) and Mount Zirkel (figs. 13, 16) are cut across vertical Precambrian 

rocks perhaps by the streams that deposited the Chugwater red beds, 

which may have been recently stripped from these high plateaus. 

PERMIAN AND TRIASSIC FORMATIONS 

Continental red beds of Permian and Triassic age make up the main 

part of the unmetamorphosed basal sedimentary section in the northern Park Range. All older Paleozoic rocks, if they ever existed here, 

were stripped away before the Permian deposition. From lower to upper, the formations present are the Permian Satanka Formation and 

Forelle Limestone, the Permian and Triassic Chugwater Formation, 

and the Triassic Chinle Formation. All but the Forelle are red beds. 

The Satanka Formation consists of red siltstone, red and green 

calcareous shale, and locally, ocher and red clay. The Forelle Limestone 

consists of gray to black crystalline, wavy-bedded limestone commonly 

with 10 to 50 percent quartz pebbles. The Satanka Formation and 

Forelle Limestone together are as much as 15 m (50 ft) thick; they 

are recognized only on the outer flanks of the range. The Chugwater 

Formation consists of thin-bedded red calcareous siltstone and shale 

120-240 m (400-800 ft) thick; in the southern part of the area it contains 5 percent quartz pebbles in the lower half of the formation. The 

Chinle Formation consists of thick-bedded red calcareous siltstone in 

the upper part, reddish-gray wavy-bedded limestone and pliable ocher 

and red clay in the middle part, and resistant red calcareous claystonepebble conglomerate and impure sandstone (Jelm equivalent in Wyoming) in the lower part. The formation is 30-180 m (100-650 ft) thick. 

Except for a few poorly preserved pieces of petrified wood, none of 

the above formations is fossiliferous in the area studied. 

JURASSIC FORMATIONS 

The Middle and Upper Jurassic marine Sundance Formation and 

the Upper Jurassic continental Morrison Formation are widespread 
GEOLOGICAL APPRAISAL 39 

Mount Zirkel 

FIGURE 13.-Mount Zirkel and Red Dirt Pass, view to northwest from north end of Flattop Mountain, August 1970. Area of smooth soil above left snowfield is downfaulted 

sliver of Chugwater Formation (R Pch). For earliest description of this locality, see 

Beekly (1915, p. 24-26). Note flat Mount Zirkel summit plateau. 
40 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

throughout the mapped area but poorly exposed, owing to their nonresistant character and tendency to landslide. The Sundance Formation consists of very poorly exposed olive-gray calcareous shale and 

gray glauconitic oolitic limestone with belemnites, mollusks, and 

foraminiferans in the upper part (which is locally missing), and soft 

massive salmon-pink (usually), yellow, or white sandstone in the lower 

part. It has a one-pebble-thick chert-pebble conglomerate at the base. 

The Sundance Formation is as much as 75 m (250ft) thick. The Morrison Formation consists of calcareous purple and green shale and 

claystone, greenish-white sandstone, and gray fresh-water algal 

limestone; it is 120-275 m (400-900 ft) thick. The Morrison Formation contains charophyte oogonia, ostracodes, and petrified wood locally. Numerous landslides are soled in the Morrison Formation. 

CRETACEOUS FORMATIONS 

The Cretaceous formations, which begin with a ledge-forming basal 

conglomerate and sandstone, are mainly nonresistant black to gray 

calcareous shales. The basal Dakota Sandstone consists of buff 

siliceous sandstone and quartz- or chert-pebble conglomerate in the 

lower part and buff siliceous sandstone and minor gray shale in the 

upper part. It is 30-120 m (100-400 ft) thick and is a persistently mappable horizon to which the discontinuous exposures of all other nearby formations can be related. Above the Dakota, the Benton Shale, 

30-180 m (100-600 ft) thick, consists of three locally separable 

members. The basal or Mowry Shale Member consists of hard siliceous 

black shale that breaks into angular equidimensional granules (locally used for road topping); it contains abundant chirocentrid fish scales, 

bones, and fecal pellets. The middle or Graneros Shale Member consists of soft black fissile noncalcareous shale with white clay beds 

representing former volcanic ash deposits. Its diagnostic fossil, Acanthoceras amphibolum Morrow, has been collected by E. A. Merewether 

(written commun., October 1973) in the structural basin traversed by 

Silver City Creek. The upper, locally resistant Juana Lopez Member 

consists of petroliferous calcareous coquina, calcarenite, and finegrained shaly sandstone containing an abundant distinctive suite of 

mollusks and ammonites, and rare shark and ray teeth (Snyder, 1977 a, 

b; 1980a, b). The next Cretaceous formation, the Niobrara Formation, 

consists of distinctive blue-gray calcareous white-spotted shale that 

weathers into chips and plates and that locally contains abundant Inoceramus and oyster fossils and less common fish scales and bones. 

The uppermost Mesozoic formation exposed in this area, the Pierre 

Shale, consists of voluminous gray shales in two members. The lower 

shaly member contains fissile gray shale that is noncalcareous except 
GEOLOGICAL APPRAISAL 41 

FIGURE 14.-View south at flat summit plateau of Flattop Mountain and Red Dirt Pass. 

(See also fig. 13.) Upper Slavonia mine located above small lake in right middle distance. 

September 1966. 

FIGURE 15.-Verticallayered amphibolite truncated by summit plane of Flattop Mountain. (See fig. 14.) View east from near Upper Slavonia mine, August 1971. 
42 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 16.-Mount Zirkel and Frying Pan Basin, looking west, August 1970. 

colored peaks and talus in center and on right are predominantly quartz moogneisses. The "frying pan" is a collapsed boulder moraine of earliest 

snow) at its head. (See also fig. 17.) Note flat summit plateau on south side 

near the base and that becomes progressively siltier to sandier in its 

upper parts. It is 700-850 m (2,300-2,800 ft) thick. The upper sandy 

member consists of interbedded brown to gray calcareous sandstone, 

siltstone, and shale with as much as 900 m (3,000 ft) exposed. 

TERTIARY ROCKS 

The Coalmont Formation of Eocene and Paleocene age is exposed 

in North Park basin along the east side of the northern Park Range. 

It consists of buff to olive-green arkosic sandstone and Precambriancobble conglomerate, with rare leaf fossils. As much as 1,300 m 

(3,400 ft) thickness may be present in the mapped area. Coal is present and has been mined just east of the mapped area. Arkosic conglomerate equated with Coalmont Formation is present at an elevation 

as high as 11,100 ft (3,383 m) on the southeast rim of Red Canyon. 

The flat summits of several peaks along the Continental Divide 

southwest of this (for example, Lost Ranger Peak and The Dome: 

Snyder, 1978, fig. 5B) at altitudes between 11,600 and 11,900 ft 

(3,536-3,627 m) may have been eroded to this level prior to Coalmont 
GEOLOGICAL APPRAISAL 

Dark-colored cliffs and talus boulders on left are mainly amphibolite; lighter 

zonite of Seven Lakes, interlayered with lesser amounts of hornblende 

Neoglacial or latest Pleistocene age with an active rock glacier (outlined by 

of summit of Mount Zirkel. 

43 

time and stripped recently of Coalmont deposits formerly present upon 

them. South of this area in the vicinity of Rabbit Ears Peak dated 

Coalmont Formation is certainly present at an elevation as high as 

9,500 ft (2,895 m) and may extend to as high as 10,300 ft (3,140 m) 

(Snyder, 1977c, 1980c). 

Sedimentary rocks of the Browns Park Formation of Miocene age 

are present locally or as an extensive blanket 335 m (1,000 ft) thick 

along the west and north margins of the map area. Two lithologies 

are most prominent, but other less common ones are also present. Most 

common are buff-colored calcareous or siliceous siltstone or sandstone, 

and conglomerate. The finer grained siltstone and sandstone units occur mostly in the middle and upper parts of the formation or away 

from the Precambrian mountains, but they may extend continuously 

to the base of the formation, even where the formation is surrounded 

completely by mountains (for example, along the upper Encampment 

River); conglomerates are mostly near the base of the formation and 

near the mountains but are interbedded with finer sediments in many 

places. The siltstones and sandstones are partly eolian and partly 

alluvial; the conglomerates are mainly alluvial and may be linear in 
44 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

trend, mirroring old stream drainages; a few are colluvial. The fine 

sediments range from wholly clastic to a mixture of clastic particles 

and airfall ash shards; either type is interlayered locally with pure 

white or gray porcellanic ash beds from about 1 em to 12 m (40 ft) 

thick. Chert beds are present but rare and may represent ash-derived 

redeposited silica. Cobbles in conglomerate are predominantly resistant Precambrian rocks and locally resistant Mesozoic rocks, but they 

commonly contain 1-5 percent nonresistant white clay blebs, probably 

altered pumice, or more likely, ash-bed fragments. Siltstone and sandstone beds are oxidized extensively to red colors and are silicified locally near some intrusives and faults; such red colors are especially 

prominent within 2 mi of Columbine and are best seen along the new 

logging road (not shown on maps) south and west of Iron Mountain. 

Conglomerate may be as unconsolidated as loose stream gravel or as 

indurated as concrete; commonly it is partly indurated with indurating 

carbonate concentrated at bottoms of cobbles. White to gray massive 

limestone locally is present near the base of the conglomerate or on 

top of Precambrian outcrops in areas where it is reasonable to infer 

that Browns Park may once have existed; such limestone may occur 

as massive unbedded deposits, as clastic dikes within Precambrian 

rocks, or as the matrix of a breccia of angular Precambrian fragments. 

Most such limestone has probably been redeposited by ground water 

near the base of the Browns Park Formation over a considerable period 

of time; some may be young, hot-spring travertine. Tuffaceous 

epiclastic volcanic breccia with fragments of silicic porphyry and dark 

shale is present west of Hahns Peak and may represent the only 

uneroded extrusive product of a volcano formerly centered on Hahns 

Peak (Segerstrom and Kirby, 1969, p. B21-B22; Segerstrom and 

Young, 1972, p. 33-34). Similar near-source pyroclastic deposits are 

known to be intercalated with the Browns Park sediments farther west 

in the Elkhead Mountains and south of Steamboat Springs along the 

Yampa River (Snyder, 1977c, 1980c). No lava flows are known to be 

intercalated with Browns Park sediments within the present mapped 

area, but capping lava flows are present on Shield Mountain and Rabbit Ears Peak just outside the study area (shown on pl. 1). 

The Browns Park Formation itself has been dated in this general 

area by a combination of paleontological and radiometric methods. 

A basal 5- to 60-cm (2-in. to 2-ft) ash bed in the northwest quadrant 

of the area has been dated, using fission-track methods, as 24.8± 

2.4 m.y. (C. W. Naeser, written commun., October 1974). A near-basal 

ash bed on Rabbit Ears Pass has also been dated, using fission-track 

methods, as 20.1± 1.9 m.y. (C. W. Naeser, written commun., July 

1976). These figures compare well with the ash in the lowermost part 

of the Browns Park Formation 40 km (25 mi) northwest of Maybell, 
GEOLOGICAL APPRAISAL 45 

dated at 24.8±0.8 m.y. (Izett and others, 1970, p. C150). West of the 

mapped area on Sand Mountain and Shield Mountain, orange siltstone 

beds are intercalated with minor white to gray ash beds 180 to 610 m 

(600 to 2,000 ft) stratigraphically above the highest Browns Park beds 

mapped on plate 1. The orange siltstone beds contain a vertebrate 

fossil suite of late Miocene age including two species of camel, and 

one species each of horse, rhinoceros, and oreodont (Buffler, 1967, pls. 

83, 84; G. E. Lewis, written communs., December 1973 and November 

1975). Four associated ash beds have been dated, using fission-track 

methods, at 9.0±2.1 to 15.8±2.6 m.y. (C. W. Naeser, written commun., 

October 1974). 

Small white to gray to black discordant intrusive bodies of several 

types cut the Tertiary section, mainly along the west margin of the 

mapped area. The types include pipes, stocks, dikes, and sills, as well 

as bodies of more irregular aspect. Most rocks are porphyritic; the 

lighter rocks contain large euhedral feldspar crystals, reacted quartz, 

or small euhedral biotite crystals, and the darker ones contain small 

olivine and pyroxene crystals. Compositions range from trachybasalt 

through intermediate trachyandesites and latites to rhyolite. Many 

people, including Snyder (1977a, b, c; 1980a, b, c), have mapped mafic 

and silicic varieties separately, and many have concluded from this 

that the suite is the usual bimodal one expected of upper Tertiary igneous rocks, but this does not appear to be the case. In the Elkhead 

Mountains the presently available rock chemistry suggests a completely uniform distribution of compositions, a continuum from the darkest 

to the lightest colored rocks. (See Snyder, 1978 for a more complete 

discussion.) In the Elkhead Mountains 10 K-Ar (potassium-argon) igneous rock ages indicate latest Miocene (McDowell, 1966; Buffler, 

1967; Segerstrom and Young, 1972); the lone intrusive in the southeast 

comer of the present area has been mapped as Oligocene(?) (Hail, 1968, 

pl. 1) but has not been dated directly. An intermediate intrusive 2.4 km 

(1.5 mi) west of Rabbit Ears Peak has been dated, using fission-track 

methods, as 17.0± 1.5 m.y. (C. W. Naeser, written commun., October 

1974; Snyder, 1977c, 1980c). 

QUATERNARY DEPOSITS 

Five types of unconsolidated Quaternary deposits are depicted on 

plate 1: till, terrace gravels, modern alluvium, landslide deposits, and 

travertine. Other surficial deposits, such as talus, rock glaciers (fig. 

1 7), or colluvium, are present but were not mapped because of small 

area or thickness. (See Snyder, 1977a, b, c; 1980a, b, c.) Till-the 

jumbled boulders and dirt deposited by former mountain glaciers-is 

mapped where it is thick enough to obscure older units, and locally 
46 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 17.-Active rock glaciers in cirque head on east side of Mount Zirkel. Aerial 

photograph, September 1966. (Compare different snow conditions in fig. 16.) 

it is in excess of 60 m (200 ft) thick. Several sets of terminal or lateral 

moraines can be recognized within this unit; the most extensive ones 

are of Wisconsin age; others are intermediate in age between these 

and the presently active rock glaciers (fig. 16). Terrace deposits are 

rounded alluvial gravels found along the sides of modern drainages 

but deposited by streams before or during the Pleistocene glaciations. 

Close to the mountains these deposits can be quite coarse, but the 

average particle size diminishes rapidly with increasing distance from 

the mountains. Modern alluvium is simply the latest alluvial or flood 

deposits of the present streams; it is mappable only in the wider 

valleys. Landslides are local slumps of bedrock material, as much as 

several miles long, that usually are soled in weak, slippery rocks like 

Morrison Formation or Pierre Shale. They may form in response to 

earthquake shaking, perhaps where weak rocks have been undercut 

by streams. Several prehistoric landslides have flowed into or across 

the main course or tributaries of the Elk River, thereby precipitating 

secondary floods of large magnitude after washouts. Travertine, the 

porous limestone deposit of warm or hot springs, has been mapped 

by Hail (1965, pl. 3) on the north side of Delaney Butte. Other small 

unmapped deposits are present at Routt Hot Spring north of Copper 

Ridge. Similar but thick travertine deposits are extensive along the 

Yampa River near Steamboat Springs (Snyder, 1977c, 1980c). 
GEOLOGICAL APPRAISAL 47 

STRUCTURE 

The complex structure now present in the rocks of the area is a composite of Precambrian folds and faults, Laramide (Late Cretaceousearly Tertiary) folds and faults, and late Miocene or post-Miocene 

faults. These structures can be documented on the basis of both direct 

and indirect evidence; Paleozoic structures, if present, cannot be accurately documented owing to the general lack of rocks of this age. 

All the known structural movements were complicated by several 

periods of Precambrian and Tertiary igneous rock emplacement interspersed with the movements. 

The widespread Precambrian volcanic and sedimentary rocks were 

isoclinally folded (and perhaps faulted) and metamorphosed to 

sillimanite grade about 1.7-1.8 b.y. ago. Hand-specimen- and outcropsize isoclinal folds are common (figs. 5B, 5C), and some folds with 

amplitudes of hundreds of meters or yards can be proven by reversed 

crossbedding on opposite fold limbs (in the quartzite body north of 

Willow Creek), by map pattern (in Soda Creek and North Fork Fish 

Creek), and by map pattern in conjunction with the observation of 

quartz sillimanite nodules oriented perpendicular to metamorphosed 

bedding (believed to be near fold crests; on Big Agnes Mountain). Folds 

having an amplitude or wavelength larger than several kilometers cannot be proven because of a paucity of units mappable at that scale. 

Some small folds have themselves been isoclinally folded, providing 

hints of an earlier history more complex than generally assumed or 

than easily documented elsewhere. Truncation of some metamorphic 

structures first by gabbro, then by quartz diorite and quartz monzonite, shows that these igneous rocks were intruded after the onset 

of metamorphism. But the abundance of gneisses and augen gneisses 

in former magmatic representatives of this igneous suite implies that 

a high proportion of the suite was intruded well before the close of 

metamorphism. Some of the tabular bodies of the quartz monzonite 

of Seven Lakes are today preserved in complex synclinal forms, for 

example, on Buck Mountain (fig. 11) and Red Elephant Mountain 

(Snyder, 1977a, 1980a, cross sectionsD-D' andE-E1, that may imply 

considerable folding following emplacement. 

Following the earlier Precambrian folding and metamorphism the 

elongate Mount Ethel batholith was emplaced 1.4 b.y. ago parallel to 

northeast-trending structure. Some of the porphyry dikes overlap 

these quartz monzonites in age, and they appear to extend the 

chemical trends developed by the Mount Ethel rocks (Snyder, 1978, 

1984); but some dikes may be much younger than the batholithic rocks. 

Following batholithic cooling, two extensive northeast-trending 

Precambrian shear zones were formed, between Soda Creek and North 

Fork Fish Creek and on Farwell Mountain. The generally medium to 
48 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

coarse-grained rocks in these areas were locally mechanically milled 

down to excessively fine grained rocks-mylonites-that have never 

been coarsely recrystallized. The true mylonites are confined to planar 

sheets as much as a few tens of meters thick and many kilometers 

long, but within the shear zones many rocks are also partly sheared 

or partly mylonitized. Some paired porphyry dike sets are offset along 

some mylonite sheets as much as 400 m (1/4 mi) (for example, northwest of BM 10,088 west of Buffalo Pass), whereas other mylonite 

sheets include sheared remnants of porphyry dikes, perhaps ones that 

were intruded along moving faults and that later helped to lubricate 

the faults (for example, in Soda Creek, south of Round Mountain Lake, 

and northeast of Big Red Park). The time of shearing and mylonitization has not been directly dated in the northern Park Range, but it 

must be younger than the Mount Ethel pluton and porphyry dikes 

and old enough that depth of burial was still sufficient to permit 

mylonitization. Farther south, northeast-trending shear zones have 

been inferred to be late Precambrian in age (Tweto and Sims, 1963, 

p. 991, 1006). To the east mylonites have been dated at 1.2 b.y. (Abbott, 1972). All the mylonites are part of a much broader northeasttrending belt of Precambrian wrench faulting believed by some to be 

1,100 km long and 160 km wide (Warner, 1978, p. 161). 

Tectonic uplift of the Park Range probably began in the late 

Paleozoic but was markedly intensified in late Mesozoic and early Tertiary time. Some early or continued uplift is suggested by missing 

stratigraphic units along the axis of the range (namely, pre-Permian 

Paleozoic rocks, Forelle Limestone, and Sundance Formation) as well 

as by the presence of some Precambrian-derived pebbles in most units. 

But uplift, folding, and faulting culminated in the Laramide orogeny 

in latest Mesozoic and earliest Tertiary times. The entire range is 

basically a giant anticline with an eroded crest. Mesozoic hogbacks 

flank the range and are preserved in isolated synclinal fault blocks 

within it. The fault blocks are mostly asymmetrical with shallow dipping rocks in depositional contact with Precambrian basement on the 

west side of the blocks and steep or overturned beds on the east side, 

overridden by basement thrust blocks. (See Snyder, 1977a, 1980a.) Exposures are incomplete, but there is some evidence of a gradation in 

dip of the east-margin faults: steep or vertical on the west side of the 

range to shallow or nearly horizontal on Independence Mountain on 

the northeast side of the range (Snyder, 1977a, 1980a). If so, this may 

indicate a cross-range gradation in Laramide tectonic forces: from 

strongly compressional on the east to less strongly compressional or, 

locally, tensional on the west. Faults offsetting Mesozoic rocks locally grade into Precambrian mylonite zones, indicating remobilization 

of earlier crustal weaknesses (fig. 18). The Coalmont Formation 
Buck 

Mountain 

GEOLOGICAL APPRAISAL 49 

FIGURE lB.-Differentially eroded steeply dipping fault plane crossing Hinman Creek 

from 9,300-ft lookout point (from topographic maps; 2,835 m) on southeast shoulder 

of Farwell Mountain. View from 1-m-wide (3-ft-wide) mylonite zone along this fault. 
50 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

presents evidence of early Tertiary continuation of Laramide uplift 

and faulting. Mountain margin facies contain large Precambrian 

boulders, and the formation itself is interleaved in thrust slices on the 

north side of Delaney Butte (Hail, 1965). 

Laramide tectonism died out in the Eocene to be replaced by erosion, sedimentation, and volcanism in the Oligocene and Miocene and 

by normal faulting in latest Miocene or Pliocene. Volcanic rocks 

erupted in the Rabbit Ears Range during Oligocene time contributed 

volcanic boulders to the Miocene North Park Formation just outside 

the eastern limit shown on plate 1. Lower Miocene lava flows are intercalated with the sparse Browns Park sediments on Rabbit Ears 

Peak and all across Rabbit Ears Pass (Snyder, 1977c, 1980c). Ash beds, 

though present in the lower part of the Browns Park Formation, are 

more numerous and more voluminous in the upper part and were succeeded by capping lava flows and numerous irregular intrusives in the 

Elkhead Mountains 10-12 m.y. ago (fig. 19; and see Buffler, 1967; 

Segerstrom and Young, 1972). This episode of intrusion was followed 

by normal faulting of diverse orientation with offsets of 300 m 

(1,000 ft) or more: the Browns Park Formation is in knife-blade-sharp 

fault contact with basement rocks in the valley of the Encampment 

River northeast of West Fork Lake; significant fault offset can also 

be demonstrated on the west side of Strawberry Park, on Copper 

Ridge, northeast of Pearl, and at many localities within 8 km (5 mi) 

of Hahns Peak. Some of the youngest Elkhead intrusives occupy faults 

offsetting the Browns Park Formation (for example, the dike on the 

east side of Little Red Park is K-Ar dated at 10.3±0.3 m.y., 

Segerstrom and Young, 1972, pl. 1, p. 41). Other faults on Hahns Peak 

or associated with the Hahns Peak horst cut the Elkhead intrusives. 

No modern fault scarps have been recognized in the area, but the concentration of recent landslides along linear fault zones from Hinman 

Park to West Fork Lake suggests their contemporaneity, perhaps 

because they were triggered by a prehistoric earthquake along a line 

of structural weakness. 

MINERAL AND GEOCHEMICAL SETTING 

TIMING OF MINERALIZATION 

Rocks of the northern Park Range have been mineralized by introduced ore elements probably four times in the geologic past, twice in 

the Precambrian, once(?) at the close of the Mesozoic and beginning 

of the Tertiary (Laramide), and at least once later in the Tertiary. The 

Precambrian events coincide with the two major episodes of igneous 

intrusion, 1.7-1.8 b.y. and 1.3-1.4 b.y. (Antweiler, 1966; Antweiler and 
GEOLOGICAL APPRAISAL 51 

FIGURE 19.-Aerial view looking southwest at northeast face of Sand Mountain, showing bedded silts (gray) and ash-rich beds (light) of Browns Park Formation along right 

and left ridges of photograph (same covered by talus in center) and silicic intrusive 

porphyry in cliffs capping Sand Mountain. Area shown has yielded numerous "Barstovian" vertebrate fossils and ash-bed zircon fission-track ages (9-16 m.y.) and is essentially the area mapped in southeast corner of Meaden Peak 7 V2' quadrangle in western 

part of map area of Snyder (1980a). Vertical span from bottom of photograph to top 

of Sand Mountain is more than 360 m (1,200 ft). 

others, 1972; Snyder, 1978, fig. 19), and although not all Precambrian 

mineralization is definitely assignable to one or the other event, some 

is directly dated and other assignments are probable, as indicated by 

the examples in table 1. The reader should note that Antweiler's 

1.0-b.y. mineralization (1966, p. 271) in evidence elsewhere in Colorado 

has not been recognized yet in the northern Park Range. The late and 

post-Mesozoic mineralization occurred in or was related to Laramide 

structures, but most deposits have not been directly dated. (See Taylor 

and others, 1968, for a discussion of this problem.) Some of the Tertiary mineralization was post-Eocene, some was post-Oligocene, and 

some was late Miocene, but whether one long period of mineralization or three or more short ones took place is not definitely known. 

Here and elsewhere in the vicinity there is evidence that elements or 

minerals originally deposited in the Precambrian have been remobilized in the Laramide or Tertiary (Tweto, 1960, p. 1406; Tweto and Sims, 

1963; Antweiler and others, 1972, p. 312; Snyder, 1978). 
52 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 1.-Ages of selected mineralization episodes in the northern Park Range 

Mineralization episode 

Greenville district copper-leadzinc-silver. 

Gilpin district copper-leadzinc-silver (includes Gilpin mines 

and Upper and Lower Slavonia mines). 

Farwell district copper-lead-zincsilver (includes Farwell mines 

and mines on uppermost King 

Solomon Creek). 

Copper-lead-zinc-silver ore from Pearl 

district, Independence Mountain, west 

side of Buck Mountain, southwest Red 

Elephant Mountain, and probably 

most anomalous values in stream 

sediments in north half of map area. 

Seven Lakes beryllium streamsediment anomaly. 

Fish Creek Fair-U claims. 

Ultramafic chromium-platinumpalladium traces. 

Elkhorn district lead-silverzinc-copper ore. 

Uranium-niobium traces in prospects in 

Bear Creek district east of Elk Park, 

uranium-thorium-rare earth Fielder 

prospect near Agua Fria Lake, interstitial fluorite in rocks of Mount Ethel 

pluton, silver trace anomaly in stream 

sediments south of Horse Thief Peak. 

Copper-silver ores south of Lone Pine 

Creek, copper-silver ores and related 

stream-sediment anomalies on east 

side of Silver City Creek basin, minor 

N orthgate fluorite. 

Uranium-fluorite veins, Crystal 

district; fluorite veins, N orthgate. 

Hahns Peak disseminated lead-silver 

ore; source of Hahns Peak gold 

placers. 

Reason for age assignment 

Lead isotopes indicate 1.7-b.y. age on a 

"best-fit" lead evolution curve (Antweiler and others, 1972, p. 310). 

Lead isotopes indicate 1.7-b.y. age on 

a "best-fit" lead evolution curve for 

Slavonia ore (Antweiler and others, 

1972, p. 310). 

K-Ar age on muscovite from mineralized 

Farwell pegmatite is 1.68±0.05 b.y. 

(Segerstrom and Young, 1972, table 3, 

p. 17). 

Intimate association with 1.7- to 1.8-b.y. 

Precambrian rocks, and by analogy 

with above. 

Associated with center of 1.7-b.y. quartz 

monzonite pluton. 

Intimate association with 1.7-b.y. rocks. 

Zircons from gabbro of Elkhorn Mountain give 207Pb/206Pb age of 1.78 b.y. 

(C. E. Hedge and Margarita Gallego, 

in Snyder, 1977 a, 1980a). 

Lead isotopes indicate 1.45-b.y. age on 

a "best-fit" lead evolution curve (Antweiler and others, 1972, p. 311). 

Intimate association with rocks of 1.4-

b.y. pluton (Snyder, 1977b, 1980b). 

"Laramide" because intimately associated with structures cutting Mesozoic 

rocks (Snyder, 1977a, b, 1980a, b; 

Steven, 1960, p. 395, 396). 

Post-Coalmont = post-Eocene for 

Crystal; post-White River = postOligocene for Northgate; both could be 

late or post-Miocene. 

Ore disseminated in or probably derived 

from porphyry with K-Ar age about 

10 m.y. (late Miocene) (Segerstrom and 

Young, 1972, table 6, p. 41; Young and 

Segerstrom, 1973; Antweiler and 

others, 1972). 
GEOLOGICAL APPRAISAL 53 

INTERPRETATION OF ORIGIN OF SULFIDE DEPOSITS 

It is worthwhile enlarging upon the description and interpretation 

of origin of the copper-lead-zinc-silver vein and replacement ores 

(generally 1.7-1.8 b.y.; table 1) for several reasons: 

1. Deposits of this worldwide type are among the most heterogeneous and complex 

of all ores (Stanton, 1972, p. 598, 610); 

2. They occur over a wide area in the northern Park Range, including some centrally 

located zones within the Mount Zirkel Wilderness and adjacent area; 

3. They have generated the most interest in this area in terms of the volume of previous 

prospecting, albeit without substantial success, but they are judged here to have 

a real potential for future economic exploitation. Sheridan and Raymond (1977, p. 

22) believed that mineable sulfide deposits may occur in the northern Park Range. 

On the other hand, Tweto, Bryant, and Williams (1970, p. C35, C36) cautioned that 

the absence of Tertiary porphyries and the offset from the Colorado mineral belt 

militate against significant Tertiary ore deposits in the Gore Range-Eagles Nest 

Primitive Area; Mount Zirkel Wilderness and adjacent area has no Tertiary porphyries exposed at the surface and is offset an additional 80-120 km (50-75 mi) 

from the Colorado mineral belt (Tweto, 1968, fig. 1). However, Doe (1978) has noted 

that the value of Cretaceous-Tertiary magmatothermal ore deposits is progressively 

greater in areas where the maximum 206Pb/204Pb ratio is toward the low end of the 

sequence 18-25; in the northern Park Range this ratio has a maximum of 18.7 (Antweller and others, 1972, p. 310). Certainly rocks of the generall.8-b.y. age and provenance have the capacity to contain massive sulfide ores in the Jerome area of 

Arizona (Anderson and Creasey, 1958; Anderson and Nash, 1972). U.S. production 

from massive sulfide ores is insignificant in comparison to porphyry copper deposits 

and Mississippi valley type lead-zinc deposits, but in Canada 80 percent of the zinc, 

39 percent of the copper, 68 percent of the lead, 62 percent of the silver, and significant amounts of gold came from this type of mineralized rock in 1971 (Sangster 

and Scott, 1976, p. 129). In Colorado molybdenum, gold, and silver, in that order, 

constitute 72 percent of the total value of the principal metals produced from 1858 

through 1964 (Tweto, 1968, p. 553). 

The Park Range ores are variable mixtures of the common iron, copper, lead, and zinc sulfides (mainly pyrite, chalcopyrite, galena, and 

sphalerite) in places with anomalous silver, tungsten, molybdenum, 

gold, mercury, and tin, locally with small gossans of iron oxide or 

hydroxide and copper hydroxide or carbonate, rich in some or all of 

these elements. The ores commonly occur in disseminated form replacing marble or calc-silicate rocks, but they may also be associated with 

pelitic schists or the spectrum of metavolcanic rocks from amphibolite 

to felsic gneiss. Blocks of massive ore with greater than 50 percent 

sulfides are present on most of the larger dumps, but relations of this 

ore to the wall rock can only rarely be studied in outcrop. In many 

dump samples the massive ore appears to be gradational with the 

disseminated ore, but some sulfides occur in sharp-margined crosscutting veins, possibly reflecting a younger (perhaps much younger) 

episode of mineralization. Oxide and silicate gangue minerals present 

in ~omposite aggregates appear to be the same as those present 

elsewhere in these high-grade wall rocks. Gahnite, a zinc aluminate, 

is present rarely in the wall rocks of the Pearl and Greenville districts 
54 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

(Read, 1903; Sheridan and Raymond, 1977, p. 20; Robert Johnson, oral 

commun., 1977; Snyder, 1984) but has not been observed elsewhere 

in the range. Alteration zones, if present at all, are narrow; usually 

the sulfide-silicate assemblage presents the appearance of being 

emplaced before or during metamorphism (Stanton, 1972, p. 625), certainly not in a much younger, separate event. 

Most importantly, many of the base-metal ores seem to occur in the 

marine metavolcanic-metasedimentary rocks near but outside of the 

complexly shaped syntectonic bodies of quartz monzonite of Seven 

Lakes. This observation for the northern Park Range is new with this 

report, and it has some implications for origin. It is true for most of 

the prospected ore bodies in the Pearl district and on Independence 

Mountain, in the Gilpin district (including the Upper and Lower 

Slavonia and Gilpin mines), on Red Elephant Mountain, on Buck 

Mountain, on Farwell Mountain, and at the "Chipmunk" claim west 

of Buffalo Pass. All prospected ore bodies of this type, except Greenville, appear to occur within 3.2 km (2 mi) of a quartz monzonite contact, but none are known either within the quartz monzonite or at its 

wall-rock contacts. Although, as mentioned above, marble is a favored 

host (nearly all marbles within 3.2 km (2 mi) of the quartz monzonite 

contact show some effects of mineralization), marbles outside the 

3.2-km (2-mi) range, along the north edge of the mapped area and east 

of Glen Eden, are not mineralized. 

The preceding facts are consistent with a diplogenetic (Lovering, 

1963) hypothermal origin of the ores, possibly weakly remobilized by 

mesogene solutions (Ridge, 1976, p. 190). The following can be visualized. The ore elements are deposited in largely unconcentrated form 

along with volcanics, volcanic sediments, or sediments. Thus, the country rocks that enclose the deposits are the ultimate source of the 

metals and gangue elements, an idea that has been advocated since 

the time of Agricola. (See Amstutz, 1964; Boyle, 1970; Bernard, 1973, 

for modem summaries.) Some, like Greenville, may have been present 

in concentrated form, but the evidence either way is meager. (Sheridan 

and Raymond (1977, p. 17, 18), who have visited the Pearl, Gilpin, ·and 

Greenville districts, believed that some deposits may have an exhalative sea-floor origin, whereas other deposits associated with calcsilicate rocks and impure marbles may have been syngenetic or 

epigenetic stratiform ore deposits in sedimentary rocks before 

metamorphism.) Following the postulated syngenetic dispersal of the 

ore elements through the eugeosynclinal rocks, quartz monzonites 

were intruded prior to or contemporaneous with the height of regional 

metamorphism, and the outflow of magmatic heat and possible solutions was the agent for magmatothermal (Doe, 1978; see also Jensen 

and Bateman, 1979, p. 258) concentration of the ore elements. This 
GEOLOGICAL APPRAISAL 55 

lithogenic (Lovering, 1963) or laterogenic (Gabelman, 1976, p. 51) concentration of ore elements could be accomplished either by the normal 

mechanism of migrating interstitial or magmatic water or by the dry 

"distillation" process of Sullivan (1958). Migration might take place 

over distances of a few meters to 3.2 km (2 mi), and carbonate hosts 

along the way would be favored sites of concentration. Many ore 

bodies resulting from such syngenetic dispersal plus later remobilization might reasonably be expected to be of small subeconomic size, 

proportional both to the small element amount originally deposited 

in dispersed form and also to the small size of the concentration 

"engine" that came along later; but some could be substantial. If the 

present surface sampling is representative of what is also present at 

reasonable depth in the crust, this favored remobilization hypothesis 

does not hold much hope for the existence of a large hidden massive 

sulfide ore body. However, if the present surface sampling is not 

representative of what is present at deeper levels, then a valuable subsurface sulfide resource could await more sophisticated prospecting. 

Mine Appraisal 

By LOWELL L. PATTEN, U.S. BUREAU OF MINES 

MINERAL RESOURCES OF THE MOUNT ZIRKEL 

WILDERNESS AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

U.S. GEOLOGICAL SURVEY BULLETIN 1554-B 
CONTENTS 

Page 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

Present investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

History and production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

Mining claims, prospects, and mineral deposits . . . . . . . . . . . . . . . . . . . . . . . . . 71 

Agua Fria Lake area (locality A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 

Beaver Creek-Norris Creek area (locality B) . . . . . . . . . . . . . . . . . . . . . . . . 73 

Raspberry Creek-Roaring Fork area (locality C) . . . . . . . . . . . . . . . . . . . . . 74 

Roaring Fork-Lone Pine Creek area (locality D) . . . . . . . . . . . . . . . . . . . . . 77 

Bear Creek prospect (locality E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 

Red Elephant Mountain prospect (locality F) . . . . . . . . . . . . . . . . . . . . . . . 79 

Windy Gulch claims (locality G) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 

Buffalo Ridge (locality H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 

Mica Basin (locality I) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 

Lower Slavonia district (locality J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Site of samples 17-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Site of samples 21-23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 

Site of sample 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 

Upper Slavonia mine (locality K) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 

Upper Gilpin Creek (locality L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 

North Fork Elk River (locality M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

Diamond Park area (locality N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

King Solomon Creek area (locality 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 

Beaver Creek-King Solomon Creek area (locality P) . . . . . . . . . . . . . . . . . . 92 

Section 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 

Section 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 

Section 23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 

Section 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

Zinc Mountain claim (locality Q) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

Beaver Creek area (locality R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Grouse Mountain area (locality S) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Willow Creek Canyon area (locality T) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Big Creek area (locality U) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 

Elk Park area (locality V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 

Soda Creek area (locality W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

Buffalo Pass area (locality X) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

Fossil fuel leases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 

58 
FIGURE 20. 

21-24. 

25. 

26. 

27. 

28. 

29. 

30-32. 

33. 

34. 

35. 

36. 

37-42. 

43. 

44-46. 

47. 

48. 

49. 

MINE APPRAISAL 

ILLUSTRATIONS 

Photograph of Mica Basin .... . 

Maps: 

21. U.S. Bureau of Mines index map, showing areas 

examined . . . . . . . . 

22. Agua Fria Lake claim area .. . .. .. . 

23. Beaver Creek-Norris Creek claim area ....... . 

24. Raspberry Creek-Lone Pine Creek claim area .. . 

Photograph of Beta opencut .............. . 

Photograph of Beta headframe . . . . . . . . . . 

Map of Pedad-DLB claims ... .. ...... . . .... . . 

Photograph of Red Elephant Mountain prospect 

Map of Windy Gulch claims near Davis Peak ... 

Photographs: 

30. Big Agnes Mountain mica prospect .. 

31. Big Agnes Mountain mica prospect, closeup 

32. Lower mica prospect ............... . 

Map of prospect workings in the Slavonia district 

Photograph of opencut north of Gilpin Creek .... 

Map of Gold Creek-Gilpin Creek mine workings 

Photograph of Slavonia mine dump 

Maps: 

37. Diamond Park prospect workings 

38. Beaver Creek-King Solomon Creek claim area .. 

39. Adit plan .... .. ...... . 

40. Zinc Mountain claim area .. . 

41. Grouse Mountain claim area ... ... . .. . 

42. Willow Creek Canyon claim area .. . . ... .. . 

Photograph of Willow Creek Canyon placer workings 

Maps: 

44. Big Creek claim area . . . ... . . ........ .. . 

45. Elk Park claim area ........ . ... .. .. . . . .... . 

46. Soda Creek claim area .............. . 

Photograph of prospect near South Fork Soda Creek ... . 

Map of Buffalo Pass prospect area .................. . 

Photograph of prospect pit near Buffalo Pass ......... . 

59 

Page 

62 

64 

72 

73 

75 

76 

76 

78 

79 

80 

82 

82 

83 

84 

86 

88 

89 

91 

93 

94 

96 

98 

99 

100 

101 

103 

104 

105 

106 

107 
60 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLES 

Page 

TABLE 2. U.S. Geological Survey analyses of U.S. Bureau of Mines samples 66 

3. U.S. Bureau of Mines analyses of Bureau of Mines samples . . . 68 

4. Private and U.S. Bureau of Mines analyses of Bureau of Mines 

samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 
MINERAL RESOURCES OF THE MOUNT ZIRKEL WILDERNESS 

AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

MINE APPRAISAL 

By LOWELL L. PATTEN, U.S. BUREAU OF MINES 

INTRODUCTION 

In 1971, the U.S. Bureau of Mines began a mineral survey of the 

Mount Zirkel Wilderness in the Routt National Forest in north-central 

Colorado. In 1972, at the request of the U.S. Forest Service, the survey 

was expanded to include approximately 170,000 acres (nearly 

700 km2; 68,900 ha (hectares)) of lands adjacent to the 295 km2 

(114 mi2) of the wilderness area. 

The study area, lying along the Continental Divide in Jackson and 

Routt Counties, has been proposed for inclusion in the National 

Wilderness System (figs. 20, 21). Altitudes generally range from 2,500 

to 3,500 m (8,000 to 11,000 ft) in rough to rolling mountainous terrain. 

The principal nearby settlements are Walden (population approximately 1,000), east of the wilderness, and Steamboat Springs (population 

approximately 5,000), immediately southwest of the study area. 

PRESENT INVESTIGATION 

The U.S. Bureau of Mines investigation of the Mount Zirkel study 

area included a study of relevant literature; a review of Bureau of Land 

Management land-status plats; a search for mining-claim location notices recorded in Jackson, Larimer, and Routt Counties; an examination 

61 
62 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 20.-View east across Mica Basin to Big Agnes Mountain from west boundary 

of Mount Zirkel Wilderness. Some mica prospects occur on south ridge of Big Agnes 

Mountain above "Mount Zirkel Wilderness" sign. 

of mining claims and prospect workings; and a general reconnaissance 

of the area. The work was performed by L. L. Patten, assisted by H. 

C. Meeves, R. A. Beach, R. J. Hurt, 0. D. Staman, and D. D. Keill. 

Courthouse records show that many mining claims have been 

located since the 1870's within and near the study area. The records 

include those of Larimer County, out of which Jackson County was 

formed in 1909. Claims that could be identified are shown on the illustrations. Many claims are not shown because of uncertainties in 

descriptions, and those that are plotted may not be accurately shown 

because of difficulties in interpreting location notices. A determined 

effort was made to visit and examine all mining claims, prospect workings, and mineralized areas. 

During the investigation, 82 samples were taken for analysis by 

standard methods, from prospect workings and from other localities 

where there was an indication of mineralization. Most were chip 

samples, but many grab samples were taken from dumps at regular 

intervals on lines or rough grids. In addition, alluvium in streams was 

sampled by panning. Some of the panned samples contained particles 
MINE APPRAISAL 63 

of gold that were readily identifiable under a 10-power (XlO) hand lens. 

Because of the sparsity of gold and the relatively small quantity of 

available placer material, appraisal consisted of a visual estimate of 

the value of the gold and a search for other minerals of value. 

Spectrographic analyses of samples were made by semiquantitative 

methods in the U.S. Bureau of Mines and U.S. Geological Survey 

laboratories (tables 2, 3), and some samples were analyzed by a commercial laboratory (table 4). Samples showing significant quantities 

of potentially valuable elements were analyzed by chemical methods. 

HISTORY AND PRODUCTION 

Mining activity began in the Hahns Peak mining district in 1865 

with Joseph Hahn's discovery of placer gold (George and Crawford, 

1909). The district is approximately 4.8 km (3 mi) west of the study 

area and about 4 km (2.5 mi) north of Hahns Peak Village. According 

to USBM (U.S. Bureau of Mines) records, significant quantities of 

placer gold and silver were produced from the district in 1907, 1909, 

1916, 1917, and 1918. The Hahns Peak activity expanded into the area 

west of Farwell Mountain, where numerous claims were staked; a little production was probably made from prospects about 3.2 km (2 mi) 

northwest of the mountain. 

The Lower Slavonia mining district, at the confluence of Gold and 

Gilpin Creeks, was the scene of considerable prospecting and claim 

staking beginning about 1905. The district, outside the wilderness but 

within the adjacent area, is in the southwest corner ofT. 10 N., R. 83 

W. The mineral activity evidently was triggered by discovery of an 

occurrence of lead-zinc-silver with a little copper. There is no record 

of production from the district. 

About 9.7 km (6 mi) up Gold Creek from the Lower Slavonia district, 

in the west canyon wall, are the remains of workings known locally 

as the Upper Slavonia mine. The workings are in the heart of the 

wilderness in the southwest corner ofT. 10 N., R. 82 W. It is reported 

that the property dates from about 1910. No records of production 

were found, but dumps indicate that the workings were significant, 

and some production is inferred. 

In Mica Basin, about 4.8 km (3 mi) northeast of the Lower Slavonia 

mining district, pegmatites have been prospected for mica for many 

years. The prospects are within the wilderness area. Although no 

records were found, it appears that trial shipments were made from 

these deposits. The records show considerable claim-staking activity 

in this area in the 1940's. To facilitate mica prospecting, a road that 

terminates at the wilderness boundary west of Mica Lake was built 

in recent years (area of prospects, fig. 20). 
64 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

107°00' 1 06°30' 41°~-----------,------~-."--~--~~----~~~--------~--,--.,-~~~-. 

DO' r--~-"""'-

T. 

12 

N. 

T. 

11 

N. 

T. 

10 

N. 

T. 

9 

N. 

T. 

8 

N. 

T. ::--::;~-----~7 

4D" 

30' 

R. 85 w. 

10 KILOMETERS 

5 MILES 

R. 84 W. R. 83 W. R. 82 w. R. 81 W. 

EXPLANATION 

Mine or prospect 

© Abandoned coal mine 

® Oil field 

Locality examined 

Approximate wilderness boundary 

muw&M® Adjacent area boundary 

N. 

T. 

6 

N. 
MINE APPRAISAL 65 

In the late 1950's, bulldozer trails and cuts were made in the vicinity of Agua Fria Lake in the southeastern part of the study area. The 

principal workings are outside the adjacent area in the southwest corner ofT. 8 N., R. 82 W. The prospecting was probably a search for 

radioactive minerals, but no records of production from the area have 

been found. 

Near the eastern boundary of the wilderness, between Raspberry 

and Roaring Fork Creeks, fluorite-bearing veins have been prospected 

since 1920. The Crystal mine, east of the study area in north-central 

T. 8 N., R. 82 W., produced 800 tons3 (728 t (metric tons)) of 

fluorspar ore between 1945 and 1949. The mine was reopened in 1970 

by the Ozark Mahoning Corp. and produced at the rate of approximately 200 tons (180 t) per day. Mining operations were discontinued 

in 1973. 

Other fluorite-bearing veins have been prospected west and northwest of the Crystal mine by two other companies: Beta Mining Co., 

of Canon City, Colo., and Geo Surveys, Inc., of Colorado Springs, Colo. 

Work by the Beta Co. included an arlit, a shaft, and pilot mining from 

opencuts. Geo Surveys, through a trenching and drilling program, 

outlined a system of fluorite veins near the wilderness boundary. Geo 

Surveys, under an agreement with Minerals Engineering Co., of 

Denver, Colo., planned several thousand feet of drifting, beginning 

in 1974.4 

3

Data from older sources are quoted in their original systems of measurement first. 4

Use of trade and company names in this report is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. 

FIGURE 21 (facing page).-Map showing localities examined by U.S. Bureau of Mines 

in the Mount Zirkel Wilderness and adjacent area, Colorado. Letters identify the following areas: A, Agua Fria Lake area (fig. 22); B, Beaver Creek-Norris Creek area (fig. 

23); C, Raspberry Creek-Roaring Fork area (figs. 24, 25, 26); D, Roaring Fork-Lone 

Pine Creek (includes Pedad-DLB claims in fig. 27); E, Bear Creek prospect (figs. 19, 

21); F, Red Elephant Mountain prospect (fig. 28); G, Windy Gulch claims (fig. 29); 

H, Buffalo Ridge (figs. 19, 21); I, Mica Basin (figs. 30, 31, 32); J, Lower Slavonia district 

(figs. 33, 34); K, Upper Slavonia mine (figs. 14, 35, 36); L, Upper Gilpin Creek (fig. 

35); M, North Fork Elk River; N, Diamond Park area (fig. 37); 0, King Solomon Creek 

area (fig. 38); P, Beaver Creek-King Solomon Creek area (figs. 38, 39); Q, Zinc Mountain claim group (fig. 40); R, Beaver Creek area; S, Grouse Mountain area (fig. 41); 

T, Willow Creek Canyon area (figs. 42, 43); U, Big Creek area (fig. 44); V, Elk Park 

area (fig. 45); W, Soda Creek area (fig. 46); X, Buffalo Pass area (figs. 47, 48, 49). 
TABLE 2.-U.S. Geological Survey analyses of samples from the Mount Zirkel Wilderness and adjacent area ~ 

[Samples analyzed by U.S. Geological Survey, Denver, Colo., by semiquantitative spectrographic analysis; reported to the nearest number in the series 1, 0.7, 0.5, ~ 

0.3, 0.2, 0.15, 0.1, .... , which represent the approximate midpoint of group data on a geometric scale. Arsenic, gold, and tungsten, normally detectable by this process, 

looked for but not found;>. more than amount shown; >>.much more than amount shown; Tr., trace; leader H. looked for but not found] ~ 

0 

Semiquantitative spectrographic analyses c:: 

z 

(ppm) ~ Sample N 

Ag B Ba Be Bi Cd Co Cr Cu La Mn Mo Nb Ni Pb Sb -~ 

~ 

11 70 so 100 »1 '000 )5,000 15 »2,000 20 1,500 300 t_:l:j - 70 300 20 - 5 t-t 

5 - 300 3 - - - 150 70 - so 70 30 5 70 - < 8 - 1,500 2 - - 5 150 70 so 500 - 10 7 70 - -t-t 

10 - 20 700 3 - 10 100 so so 500 - - 20 20 - t:J 

11 - - 200 2 - 15 150 70 70 700 - - 20 10 - t_:l:j 

~ 

z 

12 - 300 1 - - 20 so 70 so 1,500 - - 15 15 - t_:l:j 

en 213 - - 150 7 - - - 30 - 300 15 20 5 150 - en 

17 30 - 150 3 - - 5 70 2,000 50 >5,000 30 - 7 300 - > z 18 30 - 300 1.5 - - - so 700 70 )5,000 - - Tr 1,500 - t:J 319 200 - 150 3 20 70 5 20 1,500 - )5,000 150 - 5 20,000 200 z 

0 

42o 300 150 3 20 300 - 3,000 - )5,000 200 - 5 20,000 300 ~ - - ~ 

21 5 - 300 3 - - 100 1,500 100 700 - 20 7 300 - ::I: 

t_:l:j 22 10 - 1,500 3 - so - 70 700 70 2,000 - - 15 7,000 - ~ 

23 15 - 1,500 3 - - - 70 3,000 70 1,500 - - 5 2,000 - z 

25 10 - 150 3 - so - - 700 - >5,000 - - 5 70 - '"1:::1 

> 

~ 

26 10 Tr 300 1.5 - 500 30 70 3,000 - 5,000 - - 20 70 ~ 

27 15 Tr - 1.5 - 150 5 - 1,000 - >5,000 - - 7 70 - ~ 

> 28 - - 1,500 2 - - - 100 700 - 1,000 - - 5 70 - z 

29 - - 300 1 - - - 70 200 70 150 - - 5 - - 0 

30 1,500 1.5 100 70 so 70 - - 15 10 t_:l:j - - - - -

31 - - 300 1 - - 20 so 20 - 1,500 - - 10 10 
Semiquantitative spectrographic analyses 

Sample (ppm) (percent) Remarks 

Sc Sn Sr v y Zn Zr Fe Mg Ca Ti 

11 ))100 300 5,000 70 >2,000 - >1,000 10 0.5 0.3 0.2 2.0-foot chip. 

5 - - - - 10 - 300 0.1 .05 .3 • 05 1.0-foot chip • 

8 5 300 70 30 - 150 2 • 7 2 .15 0.4-foot chip. 

10 15 - - 70 30 700 150 3 1.5 2 .15 1.5-foot chip. 

11 30 - - 150 70 - 70 7 1.5 3 .3 2.1-foot chip. 

12 30 100 300 30 - 70 10 3 7 .5 1.0-foot chip. 213 10 - Tr 20 70 - 20 1 .2 .5 .07 Do. ~ 17 15 - - 20 70 7,000 300 10 5 .3 • 2 4.0-foot chip • z 18 15 - - 20 70 3,000 300 10 7 .5 • 3 2.0-foot chip • M 319 7 10 10 30 >10,000 100 10 7 3 .2 3.5-foot chip. > '"0 

420 10 20 20 30 ))10,000 150 10 7 3 .15 1.5-foot chip. '"0 

~ 

21 5 10 - - 100 )10,000 300 5 3 .3 .1 Do. > 

22 5 30 70 """" )10,000 200 2 3 3 • 15 3.0-foot chip • r:n 

> 23 - - 20 70 )10,000 200 2 3 .5 • 07 0.5-foot chip • t"" 

25 15 70 - 50 150 )10,000 70 10 7 3 • 2 3.0-foot chip • 

26 5 30 - 15 30 »10,000 70 10 1.5 1 • 1 2.5-foot chip • 

27 5 30 10 »10,000 30 10 7 10 .03 1.0-foot chip. 

28 10 - 200 20 10 700 50 10 1.5 3 .s 3.6-foot chip. 

29 5 100 20 so 150 2 .s 3 .15 3.0-foot chip. 

30 10 - 100 10 - - 200 5 .1 .3 • 15 0.5-foot chip • 

31 30 - 300 700 50 - 100 10 3 3 1 1. 0-foot chip. 

1sample 1 contained 300 ppm antimony. 3sample 19 contained 200 ppm antimony and 20 ppm bismuth. 

2sample 13 contained 0.001 percent uranium. 4sample 20 contained 300 ppm antimony and 20 ppm bismuth. ~ 

-l 
TABLE 3.-U.S. Bureau of Mines analyses of samples from the Mount Zirkel Wilderness and adjacent area 

[Samples analyzed by semiquantitative spectrographic methods and standard fire assay at the U.S. Bureau of Mines laboratory, Reno, Nev. Spectrographic analyses were made using a 3.4-meter 

Wadsworth spectrograph with a 30-inch plate holder. A margin of error of plus 100 percent and minus 50 percent is assumed. The following elements, normally detectable by this process, 

looked for but not found: As, B, Cd, Ga, Hf, In, La, Li, Nb, P, Pt, Re, Sb, Sr, Th, Th, Tl, and W. Selected samples were rerun by chemical methods. >. more than amount shown; <, less than 

amount shown; leader H. looked for but not found; blank, not looked for; 'fr., trace; M, major constituent; *, results of rerun by chemical methods. Silicon was a major constituent of all samples] 

Sample 

4 

16 

27 

14 

324 

432 

34 

36 

537 

638 

39 

40 

7 41 

742 

43 

44 

945 

46 

47 

1048 

7 49 

7so 

51 

Fire 

assay 

oz/ton 

Ag 

Tr 

Tr 

0.1 

.1 

Tr 

.1 

5.1 

Tr 

.3 

Tr 

Tr 

Tr 

• 2 

Ba 

(0.1 

.1 

.1 

.1 

.1 

< .1 

(.1 

Be 

(0.001 

(.001 

(.001 

(.001 

(.001 

(.001 

(.001 

(.001 

(.001 

(.001 

(.001 

Ca 

0.4 

.1 

.1 

M 

M 

M 

.3 

.5 

M 

.s 

.06 

2 

M 

M 

1 

.3 

.3 

.3 

.5 

.2 

.3 

.4 

.2 

.1 

Cr 

0.003 

.01 

.007 

.01 

.01 

.01 

.01 

.01 

.01 

(.003 

(.003 

.003 

.003 

.003 

.006 

.006 

.003 

.006 

.01 

.003 

(.003 

(.003 

(.003 

(.003 

(.003 

Cu 

(0.002 

.004 

.003 

.004 

.004 

.03 

.008 

.06 

.08 

.008 

*.27 

*.13 

.004 

*.11 

.03 

.04 

(.002 

*.28 

*.47 

.03 

*.23 

*.89 

.03 

.os 

.004 

Semi quantitative spectrographic analyses 

(percent) 

Fe Mg Mn Mo Ni 

(1.0 0.4 0.01 

M 

4 

6 

.4 

.4 

.4 

.os 0.002 0.002 

.05 .002 .002 

.02 (.002 

.2 .03 

.2 

2 

.03 

.05 

.2 

2 .2 

2 .2 

.05 .02 

.002 .002 

.2 (.002 (.002 

2 

3 

4 

.8 

.8 

.8 

.4 

.8 

.6 

.05 

1.5 

.2 

.1 

.2 

.2 

.2 

.1 

.2 

.1 

.05 

.2 

.05 

.01 

.1 

.1 

.02 

(.002 (.002 

(.002 (.002 

(.002 

(.002 

(.002 

.002 

.03 

(.002 

.002 

• 04 

(.002 

(.002 

(.002 

Pb 

(0.01 

.02 

.02 

.01 

.06 

.01 

.02 

7.05 

.02 

.02 

.01 

.01 

• 04 

• 01 

.01 

.01 

.01 

.04 

• 01 

.01 

.04 

Sc 

0.001 

(.005 

(.005 

(.005 

(.005 

Ti 

o.os 

.2 

.2 

.05 

.05 

.02 

.1 

.2 

.2 

.4 

.001 

.4 

• 4 

.4 

.2 

.2 

.1 

.2 

.02 

• 4 

.2 

.006 

.2 

.1 

.os 

y 

0.001 

(.001 

(.002 

(.002 

(.002 

(.002 

(.002 

(.002 

(.002 

(.002 

.002 

(.002 

(.002 

(.002 

(.002 

.001 

Zr 

(0.01 

• 007 

.03 

(.007 

(.007 

(.007 

• 01 

• 03 

• 03 

(.01 

(.01 

.01 

.01 

.01 

.01 

<.007 

(.007 

.01 

.02 

.01 

.01 

.01 

(.01 

Remarks 

1.5-foot chip. 

3.0-foot grab • 

Do. 

2.5-foot chip. 

3.0-foot chip. 

1.2-foot chip. 

5.0-foot chip • 

4.5-foot chip • 

1-foot chip • 

Dump grab. 

Do. 

1.8-foot chip. 

1.5-foot chip • 

2.2-foot chip. 

1.2-foot chip. 

0.2-foot chip • 

0.8-foot chip. 

Dump grab • 

Ore pile grab. 

Dump grab • 

Do. 

Ore pile grab • 

Dump grab • 

Do. 

Do. 

~ 

00 

a= 

0 

~ 

z 

1-:3 

N 

~ 

~ 

~ 

tr:l 

t-"4 

~ ~ 

t-"4 

t:l 

tr:l 

~ 

z 

tr:l 

CJJ 

r.n 

> z 

t:l 

z 

0 

~ ::I: 

tr:l 

~ 

z 

'"C 

> 

~ 

~ 

~ 

> z 

0 

tr:l 
52 

53 

54 

55 

56 

957 

7s8 

59 11 6o 

61 

1262 

63 

64 

65 

66 

67 

70 

71 

72 

1373 

74 

147 5 

76 

77 

78 

79 

80 

81 

82 

.1 

.1 

.1 

.2 

.3 

Tr 

• 2 

.2 

Tr 

.1 

.1 

.1 

.1 

<.1 

<.001 

.001 

<.1 

.1 

.1 <.003 .004 

.2 <.003 .004 1 

<.003 .004 >7 

.03 .01 .004 1 

<.003 .004 .4 

.003 *.34 

.1 <.003 *1.02 

.1 <.003 .003 

.03 .008 

.1 .01 .28 

M <.003 

1 <.003 

<.003 

.3 <.003 

.01 

.1 .01 

M .003 

.1 <.003 

.4 .01 

.4 .007 

>4 .02 

.1 .01 

• 06 .003 

• 5 .003 

.004 

.008 

.006 

.004 

• 004 

.008 

.002 

.13 

.008 

*.28 

.02 

.02 

.002 

.003 

5 

4 

3 

~ 

2 

.1 .01 .008 >7 

• 4 <.003 .008 

1sample 6, 16.2 pet CaF 2 (chem. analysis). 2sample 7, 13.0 pet CaF 2 (chem. analysis). 3All samples assayed for gold, but sample 24 was 

only one to contain measurable quantity: 0.01 oz/ton. 4 samples 32 and 37 contained 0.05 percent Zn. 

1 

.1 

.1 

• 2 

.02 

.2 

.2 

• 3 

.1 

• 4 

.8 

1 

.8 

.8 

.8 

3 

4 

.4 

.8 

.05 

.1 

.02 

.1 

• 1 

.02 

.01 

.OS <.002 

.01 

.02 

.1 

.03 

.4 

.05 

.1 

.OS 

.05 

.OS 

.OS 

.1 

.2 

• 2 

.1 

.1 

.1 

.02 

.2 

.02 

.002 

.002 

.002 

<.002 

.007 

.002 

.002 

• 002 

.002 

.002 

.004 

5sample 37, 0.05 pet Bi. 6sample 38, 0.01 pet Sn. 7samples 41, 42, 48, 49, 50, 

.08 

.02 

.02 

.08 

.02 

.01 

• 02 

.08 

.01 

.01 

<.01 

.01 

.01 

<.01 

.04 

.04 

.01 

.01 

.02 

<.01 

.01 

and 58 contained 0.01 pet Bi. 8sample 45, less than 0.005 pet Bi. 

.003 

.001 

.001 

.001 

.001 

.003 

.2 .001 

.OS .001 

.6 .003 

.1 <.001 

.01 

• OS <.002 

• 006 

.02 

.2 

.OS 

.01 

.2 

.2 

.1 

.1 

.1 

• 1 

.OS 

• 2 

.8 

• 2 

.2 

.1 

.1 

.001 

.001 

<.001 

<.001 

.003 

• 2 <.001 

.02 

<.01 

<.01 

<.01 

<.01 

.01 

<.01 

<.01 

• 02 

.01 

<.01 

<.01 

<.01 

<.01 

<.01 

• 01 

<.01 

<.01 

• 007 

.01 

• 01 

.01 

<.01 

Do. 

Do. 

Do • 

Do • 

Do. 

1.5-foot chip • 

0.5-foot chip • 

Do • 

Dump grab • 

Do • 

3.0-foot chip • 

Dump grab. 

Grab. 

Dump grab. 

Do • 

6.0-foot chip • 

3.0-foot chip • 

2.0-foot chip. 

Dump grab • 

1.0-foot chip • 

5.0-foot chip • 

Dump grab • 

Do • 

35.0-foot chip. 

5.0-foot chip. 

3.0-foot chip. 

6. 0-foot chip. 

<.01 Dump grab • 

<.01 1.5-foot chip • 

9samples 45, 57, 0.02 pet Sn. 10sample 48, 0.005 pet Sn. 11 sample 60, 0.01 pet v. 12 sample 62, 0.1 pet Zn. 13sample 73, 0.003 pet Co and 0.01 pet v. 14sample 75, 0.003 pet Co. 

~ 

z 

tz:j 

> "C 

"C 

~ ~ 

00. 

> t"" 

0) 

(.0 
70 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 4.-Analyses of samples from the Mount Zirkel Wilderness and adjacent area 

[Gold and silver determinations by atomic absorption (AA) and fire assay, as shown. Atomic absorption determinations by Skyline Labs, Inc., Wheat Ridge, Colo. Fire assays by the U.S. Bureau of Mines laboratory, Reno, Nev. 

All other determinations by chemical methods by Skyline Labs, Inc. <,less than amount shown; leaders(-), not 

analyzed; N.F., none found] 

------------------------------------------------------

AA Fire assay Chemical ana lysis 

Sample (ppm) (oz/ton) (percent) 

----

Au Ag Au Ag Cu Pb Zn u Th 

0.22 0.68 

5 .034 

8 (0.02 <U. 2 0.003 

9 2.0 .!)2 (0.1)1 (0.01 

1U (.02 (.2 

11 <.02 <.2 

12 <.02 (.2 

13 .001 

17 .03 20.0 • l 5 .04 .32 

18 .04 11.0 .04 • t)4 .26 

19 .25 87.0 .11 1.8 2.2 

20 .68 170.0 .26 4.2 6.8 

21 (.02 2.4 .17 .02 .48 

22 (.02 5.6 .07 .65 .78 

23 .22 25.1) .32 • 38 .75 

25 .17 6.0 JJJ .01 .95 

26 .OS 6.8 • 21 (.01 16.0 

27 <.02 7.0 .1)5 (.01 2.8 

28 (. 02 (.2 .04 .01 .05 

29 (.()2 (.2 .03 

30 (.02 <.2 

31 <.02 (.2 

33 N.F. N.F. N.F. 135 N.F. N.F. N.F'. 

68 N.F. N.F. N.F. 

69 N.F. N.F. N.F. 

78 N.F. 0.1 (.01 

79 N.F. .1 <.01 

80 N.F. .2 (.01 

1samp le 35 contained OJJ9 percent Cu. 

Beginning in 1963, an extensive drilling and geochemical exploration program was carried on for several years by William A. Bowes 

and others in the Hahns Peak, Farwell Mountain, Zinc Mountain, and 

Big Creek areas. The Hahns Peak locality is west of the adjacent area 

boundary in the north-central part ofT. 10 N., R. 85 W. The Farwell 

Mountain locality is within the adjacent area in the east-central part 

ofT. 10 N., R. 85 W. The Zinc Mountain area borders the adjacent area 

in the south-central part ofT. 10 N., R. 84 W. Exploration work in the 

Big Creek area was mainly outside the adjacent area. 

Several mines at other locations in the immediate vicinity of the 

study area have produced minor amounts of ore. These include the 

Greenville and Wolverine mines. 
MINE APPRAISAL 71 

The Greenville mine, near the town of Clark in the southeast corner 

of T. 9 N., R. 85 W., produced less than 2,000 tons (1,800 t) of ore 

between 1942 and 1958. The ore contained more than 1 oz silver per 

ton (34 ppm), a little more than 10 percent zinc, and small amounts 

of lead and copper. The sulfide mineralization occurred in gneiss and 

schist. 

The Wolverine mine, about 4.8 km (3 mi) northeast of the adjacent 

area boundary in the northeast corner ofT. 11 N., R. 82 W., produced 

less than 1,000 tons (900 t) of ore between 1902 and 1917. The ore 

contained more than 5 percent copper, a little more than 21/2 oz silver 

per ton (86 ppm), and less than 0.1 oz gold per ton (3.4 ppm). Mineralized rock consists of sulfides and oxides of copper in gneiss and in 

pegmatites. 

MINING CLAIMS, PROSPECTS, ·AND 

MINERAL DEPOSITS 

Only one patented mining claim is within the adjacent area. It is 

near the western boundary of the area in the extreme northeast corner 

ofT. 10 N., R. 85 W. (figs. 21, 38). Numerous unpatented claims have 

been located within and near the adjacent area; the claims that could 

be identified are shown on the illustrations. 

Eighty-two samples were taken for analysis from 23 localities within 

and near the adjacent area. For easy reference, all localities discussed in the text of the report have been lettered, and their locations are shown on figure 21. Values generally are discussed in the 

text of the report only for those samples with significant ore mineral 

content. 

AGUA FRIA LAKE AREA (LOCALITY A) 

The Agua Fria Lake area (locality A) is southwest of Agua Fria Lake 

near the southeastern boundary of the wilderness on the upper 

drainage of Beaver Creek. The area examined is in the southwest corner ofT. 8 N., R. 82 W. (fig. 21). Hail (1965) discussed the geology 

of this area. Between 1956 and 1970, bulldozer cuts were made in exploring pegmatites in Precambrian quartz monzonite. The workings, 

on a group of 60 claims, are partly within the Mount Zirkel Wilderness 

and adjacent area and partly outside (fig. 22). The principal workings 

are about 0.5 km (1/3 mi) south of the Agua Fria Lake dam where 

several sidehill cuts were made by bulldozing and blasting. The largest 

cut is about 30m (100ft) long and 6 m (20ft) deep; it bearsS. 15° W. 

Material exposed consists mainly of quartz, feldspar, and other 
72 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

'I 

'I 

I 

0.5 

EXPLANATION 

D Lode claim 

1 MILE 

X Site of prospect workings 

.1 Sample locality 

2 KILOMETERS 

...1.. ....1... ..J.. Approximate wilderness boundary 

Adjacent area boundary 

FIGURE 22.-Mining claims and sample locality in the vicinity of Agua Fria Lake 

(loc. A). 

normal pegmatite minerals, together with a very small amount of large 

biotite crystals (as much as 8 in. in length) and one pod containing 

biotite and dark-colored, highly radioactive, complex minerals. 

Analyses of sample 1 from the 60-cm (2-ft) pod showed 0.22 percent 

uranium and 0.68 percent thorium (tables 2, 4). Significant amounts 

of lanthanum, niobium, scandium, strontium, and yttrium were 

detected by spectrographic analysis. (Also see table 9.) 
MINE APPRAISAL 73 

BEAVER CREEK-NORRIS CREEK AREA (LOCALITY B) 

Claims and prospects in the Beaver Creek-Norris Creek area (locality B) are in the south-central part ofT. 8 N., R. 82 W. (fig. 21), and 

are shown on figure 23. In west-central section 27, several bulldozer 

EXPLANATION D Lodeclaim 

Site of prospect workings 

>-1- Caved adit 

.3 Sample locality 

Trail 

Primitive road 

0.5 

I 

\ 

I 

/ / 

/ 

( 

I 

\ 

/ 

\ 

I 

1~--i!!itlil / 

2 KILOMETERS 

1 MILE 

N 

1 

FIGURE 23.-Mining claims and prospects in the Beaver Creek-Norris Creek area 

(loc. B). 
74 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

pits have been dug in steeply dipping Morrison Formation. Because 

the claims were located in the 1950's (a time of widespread uranium 

prospecting), and because the background reading is somewhat above 

normal, it is assumed that uranium was the object of the activity. The 

northernmost of three pits gave a reading of 0.05 milliroentgens,per 

hour. A 45-cm (1.5-ft) chip sample (sample 2) in light-gray shale showed 

no significant radiometric reading, and the spectrographic analyses 

showed no anomalous metals (table 3). 

About 2.4 km (1.5 mi) north of the three pits, the Grizzly Helena 

Trail crosses Norris Creek. West of the trail on the south bank of the 

creek, an adit (now caved) was driven along a north-south fault zone 

in altered igneous rock containing quartz and pyrite. Remnants of the 

dump north of the creek indicate that the underground workings may 

have been extensive. Two samples (3, 4) of material from the fault zone 

contained no mineral values of consequence (table 3). 

RASPBERRY CREEK-ROARING FORK AREA (LOCALITY C) 

The Raspberry Creek-Roaring Fork area (locality C) is just east of 

the wilderness and adjacent area boundaries in the north-central part 

ofT. 8 N., R. 82 W. (fig. 21). Claims and workings within the area are 

shown on figure 24; most of them are east of the study area. Quartzfluorite veins are exposed, mostly along north-trending high-angle 

faults in quartz monzonite; the veins contain traces of uranium. Beginning in the 1920's, numerous excavations were made in this area during fluorspar exploration (Hail, 1965). One of the old workings, known 

as the Crystal mine, was reopened in 1945 and produced about 800 

tons (726 t) of fluorspar ore before it was shut down in 1949. The mine 

was again reopened in 1970 by the Ozark Mahoning Corp. and produced at the rate of approximately 200 tons (180 t) per day from 

underground and opencut workings. The ore was shipped to the company's mill at Northgate, Colo. In 1973, production was discontinued 

because of excessive dilution resulting from weak vein walls. The veins, 

as much as 4.6 m (15ft) and more in width, contain bodies of nearly 

pure fluorite, but an average grade of only about 50 percent calcium 

fluoride was produced in mining. 

About 1.6 km (1 mi) northwest of the Crystal mine, the Beta Mining Co., of Caiion City, Colo., has explored fluorite-bearing veins similar 

to those of the Crystal mine on a group of approximately 30 claims. 

Workings include a 240-m-long (800-ft-long) open cut, a 70-m (225-ft) 

adit, and a shallow shaft (figs. 25, 26). 

In the fall of 1971, Geo Surveys, Inc., of Colorado Springs, Colo., 

located 203 claims of the Spar group adjacent to the Ozark Mahoning 

and Beta properties, and mostly west and north of them. A trenching 
MINE APPRAISAL 

N 

1 

2 KILOMETERS 

0.5 1 MILE 

EXPLANATION 

D Mining claim Primitive road 

X Site of workings Maintained road 

>- Ad it 

F Fluorspar outcrop 

...!... ..!.. .J.. Approximate wilderness 

boundary 

Adjacent area boundary 

Trail 

FIGURE 24.-Fluorspar mines, prospects, and occurrences in the 

Raspberry Creek-Roaring Fork-Lone Pine Creek area (loc. C). 

75 
76 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 25.-Beta Mining Co. opencut. 

FIGURE 26.-Beta Mining Co. headframe. 
MINE APPRAISAL 77 

and drilling program on the property in 1972 and 1973 disclosed 

significant fluorite-bearing veins, mainly on the ridge east of Red Canyon near the wilderness boundary and north of the Beta property. 

Plans for future development of the property include an adit to be 

driven by Minerals Engineering Co., of Denver, Colo. 

Other minor fluorite occurrences were seen in Red Canyon (as 

marked "F" on fig. 24). These were veinlets containing up to one-half 

inch of fluorite. 

ROARING FORK-LONE PINE CREEK (LOCALITY D) 

The Roaring Fork-Lone Pine Creek area (locality D) straddles the 

wilderness boundary in south-central T. 9 N., R. 82 W. (fig. 21). Workings are outside the wilderness, but some claims extend into it 

(fig. 24). Fluorite-bearing veins, similar to those in locality C, were 

prospected in the 1920's. In the 1950's, the veins were prospected 

for uranium (Malan, 1957) by bulldozer trenching. Thirty-five claims, 

the Pedad and DLB groups, were located in the area. The Pedad 

workings are shown on figure 27. A Geiger counter traverse of the 

area revealed a substantial count in an 18-m (60-ft) trench at the north 

end of a stripped area. A narrow fault zone, crossing the east end of 

the trench, contains small amounts of purple fluorite. A 30-cm (1-ft) 

chip sample (5) from the north wall of the trench, where the highest 

Geiger counter reading was obtained, contained 0.03 percent uranium 

(table 4). A fault zone, presumably the same, has been prospected in 

the southernmost cut. No significant radioactivity was detected in 

the cut, but samples contained fluorite. Two chip samples (6, 7) 

across the fault showed 75 em (2.5 ft) of 16.2-percent CaF2 and 90 em 

(3 ft) of 13.0-percent CaF 2 (table 3). The owners plan further 

exploration. 

BEAR CREEK PROSPECT (LOCALITY E) 

The Bear Creek prospect (locality E) is within the adjacent area in 

the north-central part ofT. 9 N., R. 82 W. (fig. 21). A 15-m (50-ft) adit 

is in the north wall of the canyon of Bear Creek, a few hundred feet 

from the canyon mouth and about 30 m (100ft) above the stream. 

The adit, bearing N. 60 o E., was driven in steeply dipping layered 

gneiss along an iron-stained layer containing pyrite and traces of copper minerals. A chip sample (8), taken across an altered layer at the 

face, contained only 70 ppm copper (table 2). 
78 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ Prospect pit 

Sample locality 

50 100 150 METERS 

200 400 FEET 

EXPLANATION 

Primitive road 

II 

II 

II 

\Ll II -.:. \\ 0 \I 0 t 

~ 

~ 

' 

~ 

t 

II 

II 

1/ 

II 

II " II 

II 

II 

I! 

1/ 

1/ 

I/ 

I! 

II 

II 

II 

II 

II " 

1/ 

It 

II 

II 

..J....L..J.. Approximate wilderness boundary 

FIGURE 27.-Prospect workings and sample localities on the Pedad-DLB claims 

(part of loc. D). Contours are in feet; contour interval 100 ft (30.5 m). 
MINE APPRAISAL 79 

RED ELEPHANT MOUNTAIN PROSPECT (LOCALITY F) 

The Red Elephant Mountain prospect (locality F) is within the study 

area just east of the wilderness boundary in the southwest corner of 

T. 11 N., R. 82 W. (fig. 21), near the canyon of Forester Creek. An 

adit was driven 18m (60ft) S. 75 oW. in an iron-stained zone in steeply dipping layered gneiss (fig. 28). A crosscut extends 7.6 m (25 ft) 

N. 5o W. from the end of the adit. A random sample (9) of loose surface material, rich in pyrite, was analyzed spectrographically. It contained 2 ppm silver and 0.02 percent copper (table 4). Three chip 

samples (10-12) were taken across the iron-stained zone above the portal of the adit; assay values were of no significance (tables 2, 4). A 

search for mineral-claim locations showed no claims corresponding to 

the Red Elephant Mountain site. 

WINDY GULCH CLAIMS (LOCALITY G) 

The Windy Gulch group of 19 claims (locality G) is within the adj acent area just north of the wilderness boundary in the east-central 

part of unsurveyed T. 11 N., R. 83 W. (fig. 21). The claims were located 

in 1957 northeast of Davis Peak (fig. 29). Bedrock in the area consists 

of gneiss containing numerous pegmatite dikes. A shallow pit is near 

a small lake in the eastern part of the group. A higher than background 

FIGURE 28.-Red Elephant Mountain prospect (F). Height of face about 3-4m (10-15 ft). 
80 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

/'"\ 

/ I 

// I / I / I 

I 

I 

I 

I 

\ 

\ 

\ 

\ 

\ 

' ,_ 

/ 

/ / / / 

------- -

0.5 1 MILE 

EXPLANATION 

D Mining claims 

X Prospect pit 

.13 Sample locality 

Trail 

.J....J.....J.. Approximate wilderness boundary 

Adjacent area boundary 

/ 

/ 

2 KILOMETERS 

N 

1 

FIGURE 29.-Mining claims and prospect pit near Davis Peak. Part of loc. G. 
MINE APPRAISAL 81 

Geiger counter reading was obtained at the south wall of the pit, but 

uranium content of a 30-cm (1-ft) chip sample (13) was negligible (table 

2). 

BUFFALO RIDGE (LOCALITY H) 

Buffalo Ridge (locality H) is about 4.8 km (3 mi) north of Davis Peak 

in the northern part of the area that was investigated. Several mining 

claims were located at the site, which is east of the study area in the 

north-central part of unsurveyed T. 11 N., R. 83 W. (fig. 21). About 0.8 

km (0.5 mi) east of the ridge, a rusty quartz vein parallels the layering 

in gneiss. The strike of the steeply dipping vein is N. 70° E. A 40-cm 

(1.2-ft) chip sample (14), taken across the vein in a shallow prospect 

pit, contained 0.03 percent copper and 0.01 percent lead (table 3). 

MICA BASIN (LOCALITY I) 

Mica Basin (locality 1), a glaciated bowl bounded on the northeast 

by Big Agnes Mountain, has been the site of many recorded mining 

claims dated mostly in 194 7 and 1948. Mica Basin is within the 

wilderness in the central part of unsurveyed T. 10 N., R. 83 W. (fig. 

21 ). Bedrock in the area is a complex mass of schist and gneiss containing many pegmatites. At two shallow prospect workings, the 

pegmatites contain large mica crystals. 

The upper prospect is on the steep southwest slope of Big Agnes 

Mountain at an elevation of 11,600 ft (3,540 m). Here, a 3.7-m-thick 

(12-ft-thick) horizontal tabular pegmatite body has been prospected 

(figs. 30, 31) by a 3-m (10-ft) adit bearing N. 45 o E. The pegmatite is 

near the top of a ridge and crops out on both sides. The outcrops contain quartz, feldspar, and large muscovite crystals. The western outcrop contains crystals as wide as 30 em (12 in.); the eastern one has 

smaller crystals. 'fraces of copper minerals were found on the adit 

dump, but there has been no significant copper mineralization. 

Although some of the crystals are quite large, the mica is of scrap quality because of parting planes. 

The lower prospect is about 0.8 km (0.5 mi) southeast of Mica Lake 

(fig. 32). An irregularly shaped pegmatite, composed mostly of quartz 

and feldspar, contains crystals of muscovite and biotite at least 38 em 

(15 in.) across. The pegmatite has been prospected by a shallow 7.6-mwide (25-ft-wide) cut. The mica crystals contain parting planes that 

make the material scrap grade. 
82 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 30.-Big Agnes Mountain mica prospect. Part of loc. I. Adit (arrow) about 5 ft 

high. 

FIGURE 31.-Big Agnes Mountain mica prospect, showing mica crystals in pegmatite 

quartz. 
MINE APPRAISAL 83 

FIGURE 32.-Lower mica prospect, Mica Basin. 

LOWER SLAVONIA DISTRICT (LOCALITY J) 

The Lower Slavonia district (locality J) is on the west-central 

wilderness boundary at the junction of Gold and Gilpin Creeks in the 

southwest corner of unsurveyed T. 10 N., R. 83 W. (fig. 21). Several old 

buildings remain of a settlement known as Slavonia, probably built in 

the late 1800's during a prospecting "rush." Several prospect workings 

lie in the immediate vicinity, but most are outside the wilderness. 

Sulfide mineralization in the Lower Slavonia district appears to have 

resulted in replacement of limy layers in banded gneiss. The limy 

mineralized zones are thin and contorted and show little evidence of 

continuity. Therefore, although the Precambrian gneiss contains a 

number of such mineralized deposits, they all appear to be small and 

erratic. 

Three prospects were examined in the Lower Slavonia district (fig. 33). 

SITE OF SAMPLES 17-20 

An opencut above a caved adit is about 0.8 km (0.5 mi) west of the 

junction of Mica and Gilpin Creeks and a few hundred feet inside the 

wilderness boundary at an elevation of about 9,300 ft (2,840 m). 
84 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

N 

1 

0.5 

EXPLANATION 

>+- Caved adit 

• 21 Sample locality 

Trail 

• Cabin 

1 MILE 

..1.. .J.. ..1.. Approximate wilderness boundary 

Adjacent area boundary 

2 KILOMETERS 

FIGURE 33.-Prospect workings in the Lower Slavonia district (loc. J). 
MINE APPRAISAL 85 

Although the dump is scattered down the mountainside, it probably 

represents several hundred feet of drifting. The opencut is about 6 m 

(20 ft) deep (fig. 34) and exposes a steeply dipping iron-stained sulfidebearing zone in layered gneiss. The zone strikes N. 70° W. and contains visible galena, sphalerite, and pyrite. Chip samples were taken 

across 2.9 m (9.5 ft) of the mineralized zone with results shown here 

(sample 20 was a resample of the most mineralized part of sample 17): 

Width Au Ag Pb Zn Cu 

Sample 

Feet Meters (ppm) (percent) 

17 4.0 1.2 0.03 20 0.04 0.32 0.15 

18 2.0 .6 .04 11 .04 .26 .04 

19 3.5 1.1 .25 87 1.8 2.2 .11 

20 1.5 .5 .68 170 4.2 6.8 .26 

Spectrographic analyses are listed in table 2, chemical analyses in table 

4. The mineralized zone is exposed for about 50 ft. The zone pinches 

out in a rocky ridge to the northwest. Any southeastern extension 

of the zone below the arlit would be covered by debris and vegetation. 

SITE OF SAMPLES 21-23 

A caved arlit and a cavelike excavation are on the east bank of Gilpin 

Creek, about 0.5 km (1/3 mi) upstream from its junction with Gold 

Creek and about 150m (500ft) west of the wilderness boundary. The 

arlit, reportedly 45 m (150ft) long, has a dump that has been partly 

washed away by Gilpin Creek. These excavations penetrate a steeply 

dipping narrow sulfide zone in layered gneiss. The zone strikes S. 65 o 

E. and contains visible galena, sphalerite, and chalcopyrite. Analyses 

of three chip samples (21-23) taken across the zone are shown: 

Width 

Sample 

Feet Centimeters 

21 1.5 45 

22 3.0 90 

23 .5 15 

[Leaders (--), not looked for] 

Au Ag 

(ppm) 

2.4 

5.6 

0.22 25 

Pb 

0.02 

.65 

.38 

Zn 

(percent) 

0.48 

.78 

.75 

Cu 

0.17 

.07 

.32 
86 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 34.-0pencut north of Gilpin Creek, site of samples 17-20. 
MINE APPRAISAL 87 

Spectrographic analyses are listed in table 2, chemical analyses in 

table 4. 

The sulfide zone pinches out a short distance above the excavation, 

and any extension of the zone below is covered by debris. There is 

no indication of the zone in the exposed bedrock on the west bank of 

the creek. 

SITE OF SAMPLE 24 

A caved arlit that penetrates a fault zone bearing N. 5o E. in altered 

gneiss is on the west bank of Gilpin Creek about 215m (700ft) above 

its junction with Gold Creek. The nearby ruins of a building contain 

the remains of water-driven machinery. A 1.5-m (5-ft) chip sample (24) 

taken across the fault zone above the portal contained (table 3) 0.01 

oz gold per ton (0.3 ppm) and 0.1 oz silver per ton (3 ppm). 

UPPER SLAVONIA MINE (LOCALITY K) 

The Upper Slavonia mine (locality K) is in the central part of the 

wilderness just west of the Continental Divide in the southwest corner ofT. 10 N., R. 82 W. (fig. 21). The workings are shown on figure 35. 

The main arlit of the mine was driven into the west wall of the canyon of Gold Creek, about 9. 7 km (6 mi) above its confluence with Gilpin 

Creek. The arlit, now caved, is reported to have been 105m (350 ft) 

long, and the size of the dump appears to confirm this (fig. 36). At 

the minesite are the ruins of several cabins and the remains of a 

hydraulically powered compressor. The original wagon road to the 

property is now used as a pack trail. The area has been covered by 

several groups of mining claims since 1910, which is probably about 

the time that most of the work was done. There is no record of production. The arlit was driven into a steeply dipping west-striking ironstained zone in layered gneiss that crops out above the caved portal. 

The zone includes a layer of hornblende gneiss containing visible 

sphalerite. A chip sample (25) taken across the zone above the arlit 

contained 0.95 percent zinc and 0.03 percent copper (table 4). About 

60 m (200ft) west, also on the steep mountainside, is a caved stope. 

The working is in an iron-stained zone, probably the same as that of 

the arlit; the walls contain visible sphalerite. A 75-cm (2.5-ft) chip sample (26) across the iron-stained zone in the east wall of the open stope 

contained 16 percent zinc and 0.21 percent copper (table 4). 

About 0.4 km ( V4 mi) northwest of the main arlit at an elevation of 

approximately 11,000 ft (3,350 m), a 4.6-m (15-ft) shaft has been sunk 
88 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

N 

1 29~ 

0.5 1 MILE 

EXPLANATION 

!l Caved shaft 

--< Ad it 

-+< Caved adit 

Prospect pit 

.25 Sample locality 

Trail 

Primitive road 

I 

,, 

~/ \ / \ 

\ 

\ 

I 

I 

I 

I 

I 

) 

~ 

( 

J 

\ I ( / \ -/ ' / ' / \ / 

Ute X 

Pass I ~ \ 

2 KILOMETERS 

FIGURE 35.-Mine workings and sample localities in the Gold Creek-Gilpin Creek 

area, in loc. K. 
MINE APPRAISAL 89 

FIGURE 36.-View north of Upper Slavonia mine dump area. Man gives scale. 

in an iron-stained sulfide-bearing zone in layered gneiss that strikes 

N. 40° W. A 30-cm (1-ft) chip sample (27), taken across the zone in 

the north wall of the shaft, assayed 2.8 percent zinc and 0.05 percent 

copper (tables 2, 4). 

The mineralized zones exposed in the separate workings have a similar appearance and mineralogy, suggesting that the zone is continuous. 

Verification of continuity, however, is not possible because of surface 

debris, including a rock slide between the open stope and the shaft. 

About 250m (800ft) south of the main adit, another steeply dipping, westward-bearing iron-stained zone in gneiss has been prospected 

by a small pit. A 1.1-m (3.6-ft) chip sample (28) contained 0.04 percent 

copper (tables 2, 4). 

UPPER GILPIN CREEK (LOCALITY L) 

Several groups of mining claims were located in the upper drainage 

of Gilpin Creek in the late 1940's and early 1950's (fig. 35). The claims 

of upper Gilpin Creek (locality L) are within the wilderness in the 

southeastern part of unsurveyed T. 10 N., R. 83 W. (fig. 21). The only 

working observed in the area is an adit about 1,220 m (4,000 ft) northwest of Gilpin Lake at an elevation of approximately 10,500 ft 
90 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

(3,200 m). The adit bears N. 20° W. for 9 m (30ft) and then N. 40° 

E. for 5.5 m (18ft). Traces of copper minerals were seen on the dump. 

A 90-cm (3-ft) chip sample (29), taken across the face in light-colored 

gneiss, contained 0.03 percent copper (table 4). 

A 15-cm (0.5-ft) chip sample (30) was taken across the outcrop of 

an iron-stained band in gneiss on the east-sloping mountainside, approximately 1,850 m (6,000 ft) northwest of Gilpin Lake at an elevation of approximately 10,800 ft (3,300 m). Metal content was not 

significant (tables 2, 4). 

NORTH FORK ELK RIVER (LOCALITY M) 

Several groups of claims, located in 194 7 and 1948, were described 

as being in the upper drainages of North Fork Elk River (locality M). 

The area is in the wilderness just west of the Continental Divide in 

the east-central part of unsurveyed T. 10 N., R. 83 W. (fig. 21). Reconnaissance of the area revealed no workings. A 30-cm (1-ft) chip sample (31) was taken across the outcrop of a black iron-stained layer in 

gneiss about 1,070 m (3,500 ft) east of Big Agnes Mountain. An assay 

for gold and silver was negative (tables 2, 4). 

DIAMOND PARK AREA (LOCALITY N) 

The Diamond Park area (locality N) is well within the adjacent area 

near the western boundary of the wilderness in the extreme northeast 

comer ofT. 10 N., R. 84 W. (fig. 21). All the workings are within 1.6 km 

(1 mi) of the wilderness boundary (fig. 37). Diamond Park, an open 

meadow at the mouth of the Precambrian part of the canyon of North 

Fork Elk River, has been the site of a number of mining-claim locations. A traverse of the area, however, revealed no workings, claim 

monuments, or mineralized rock. 

About 1.6 km (1 mi) north of Diamond Park, near the southern headwaters of Stevens Creek, a 2.4-m-deep (8-ft-deep) trench bearing S. 55 o 

E. has been excavated on a fault zone in iron-stained gneiss containing abundant garnet with a little copper stain. A 1.4-m (4.5-ft) chip 

sample (32) across the north wall contained 0.06 percent copper (table 

3). About 610 m (2,000 ft) N. 30° E. of the trench, a prospect pit has 

been sunk on what may be the same fault zone in gneiss; the zone 

shows a little copper stain. A grab sample (33) from the pit dump contained no metal values of consequence (table 4). Two other workings 
N 

1 

MINE APPRAISAL 

.32 

X 

35.x 

X 

.33-34 

X 

0.5 

EXPLANATION 

Prospect pit 

.32 Sample locality 

Trail 

1 MILE 

..J.. ..l.. ..L. Approximate wilderness boundary 

Adjacent area boundary 

91 

2 KILOM ETERS 

FIGURE 37.-Prospect workings and sample localities north of Diamond Park 

(loc. N). 
92 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

were examined at points about 60 m (200ft) and 360m (1,200 ft) north 

of sample site 33. The first is a pit that exposes a 30-cm (1-ft) quartzcalcite vein. A chip sample (34) across the vein contained 0.08 percent copper (table 3). At the second site, two trenches were cut in an 

iron-stained zone consisting mainly of quartz and garnet with a little 

chalcopyrite. A 1.8-m (6-ft) chip sample (35) across the zone in the 

southern trench contained 0.09 percent copper (table 4). Molybdenite 

was identified in one 15-cm (6-in.) rock fragment from the dump, but 

no more of the mineral was found in the area. 

KING SOLOMON CREEK AREA (LOCALITY 0) 

Two workings were examined in the King Solomon Creek area (locality 0), which is within and near the western boundary of the adjacent 

area in the northeast corner ofT. 10 N., R. 85 W. The workings are 

shown on figure 38. The first working is a caved adit that bears N. 25 o 

E. in gneiss. A dump grab sample (36) contained no mineral values 

of consequence (table 3). 

About 430 m (1,400 ft) southeast of sample site 36, another caved 

adit approximately 15m (50ft) in length bearsS. 50° E. in dark gneiss. 

A patented claim described in this locality seemingly does not coincide with this working, although the original claim probably included 

it. Vein material on the dump consists of iron-stained quartz with considerable galena and malachite. A grab sample (37) of the dump contained 5.1 oz silver per ton (175 ppm), 7 percent lead, 0.3 percent 

copper, and 0.05 percent bismuth (table 3). Bedrock is exposed southeast of the caved adit, but no vein is evident. The northwestern extension of the vein, if it exists, is covered by alluvium. On the basis 

of the values contained in sample 37, the working warrants further 

investigation as a mineral prospect. 

BEAVER CREEK-KING SOLOMON CREEK AREA (LOCALITY P) 

Since about 1895, there has been considerable prospecting in the 

Beaver Creek-King Solomon Creek area (locality P), which lies along 

the western boundary of the adjacent area in the east-central part of 

T. 10 N., R. 85 W. (fig. 21). Numerous workings were examined in sees. 

11, 13, 14, and 23, as shown on figure 38. 

SECTION 11 

Section 11 contains numerous prospect workings, and most of the 

section has been covered by mining claims (figs. 38, 39). Fourteen 
MINE APPRAISAL 

N 

1 

I! 

R. 85 W. 1 

0.5 

EXPLANATION 

D Patented mining claims 

l<il Caved shaft 

>--- Ad it 

>+- Caved adit 

24 

2 KILOMETERS 

1 MILE 

X Prospect pit or trench 

• 59 Sample locality 

Primitive road 

Adjacent area boundary 

93 

T. 

FIGURE 38.-Patented mining claims and prospect workings in the Beaver CreekKing Solomon Creek area (locs. 0 and P). 
94 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

N 

1 15 30 METERS 

50 100 FEET 

FIGURE 39.-Adit in west-center sec. 11, T. 10 N., R. 85 W., site of samples 38-42. 

samples were taken at four workings within the section but outside 

the adjacent area. 

38-42: At this locality, a 120-m (400-ft) adit partly caved at the portal was driven on 

a granite dike (fig. 39). Samples 38-42 (table 3) contained only small amounts 

of copper (less than 0.20 percent) and minor lead (less than 0.05 percent). 

43: This working is a 20-m (67-ft) adit driven N. 70 o E. in Precambrian schist. Sample 43, taken in a fault zone 15 m (50ft) in from the portal, contained nothing 

of interest (table 3). 

44-50: Samples 44-50 (table 3) are from the dumps of caved shafts and adits in the 

north-central part of the section. Gold and silver values were negligible, copper 

values ranged from 0.03 to 0.89 percent, and lead from 0.01 to 0.04 percent. 

Two samples (45, 48) contained 0.47 and 0.89 percent copper, respectively. 

They were from ore(?) piles. 

51: A grab sample (51) was taken from the dump of a prospect pit in light-colored 

gneiss with quartz and muscovite. The sample contained 0.04 percent lead 

(table 3). 

SECTION 14 

Three samples were taken at three workings in section 14 (fig. 38). 

The workings are west of the adjacent area boundary. 

52: Sample 52 was a grab sample from a dump at a shallow prospect pit in gneiss with 

quartz. It contained minor (0.08 percent) lead (table 3). 

53: The dump of a shallow prospect pit in pegmatite was sampled (53) at this site. 

Assay results showed no significant metal concentration (table 3). 

54: A grab sample (54) from the dump of what appears to be a caved adit did not contain anomalous metal values (table 3), although the dump, composed of gneiss 

and quartz, showed some copper stain. 

SECTION 2.3 

Two workings were examined and sampled in section 23 (fig. 39). 

The prospects are west of the adjacent area boundary. 
MINE APPRAISAL 95 

55: At this site, a grab sample (55) from near a prospect pit in sandstone yielded 0.08 

percent lead (table 3). 

56: Sample 56 assayed traces of gold and silver (table 3). It was taken from the dump 

of a caved adit driven in quartz-bearing sandstone. 

SECTION 13 

In section 13 within the adjacent area, five samples were taken at 

five workings (fig. 38). 

57: This working is a trench in gneiss with quartz veinlets and copper stain. A dump 

sample (57) contained 0.1 oz of silver per ton (3 ppm), 0.34 percent copper, and 

0.02 percent lead (table 3). 

58: At this locality, two pits about 3m (10ft) deep have been sunk on erratic quartz 

veins containing small amounts of bornite; the country rock is gneiss. A 15-cm 

(0.5-ft) chip sample (58) across one of the more heavily mineralized zones contained 1.02 percent copper (table 3). 

59: At this site, a trench in gneiss has exposed a narrow quartz vein. Assay values 

from a 15-cm (0.5-ft) chip sample (59) were negligible (table 3). 

60: A grab sample (60), taken from a dump at a pit in gneiss, contained anomalous 

metal values (table 3). Southwest of the sample site, the remains of a small placer 

operation are in the bottom of a small draw that drains the northwestern slope 

of Farwell Mountain. The material that was worked from the stream bed is very 

coarse and of small volume. Very little loose material remains undisturbed in 

the area; no sampling was attempted. 

61: Near the eastern boundary of section 13 a 4.6-m (15-ft) pit has exposed a copperstained quartz vein in gneiss. A dump grab sample contained traces of gold and 

lead, 0.3 oz (10 ppm) silver per ton, and 0.3 percent copper (table 3). 

ZINC MOUNTAIN CLAIM (LOCALITY Q) 

Locality Q is west of the wilderness and partly within the adjacent 

area in the south-central part ofT. 10 N., R. 84 W. (fig. 21). This claim 

group, named Zinc Mountain by local prospectors, is on a prominence 

west of North Fork Elk River between Hole-In-Wall Canyon and Scott 

Run. The ZM claim group was located in 1967 by William A. Bowes; 

it covers the north half of the mountain, as shown on figure 40. The 

old prospect pits (shown by a single symbol on fig. 40) are of unknown 

origin. Both workings are in gneiss containing marble and garnet, and 

exhibiting a little copper stain. A 90-cm (3-ft) chip sample (62) from 

one of the pits contained no metal values of consequence (table 3). 

Bowes built a road to the property and dug four north-trending 

bulldozer cuts, 45 to 60 m (150 to 200 ft) long, across the northern 

part of the prominence in an attempt to crosscut a suspected easttrending mineralized zone; his efforts were unsuccessful. Grab samples 

(63-66), taken from each of the four pits, contained very low metal 

values (table 3). 
96 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

D Mining claims 

Prospect pit 

>--< Prospect trench 

.66 Sample locality 

0.5 

EXPLANATION 

2 KILOMETERS 

1 MILE 

Trail 

Primitive road 

Adjacent area boundary 

FIGURE 40.-Claims and prospect workings in the Zinc Mountain claim area (loc. 

Q). Contour interval 200 ft; 1 ft = 0.3 m. 
MINE APPRAISAL 97 

BEAVER CREEK AREA (LOCALITY R) 

The Beaver Creek area (locality R) lies along the western boundary 

of the adjacent area in the eastern part ofT. 10 N., R. 85 W. (fig. 21). 

Land paralleling Beaver Creek, which flows south between Hahns 

Peak and Farwell Mountain, has been covered by numerous placer mining claims over a period of many years. Placer mining has been conducted at a number of locations in the vicinity, including Ways Gulch 

(south of Hahns Peak), Little Red Park (north of Hahns Peak), and 

near Hahns Peak Village (George and Crawford, 1909). The placer gold 

appears to have originated near Hahns Peak (Segerstrom and Young, 

1972). During this investigation, samples of gravel were panned at 

a number of locations along Beaver Creek just west of the study area 

boundary. Only sparse fine flakes of gold, estimated at less than 

0.01 ppm of the gravel, were found in the panned concentrates. 

GROUSE MOUNTAIN AREA (LOCALITY S) 

The Grouse Mountain area (locality S) is just west of the adjacent 

area in the southeastern part ofT. 10 N., R. 85 W. (fig. 21). The area 

has been the site of mining-claim activity and some prospecting (fig. 

41). Three samples (67 -69) from a trench and two prospect pits contained only low metal values (tables 3, 4). 

WILLOW CREEK CANYON AREA (LOCALITY T) 

The Willow Creek Canyon area (locality T) lies within the adjacent 

area in the northeastern part ofT. 9 N., R. 85 W. (fig. 21). Willow Creek 

Canyon has been the site of placer mining claims, as shown on figure 

42, located mostly in 1966. The upper end of the canyon was mined 

many years ago by placer methods for several hundred feet (fig. 43). 

Water was brought in by a ditch that tapped Beaver Creek. The stream 

appears to have been mined to bedrock. Placer gold obviously was 

recovered, but no record of production was found. Four samples were 

taken from the banks of Willow Creek, as shown on figure 42. The 

samples were panned, and the quantity of gold estimated. Although 

fine flakes of gold are common in material on or near bedrock, both 

the quantity of the placer material and its estimated grade are insignificant. No indication of recent work was found. 

Opposite the mouth of Lester Creek and a little downstream, a 6-m 

(20-ft) trench, bearing N. 75 oW., was excavated in layered gneiss and 

quartzite. A 90-cm (3-ft) chip sample (70) from the trench wall contained no anomalous metal (table 3). 
98 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

N 

1 

2 KILOMETERS 

0.5 1 MILE 

EXPLANATION 

~ Mining claims ===== Primitive road 

X Prospect pit or trench Adjacent area boundary 

• 69 Sample locality 

FIGURE 41.-Mining claims and prospect workings in the Grouse Mountain 

area (loc. S). Contour interval 200 ft. 
MINE APPRAISAL 

0.5 

EXPLANATION 

~ Mining claims 

X Prospect pit 

• 70 Sample locality 

Primitive road 

Maintained road 

1 MILE 

Adjacent area boundary 

N 

1 

2 KILOMETERS 

FIGURE 42.-Mining claims and sample localities in Willow Creek 

Canyon (loc. T). Contour interval 200 ft. 

99 
100 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

FIGURE 43.-Abandoned placer workings at the upper end <A Willow Creek Canyon. 

BIG CREEK AREA (LOCALITY U) 

The Big Creek area (locality U) is near the western adjacent area 

boundary in the south-central part ofT. 9 N., R. 84 W., and the northcentral part ofT. 8 N., R. 84 W. (fig. 21). One group of 14 claims (the 

Haskell claims) was located in the drainage of Big Creek, as shown 

on figure 44. Three old workings were examined and sampled in the 

area. 

Just inside the study area in the southwest corner of section 33, 

a 24-m (80-ft) arlit was driven in layered gray gneiss that carries some 

copper mineralization. A 0.6-m (2-ft) chip sample (71), taken across 

a copper-stained zone above the portal, contained 0.13 percent copper (table 3). 

Just outside the adjacent area in the southeast corner of section 

33, a grab sample (72) was taken from the dump of a caved arlit that 

had been driven north in schist. The sample yielded 0.04 percent lead 

on analysis (table 3). 

About 90 m (300ft) north and up the hillside from the caved arlit, 

a 30-cm (1-ft) copper-stained zone in gneiss was sampled (73). The sample contained 0.28 percent copper (table 3). This sample site is probably just inside the adjacent area boundary. 
MINE APPRAISAL 

9 

R. 84 W. 

0.5 1 Mll!f 

EXPLANATION 

0 : Mining claims. 

>- Adit 

>+- Caved: adit 

X Prospect: pit 

.73 Sample lacarttv 

Trail 

Adiacent area boundarry 

Floyd~ 

Peak 

34 

101 

·r. 

9 

N. 

FIGURE 44.-Mining claims and prospect workmgs in the Big Creek: area tU). 

ELK PARK AREA (LOCALITY V) 

The Elk Park area (locality V) straddles the southwestern boundary 

of the adjacent area in the northwestern art ofT·. 1 N., R. 84 W. 
102 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

(fig. 21). In 1903, several claims were located west of the adjacent area 

boundary (fig. 45). Three prospect workings, all in section 9, were examined. The workings are prospect pits that were sunk in altered igneous rock. A 2-m (6-ft) chip sample (7 4) was taken at the northernmost 

pit; the other samples (75, 76) were grab samples from dumps. Only 

low metal values were contained in the samples (table 3). 

SODA CREEK AREA (LOCALITY W) 

The Soda Creek area (locality W) straddles the southern boundary 

of the adjacent area in the southeast corner ofT. 7 N., R. 84 W. 

(fig. 21). Routt County records show that 14 mining claims were 

located in 1954 in the Soda Creek area. Six of the claims are shown 

on figure 46. 

Because of the date of location and the fact that there is slightly 

anomalous radioactivity in the area, it is assumed that the claims were 

located for uranium. The area contains numerous large pegmatite dikes 

that have a somewhat high background radiation, possibly owing to 

their potassium content. One of the dikes east of the Dry Lake Campground has a high feldspar content, nearly pure in places. Although 

Colorado feldspar deposits presently have little or no market, the dike 

may have value as a future source of feldspar. A chip sample (77) taken 

at 30-cm (1-ft) intervals across 11m (35ft) of another pegmatite dike 

contained nothing of interest (table 3). 

A bulldozer trail leads from the Buffalo Pass road to a prospect that 

is on a knoll south of and above South Fork Soda Creek (fig. 4 7). Here, 

a nearly vertical dark layer in gneiss strikes N. 85 o W.; it ha$ been 

prospected by a series of shallow pits about 3.6 m (12 ft) apart for 

a distance of about 23m (75ft). Trace amounts of a highly radioactive yellow mineral, probably carnotite, gave a high Geiger counter 

reading. Chip samples (78-80) were taken at the middle and both ends 

of the outcrop. The samples contained 0.1 oz silver per ton (3 ppm), 

but less than 0.01 percent uranium (table 3). 

BUFFALO PASS AREA (LOCALITY X) 

The Buffalo Pass area (locality X) is at the southeastern boundary 

of the adjacent area in the south-central part of unsurveyed T. 7 N., 

R. 83 W. (fig. 21). Two prospect pits, in the vicinity of Buffalo Pass, 

have been sunk on a northeast-trending fault zone (fig. 48). The pits 

are outside the adjacent area and are about 450 m (1,500 ft) apart. 
Rocky 

6 Peak 8 

MINE APPRAISAL 

R. 84 W . 

0.5 1 MILE 

EXPLANATION 

D Mining claims 

X Prospect pit 

.74 Sample locality 

Trail 

Adjacent area boundary 

3 

15 

2 KILOMETERS 

103 

T. 

7 

N. 

FIGURE 45.-Mining claims and prospect workings in the Elk Park area (V). 
104 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

2 KILOMETERS 

0.5 1 MILE 

EXPLANATION 

CJ Mining claims 

X Prospect pit 

.77 Sample locality 

F Pegmatite with high feldspar 

Trail 

Maintained road 

Adjacent area boundary 

FIGURE 46.-Mining claims and prospect pits in the Soda Creek area (W). 
MINE APPRAISAL 105 

FIGURE 47.-Prospect near South Fork Soda Creek. 

A grab sample (81) from the dump at a pit that was sunk on a steeply 

dipping iron-rich bed in gneiss contained 6 percent iron (table 3). Figure 

49 is a photograph of the working. The other pit exposes light-colored 

schist, part of which is impregnated with pyrite. A 45-cm (1.5-ft) chip 

sample (82) across the heaviest pyrite zone contained negligible metal 

values (table 3). 

FOSSIL FUEL LEASES 

During the past 50 years, oil and gas leases have been issued covering 

land along the eastern boundary of the adjacent area. The leased areas 

include the uplifted western edge of the sedimentary rocks of the North 

Park basin, but the formations have not been found to contain significant oil and gas deposits. Nearest production to the study area is from 

the recently discovered Lone Pine field (marked by a circled 0, fig. 21) 

near Delaney Lakes, about 8 km (5 mi) east of the adjacent area. 

West of the adjacent area in 1J>s. 7, 8, and 9 N., R. 85 W., there has 

been sporadic leasing for oil and gas since 1925, also without discovery 

of oil and gas deposits. 
106 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

N 

1 

0.5 

EXPLANATION 

X Prospect pit 

• 81 Sample locality 

Trail 

Primitive road 

Maintained road 

1 MILE 

Adjacent area boundary 

2 KILOMETERS 

FIGURE 48.-Prospect pits and sample localities in the Buffalo Pass area (X). 
MINE APPRAISAL 107 

FIGURE 49.-Prospect pit near Buffalo Pass. 

Small amounts of coal have been produced from two locations 

(marked by a circled C, fig. 21) both about 3.2 km (2 mi) east of the 

study area (Hail, 1965). The Mitchell mine (T. 8 N., R. 82 W.) is in 

the Coalmont Formation of Tertiary age, and the Monahan coal mine 

(T. 10 N., R. 81 W.) is in the Pierre Shale of Cretaceous age. Both mines 

are now abandoned. The Coalmont Formation contains abundant coal 

in other parts of the basin (Madden, 1977 a, b); the Pierre Shale contains a small amount of coal. Very little of the adjacent area is underlain by these formations. 

Evaluation of Surface 

Metallic and Nonmetallic 

Resource Potential 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY 

MINERAL RESOURCES OF THE MOUNT ZIRKEL 

WILDERNESS AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

u·.s. GEOLOGICAL SURVEY BULLETIN 1554-C 
CONTENTS 

Page 

Geochemical appraisal of surface metallic resource potential . . . . . . . . . . . . . . 113 

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 

Definition of geochemical anomaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

General evaluation of surface anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

Metallic deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 

Copper, lead, zinc, silver, and related elements . . . . . . . . . . . . . . . . . . . 139 

Uranium, thorium, and related elements . . . . . . . . . . . . . . . . . . . . . . . . 140 

Uranium and thorium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 

Rare earth prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7 

Chromium, platinum, and related elements . . . . . . . . . . . . . . . . . . . . . . 148 

Chromium, cobalt, and nickel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 

Platinum and palladium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 

Other elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 

Evaluation of surface nonmetallic resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 

Fluorspar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 

Other rock commodities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 

Coal, oil, and gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7 

Geothermal resource appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 

Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 

ILLUSTRATIONS 

Page 

FIGURE 50. Typical cumulative frequency plots of rock AA Ph (atomic absorption lead) and Spec Cu (spectrographic copper) ...... 116 

51. Map test of detectability of known ore zones by analysis of 

stream sediments .................................. 135 

52-78. Computer-generated maps of anomalous element distribution: 

52. Rock Spec Cu (spectrographic copper) .......... 160 

53. Rock AA Cu (atomic absorption copper) ........ 161 

54. Stream-sediment Spec Cu (spectrographic copper) 162 

55. Stream-sediment AA Cu (atomic absorption copper) 163 

56. Rock Spec Pb (spectrographic lead) ............ 164 

57. Rock AA Pb (atomic absorption lead) .......... 165 

58. Stream-sediment Spec Pb (spectrographic lead) .. 166 

59. Stream-sediment AA Pb (atomic absorption lead) 167 

60. Rock Spec Zn (spectrographic zinc) ............ 168 

110 
EVALUATION OF SURFACE POTENTIAL 111 

Page 

61. Rock AA Zn (atomic absorption zinc) . . . . . . . . . . 169 

62. Stream-sediment Spec Zn (spectrographic zinc) . . 170 

63. Stream-sediment AA Zn (atomic absorption zinc) 171 

64. Rock Spec Ag (spectrographic silver) . . . . . . . . . . . 172 

65. Rock AA Ag (atomic absorption silver) . . . . . . . . . 173 

66. Stream-sediment Spec Ag (spectrographic silver) . 17 4 

67. Stream-sediment AA Ag (atomic absorption silver) 175 

68. Rock AA Au (atomic absorption gold) . . . . . . . . . . 176 

69. Stream-sediment AA Au (atomic absorption gold) 177 

70. Rock Inst Hg (instrument-detected mercury) . . . . 178 

71. Rock Spec Sb (spectrographic antimony) . . . . . . . 179 

72. Rock Spec As (spectrographic arsenic) . . . . . . . . . 180 

73. Rock Spec W (spectrographic tungsten) . . . . . . . . 181 

7 4. Rock Spec Sn (spectrographic tin) . . . . . . . . . . . . . 182 

75. Stream-sediment Spec Sn (spectrographic tin) . . . 183 

76. Rock Spec Cd (spectrographic cadmium) . . . . . . . . 184 

77. Rock Spec Bi (spectrographic bismuth) . . . . . . . . . 185 

78. Rock Spec Ga (spectrographic gallium) . . . . . . . . . 186 

79. Map showing localities of measured thorium and uranium . 187 

80-89. Computer-generated maps of anomalous element distribution: 

80. Rock Spec Mo (spectrographic molybdenum) . . . . 188 

81. Stream-sediment Spec Mo (spectrographic 

molybdenum) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 

82. Rock Spec Nb (spectrographic niobium) . . . . . . . . 190 

83. Stream-sediment Spec Nb (spectrographic niobium) 191 

84. Rock Spec La (spectrographic lanthanum) . . . . . . 192 

85. Stream-sediment Spec La (spectrographic lanthanum) 193 

86. Rock Spec Y (spectrographic yttrium) . . . . . . . . . . 194 

87. Stream-sediment Spec Y (spectrographic yttrium) 195 

88. Rock Spec Cr (spectrographic chromium) . . . . . . . 196 

89. Stream-sediment Spec Cr (spectrographic chromium) 197 

90. Map showing localities of measured platinum and palladium 198 

91-104. Computer-generated maps of anomalous element distribution: 

91. Rock Spec Co (spectrographic cobalt) . . . . . . . . . . 199 

92. Stream-sediment Spec Co (spectrographic cobalt) 200 

93. Rock Spec Ni (spectrographic nickel) . . . . . . . . . . . 201 

94. Stream-sediment Spec Ni (spectrographic nickel) . 202 

95. Rock Spec Ba (spectrographic barium) . . . . . . . . . 203 

96. Rock Spec Be (spectrographic beryllium) . . . . . . . 204 

97. Stream-sediment Spec Be (spectrographic beryllium) 205 

98. Rock Spec Sc (spectrographic scandium) . . . . . . . . 206 

99. Stream-sediment Spec Sc (spectrographic scandium) 207 

100. Rock Spec Sr (spectrographic strontium) . . . . . . . 208 

101. Stream-sediment Spec Sr (spectrographic strontium) 209 

102. Rock Spec V (spectrographic vanadium) . . . . . . . . 210 

103. Stream-sediment Spec V (spectrographic vanadium) 211 

104. Stream-sediment Spec Zr (spectrographic zirconium) 212 

105. Map showing association of interstitial fluorite with rocks of 

the Mount Ethel pluton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 
112 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 5. 

6. 

7. 

8. 

9. 

10. 

11. 

TABLES 

Page 

Summary of anomalous rock geochemical data shown on individual 

element maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 

Summary of anomalous stream-sediment geochemical data shown 

on individual element maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 

Summary of semiquantitative spectrographic data forumninera1ized 

cry-stanine rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

Delayed-neutron determinations of thorium and uranium in selected 

stream sediments and rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 

Analysis of Agua Fria rare-earth ore . . . . . . . . . . . . . . . . . . . . . . 148 

Association of measured chromite and Cr20 3 in ultramafic rocks 149 

Measured platinum and palladium in mafic and ultramafic rocks 151 
MINERAL RESOURCES OF THE MOUNT ZIRKEL WILDERNESS 

AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

EVALUATION OF SURFACE METALLIC 

AND NONMETALLIC RESOURCE POTENTIAL 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY 

GEOCHEMICAL APPRAISAL OF 

SURFACE METALLIC RESOURCE POTENTIAL 

PROCEDURE 

To evaluate mineral resources near the land surface, the U.S. 

Geological Survey collected 1,985 rock samples, and most of these were 

studied in thin section. A total of 314 rock samples were collected 

specifically for geochemical studies, many from now-abandoned mine 

dumps, mine faces, or prospect pits. Of these, 45 percent contain visible ore minerals, 38 percent came from altered rocks, and 17 percent 

represent rock without visible evidence of mineralization. Ore samples 

were characterized by green to blue copper minerals but also included 

iron-manganese sulfide-oxide gossan, as well as chalcopyrite, galena, 

sphalerite, fluorite, and rare molybdenite. The non-ore altered rocks 

contain quartz, chalcedony, carbonate, magnetite, or hematite veins, 

iron-stained joints, or rocks variously chloritized, argillized, sericitized, silicified, epidotized, feldspathized, or limonitized; some are 

sheared to mylonite or fault breccia. Other analyzed rocks included 

basal conglomerate, tuffaceous sandstone or siltstone, and basal 

limestone or limestone breccia of the Browns Park Formation, coarsely 

crystalline pegmatites, marble or calc-silicate rocks, or ultramafic 

rocks, and a few Precambrian or Tertiary porphyry dikes and their 

113 
114 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

contained wall-rock inclusions. The geochemical samples were 

crushed, split, and routinely analyzed by six-step semiquantitative 

emission spectrographic methods for 30 elements (Fe, Mg, Ca, Ti, 

Mn, Ag, As, Au, B, Ba, Be, Bi, Cd, Co, Cr, Cu, La, Mo, Nb, Ni, Pb, 

Sb, Sc, Sn, Sr, V, W, Y, Zn, and Zr; some also analyzed for Ga), by 

atomic absorption photospectrometric methods for Ag, Au, Cu, Pb, 

and Zn, and by instrumental detector for Hg. Twenty-two of these 

samples were anomalously high in niobium and were subsequently 

analyzed by delayed neutron determination for thorium and uranium. Ninety-seven ultramafic and related rocks were analyzed by 

chemical methods (as in Talanta, 1968, v. 15, p. 111-117) for platinum, 

palladium, and rhodium (no rhodium found); many of these contain 

chromite and 14 were analyzed by chemical or colorimetric methods 

for Cr20 3• 

Samples of stream sediments from 1,255 localities were analyzed 

in an effort to identify key elements characterizing individual 

drainage areas. Weathering, erosion, and soil movement constantly 

change patterns of rock outcrops and surficial cover, first exposing, 

then hiding potential bedrock ore deposits, with the result that the 

present surface evidence for some smaller ore deposits may consist 

exclusively of downstream detritus. The preferred sample type consisted of about 140 cubic centimeters (22 in.3) of typical fine sand, 

silt, or clay collected in a special water-permeable metal-free paper 

bag. Some samples from cascading mountain streams were necessarily coarser. A few panned heavy mineral concentrates also were 

collected and analyzed. All samples were dried and sieved, and the 

minus-80-mesh fractions were mixed and split. Splits were then 

routinely analyzed by six-step semiquantitative emission spectrographic methods for 30 elements (same elements as analyzed for 

in rock samples) and by atomic absorption photospectrometric 

methods for silver, gold, copper, lead, and zinc. Splits of 33 selected 

samples were analyzed later by delayed neutron determination for 

thorium and uranium. 

DEFINITION OF GEOCHEMICAL ANOMALY 

The amount of an analyzed element that is ''background,'' that is, 

within normal expectations, or "anomalous," that is, anomalously 

higher than background, varies for every element of either rock or sediment and for every geologic host and environment. Theoretically, any 

host that has been partially replaced or added to by variable amounts 

of ore solutions of much different overall composition should demonstrate bimodal or polymodal frequency distributions for appropriate 
EVALUATION OF SURFACE POTENTIAL 115 

elements from multiple analyzed samples. The trough(s) between the 

modal peaks would then be a convenient threshold class for distinguishing most background from most anomalous element values. 

In reality, the populations of data are seldom simple (for example, here 

it was deemed impractical to try to separate the data for all the 

Precambrian lithologies concerned), and it is often difficult to distinguish a bimodal distribution from an unevenly skewed single distribution. On R. L. Earhart's advice, the writer found it easier to pick the 

background-anomalous threshold by plotting the cumulative frequency data on semilogarithmic percentage paper. Two of the best 

examples are shown on figure 50, where the elbow of the cumulative 

curve defines the background-anomalous threshold. The system also 

works satisfactorily with less linear (more irregular) cumulative 

distributions or those with a less elongate distribution. In case of any 

remaining uncertainty, a conservatively low threshold value was 

chosen. In a few cases (examples, gold, tungsten), only a few unqualified values were reported, and it was assumed in these cases that the 

threshold was below the limit of analytical detection. Conveniently, 

therefore, all the background values (most of the data) can be 

dropped from further consideration in this surface mineral resource 

assessment. 

Two qualitative checks on the approximate validity of the anomaly 

thresholds are available. First, the lowest anomalous value chosen is 

listed for every element in tables 5 and 6 and on each of the detailed 

element map figures. These can be compared with the average element 

values for the different types of crystalline rocks as presented in the 

compilation of semiquantitative spectrographic analyses of 136 unmineralized crystalline rocks in table 7. In general, the elemental values 

considered anomalous by this technique in the Park Range rocks or 

stream sediments are equal to or greater than the average values for 

the various types of unmineralized crystalline rocks listed in this table, 

but there are several exceptions, and the reader should compare the 

data sets for details. Second, the anomalous element value limits can 

be compared with the known crustal abundances of various elements 

that are available in the professional literature. When this is done, 

all the analyzed elemental values considered anomalous in Park Range 

rocks or stream sediments are equal to or many times greater (as much 

as 6,000 times greater) than the average amounts of these elements 

as reported in common crustal rocks and sediments (Goldschmidt, 

1954; Turekian and Wedepohl, 1961, table 2; Clark and others, 1966, 

p. 528-538; Solomon, 1976, table 1, p. 45), with the exception of 

chromium and nickel in ultra basic rocks. It seems reasonable to conclude that these different determinations of anomalous chemistry 

generally reinforce each other. 
116 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

10,000 

5000 

z 

0 

::::i 

..J 

~ 

a: 

w 1000 a.. 

en 

1-

a: 

<( 

a.. 500 

~ 

u) 

~ 

u 

0 

a: 

.J5 

Q. 

<( 

<( 

100 

50 

10 

A 

80 

Back- Anomalous values 

ground 

PPM CLASSES, AA Pb, ROCKS 

10 20 30 40 50 60 70 80 90 

CUMULATIVE FREQUENCY, IN PERCENT 

I 

I+ 

I 

I+ 

98 

FIGURE 50.-Typical cumulative frequency plots of the population of rocks ana-

(crosses) and B, six-step semiquantitative emission spectrographic methods for 

insets of frequency distributions for the same analyses. Anomalous values (patquency curve, are the only values shown on detailed map figures of these and 

mal semilogarithmic Spec scale by approximations shown. On Spec Cu diagram, 

5,000G analyses were remeasured in later 20,000G mode. 
EVALUATION OF SURFACE POTENTIAL 117 

10,000 

(/) 

60 w 

:::> 

..J 

~ 

> 

Anomalous Back- values ground 

z values 

0 

::J 

....J 

~ 

a: 1000 LU 

0.. 

en 

1-

a: 

<( 

0.. 

?; 

vi 

~ 

u 

0 

a: 

u = 

u 

LU 100 0.. 

(/) 

50 

10 

B 

5 2L ____ _LLL1LQ----2~Q---3LQ __ 4~Q--5~Q--6~Q--~7Q--_J8Q-----9LQ------~98 

CUMULATIVE FREQUENCY, IN PERCENT 

lyzed by A, atomic absorption photospectrometric methods for lead (AA Pb) 

copper (Spec Cu) (open circles), on semilogarithmic-percentage paper, and with 

terned), defined as those higher than major deflection of percent cumulative freother elements. The arithmetic-scale AA values are computer adapted to the norhighest four values shown would be expected to move right if an earlier set of 
TABLE 5.-Summary of anomalous rock geochemical data shown on individual element maps in the vicinity of the Mount Zirkel Wilderness 

[Spec, analysis obtained by standard semiquantitative spectrographic techniques; AA, analysis by atomic absorption techniques; Inst, analysis by instrumental techniques. L, less than; 

G, greater than. Because these analyses were performed over a period of years during which the Land G limits varied for many different elements, symbol boundary values are chosen 

to eliminate the effect of these variations. Total number of analyses (shown in parentheses; below concentration) given for each symbol may vary slightly from actual totals on element 

maps because some samples lie outside the area of the element maps and were therefore excluded from them. Localities of individual analyses of particular interest should be checked 

against plate 2 (where their positions are accurately shown); individual element maps frequently distort the locations slightly in order to alleviate crowding. For rock geochemistry: anomalous 

single highs or prominent clusters of data are mentioned where pertinent for each analyzed element selected. Note that presence of anomalous concentrations of an element, although providing targets in any search for economic concentrations, does not guarantee that economic concentrations are present. Areas within present boundaries of Mount Zirkel Wilderness or 

adjacent area are italicized. Lack of anomalous atomic absorption (AA) data near Greenville district is due to lack of AA analyses in this area] 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Rock sample data (coded "A"') Symbol code, in parts per million 

Element with chosen values 

Spec Ag: All 153 unqualified values + 

23 L values. 

AA Ag: 5 ppm and greater -----------

Spec As: All 9 unqualified values + 63 

L values. 

AA Au: 0.05 ppm and greater --------

Smallest 

symbol 

0.5L, 0.5-3 

(86) 

0.5-0.7 

(55) 

200L 

(63) 

0.05-0.3 

(25) 

Next to 

smallest 

5-30 

(55) 

7.5-54 

(27) 

(None) 

0.35-1.5 

(10) 

Next to 

largest 

50-300 

(31) 

55-250 

(13) 

200-1,500 

(7) 

3-5.5 

(4) 

Largest 

symbol 

500-3,000 

(4) 

500-2,600 

(4) 

2,000-5,000 

(2) 

20 

(1) 

Rock geochemistry 

Spec Ag: Maximum 3,000 ppm, 

from Elkhorn mine galena sample. Data clusters: Elkhorn, 

Farwell, Gilpin, Greenville, and 

Pearl districts, west side Buck 

Mountain, Lone Pine Creek 

area, southwest of Red 

Elephant Mountain. 

AA Ag: Same maximum and 

clusters, except Greenville 

lacking. 

Spec As: Maximum 5,000 ppm at 

Master Key mine north of Columbine; secondary highs at 

Crystal mine-Pedad claim area. 

Prominent cluster of trace 

amounts in Greenville district. 

AA Au: Maximum 20 ppm from 

Fe-cemented quartz breccia at 

1-' 

1-' 

CX> 

a= 

0 

~ 

z 

t-3 

N 

H 

::d 

~ trj 

1:-4 

~ H 

1:-4 

tl 

trj 

::d 

z 

trj 

00 

00 

> z 

tl 

z 

0 

~ ::Il 

trj 

::d 

z 

'"0 

> ::d 

~ 

::d 

> z 

0 

trj 
Spec Ba: 3,000 ppm and greater (13) ---

Spec Be: 5 ppm and greater (36) ------

Spec Bi: All 57 unqualified values + 56 

L values. 

Spec Cd: All 22 unqualified values + 56 

L values. 

3,000 

(5) 

5, 7 

(25) 

10L, 20L, 

10, 15 

(79) 

20L, 50L, 

20, 30 

(59) 

5,000 

(6) 

10, 15 

(9) 

20-100 

(19) 

50-100 

(9) 

5,000G 

(1) 

20, 30 

(2) 

150-700 

(11) 

150-300 

(3) 

(None) 

(None) 

1,000, 

1,000G 

(4) 

500, 

500G 

(7) 

mine north of Gilpin Creek and 

Gilpin Lake. 5.5 ppm in sulfide 

ore Wolverine mine, Pearl 

district; 3 and 4 ppm in quartzgalena veins, Elkhorn mine. 

Clusters: Elkhorn, Farwell, 

Gilpin and Pearl districts, Buck 

Mountain, Red Elephant 

Mountain. 

Spec Ba: Maximum >5,000 ppm 

in copper-iron pegmatite ore 

south of Republic Creek, Pearl 

district. 

Spec Be: Maximum 30 ppm in 

iron-stained breccia south of 

Lone Pine Creek. Clusters: 

Farwell and Pearl districts. 

Spec Bi: Maximum >1,000 ppm in 

sulfide ore Wolverine mine, 

Pearl district. Important 

clusters: Buck Mountain and 

Farwell and Pearl districts. 

Lesser clusters: Gilpin, Greenville, west of Buffalo Pass. 

Spec Cd: Maximum >500 ppm 

from galena veins Elkhorn 

mine, sulfide ore at both Lower 

and Upper Slavonia mines, and 

iron-manganese ore Independence Mountain. Clusters: 

Elkhorn, Gilpin, Greenville, 

Pearl districts. 

tz::j 

< 

> t-t 

c:: 

> 1-3 

~ 

0 

2: 

0 

"'%j 

r:n 

c:: 

~ "'%j 

> C1 

tz::j 

~ 1-3 

tz::j 

2: 

1-3 

> t-t 

"""'"' 

"""'"' 

~ 
TABLE 5.-Summary of anomalous rock geochemical data shown on individual element maps-Continued 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Rock sample data (coded "A"I Symbol code, in parts per million 

Element with chosen values 

Spec Co: 50 ppm and greater (20) -----

Spec Cr: 100 ppm and greater (35) ----

Spec Cu: 50 ppm and greater 

(173 + 22G values). 

Smallest 

symbol 

50, 70 

(11) 

100-200 

(20) 

50-300 

(85) 

Next to Next to 

smallest largest 

100, 150 200 

(6) (3) 

300-700 1,000, 

1,500 

(9) (5) 

500-3,000 5,000-20,000, 

5,000G-20,000G 

(52) (58) 

Largest 

symbol 

(None) 

2,000, 

3,000 

(1) 

(None) 

Rock geochemistry 

Spec Co: Maximum 200 ppm Bear 

Creek peridotite. Cluster in 

olivine gabbro phase of gabbro 

of Elkhorn Mountain; other 

associations with mafic or 

ultramafic rock bodies too small 

to map. 

Spec Cr: Maximum 3,000 ppm in 

Troutman Draw malachitic 

hornblendite, Pearl district. 

Also associated with ultramafic 

rocks south Farwell, Three 

Island Lake, Bear Creek, and 

Elkhorn olivine gabbro. 

Spec Cu: All of numerous >20,000 

ppm analyses from malachitic 

ores of the Pearl or Farwell 

districts, but a large suite of 

>5,000 ppm analyses are from 

an early suite of Greenville 

rocks. Other clusters: Elkhorn, 

Gilpin, Buck Mountain, south of 

Lone Pine Creek, west of Buffalo Pass and Round Mountain. 

~ 

to:) 

0 

a:: 

0 

~ 

z 

t-3 

N 

1-4 

~ 

@ 

I:'"' 

1-4 

~ 

I:'"' 

t:l 

t:tj 

r.n 

~ en 

> z 

t:1 

z 

0 

8 

~ 

~ 

~ 

~ z 

0 

t:tj 
AA Cu: 280 ppm and greater (87) 280-2.100 2,500-15,000 18,000-146,000 152,000-210,000 AA Cu: The five highest analyzed 

(32) (41) (13) (3) values (140,000-210,000 ppm) 

are all from the Farwell or Pearl 

districts. Clusters similar to 

Spec Cu, except for lack of 

Greenville analyses. 

Spec Ga: All 35 unqualified values lOL, 20L, 10 15, 20 30, 50 70, 100 Spec Ga: Maximum 100 ppm in 

+ 24 L values (30) (22) (6) (1) Greenville ore. Data very trl 

(very incomplete data). limited, but anomalies at <: 

> 

Greenville district, Strawberry t-4 

c:: Park-Copper Ridge, in Willow > 

Creek, and at head of landslide t-3 

south of Hinman Park. 0 

z 

Inst Hg: 0.09 ppm and greater (70 + 0.04-0.24 0.28-0.8 0.85-5.5 10, lOG Inst Hg: Maximum >10 ppm in 0 

3 G values). (40) (21) (8) (4) botryoidal iron-gossan at Gilpin "'%j 

mine, and iron-silica boxwork, en 

c:: 

Crystal mine. ~ 

Spec La: 50 ppm and greater (62) ----- 50, 70 100, 150 200, 300 500 Spec La: Maximum 500 ppm iron- "'%j 

> 

(44) (14) (3) (1) stained pegmatite northeast of () 

trl 

Red Hill Ranch. Cluster Bear 'i:l 

Creek district. 0 

Spec Mo: All 66 unqualified values + 2L, 5L, 2, 3 5-30 50-300 500-1,500 Spec Mo: Maximum 1,000 ppm 

t-3 

trl 

48 L values. (57) (39) (15) (1) from malachitic garnet rock z 

t-3 

west side Buck Mountain. ~ 

> Clusters: Pearl, Farwell, Gilpin, t-4 

and Greenville districts, 

Crystal-Pedad claim area. 

Spec Nb: 20 ppm and greater (22) ----- 20 30 50, 70 100, 150 Spec Nb: Maximum 150 ppm 

(11) (7) (3) (1) malachitic muscovite pegmatite, 

Farwell. Other highs: Soda 

Creek, south Lone Pine Creek. ....... 

t.:) 

....... 
TABLE 5.-Summary of anomalous rock geochemical data shown on individual element maps-Continued 1-' 

1:\:) 

1:\:) 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness a= Rock sample data (coded "A"I Symbol code, in parts per million Rock geochemistry 0 

~ 

Element with chosen values Smallest Next to Next to Largest z 

symbol smallest largest symbol t-3 

N 

1-t 

Spec Ni: 20 ppm and greater (61) ----- 20, 30 50-100 150-300 500, 700 Spec Ni: Maximum 700 ppm in ~ 

(35) (15) (6) (5) Bear Creek peridotite and ~ 

tz:j 

dunite segregate of gabbro of t-t 

Elkhorn Mountain. 1-t 

~ 

Spec Ph: 50 ppm and greater (109 + 50-300 500-3,000 5,000-15,000, Spec Ph: Maximum >20,000 ppm t-t 

0 15 G values). 5,000G, 20,000G from Greenville soil; In- tz:j 

(63) (35) (6) (None) dependence Mountain iron- ::0 

z 

manganese ore; and quartz- tz:j 

galena or quartz-pyrite veins r.n 

r.n in or near the Elkhorn mine. > 

15,000 ppm Gilpin mine; z 

0 

>5,000 ppm cluster at z 

Greenville. Other clusters: 0 

Lower Slavonia to Red Dirt ~ 

t-3 

Pass, Pearl, Bear Creek. ::c: 

tz:j 

AA Ph: 30 ppm and greater (89) ------ 30-120 130-1,000 1,300-10,000 14,000-68,000 AA Ph: Maximum 68,000 ppm ::0 

(39) (23) (20) (7) quartz-galena vein Elkhorn z 

mine. Other maximums and ~ 

> clusters similar except Green- ~ 

ville and Lower Slavonia ~ 

~ analyses lacking, and King > 

Solomon Creek high is new with z 

0 AA data. tz:j 

Spec Sh: All 18 unqualified values + 100L 100-200 300-500 700, 1,000 Spec Sh: Maximum 1,000 ppm 

51 L values. (51) (11) (5) (2) and highest cluster Elkhorn 

mine. Second highest cluster 

Greenville mine. 
Spec Sc: 20 ppm and greater (57) ----- 20 30 50 70. 100 Spec Sc: Maximum 100 ppm in 

(29) (22) (4) (2) pyritic gabbro near Dudley 

Creek. Concentrated in epidote 

or hornblende rocks. 

Spec Sn: All 58 unqualified values + 10L, 10, 15 20, 30 50, 70 100, 150 Spec Sn: Maximum 150 ppm in 

43 L values. (69) (17) (12) (3) Upper Slavonia and Farwell ore; 

100 ppm in iron-gossan at 

Gilpin mine. Clusters: Upper trj 

Slavonia, Farwell, southwest < 

> Pearl, and Greenville districts. t"" 

Spec Sr: 1,000 ppm and greater (9 + 1,000 1,500 2,000 5,000G Spec Sr: Maximum >5,000 ppm 

c::: 

> 

1 G). (3) (2) (4) (1) epidote rock Soda Creek. All t-3 

concentrations associated with -0 

epidote. z 

0 

Spec V: 30 ppm and greater (163) ----- 30-70 100, 150 200, 300 500, 700 Spec V: Maximum 700 ppm in l'%j 

(73) (59) (27) (4) epidote-veined amphibolite near rn 

c::: a shear zone, Black Mountain. ~ 

Commonly concentrated in l'%j 

> 

epidote amphibole rocks. Many n 

trj 

clusters in north half or ~ 

southwest corner of area. 0 

Spec W: All 10 unqualified values + 50L 50-100 150-300 500-1,000 Spec W: Clusters: Pearl (includes t-3 

trj 

62 L values. (62) (4) (3) (3) maximum 1,000 ppm in mala- z 

t-3 

chite ore), Farwell, and Green- -

> ville districts. t"" 

Spec Y: 50 ppm and greater (61) ------ 50, 70 100, 150 200, 300 500 Spec Y: Maximum 500 ppm in 

(44) (14) (2) (1) malachitic muscovite, Farwell; 

most in 150-300 ppm range in 

association with fluorite. 

......... 

~ 

Clj 
TABLE 5.-Summary of anomalous rock geochemical data shown on individual element maps-Continued 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Rock sample data (coded "A") Symbol code, in parts per million 

Element with chosen values 

Spec Zn: All 100 unqualified values 

+ 27 L values and 32 G values. 

AA Zn: 30 ppm and greater (196) 

Smallest Next to Next to 

symbol smallest 

100L, 200L, 1,000-7,000 

100-700 

(77) (42) 

30-260 

(131) 

280-2,500 

(34) 

largest 

10,000 

(8) 

2,900-25,000 

(22) 

Largest 

symbol 

10,000G 

(32) 

40,000-200,000 

(9) 

Rock geochemistry 

Spec Zn: Prominent clusters in 

the Greenville and Elkhorn 

districts, in an east-west zone 

across the Pearl district, and at 

both the Lower and Upper 

Slavonia mines. 

AA Zn: Maximum 200,000 ppm 

from galena-quartz vein at the 

Elkhorn mine; 190,000 ppm 

from ore both at Independence 

Mountain and Upper Slavonia 

mines. Clusters same as Spec 

Zn except Greenville and Lower 

Slavonia analyses lacking, and 

additional small cluster present 

in northern Farwell district. 

~ 

~ 

~ 

=:: 

0 

c:::: 

z 

1-3 

N 

; 

~ 

t_:rj 

t-4 

~ 

-t-4 

tJ 

t_:rj 

~ 

z 

t_:rj 

00 

00 

> z 

tJ 

z 

0 

~ ::t: 

t_:rj 

~ 

z 

'"0 

> 

~ 

~ 

~ z 

0 

t_:rj 
TABLE 6.-Summary of anomalous stream-sediment geochemical data shown on individual element maps in the vicinity of the Mount Zirkel 

Wilderness 

[Spec, analysis obtained by standard semiquantitative spectrographic techniques; AA, analysis by atomic absorption techniques; L, less than; G, greater than. Because these analyses were 

performed over a period of years during which the L and G limits varied for many different elements, symbol boundary values are chosen to eliminate the effect of these variations. Total 

number of analyses (shown in parentheses below concentration) given for each symbol below may vary slightly from actual totals on element maps because some samples lie outside the 

area of the element maps and were therefore excluded from them. Localities of individual analyses of particular interest should be checked against plate 2 (where their positions are accurately shown); individual element maps frequently distort the locations slightly in order to alleviate crowding. In right column, anomalous single highs or prominent clusters of data are mention· 

ed where pertinent for each analyzed element selected. Note that presence of anomalous concentrations of an element, although providing targets in any search for economic concentrations, 

does not guarantee that economic concentrations are present. Areas within present boundaries of Mount Zirkel Wilderness or adjacent area are italicized] 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Sediment sample data (Coded "B ") Symbol code in parts per million 

Element with chosen values 

Spec Ag: All 16 unqualified 

values + 34 L values. 

AA Ag: 14 ppm and greater 

(9). 

Smallest 

symbol 

0.5L 

(34) 

0.4 

(4) 

Next to 

smallest 

0.5, 0.7 

(12) 

0.5 

(3) 

Next to 

largest 

1 

(2) 

1 

(1) 

Largest 

symbol 

2 

(2) 

2 

(1) 

Stream-sediment geochemistry 

Spec Ag: Maximum 2 ppm 1 mile westsouthwest of Stump Park in unmapped 

tributary of Encampment River, and in 

Greenville Creek just below lower 

Greenville mine. Clusters (mostly trace 

amounts) in the northwest part of area 

in streams below Tertiary intrusives, 

south of Horse Thief Peak, and in 

Silver City basin. 

AA Ag: Maximum 2 ppm and cluster in 

Greenville Creek just below lower 

Greenville mine. 1 ppm in Beaver Creek 

tributary draining the east side of 

Hahns Peak. Besides other lesser 

values, three of less than 0.5 ppm (not 

shown on map) in vicinity of Hahns 

Peak. 

t%'J 

< > 8 

~ 0 

z 

0 

1-.rj 

en 

c:: 

~ 

~ ~ ~ 

~ 

1-" 

t-.:1 

C11 
TABLE 6.-Summary of anomalous stream-sediment geochemical data shown on individual element maps-Continued 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Sediment sample data (Coded "B") 

Element with chosen values 

AA Au: All 7 unqualified 

values. 

Spec Be: 5 ppm and greater 

(13). 

Spec Co: 50 ppm and greater 

(31). 

Spec Cr: 500 ppm and 

greater (48 + 1 G value). 

Smallest 

symbol 

(None) 

(None) 

(None) 

500 

(33) 

Symbol code in parts per million 

Next to 

smallest 

(None) 

(None) 

(None) 

700 

(8) 

Next to 

largest 

0.05-0.1 

(5) 

5 

(9) 

50 

(29) 

1,000, 1,500 

(6) 

Largest 

symbol 

0.2 

(2) 

7 

(4) 

70 

(2) 

2,000, 5,000G 

(2) 

Stream-sediment geochemistry 

AA Au: Maximum 0.2 ppm from head of 

Silver City Creek, and east of Bear 

Mountain. Not much detectable gold in 

stream sediments. 

Spec Be: Maximum 7 ppm and a notable 

cluster in streams near the type locality 

of the quartz monzonite of Seven 

Lakes; a few others within the Mount 

Ethel pluton. 

Spec Co: Two maximum values of 70 

ppm; one east of Three Island Lake; the 

other associated with a tight cluster 

from streams issuing from beneath rock 

glaciers north of Ute Lake. Other 

clusters on Buck Mountain, and in the 

northeast part of the gabbro of Elkhorn 

Mountain. 

Spec Cr: Isolated maximum of greater 

than 5,000 ppm in a tributary of Silver 

City Creek south of Big Red Park. 

Most anomalous values, including a 

secondary maximum of 2,000 ppm and 

an associated tight cluster, are within 5 

miles of Twin Lake. Another tight 

cluster on east side Buck Mountain. 

1--' 

t..:> 

m 

a:: 

0 

c: 

z 

1-3 

N 

; 

~ t_:l:j 

t"" 

:E 

~ 

t"" 

tj 

t_:l:j 

:;:o 

z 

t_:l:j 

r:n 

r:n 

> z 

tj 

z 

0 

:;:o 

1-3 

::I: 

t_:l:j 

:;:o 

z 

~ :;:o 

~ 

~ z 

0 

t_:l:j 
Spec Cu: 50 ppm and greater 50 70 100, 150 200, 300 Spec Cu: Maximum 300 ppm in Green-

(324). (159) (144) (17) (4) ville Creek just below lower Greenville 

mine, and in Silver City Creek; 200 

ppm in unmapped tributary of Silver 

City Creek east of Silver City basin. 

Except for a Greenville cluster, nearly 

all the anomalous values are located in 

the north half of the map area, concen- t_:l:j 

trated in a 5-mile-wide belt stretching <! 

> from Lone Pine Creek to west of ~ 

Elkhorn Mountain, with only scattered c:::: 

> 

values in the Pearl district. t-3 

~ 

AA Cu: 30 ppm and greater 30-35 40-55 60-120 200-250 AA Cu: Maximum 250 ppm and next two 0 

z (305). (169) (105) (27) (4) values (230 and 220 ppm) confirm three 0 

Spec Cu maximums mentioned above. ""j 

Silver City Creek anomalies may be rn 

c:::: related to mineralization along faults ::0 

cutting rocks of Silver City basin. ""j 

> 

Overall anomalous pattern confirms a 

t_:l:j 

Spec Cu pattern, especially in Gilpin 'i::l 

district, but with additional clusters on 0 

t-3 Farwell Mountain and in Whiskey t_:l:j 

Creek, and fewer values near Pearl. z 

t-3 Spec La: 100 ppm and 100 150 200 300 Spec La: Maximum 300 ppm west of ~ 

> greater (7 4). (44) (21) (7) (2) Seven Lakes (in center of cluster), and ~ 

along Encampment tributary west of 

Buffalo Ridge. Additionally, there is a 

loose cluster centered on the Gilpin 

district, and a tight cluster along a 

quartz monzonite contact west of 

Battle Ridge. 1--' 

1::...:> 

-l 
TABLE 6.-Summary of anomalous stream-sediment geochemical data shown on individual element maps-Continued ...... 

to.:> 

00 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness s:: 

Sediment sample data (Coded "B") Symbol code in parts per million Stream-sediment geochemistry 0 

Smallest Next to Next to Largest c:: Element with chosen values z 

symbol smallest largest symbol 1-3 

N 

Spec Mo: All 21 unqualified 5L,5 7, 10 15, 20 30, 50 Spec-Mo: Maximum 50 ppm and cluster ~ 

!;:d 

values + 1 L value. (5) (13) (3) (1) east of Ceanothuse Lake (northeast of ~ 

tlj 

Rainbow Lake). Another cluster near tot 

Farwell mine. :E 

Spec Nb: 20 ppm and greater 20 30, 50 70, 100 Spec Nb: Maximum 100 ppm from two ...... tot 

(36). (28) (6) (None) (2) localities in South Fork Mad Creek tJ 

tlj 

above the junction with the main stem !;:d 

of Mad Creek. One linear cluster ex- z 

tlj 

tends from Seven Lakes to Black r:n 

r:n Mountain. > 

Spec Ni: 50 ppm and greater 50 70 100 150-300 Spec Ni: Maximum 300 ppm in stream is- z 

(327). (178) (112) (23) (14) suing from rock glacier between Twin tJ 

z and Ute Lakes; 200 ppm in Encamp- 0 

ment tributary southwest of Gem Lake. !;:d 

1-3 

Anomalous pattern broadly parallel to ::I: 

that of copper with a wide belt between tlj 

!;:d 

Lone Pine Creek and west of Elkhorn z 

Mountain, but with the absence of a ~ 

> maximum in the Greenville district. !;:d 

Spec Ph: 50 ppm and greater 50 70 100, 150 700 Spec Ph: Maximum 700 ppm and 150 ~ 

(159). (110) (38) (10) (1) ppm cluster in Greenville Creek below !;:d 

> lowest Greenville mine; 150 ppm in z 

Gilpin Creek tributary below Gilpin 0 

tlj 

mine. Broad concentration of 

anomalous values in triangular area 
AA Pb: 30 ppm and greater 

(168). 

Spec Sc: 50 ppm and greater 

(116). 

Spec Sn: All 9 unqualified 

values + 7 L values. 

30-35 

(88) 

(None) 

10L 

(7) 

40-55 

(66) 

50 

(99) 

10, 15 

(5) 

60-100 

(9) 

(None) 

20, 30 

(2) 

130-570 

(5) 

70 

(17) 

50, 70 

(2) 

with Lone Pine Creek, Silver City 

basin, and Seven Lakes near comers of 

triangle. No apparent stream-sediment 

anomaly below Elkhorn mine! 

AA Pb: Maximum 570 ppm and other 

similar values below Greenville and 

Gilpin mines. Similar overall anomaly 

pattern to Spec Pb, especially with 

tight Greenville cluster and broad 

Gilpin cluster, but with more 

anomalous values in Damfino and lower 

Encampment drainages. 

Spec Sc: Maximum 70 ppm at 17 

localities in north half of map area. 

Anomalous values fall in broad belt 

reminiscent of copper and nickel, but 

with nothing west of Whiskey Creek. 

Spec Sn: Maximum 70 ppm in tributary 

of South Fork Hog Park Creek just 

southeast of where the Continental 

Divide passes into Wyoming; 50 ppm 

northwest of Dome Peak; 30 ppm in a 

tributary of the Encampment River 

southeast of the Guard Station; 20 ppm 

in a tributary of Middle Fork Little 

Snake River east of Big Red Park. 

Small cluster near Rainbow Lake. 

t_%j 

~ ~ 

c 

> 

~ 

0 

z 

0 

"%j 

U'1 

c 

~ 

"%j 

> 0 

t_%j 

""0 

0 

~ z 

~ 

> 

~ 

,__. 

t-,j 

~ 
TABLE 6.-Summary of anomalous stream-sediment geochemical data shown on individual element maps-Continued 

Map symbol key for selected geochemical data of Mount Zirkel Wilderness 

Sediment sample data (Coded "B"l Symbol code in parts per million 

Element with chosen values 

Spec Sr: 500 ppm and 

greater (88). 

Spec V: 300 ppm and greater 

(97). 

Spec Y: 70 ppm and greater 

(407). 

Smallest Next to Next to 

symbol 

(None) 

(None) 

70 

(297) 

smallest 

500 

(71) 

300 

(89) 

100, 150 

(98) 

largest 

(None) 

500 

(7) 

200 

(10) 

Largest 

symbol 

700 

(17) 

700 

(1) 

300 

(2) 

Stream-sediment geochemistry 

Spec Sr: Maximum 70 ppm at 17 

localities, mainly in the north half of 

the map area. Main cluster Three 

Island Lake to Bear Mountain; another 

southwest of West Fork Lake; another 

along Soda Creek-Fish Creek shear 

zone. 

Spec V: Maximum 700 ppm from natural 

magnetite concentrate in Big Creek 

southwest of Floyd Peak. Other highest 

anomalous values from magnetite concentrates or streams draining Mesozoic 

rocks. Main cluster in north half of 

map area similar to that for copper and 

nickel. 

Spec Y: Maximum 300 ppm in Beaver 

Creek northwest of Big Creek Lake, 

and Mica Creek above Gilpin Creek. 

Most anomalous values scattered 

throughout north half of map area. 

I-' 

~ 

0 

a= 

0 

c::: 

z 

t-3 

~ 

; 

~ 

tr1 

t-t 

~ 

"'""" t-t 

t;:j 

tr1 

~ 

z 

tr1 

00 

00 

> z 

t;:j 

z 

0 

~ 

t-3 

:::c: 

tr1 

~ 

z 

~ 

> 

~ 

~ 

~ z 

0 

tr1 
Spec Zn: All 31 unqualified 

values + 26 L values. 

AA Zn: 125 ppm and greater 

(61). 

Spec Zr: 500 ppm and 

greater (110 + 5 G values). 

200L,200,300 500,700 

(48) (4) 

125-170 

(29) 

500 

(47) 

180-260 

(20) 

700 

(44) 

1,000, 1,500 

(4) 

270-480 

(9) 

1,000 

(19) 

2,000, 3,000 

(1) 

850-2,700 

(3) 

1,000G 

(5) 

Spec Zn: Maximum 3,000 ppm in Greenville Creek below lowest Greenville 

mine, with next four highest values 

(1,000-1,500 ppm) successively 

downstream from this. Smaller cluster 

around Bighorn Lake. 

AA Zn: Maximum 2, 700 ppm and same 

concentration of highest values in 

Greenville Creek. Clusters from Bighorn 

Lake to Gilpin Lake, and east of Hahns 

Peak. 

Spec Zr: Maximum greater than 1,000 

ppm from mouth of Hot Spring Creek; 

above Twisty Park; east of Seven 

Lakes; in South Fork Big Creek above 

the Pearl smelter; and in a tributary of 

Silver City Creek south of Big Red 

Park (same sample with highest 

chromium). Many samples clustered in 

east-west belt in northernmost quarter 

of map area. 

trj 

< 

> 

~ 

c::: 

> >-3 

0 

z 

0 

"%j 

rn 

c::: 

~ "%j 

> 0 

t_:l:j 

"t1 

0 

>-3 

t_:l:j 

z 

>-3 

> 

~ 

....... 

~ 

....... 
132 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 7.-Summary of semiquantitative spectrographic 

[Data values for all columns: top, low; boldface, average; bottom, high. Average is generally the mode; average is 

collected by George L. Snyder, 1965-72. Semiquantitative spectrographic analyses by J.C. Hamilton (USGS lab 

B. Wayne Lanthom (USGS lab numbers D141154-D141162, Jan. 8, 1970); Leon A. Bradley (USGS lab numbers 

D103027-Dl03060, Feb. 1, 1972); and Harriet G. Neiman (USGS lab numbers D103296-Dl03319, Apr. 25, 1973). 

detected in amount greater than shown; L, detected in amount less than shown] 

Number 

of Number of Fe Mg Ca Ti Mn B 

samples rocks Sample types (weight percent) 

analyzed represented 

8 5 Tertiary intrusives (of 3 1 2 0.3 300 ION 

intermediate compo- 5 3 5 0.7 700 lON 

sition). 7 5 7 1 700 lOL 

13 13 1.4-b.y. felsic plutonic 0.7 0.03 0.15 0.02 20 

rocks (mainly quartz 2 0.3 1.5 0.15 200 ION 

monzonite and 3 0 1.5 0.3 500 -

granite). 

4 4 1.4-b.y. mafic plutonic 5 1 1.5 0.5 500 -

rocks (granodiorite, 7 1.5 3 0.7 700 lON 

diabase). 7 2 5 0.7 700 -

14 14 1. 7 -b.y. felsic plutonic 0.7 0.1 0.2 0.05 70 -

rocks (mainly quartz 3 0.5 (1) 0.15 200 lON 

monzonite and 7 0.7 3 0.3 500 -

granite). 

13 13 1.7-b.y. mafic plutonic 1 0.3 2 0.005 200 -

and volcanic rocks 7 7 7 0.3 1000 lON 

(tonalite, gabbro, lOG 7 10 5000 -

amphibolite). 

45 38 1.7-b.y.(?) ultramafic 3 3 0.03 0.01 300 ION 

rocks (peridotite, (10) 10 3 0.1 1000 lON 

dunite, horn- lOG lOG lOG 0.3 2000 20 

blendite). 

2 2 1.7-b.y.(?) pegmatite 0.15 0.015 0.2 0.03 70 - dikes. (0.5) (0.05) (0.5) (0.05) (100) lON 

1 0.1 1 0.07 100 -

5 5 1.7-b.y. felsic gneiss 1 0.015 0.3 0.05 150 -

country rock. 3 (0.7) (1.5) 0.3 (500) lON 

10 2 3 0.5 1500 -

19 8 1.7-b.y. pelitic schist 0.5 0.2 0.03 0.05 100 ION 

or felsic sillimanitic 1.5 0.7 0.5 0.2 (500) lON 

pod-rock. 10 1.5 1 0.3 1000 30 

5 5 1.7-b.y. marble and 1.5 1 10 0.05 700 -

calc-silicate rock. 2 1.5 lOG 0.1 1500 lON 

lOG 3 lOG 0.15 7000 -

1 1.7-b.y. quartzite --- (2) (0.2) (0.05) (0.3) (50) (lON) 

7 7 Conspicuously reddish 10 0.7 1 0.1 700 lON 

soils (mostly over- lOG 5 2 0.15 1500 lON 

lying dunite). lOG 7 3 0.3 1500 lOL 

136 115 
EVALUATION OF SURFACE POTENTIAL 133 

data for unmineralized crystalline rocks, Park Range, Colorado 

the mean-in parentheses-where the data are bimodal or where there are too few data for mode. All samples 

numbers D101275-D101279, Jan. 20, 1966); G.W. Sears, Jr. (USGS lab numbers D101640-D101658, Mar. 3, 1967); 

D102923-D102926, April 22, 1971); Larry D. Forshey (USGS lab numbers D154815-Dl54855, Dec. 3, 1971, and 

Looked for but not found: Ag, As, Au, Bi, Cd, Pd, Pt, Sb, Sn, Te, U, W, Zn. N, not detected at limit shown; G, 

Ba Be Co Cr Cu La Mo Nb Ni Pb Sc Sr v Y Zr 

1500 

3000 

5000 

50 

I500 

1N 

I 

2 

1N 

2 

2000 3 

1000 1 

2000 I.5 

2000 

500 

I500 

2 

IN 

2 

3000 5 

20 

(IOO) 

1N 

IN 

15 

30 

50 

200 

50 300 

3 1 

5 5 

30 

30 

30 

IOO 

70 150 

IN 30N 

3 I50 

10 20 20 300 

10 15 20 100 

20 (50) (50) I50 

30 100 

3N 1N 

5 5 

70 200 

1N 30N 

(3) 50 

IO 30 10 200 

3N 2 

50 300 

3 

70 

30N 

30N 

(parts per million) 

3N 10 

5 20 

5 20 

3N 10 

3N IO 

3 50 

10 

5L IO 

10 

10L 

3N IO 

15 

70 

I 50 

20 10 

30 20 

1500 

I500 

70 

I 50 

300 50 

3N 20 

3N 30 

30 3000 300 

5N 20 10 

5 200 30 

15 70 

20 I50 

30 200 

10 30 

20 150 

10 50 10 500 100 50 300 

10 

30 

10 I5 

I5 20 

500 100 

500 200 

30 150 

30 (200) 

50 15 20 IOOO 

3N 10N 5N 100 

3N 20 5 (200) 

200 30 300 

7N 10N 70 

50 20 150 

7 50 15 700 70 70 200 

3N 10N 3N 10N 5N 50 10 10N 10N 

3N ION IOO ION 30 700 (IOO) ION ION 

1000 1.5 50 700 150 70L 7 20L 150 15 70 1500 300 30 150 

5 1N 20 100 1 3N 10N 100 5N 20 

50 IN. 50 I500 50 30N 3N ION (500) 

10N 5 

ION 15 

30 100 

70 70 

10N 10N 

IO ION 

700 1.5 150 5000 300 10 20L 1000 300 200 15 50 

150 1N 

(1) 

2000 1.5 

30 

I500 

1500 

700 

IOOO 

1 

I 

3 

1N 

2 

2000 3 

15 1N 

(200) (1.5) 

1 1 30N 

3N (2) 

2 

(3) 3N IOL 

7 70 

3N 1N 1 30 

3N (2) (2) 70 

20 20 200 70 

3N 1N 1N 30N 

3N 1 (2) 70 

20 I50 

3N 1 

3N I 

20 

2 

(5) 

70 

30N 

30N 

10N 

3N IOL 

30 

10L 

3N 10 

15 

10N 

3N lOL 

700 3 50 

(I50) (IN) (3N) 

500 300 100 10 

(30) (3) (30N) (3N) (15) 

20 20 

3N (30) 5N 

50 300 

3N 10N 5N 5 

3L ION 5N 200 

10 30 

3N 15 

3N I5 

50 500 

5N 30 

(5) I50 

30 50 20 200 

3N 10N 5N 20 

3N 20 7 (I50) 

5N 10L 10N 

(5) 

7 10 70 

5N 20 100 

5N (50) IOO 

300 100 300 

5N 10 100 

5L 50 IOO 

150 100 500 

5N 10 20 

5N 50 70 

150 

(3N) 

I50 20 1500 100 

(10) (5) (10) (30) 

200 1N 7 70 20 30N 10N 20 15 10 

20 I5 

100 50 

I50 100 

70 200 

(10)(150) 

10 50 

200 IN IOO I500 I50 30N 3N lOL 300 10 70 

700 1.5 100 1500 150 70 10L 700 30 20 300 150 30 100 
134 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

GENERAL EVALUATION OF SURFACE ANOMALIES 

Attempt was made to evaluate the reliability of geochemical sampling of stream sediments under local conditions as a guide to ore 

deposits that crop out at the surface. Would sediment samples reflect 

anomalous values downstream from known ore deposits? The attempt 

was made on Greenville Creek in the vicinity of the Greenville mine, 

an area of known geology, variable topography, and easily accessible 

sediments. (See fig. 51.) Conditions were purposely chosen to minimize 

extraneous variables. Most collections were made in one-half day; all 

were collected by one person; most samples were analyzed in a single 

batch by a single analyst using comparable analytical techniques. 

Stream sediments were collected in Greenville Creek at intervals of 

150 to 300m (500-1,000 ft), providing much closer control than the 

average spacing elsewhere throughout the mapped area. 5 The results 

illustrate both the strengths and weaknesses of the Park Range sampling system. Under favorable topographic conditions the sampling 

net is probably adequate, but, under unfavorable conditions, there is 

no assurance that an ore deposit of a certain type could not slip 

undetected through the net spacing. The reader should note that, with 

the elements indicated in figure 51, under high-transport conditions 

zinc is detectable farthest downstream, silver least far, and copper 

and lead for intermediate distances, averaging about 1.2 km (3/4 mi). 

Conditions are less favorable in rolling upland topography, where, 

despite visible ore in outcrop and a clear contribution to the nearby 

soil, speed of transport is apparently low enough that this soil has 

not moved very far (less than 0.5 km, 1/3 mi) from its site of origin. 

Other things being equal, therefore, geochemical analysis of stream 

sediments has a greater chance of detecting an exposed ore deposit 

in environments with rugged topography than in subdued topography 

situations. Partially offsetting this topographic effect is the fact that 

tributary density, and hence sampling density, is often greatest in 

high-basin subdued-topography environments, where the drainage patterns are in the process of being established. 

5

Reference to plate 2 will show that the sediment-sample spacing has varied along streams from intervals of 

0.15-3 km (0.1-2 mi) and with an average of about 0.8 km (0.5 mi). The sampling net is less dense in the south 

half of the map area, where the work began and where visible shows of ore were less numerous. As the work progressed to the north half of the map area and as shows of basement ore became more numerous, the sediment sampling 

density increased commensurately, with the result that sampling control is most complete in the area of greatest 

surface mineral potential. 
EVALUATION OF SURFACE POTENTIAL 

106°55' 

1000 2000 

5000 

EXPLANATION 

Ag l Cu 

Zn I Pb 

Sample point - Showing con ce ntra ~ 

tion in ppm; N, not detected 

3000 METERS 

10,000 FEET 

135 

106°52 ' 30" 

FIGURE 51.-Test, under both favorable and unfavorable conditions, of detectability 

of selected elements near known Greenville mine ore zone(s) by AA (atomic absorption) analysis of stream sediments. Note that steep canyon topography creating rapidtransport environment apparently favors detection over stable-upland environment. 

All samples are stream sediment unless shown as " (soil)." 
136 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Stream-sediment geochemical analysis can have very positive 

results, indicating anomalously high target areas that might warrant 

more assiduous search by private interests. It can narrow or pinpoint 

targets and, conceivably, save exploration expenses. However, lack 

of a geochemical anomaly does not by itself guarantee lack of an exploitable deposit at depth. Negative evidence can never be equivalent 

to complete mathematical proof; it is merely statistical. Whatever 

deposits are found as a result of this or other geochemical studies, 

others will certainly be missed; some "blind" deposits may eventually be found by other techniques, whereas some may never be found. 

A potentially economic deposit may fail to create a significant geochemical anomaly for any of the following reasons: 

1. The deposit may be uBder sufficient cover to prevent guide elements from reaching 

the surface in detectable amounts. 

2. The deposit may consist of materials too light or too soluble to linger in stream 

sediments (for example, chlorine, sodium, carbon dioxide). 

3. The local conditions of topography may not favor transport away from the site. 

(See fig. 51.) 

4. Evidence of a small source can be flooded out if it is near a large volume of sediment that can rapidly dilute its detritus. 

5. The definition of an economic deposit varies with time. Economic conditions in the 

society at large have a definite effect. There are numerous examples where yesterday's gangue is today's ore, or where yesterday's conditional resources are today's 

demonstrated reserves (Brobst and Pratt, 1973a, p. 4; 1973b, p. 4; U.S. Geological 

Survey, 1975, p. 4). 

All the above negative provisions, and probably others unmentioned, 

are pertinent in an evaluation of the present geochemical survey of 

the Mount Zirkel area. It is estimated that 20 percent of the area is 

under thick cover, near large sources of diluting alluvium, topographically gentle, or otherwise unsuitable, so that only minimum benefit 

would be derived from collection of geochemical samples. Of the 80 

percent of the area where the sampling is most valid, perhaps 90 percent of this has been sampled, the remaining 10 percent missed due 

to sampling inefficiencies, mainly the thinner coverage early in the 

program. If these estimates are anywhere near correct, this means 

that one-fourth, or slightly more, of the area could harbor anomalous 

geochemistry undetected or undetectable by this stream-sediment 

sampling program. However, the sediment geochemical survey is supplemented by the field observations of the surveyors and by the rocksample geochemical survey. The reader should note that the coverage 

net of traverses walked by the field mappers was substantially the 

same throughout the area from south to north and from beginning 

to end of the work. Covering or diluting detrital sediments, soil, colluvium, or till may contain fragments of mineralized rock undetectable 

by analysis of downstream detritus but physically observable by 

surveyors at or near the site of origin, especially by surveyors actively 
EVALUATION OF SURFACE POTENTIAL 137 

looking for such signs of mineralized rock. Also, in addition to the 426 

samples of potential ore analyzed, more than 1,671 additional rock 

samples were collected of the more typical unmineralized rocks of the 

area, and these have provided additional chemical data useful for 

evaluating the surface mineral potential of the area. 

The following tabulation gives the best current appraisal of the 

likelihood of various types of ore deposits being present near the surface in the Mount Zirkel area: 

Large high-grade deposits.-Except for elements like Si, AI, Fe, Mg 

and Ca locked in silicates, deposits of this type are not known to be 

present at the present ground surface and none are likely to have been 

missed. 

Large low-grade deposits.-Some of these are certainly present, 

several discovered as a result of this survey, and it is unlikely that 

any were missed. For example, the presence of copper and chalcophile 

elements in metavolcanics near quartz monzonite contacts in the north 

half of the mapped area, the concentration of interstitial fluorite in 

rocks of the Mount Ethel pluton, and the occurrence of beryllium in 

the vicinity of Seven Lakes are either newly discovered or better 

understood as a direct result of this survey. The large area covered 

by each of these mineral concentrations makes it virtually impossible for similar deposits to exist undetected within the current net of 

samples and observations. 

Small high-grade deposits.-Some of these were detected in several 

ways or by several techniques; others were detected by some but 

missed by other techniques; some may have been missed altogether. 

For example, the Greenville mine(s) ore zone varies from 0.3 m (1ft) 

to several meters or yards wide and is more than a mile long; malachitic 

bloom is readily observable in outcrop or underground, but evidence 

of the zone is missing where it totally disappears beneath younger 

cover rocks. Nevertheless, the topographically most favorable exposures of this zone were detectable in nearby stream sediments at 

least as close as 1.2 km (% mi) away. (The exact distance varies slightly 

for different elements; see fig. 51.) One can say with confidence that 

not many lower Greenvilles could have slipped undetected through 

this survey. In contrast, the Elkhorn mine ore zone was not readily 

observable in outcrop or underground, but the dump yielded 2.5- to 

1 0-cm chunks of simple galena veins that were the highest sources 

of rock silver, lead, and zinc in this study. The stream sediment nearest 

to the Elkhorn mine was collected less than 260 m (900 ft) directly 

downhill from the mine, and this was supplemented by four other 

stream sediments downdrainage at successively greater intervals to 

Whiskey Park. None of these sediments provided analytically 

anomalous silver, lead, or zinc! On this basis, it seems clear that many 
138 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

undiscovered Elkhorns could exist undetected throughout the Mount 

Zirkel area. Although the Elkhorn mine has been only submarginally 

economic, the distinct possibility of thin "blind" veins containing 

economically precious metals like silver or gold cannot be discounted. 

Small low-grade deposits.-Several of these are known to be present and many others may have been missed, but, in either case, they 

appear to be of minimal economic interest. Small low-grade deposits 

could be marginally economically interesting for at least two reasons: 

(1) They could lead to something bigger. With the publication of the 

data contained in this report, it is presumed that other parties will 

pursue this possibility. (2) They could be low-grade in many elements 

(multicommodity) so that the aggregate element value makes exploitation possible. No small low-grade multielement deposits of economic 

interest are known in the Mount Zirkel Wilderness and vicinity, but 

they were carefully searched for in at least one type of deposit, the 

ultramafic rocks, which are potential sources of cobalt, chromium, 

nickel, platinum, palladium, and other elements. To summarize here, 

it seems unlikely that these small low-grade surface ultramafic 

deposits will soon be economic even with a multielement consideration. 

METALLIC DEPOSITS 

The distribution of various metallic elements will be described herein 

emphasizing unusual or anomalous concentrations and utilizing the 

geochemical surveys of both rocks and stream sediments. The 

geochemical survey data are summarized in tables 5 and 6 and on individual element maps (figs. 52-104, 107, 108) that group the 

anomalous data using no more than four sizes of map symbols (largest 

symbol equals largest anomaly). (Symbols are explained in tables 5 

and 6.) The elements are grouped here in the following categories: 

1. Copper-lead-zinc-silver plus gold, mercury, antimony, arsenic, tungsten, tin, cadmium, bismuth, and gallium; 

2. Uranium-thorium plus molybdenum, niobium, lanthanum, yttrium, and other rare 

earths; 

3. Chromium-platinum plus palladium, cobalt, and nickel; 

4. Major elements, iron, magnesium, calcium, titanium, and manganese plus minor 

elements boron, barium, beryllium, scandium, strontium, vanadium, and zirconium. 

The reader should note that each element map purposely separates 

data from that of all other elements, that rock and stream-sediment 

data are separated, and that spectrographic, atomic absorption, and 

instrumental data are also separated. This permits not only independent scrutiny of each body of data but also the dual comparison of 
EVALUATION OF SURFACE POTENTIAL 139 

whatever individual sets of data are desired to be compared. Because, 

for reasons of analytical technique, sampling variance, mineral 

distribution, or other unknown factors, no two of the data sets are 

completely identical6 (see comments in tables 5 and 6), it is believed 

that this ability to make independent comparisons will be useful to 

most readers. This separate portrayal of individual elements encourages maximum freedom in following individual geochemical insights toward mineral resource exploration or assessment. 

COPPER, LEAD, ZINC, SILVER, AND RELATED ELEMENTS 

The detailed distribution of anomalous rock and stream-sediment 

copper, lead, zinc, silver, gold, mercury, antimony, arsenic, tungsten, 

tin, cadmium, bismuth, and gallium are shown, in order, on figures 

52-78. Chosen anomaly limits plus observed locations of maximum 

values and prominent clusters of anomalous data are summarized in 

tables 5 and 6 and figures 107-109. Some other elements grouped for 

convenience with later sets of data also have some geochemical patterns analogous to those of the elements grouped here. For details, 

the reader should refer to the detailed data, but, in general, most of 

the multielement anomalies found or indicated have been from five 

districts: 

1. Elkhorn: Rock maxima for silver, cadmium, lead, antimony, and zinc. Includes 

Elkhorn mine. 

2. Farwell: High rock copper, lead, tin, tungsten, and zinc, not to mention rock maxima in niobium and yttrium and a molybdenum cluster in stream sediments. Includes mines north and west of Farwell Mountain, some within present adjacent 

area boundary. 

3. Gilpin: Rock maxima in gold, mercury, and tin, plus high rock zinc and high rock 

and stream-sediment lead. Includes Lower and Upper Slavonia mines (figs. 14, 36), 

scheelite reported from here by Tweto (1960, p. 1408); two mines referred to herein 

as the Gilpin mines (fig. 3), all of which had their main activity after the turn of 

the century; and other unnamed prospects near the head of Gilpin Creek. This is 

the only major district entirely within the wilderness. In fact, it could hardly be 

more centrally located (see figs. 3, 14), and it appears that, if a valuable mineral 

resource is eventually proven here, it will be most difficult to resolve both economic 

exploitation and preservation of wilderness values. 

4. Greenville: Rock lead and gallium maxima, high rock copper, tungsten, and zinc, 

and stream-sediment maxima for silver, copper, lead, and zinc. Includes Greenville 

mine, the only mine known to have shipped base metal ore recently; according to 

local authority six truck loads of ore were taken to smelter from the Greenville mine 

during World War I I. Greenville has been the site of much sophisticated geophysical 

prospecting and drilling during the 1960's and 70's and was the study site of a detailed Colorado State University thesis being prepared in 1976 (Johnson, 1979). 

6

When spectrographic and atomic absorption analyses measured for identical samples are compared, for example, on rock Cu, 63 percent (or five out of eight) of the sample points are within two steps of equivalence. 
140 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

5. Pearl (for a historical account of the turn-of-the-century copper mines, see Spencer, 

1903): Rock maxima in bismuth, copper, and tungsten, plus high rock gold, lead 

and zinc. Multielement anomalies in each of five separate centers within the Pearl 

district, each of which has had extensive mining or prospecting. Mining in the Pearl 

district flourished just after the turn of the century and ceased about 1908. The 

Wolverine was said to have been the oldest and richest mine with a vein of ore containing 10 to 40 percent copper, and minor silver and gold values. A smelter was 

finished in 1905, but it was never operated; the chimney still stands near the Pearl 

townsite (Ryan, 1976, p. 12, 13). The Cap Rock mine, on Independence Mountain 

east of Wheeler Creek, was in an active exploration phase in 1977 (W. H. Raymond, 

oral commun., 1977); other company explorations were conducted in the Pearl district 

at least through 1979. 

Several smaller copper-lead-zinc-silver-gold and related multielement 

anomalies with some mineral resource potential occur within the 

Mount Zirkel Wilderness and adjacent area (fig. 109). Two anomalies 

which apparently are unprospected are worth mentioning. An area just 

inside the adjacent area boundary on the east side of Silver City Creek 

basin (pl. 2) has contributed the stream-sediment gold maximum and 

high stream-sediment copper values. These may be related to mineralization along the Laramide thrust on the east side of the basin. The 

other area, between Big Horn Lake (pl. 2) and the Continental Divide, 

has an anomalous zinc cluster in stream sediments. 

Marginally profitable gold placers have been worked in the past in 

gravels flanking the mountain range (outside the Mount Zirkel 

Wilderness and adjacent area). Those on Independence Mountain have 

been described by Beekly (1915, p. 117) and Hail (1965, p. 123, 124), 

and those on Hahns Peak have been discussed by Gale (1906), George 

and Crawford (1909), Antweiler, Doe, and Delevaux (1972), and Young 

and Segerstrom (1973, p. 3-6). There is no indication of appreciable 

amounts of placer gold within the area of present interest. 

URANIUM, THORIUM, AND RELATED ELEMENTS 

Grouped together by reason of preferred association are uranium, 

thorium (fig. 79), molybdenum (figs. 80, 81), niobium (figs. 82, 83), lanthanum (figs. 84, 85), and yttrium (figs. 86, 87). Nevertheless, there 

is much overlap among the elements of this group and those of other 

groups. The molybdenum rock maximum of 1,000 ppm is associated 

with sulfide ore on the west side of Buck Mountain (pl. 2), and a prominent molybdenum sediment cluster is associated with niobium and 

yttrium in sulfide ores of the Farwell district. The molybdenum sediment maximum is east of Ceanothuse Lake (pl. 2) in the 1.4-b.y. Mount 

Ethel pluton, a preferred host for other elements of this group-for 

example, the niobium sediment maximum in South Fork Mad Creek 

(pl. 2). However, some uranium, thorium, niobium, and lanthanum are 

associated with the sediment beryllium cluster in 1.7-b.y. quartz 
EVALUATION OF SURFACE POTENTIAL 141 

monzonites near Seven Lakes (pl. 2). And uranium, molybdenum, and 

yttrium are associated with Tertiary fluorite veins, especially in the 

Crystal-Pedad claim area (figs. 24, 27; pl. 2). None of the elements of 

this group has been the source of economic deposits, although the 

elements are believed to have been actively prospected in the Bear 

Creek district and other areas. Elsewhere in Colorado, vanadium is 

an accessory element locally associated with uranium that enabled the 

extraction of uranium ores which otherwise would have been 

uneconomic to develop (Morse and Curtin, 1977, p. 10), but this 

association does not appear to be prominent in the northern Park 

Range. 

URANIUM AND THORIUM 

Uranium and thorium are not known to be present in the northern 

Park Range in significant amounts except for small specimens notable 

as mineralogical curiosities rather than as parts of ore deposits (0.176 

percent U 30 8 was the average grade of uranium ore mined in the 

United States in 1974 (Woodmansee, 1974, p. 1327) whereas 0.15 percent U30 8 was projected as minable by 1979 (Morse and Curtin, 

1977, fig. 12, p. 31)). Selected Park Range minerals may contain 

uranium and thorium in amounts of 1 percent (10,000 ppm) or more. 

A survey of a handful of old analyses reported in the literature and 

61 new analyses indicates minor concentrations (generally a few tens 

or less, rarely hundreds or thousands, of parts per million) associated 

with several types of geological environments, which will be recounted 

herein. Detailed searches in the vicinity of known deposits or in these 

relatively favorable environments will possibly turn up larger buried 

uranium and thorium deposits than are now known, but there is little 

evidence to encourage the belief that large, economically exploitable 

ore deposits will be found at the ground surface. A recent compilation of uranium districts in Colorado shows none in Jackson or Routt 

Counties (Morse and Curtin, 1977, fig. 4, p. 56-58). The new analyses 

are contained in tables 2, 4, and 8. About half of the new analyses 

are on stream sediments and half on rock samples; most are mixtures 

of common silicate minerals, many with an indication that they are 

rich in iron (sulfide, oxide, or silicate). All the new analyses plus all 

the old ones that could be located are shown on figure 79. 

Higher than normal radioactivity measured in the northern Park 

Range has been attributed to a variety of primary or secondary 

uranium- or thorium-containing minerals or to mineralogic environments. Reported radioactive minerals include uraninite or pitchblende, 

zircon, xenotime, allanite, fergusonite, euxenite, carnotite, black 

chalcedony or dark-purple fluorite, as well as secondary alteration 
142 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE B.-Delayed neutron determinations of thorium and uranium in stream 

sediments and rocks of the northern Park Range, Colorado, that contain 20 ppm or 

greater niobium 

[Average sample size 8 g (range 1-13 g) except where marked "insufficient sample." For description of analytical 

technique see Millard, 1976. Do., entry same as preceding; for localities see plate 2] 

Field Lab. No. Nb Th u Remarks 

No. (ppm) 

Stream sediments 

71 ADS 123 20 13.97 3.98 Hot Spring Creek above 

Elk Park. 

84 ADS 136 20 22.21 5.44 Southwest of Horse Thief 

Peak. 

89 ADS 141 100 22.64 9.43 South Fork Mad Creek. 

194 ADW023 20 6.64 3.79 Newcomb Creek at toe of 

landslide in Morrison 

Formation. 

203 ADW032 20 9.05 5.34 Head of Whalen Creek. 

3 AMT485 20 6.99 6.04 North Three Island Creek. 

6 AMT488 20 30.79 8.29 Mouth of Hot Spring 

Creek. 

20 AMT502 20 7.95 4.02 Natural magnetite concentrate, Big Creek. 

23 AMT505 20 21.98 8.04 Do. 

26 AMT508 20 9.70 4.37 Mucky sediment northwest 

of Moon Hill. 

32 AMT514 20 36.15 19.94 Panned heavy minerals, 

North Fork Elk River 

near Seedhouse. 

33 AMT515 20 29.40 9.76 Mouth of Mad Creek. 

42 AMT524 100 146.01 24.68 South Fork Mad Creek at 

trail. 

43 AMT525 30 25.65 20.93 7 ,800-ft altitude Mad 

Creek. 

45 AMT527 30 48.48 13.66 Soda Creek above Gunn 

Creek. 

46 AMT528 30 52.90 9.05 Gunn Creek above Soda 

Creek. 

47 AMT529 20 13.37 5.22 Soda Creek. 

50 AMT532 20 30.26 8.68 Gunn Creek tributary. 

52 AMT534 20 47.33 9.70 Hot Spring Creek. 

53 AMT535 20 52.24 14.23 Bear Creek. 

57 AMT539 20 26.19 9.56 East fork Gunn Creek. 

58 AMT540 20 30.89 17.13 Soda Creek above South 

Fork. 

674 BFM 952 20 Insufficient Encampment River 

sample tributary from Seven 

Lakes area. 

682 BFM960 20 19.65 17.82 9,460-ft altitude Encampment River. 

688 BFM 966 20 8.15 5.88 East of West Fork Lake. 
EVALUATION OF SURFACE POTENTIAL 143 

TABLE B.-Delayed neutron determinations of thorium and uranium in stream 

sediments and rocks of the northern Park Range, Colorado, that contain 20 ppm or 

greater niobium-Continued 

Field Lab. No. Nb Th u Remarks No. (ppm) 

Stream sediments-Continued 

694 BFM 972 20 Insufficient North of West Fork Lake. 

sample 

697 BFM 975 20 Insufficient West of West Fork Lake. 

sample 

698 BFM 976 20 7.68 11.30 Northwest of West Fork 

Lake. 

266 BFN 167 20 19.13 18.66 Stream draining Seven 

Lakes area. 

288 BFN 189 30 22.35 19.06 Do. 

289 BFN 190 20 12.11 10.15 Do. 

293 BFN 194 30 12.60 12.15 Do. 

388 BFN 288 20 Insufficient Stream draining Seven 

sample Lakes area. 

786 LAA 432 20 40.65 9.29 Silver City Creek tributary 

below Dakota Sandstone. 

902 LAA 548 20 5.87 5.52 Middle Fork Little Snake 

River tributary. 

1057 LAA 704 30 12.90 4.46 Lester Creek tributary 

below Browns Park Formation. 

Rock samples 

250 ADS 518 30 16.95 6.08 Chloritized pelitic gneiss 

near fault. 

263C ADS 523 30 46.37 4.89 Hematitic granite from 

prospect pit above head 

of Bear Creek. 

289 ADS 530 30 13.96 8.57 Mylonite below pegmatite, 

Soda Creek. 

322 ADS 533 20 12.57 34.38 Epidote rock north of head 

of Soda Creek. 

411 ADS 540 20 6.26 2.03 Plagioclase-augen mylonite 

from north-northeast of 

Buffalo Mountain. 

607 ADV984 50 34.43 258.11 Yellow ferrous breccia 

from Pedad claim north 

of Roaring Fork. 

736 BFO 744 20 2.72 3.56 Malachitic amphibolite 

from pit near head of 

Republic Creek. 

793 BFO 762 20 1.05 12.96 Porous ferrous amphibolite, Wolverine 

mine upper dump. 
144 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE B.-Delayed neutron determinations of thorium and uranium in stream 

sediments and rocks of the northern Park Range, Colorado, that contain 20 ppm or 

greater niobium-Continued 

Field Lab. No. Nb Th u Remarks 

No. (ppm) 

Rock samples-Continued 

845 BFO 771 30 6.79 2.58 Epidotitic pyritic granite 

dike, 11,400-ft altitude 

Bear Ridge. 

1130 BFO 810 20 14.03 7.69 Iron-stained granite gneiss, 

Mica Basin. 

1180 BFO 830 30 8.56 1.64 Iron-stained gneiss from 

pit on ridge north of 

Agnes Creek. 

1385 LAA 979 20 3.66 1.33 Altered granite gneiss east 

of Ryan Park. 

1404 LAA 981 20 7.38 3.94 Mylonitized trachyande.site 

dike, Ellis Trail, South 

Fork Hog Park Creek. 

1565 LAA 994 150 18.56 3.17 Malachitic pegmatite, central Farwell mine. 

1566 LAA 995 30 1.67 12.42 Malachitic dump rock, 

west Farwell mine. 

1573 LAA 997 20 14.41 8.08 Malachite, east Farwell 

mine. 

1574 LAA 998 20 6.12 2.95 Malachite, central Farwell 

mine. 

1594 LAB 004 20 4.26 1.55 Pegmatite from pit east of 

Crane Park. 

1596 LAB 005 30 6.93 7.16 Mylonitized trachyandesite 

dike along thrust fault 

northeast of Big Red 

Park. 

1607 LAB 009 70 5.30 10.78 Pegmatite with green ferrous mineral from gully 

on southwest shoulder of 

Farwell Mountain. 

1608 LAB 010 70 3.26 3.76 Pegmatite with red ferric 

mineral from gully on 

southwest shoulder of 

Farwell Mountain. 

1817 LBH 993 20 17.15 6.33 Baked shale inclusion in 

City Mountain Tertiary 

intrusive. 
EVALUATION OF SURFACE POTENTIAL 145 

products like autunite, uranophane, gummite, and a suite of unidentified yellow-orange efflorescent incrustations commonly labeled as 

uranium and radium sulfates. Uraniferous spring waters and peat have 

been described west of Lake John in northwestern North Park (Malan, 

1957, p. 129-133). The association of radioactivity with iron enrichment, alteration, or staining, noted in the preceding paragraph, has 

also been noted in the vicinity by others (E. P. Beroni, written commun., August 1950; Beroni and Derzay, 1955; Grutt and Whalen, 1955, 

p. 128), but not all iron-rich areas are radioactive. The Ace High No. 

1 claim or Upper Slavonia mine is characterized by numerous ironrich zones in Precambrian gneiss. These were extensively examined 

by J. W. Adams (written commun., July 31, 1951) both underground 

and on the surface, and no significant radioactivity was detected. 

The present study shows that anomalously high uranium and 

thorium are preferentially associated with several varieties of Precambrian rocks or structures and less commonly with Mesozoic or Tertiary rocks. Precambrian pegmatites or plutonic granites seem to be 

more favorable than mafic intrusives or the metasedimentary and 

metavolcanic rocks. Among the plutonic granites, those of 1.4-b.y. age 

contain more uranium and thorium localities than those of 1.7-b.y. age, 

but the 1.7-b.y. granite contains one notable concentration. 

Pegmatites of various ages have been the source of the richest 

deposits of both uranium and thorium in the northern Park Range, 

but the volumes of all known deposits are small and uneconomic. A 

few large specimens of uraninite or euxenite are reported to have been 

collected from a mica-beryl pit in pegmatite at the E. C. Ellis property in Mica Basin (pl. 2). One such specimen approximately 7 inches 

in diameter and weighing 26 pounds assayed 86 percent U (E. P. Beroni 

and F. A. McKeown, written commun., September 1960). A less 

unusual sample of radioactive biotite from the Mount Zirkel area was 

reported to contain 0.1 percent (1,000 ppm) uranium (Beroni and 

McKeown, 1952, p. 39). The Mica Basin pegmatites contain book 

muscovite and beryl as well as uraninite (Adams, 1964, p. 171). Besides 

containing greater than 20 percent rare earths and yttrium, the Fielder 

prospect in pegmatite near Agua Fria Lake (pl. 2) also contains as 

much as 1.5 percent (15,000 ppm) Th and 0.7 percent (7,000 ppm) U 

(table 9 with rare earth prospect description follows). E. R. Mabes 

(written commun., September 14, 1950) reported 0.3-0.7 percent 

(3,000-7,000 ppm) U in samples described as pegmatite from the FairU claims area in North Fork Fish Creek (eastern locality below south 
146 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

edge of area of fig. 79). Beroni and McKeown (1952, p. 24-30) reported 

uranium analyses of nine samples from this area (0.002-0.054 percent 

U) (20-540 ppm) and constructed an isoradioactivity map (Beroni and 

McKeown, 1952, fig. 5) of the Fair-U claims area, showing "pod-shaped 

radioactive zones 1 to 20 feet in length-highest along the gradational 

contacts between the granitic rocks and the schist" (Beroni and 

McKeown, 1952, p. 27). They reported that "the deposits are not now 

of commercial interest" (Beroni and McKeown, 1952, p. 30). Beroni 

and Derzay (1955) later reported that selected samples from the Fish 

Creek district contained as much as 0.3 percent (3,000 ppm) U. In the 

present study (table 8), pegmatites on Farwell Mountain (samples 

1565, 1566, 1573, 1574, 1607, 1608), along Middle Fork Little Snake 

River (sample 1594) and along Soda Creek (sample 89) contain as much 

as 19 ppm Th and 12 ppm U. Pegmatite muscovite from the Farwell 

mine has a reported K-Ar age of 1.7 b.y. (Segerstrom and Young, 1972, 

p. 17), but the pegmatite at Agua Fria Lake that cuts rocks of the 

1.4-b.y. Mount Ethel pluton, though not dated directly, must be 

1.4 b.y. or younger in age. 

The 1.4-b.y. granitic rocks have supplied many uraniferous stream 

sediments and several anomalous outcrops. Most important of these 

are the Pedad and James Bird claims and Crystal mine, where as much 

as 3,400 ppm U (Malan, 1957, p. 126) and 34 ppm Th (pl. 3, sample 

607) are known. However, within the 1.4-b.y. Mount Ethel pluton, 

these deposits are associated with much younger (Tertiary?) fault breccias and associated fluorite veins that crisscross the northeastern part 

of the pluton. Sample 607 was one of four samples collected by Snyder 

from the Pedad claim area. One was a red breccia, one, a yellow breccia (607); one, a white breccia; and one a fluorite vein. Only the yellow 

breccia (607) contained anomalous niobium, and, therefore, it was the 

only one of Snyder's samples from this area analyzed for uranium and 

thorium. The Agua Fria Lake rare earth prospect is within the Mount 

Ethel pluton also, as is stream-sediment sample 203, over the ridge 

from Agua Fria Lake. The uraniferous spring waters and peat west 

of Lake John (Malan, 1957, p. 129-133) must be derived from waters 

passing through Mount Ethel rocks. A large assemblage of anomalous 

stream sediments and rocks is present in the southwestern part of 

the Mount Ethel pluton (fig. 79). These samples contain as much as 

146 ppm Th and 34 ppm U and include sediment samples 42, 43, 47, 

50, 52, 53, 57, 71, 84, and 89 and rock samples 263C and 322. In addition, three rock samples are from possible 1.4-b.y. dikes outside the 

Mount Ethel pluton: sample 845 on Bear Ridge, and samples 1404 

and 1596 from two localities in a single porphyry dike northeast of 

Big Red Park. 
EVALUATION OF SURF ACE POTENTIAL 147 

Although covering a much greater area, the remaining Precambrian 

rocks have given rise to a proportionately smaller number of anomalous samples. One notable anomalous area in the vicinity of Seven 

Lakes coincides with a beryllium high in 1.7-b.y. granite (fig. 97). There, 

stream sediments 266, 288, 289, 293, and 682 have as much as 22 ppm 

Th and 19 ppm U. A few other scattered samples are also related to 

1.7-b.y. granite (688, 698, 736, 1130, 1385) or metasedimentary or 

metavolcanic rocks (20, 23, 58, 89, 250, 411, 793, 902, 1180). Three 

of the latter (89, 250, 411) are related to Precambrian faults in the Soda 

Creek-Fish Creek mylonite zone. Beroni and McKeown (1952, p. 40) 

listed 20 ppm U from "granite taken from road cut, north of Steamboat Springs, Colo.," but with exact locality or type of granite otherwise unidentified. 

As much as 53 ppm Th and 14 ppm U in this study can be related 

to Mesozoic or Tertiary rocks. Malan (1957, p. 135, 136) reported 

uranium mineralization associated with Dakota Sandstone south of 

Rabbit Ears Pass. The only evidence of similar mineralization in this 

area might come from stream sediments 26, 194, and 788. Other 

anomalous sediments from streams draining Mesozoic rocks are 

samples 6, 32, and 33. Beroni and McKeown (1952, p. 39) reported 

20 ppm uranium from Mancos Shale northwest of Hahns Peak. 

Analyzed rock sample 1817 is of a shale inclusion, presumably Mancos, in the Tertiary City Mountain intrusive northwest of Hahns Peak. 

McConnell (1960, p. 64) reported two small uranium prospects in 

Mesozoic rocks on the northeast side of Hinman Park. Grutt and 

Whalen (1955, p. 128) regarded the Miocene Browns Park Formation 

as the most favorable formation to prospect for uranium, but the only known prospect in the Browns Park Formation in this vicinity is 

east of the northeast corner of the area of figure 79 (U.S. Geological 

Survey and Colorado Geological Survey, 1977). S. J. Luft (oral commun., 1980) reported that, although generally a favorable horizon for 

uranium deposits, the Browns Park Formation in the vicinity of the 

northern Park Range is here considered unfavorable for uranium 

deposits. However, there are four anomalous sediments from streams 

draining the Browns Park Formation: three in Strawberry Park (45, 

46, 47) and one in Lester Creek (1057). In addition, Beroni and 

McKeown (1952, p. 38, 40) reported 30 ppm U from a post-Browns 

Park intrusive at Hahns Peak, and 20 ppm U from post-Browns Park 

tufa at Steamboat Springs. 

RARE EARTH PROSPECT 

Rare earth elements are concentrated in a few cubic meters of a 

pegmatite at the Fielder prospect near Agua Fria Lake. Samples from 
148 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

this locality have been analyzed both by the U.S. Geological Survey 

(J. W. Adams, written communs., March 13, 1966 and February 13, 

1974) and the Bureau of Mines (see discussion on p. 65, 72; table 1). 

Although the volume of the known deposit is miniscule, its unique 

chemistry (>10 percent rare earths) and mineralogy are interesting. 

Adams reported (table 9) the following six-step spectrographic analysis 

of the ore (results reported in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, and 

0.1, ... ) (Field No. JA-66-1, Lab. No. D121579). 

TABLE 9.-Analysis of Agua Fria Lake rare-earth ore, in percent 

[Bastnaesite, fergusonite, xenotime, and zircon were identified by Adams in methylene iodide-heavy magnetic and 

nonmagnetic mineral fractions of sample J A-66-1, apparently a first observation of this assemblage in Jackson 

County (Eckel, 1961; Vanderwilt, 1947l] 

Si >10 Ag <0.0002 Cr <0.0015 HgO Pr 0.3 Te 0 

AI >10 As 0 Cu <0.001 In 0 Pt 0 Th 1.5 

Fe 5 Au <0.005 Dy 1 La 1.5 Re 0 Tl 0 

Mg 0.7 B 0.015 Er 1 Lu 0.15 Sb 0 Tm 0.2 

Ca 1.5 Ba 0.1 Eu 0.02 MoO Sc <0.1 u 0.7 

Na 5 Be 0.005 Ga 0.01 Nb 0.3 Sm 0.7 v 0.01 

K <1.5 Bi 0 Gd 0.3 Nd 1.5 Sn 0 w 0 

Ti 0.1 Cd <0.01 Ge 0 Ni 0 Sr 0.05 y >10 

p 3 Ce 1.5 Hf 0.3 Pb 0.15 Ta <0.02 Yb 1.5 

Mn 0.7 Co 0.02 Ho 0.3 Pd 0 Tb 0.15 Zn <0.1 

Zr 7 

CHROMIUM, PLATINUM, AND RELATED ELEMENTS 

Chromium, platinum, palladium, cobalt, and nickel are clearly 

associated in the study area; their distributions are illustrated on 

figures 88-94, respectively. These elements, and perhaps also some 

of the chalcophile elements and some vanadium, are concentrated in 

ultramafic rocks present in numerous small alpine-type bodies 

throughout the crystalline rocks of the northern Park Range. All are 

"anomalous" by the definition accepted for the other elements, but 

none are present in amounts exceptionally large for ultramafic rocks 

as a class; most of these elements are the products of normal igneous 

differentiation rather than late ore introduction. Economic platinoid 

concentrations are not found elsewhere in any alpine-type ultramafic 

intrusions (Stanton, 1972, p. 326). 

CHROMIUM, COBALT, AND NICKEL 

Chromium, cobalt, and nickel were analyzed routinely by the usual 

semiquantitative spectrographic methods in the samples submitted 

as potentially mineralized rock. The maximum rock chromium in these 

analyses was 3,000 ppm in the Troutman Draw malachitic 
EVALUATION OF SURFACE POTENTIAL 149 

hornblendite that also had the maximum platinum plus palladium. 

However, ultramafic rocks analyzed for platinum and palladium were 

also analyzed routinely by the same technique for chromium, and two 

of these showed 5,000 ppm Cr-a giant orthopyroxene crystal out of 

a Sawtooth Range peridotite and a dunite phase from the gabbro of 

Elkhorn Mountain. The maximum rock cobalt and nickel were both 

measured in the Bear Creek7 peridotite, the largest single ultramafic 

body in the range. A northern extension of this body may be largely 

covered by rock glaciers, as streams issuing from beneath rock glaciers 

between Ute and Twin Lakes provided the highest measured streamsediment cobalt and nickel. The highest sediment chromium, 

>5,000 ppm, came from a tributary of Silver City Creek south of Big 

Red Park that drains Mesozoic sedimentary rocks; the same sediment 

sample provided the highest Zr, an association possibly explained as 

an assemblage of heavy minerals. The correlation of chromite observed 

in thin section with analytically determined rock Cr20 3 is shown in 

table 10. 

7

This Bear Creek is north of Lone Pine Creek on the east side of the range, not the Bear Creek for which the 

previously mentioned Bear Creek district is named on the west side of the range north of Steamboat Springs. 

TABLE 10.-Association of measured chromite and Cr20 3 in ultramafic rocks 

[Do., same as entry preceding] 

Sample 

No. 

116 

1078 

1194 

1410 

1411 

1412 

1413 

1428 

Rock 

type 

Dunite ------------------------

Chromite peridotite -------------

Orthopyroxene crystal (with 5 percent 

magnetite). 

Olivine gabbro ------------------

Olivine gabbro ------------------

Lherzolite ----------------------

Olivine gabbro ------------------

Harzburgite --------------------

1472 Dunite ------------------------

1501-A Norite -------------------------

1606 Anorthositic gabbro -------------

1685 Gabbro ------------------------

1765 

1781 

1927 

1985 

Gabbro ------------------------

Diorite phase of gabbro of Elkhorn 

Mountain. 

Pargasite peridotite -------------

Basalt dike in gabbro ------------

Volume 

percent 

chromite 

(by point 

counting) 

0.25 

2.1 

0 

0 

0 

1.1 

0 

::::: 1 

0 

0 

0 

0 

0 

0 

0 

.34 

Weight Analytical 

percent method 

Cr20 3 

0.19 Wet chemical. 

.49 Colorimetric. 

.73 Spectrographic. 

.048 Colorimetric. 

.089 Do. 

.36 Do. 

.054 Do. 

.23 Do. 

.73 Spectrographic. 

.042 Colorimetric. 

<0.029 Do. 

. 051 Do . 

.02 Do. 

<0.02 Do. 

.08 Do. 

.03 Do. 
150 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

PLATINUM AND PALLADIUM 

Platinum and palladium are present in minute quantities in some 

mafic and ultramafic Precambrian rocks, generally of small volume, 

in the northern Park Range, but no convincing evidence exists of a 

significant economic resource near the ground surface. Both maximum 

total platinum plus palladium and average total platinum plus 

palladium are at least two orders of magnitude less at all northern 

Park Range localities than at the New Rambler mine, Medicine Bow 

Mountains, Wyo. (Theobald and Thompson, 1968), where the volume 

of mineralized rock is large and where there are also significant values 

of copper, gold, silver, and arsenic. The most interesting body for further prospecting, the 2.7-km-long (1.7-mi-long) pargasite peridotite between Lone Pine Creek and Bear Creek on the east side of the range 

(pl. 1), contains an observed maximum of 0.05 ppm Pt plus Pd. 

Ninety-seven samples from 33 localities of mafic and ultramafic rock 

were searched for platinum, palladium, and rhodium (analyzed for as 

in Talanta, 1968, v. 15, p. 111-117); of these, 35 samples (includes some 

duplicates) from 14localities contained measurable platinum and (or) 

palladium (none contained measurable rhodium, reported as 

<0.005 ppm Rh in all samples). The measurable platinum and 

palladium are listed here in table 11 and figure 90. The average 

measured platinum plus palladium from the 14localities is 0.02 ppm, 

but half of the localities also contained one or more samples without 

measurable platinum or palladium, and these are not entered into the 

averages. The maximum, 0.09 ppm Pt plus Pd, is from a single prospected outcrop of malachitic hornblendite at the Troutman locality 

near the road southeast of Pearl. This compares with a maximum of 

10 ppm Pt plus Pd and an average of 1 ppm Pt plus Pd at the New 

Rambler mine (Theobald and Thompson, 1968) and a maximum of 

0.28 ppm Pt plus Pd and an average of 0.04 ppm Pt plus Pd from mafic 

amphibolites of the Sierra Madre of Wyoming (Houston and others, 

1955). Only one sample, of several analyzed, from the normal gabbro 

of Elkhorn Mountain contained a measurable trace of Pd, that from 

the Whiskey locality (table 11). This compares with a trace of Pt and 

0.010 ppm Pd measured in a typical norite from the gabbro body near 

Lake Owen, Wyo. (Theobald and Thompson, 1968). 

Of the known platinum-palladium localities, most are either too small 

in volume or too lean in grade to be worth further prospecting. Most 

of the ultramafic bodies sampled are single outcrops or small areas 

measured in feet or tens of feet. A few of the larger bodies have dimensions in thousands of feet and several of these, especially the Bear 

Creek locality, may reward more detailed prospecting efforts. Except 

for the Troutman locality with 10,000 ppm Cu, most have a maximum 

of 300 ppm Cu, and nothing else known to be of economic interest. 
EVALUATION OF SURFACE POTENTIAL 151 

TABLE 11.-Measured platinum and palladium in mafic and ultramafic Precambrian 

rocks of the northern Park Range 

[Tr .. trace; Do .• entry same as preceding] 

Figure 90 Field Lab. Pt Pd Remarks 

locality No. No. (ppm) (ppm) 

Whiskey --- 1685 D160907 <0.010 Tr. Gabbro of Elkhorn Mountain. 

Olivine ---- 1412 D160884 <0.010 0.007 Coronitic lherzolite with 

chromite (0.36 percent 

Cr20 3). 

1441 D160895 .021 .010 Foliated peridotite. 

1472 D160899 <.010 .024 Coronitic peridotite. 

Damfino --- 1049 D154837 <0.010 .006 Amphibole peridotite with 

spinel. 

1050 D154838 Tr. .011 Serpentinite. 

Buffalo ---- 1041 D154836 <0.010 .008 Carbonatite or marble 

associated with hornblendite. 

Troutman 910 D154833 0.060 .026 Actinolite-chlorite-magnetitemalachite rock. 

910 D160878 .028 .022 Do. 

Sawtooth 1193 D154851 0.016 .010 Tremolite-chlorite matrix of 

sample 1194. 

1193 D160881 .020 .011 Do. 

1194 D160882 .012 .004 10 em ( 4 in.) hypersthene 

crystal. 

Gilpin ----- 1202 D154852 <0.010 .004 Hornblende-hypersthene-spinel 

peridotite. 

Big Agnes 1112 D103055 <0.010 .007 Talc-biotite-tremoliteanthophyllite-chlorite rock. 

Wapiti ---- 116F D141158 0.014 .014 Fresh dunite. 

116W D141159 .017 .017 Weathered dunite. 

117 D141160 .012 .014 Fresh dunite. 

1116 D103056 .014 .015 Do. 

1116 D160880 .013 .012 Do. 

1117 D154842 Tr. .006 Dunite soil. 

1118 D154843 .015 .008 Do. 

1119 D154844 .011 .005 Do. 

1120 D154845 Tr. .007 Do. 

1121 D154846 .012 .009 Do. 

South Fork 74 D154815 <0.010 .006 Hornblendite. 

75 D154816 .013 .019 Do. 

Three Island 1070 D103047 <0.010 .004 Pargasite peridotite. 
152 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 11.-Measured platinum and palladium in mafic and ultramafic Precambrian 

rocks of the northern Park Range-Continued 

Figure 90 Field Lab. Pt Pd Remarks 

locality No. No. (ppm I (ppml 

Bear Creek 752 D154832 0.037 .011 Poikilitic pargasite peridotite. 

1016 D154834 .031 .008 Pargasite-chlorite-magnetite 

rock. 

1017 D103036 .018 <0.004 Pargasite serpentinite. 

1018 D103037 .024 .012 Poikilitic pargasite peridotite. 

1018 D160879 .017 . 010 Do . 

Boettcher 672 D154825 <0.010 .009 Actinolite-talc rock. 

Spring ----- 273 0154817 <0.010 .006 Peridotite with chromite. 

1078 D103050 <0.010 .004 Peridotite with chromite (0.49 

percent Cr 20 3). 

The Bear Creek locality consists of a long, linear intrusive that crosses 

a rugged mountain ridge (mapped on pl. 1). The body is 2. 7 km (1. 7 mi) 

long and as much as 430 m ( 1,400 ft) wide; it is exposed over a vertical 

distance of 440 m (1,450 ft), and it probably projects yet another 170 

m (550ft) deeper than this under the center of the mass (Snyder, 1977a, 

1980a, section E-El Where freshest, as on the north side of the ridge 

between Bear Creek and Lone Pine Creek, the exposed rock has a curious poikilitic structure with olivine phenocrysts set between pargasite 

oikocrysts containing clinopyroxene chadacrysts. Elsewhere, the 

olivine and clinopyroxene are extensively altered to chlorite, magnetite, 

and serpentine. The peridotite at the Bear Creek locality is completely within the present boundary of the Mount Zirkel Wilderness. 

Some peridotites within the mapped olivine gabbro phase of the gabbro of Elkhorn Mountain contain as much as 0.03 ppm Pt plus Pd. 

(See the Olivine locality, table 11.) The peridotites are believed to be 

a volumetrically minor part of the olivine gabbro mass, but the mass 

is well exposed only on peak 9,731 along the Continental Divide; most 

of the olivine gabbro is covered by humic tundra soil supporting dense 

grasslands or forests that could hide more extensive ultramafic rocks. 

If so, the volume of the olivine gabbro, more than a cubic mile (Snyder, 

1977a, 1980a, sectionA-A1, might mean that peridotites could increase 

with depth. Peak 9,731 may be reached via a jeep road along the Continental Divide that branches off the old Ellis Trail. The olivine gabbro is well outside the present Mount Zirkel Wilderness boundary but 

within the adjacent area. 

Another ultramafic rock of barely conceivable economic interest lies 

astride the Mount Zirkel Wilderness boundary on the ridge southwest 

of Three Island Lake (the Three Island locality of table 11 and fig. 90). 
EVALUATION OF SURFACE POTENTIAL 153 

Here an irregular pargasite peridotite with minor malachite occupies 

a body as much as 1.45 km (0.9 mi) long by 0.9 km (0.6 mi) wide. This 

rock contains as much as 700 ppm Cu and 0.004 ppm Pd, not in itself 

of much economic interest. However, nearby marble (sample 1069, pl. 

2) contains 15 ppm Ag, 1,000 ppm Cu, 3,000 ppm Ph, and 1,000 ppm 

Zn. The marble, unprospected except for this sample, is presumed to 

be in contact with the peridotite under a covered zone, but nothing 

is known about the contact. 

OTHER ELEMENTS 

The other elements whose highlights of distribution are summarized 

here are the "majors," iron, magnesium, calcium, titanium, and 

manganese, and the other analyzed "minors;' boron, barium (fig. 95), 

beryllium (figs. 96, 97), scandium (figs. 98, 99), strontium (figs. 100, 

101), vanadium (figs. 102, 103), and zirconium (fig. 104). None of these 

elements occurs in amounts or combinations even approaching 

economic deposits, but some have been or could be useful guides to 

other metal concentrations. 

The major elements-iron, magnesium, calcium, titanium, and 

manganese-show some definite associations. Almost all rock analyses 

that show maxima of 20 percent or greater Fe (12 samples) are from 

rocks with introduced pyrite or containing hematite-limonite gossan, 

many from the Gilpin mines or Upper Slavonia. All rock analyses that 

show maxima of 10 percent Mg (24 samples) are from mafic, ultramafic, 

or calc-silicate rocks, some mineralized. All rock analyses that show 

maxima of 20 percent or more Ca (35 samples) are from introduced 

or original carbonate or fluorspar rocks. Rock maxima of greater than 

1 percent Ti are from two samples of sheared or veined granite at the 

Elkhorn mine; eight rock samples with 1 percent Ti are epidotized rock 

or porphyry dikes. Excluding monomineralic rocks, the Mn rock maxima of greater than 5,000 ppm (35 samples) occur in gametiferous rocks 

or ores, particularly ores from the Pearl district, or the Upper Slavonia 

or Greenville mines. The stream-sediment analyses show the following maxima: 20 percent Fe (1 sample) and 15 percent Fe (47 samples); 

7 percent Mg (5 samples); 10 percent Ca (3 samples);> 1 percent Ti (37 

samples); >5,000 ppm Mn (2 samples) and 5,000 ppm Mn (6 samples). 

Excluding the few panned heavies or visible magnetite stream concentrates, the highest iron, magnesium, and titanium favor the streams 

draining the northern part of the gabbro of Elkhorn Mountain or the 

quartz monzonite north of this, whereas the highest Ca and Mn are 

apparently scattered without discernible areal preference. 

Boron has different rock and stream-sediment affinities, unlike other 

elements that show similar affinities for both rock and stream-sediment 

samples. The rock highs of 30 to 100 ppm B (15 samples) occur in 
154 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

chloritized or mylonitized rock near the north side of the Soda CreekFish Creek mylonite zone, in mineralized rock (commonly quartz 

veined) from the Bear Creek district, near the Elkhorn mine, and on 

the Master Key mine dump (near Columbine), or from weathered or 

serpentinized peridotite either in the Bear Creek ultramafic body or 

within the olivine gabbro phase of the gabbro of Elkhorn Mountain. 

The anomalous stream sediments show values of 30 ppm B (65 

samples), 50 ppm B (34 samples), 70 ppm B (6 samples), and 100 ppm 

B (6 samples); and the data furnish one of the best geologic correlations in the area: 84 percent of the values 30 ppm or greater, 89 percent of those 50 ppm or greater, and 92 percent of those 70 ppm or 

greater drain areas of Mesozoic rocks, mainly shales. Apparently the 

boron attached to sedimentary clays is mobile enough to be a good 

indicator of Mesozoic sedimentary rocks updrainage. Several alluvial 

basins with Precambrian rocks on one side and Mesozoic rocks on the 

other infallibly show more boron in the sediment of the tributaries 

from the Mesozoic rocks. 

The distribution highlights of the remaining minor elements are summarized in tables 5 and 6 and following. Eight samples showing high 

rock barium (5,000 ppm or greater) are from various potentially 

mineralized rocks in the northeast quarter of the mapped area. The 

stream-sediment barium maximum of 1,500 ppm (24 samples) is partly scattered without discernible pattern, partly clustered (9 samples) 

in the Beaver Lake-Three Island Lake-Gold Creek area; the latter 

cluster may be related to a crosscutting porphyry dike swarm in this 

area; other Ba sediment samples may be related to Elkhead Tertiary 

intrusives updrainage or the hot spring effluents near Steamboat 

Springs. The beryllium concentration in all stream sediments derived 

from the Seven Lakes area (fig. 97) is truly remarkable, especially in 

view of the fact that no bedrock minerals or anomalous rock samples 

have been identified as the source of the anomaly. Possibly beryllium, known to be concentrated in the residual phases of magmatic 

sequences (Goldschmidt, 1954, p. 206), is here concentrated in beryl 

or another late magmatic mineral near the central, last-crystallizing 

part of the complex pluton of the quartz monzonite of Seven Lakes, 

but in amounts too tiny for it to be recognized yet in thin sections 

of the rocks of this area. Later erosion set loose subtle alluvial concentration processes that permitted the anomaly to be discovered. 

A pronounced sediment beryllium low is associated with the gabbro 

of Elkhorn Mountain. Scandium, strontium, and vanadium are all 

concentrated in epidotitic rocks of the Mount Zirkel area, and strontium sediments especially may show some association with shear 

zones. Scandium and vanadium sediment distribution patterns show 

some similarities to copper and nickel patterns, but some sediment 
EVALUATION OF SURFACE POTENTIAL 155 

vanadium also mirrors some sediment boron associations. Zirconium, 

though present in most, does not have a very wide spread of values 

in rocks; the rock maximum of 1,000 ppm occurs in a porphyry dike 

on Bear Ridge, and two other zirconium rock highs (of six with 

500 ppm or greater) are from separate samples of another porphyry 

dike caught up along the Laramide thrust northeast of Big Red Park. 

EVALUATION OF SURFACE 

NONMETALLIC RESOURCES 

The principal nonmetallic resource of the northern Park Range is 

fluorspar, but other rock commodities have been mined sporadically 

or are potentially available. Energy resource potential and the 

"mineral," water, are also discussed. 

FLUORSPAR 

Veins of sometimes-economic fluorspar (defined as 30-percent CaF 2 

in 1974; Wood, 1974, p. 570) are present just outside the east boundary of the Mount Zirkel Wilderness south of Red Canyon, and some 

of these veins are known to extend into the wilderness area. Others 

may be present well within the wilderness near the center or north 

margin of the Mount Ethel pluton, where microscopic and mapping 

evidence indicates an abundant supply of suitable 1.4-b.y. source rocks 

(fig. 105), but these areas have not been prospected in detail for 

fluorite. However, reconnaissance geologic mapping by Snyder 

throughout the area of the 1.4-b.y. Mount Ethel pluton from 1965 to 

1967 showed significant vein fluorite only in the area just outside the 

east boundary of the wilderness south of Red Canyon, and on Delaney 

Butte, and it is believed that concentrated fluorite resources are slight 

at the ground surface within the present wilderness boundary 

(fig. 109). 

Fluorspar has been mined sporadically from veins at N orthgate on 

the north side of North Park since 1922; production has been erratic 

in periods of 1-9 years, some in each decade since mining began 

(Steven, 1960; Van Alstine, 1964; Brady, 1975; Shawe, 1976). During 

the last period of production, 1968-73, considerable interest was 

developed also in Park Range fluorite within trucking distance of the 

N orthgate mill. The Crystal mine was reopened south of Red Canyon, 

and much prospecting was done on other adjacent properties and on 

Delaney Butte. However, only the Crystal mine produced ore for the 

Northgate mill before it closed in 1973 (Brady, 1975, p. 10; Smith, 1974, 

p. 158; Wood, 1974, p. 570). 
156 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

The Park Range fluorspar occurs as mammillary or euhedral-crystal 

veins or fluorite-cemented fault breccias and contains silica, locally 

grading out into high-silica low-fluorite veins. The fluorite is purple, 

green, or white. The veins are poorly dated but, by analogy with Northgate, are probably mainly late or post Oligocene in age. All veins occur within 1.4-b.y. granite or thin Oligocene sediments overlying such 

granite. Granites in the Mount Ethel pluton preferentially contain interstitial fluorite (absent in most other Precambrian rocks in the northern Park Range), especially the quartz monzonite of Roxy Ann Lake 

(Snyder, 1978, table 7, figs. 17, 18, p. 26-33; fig. 17 is repeated herein 

as fig. 105). Most of this fluorite is magmatic and was deposited contemporaneously with the other Mount Ethel mineral grains, but some 

has been demonstrated to have been mobile in the Precambrian since 

its first deposition. More may have become mobile in the Tertiary 

(some nearby fluorite has been mobile in the Quaternary: Tweto and 

others, 1970, p. C69), becoming concentrated during redeposition in 

open veins or breccias near its inferred source of supply in the 1.4-b.y. 

Precambrian granites. If so, data like that presented in figure 105 will 

be a useful guide for further prospecting. (Such a conclusion is consistent with fluid inclusion studies at N orthgate which indicated that 

the fluorite-depositing solution was predominantly meteoric water 

(Shawe, 1976, p. 58).) 

Apparently, the geologic environment just cited is common, perhaps 

preferred, for Colorado fluorspar. Eleven (one-third) of the Colorado 

fluorite deposits compiled by Brady (1975) are associated with 1.4-b.y. 

intrusive plutons as mapped by Tweto (1976b). (Four are associated 

with the 1-b.y. Pikes Peak Granite, nine with younger sedimentary 

or volcanic cover, nine with all other Precambrian rock.) 

Geologic associations other than those previously cited have also 

been cited for North American fluorspar deposits, including Crystal 

and Northgate. Van Alstine (1976) has noted that North American 

fluorspar districts are localized near continental rift zones (for this 

area, specifically, the Rio Grande graben and its northern projections), 

and he believed that large volumes of fluorine have leaked upward from 

the lower crust or mantle along and near these rifts. This interpretation has been disputed by Lamarre and Hodder (1978), who preferred 

to derive their fluorine by melting phlogopite during the production 

of alkalic magmas along the deepest parts of two imbricate subduction zones. Their model has fluorine carried in the alkalic magma as 

SiF4, which reacts with crustal water to produce HF and Si02, and 

then with Ca+2 to precipitate CaF 2 and Si02 along surface tension 

fractures. Shawe (1979) has noted that the timing and composition of Tertiary magmas associated with fluorite deposition in the 

Western United States are different from that proposed by Lamarre 
EVALUATION OF SURFACE POTENTIAL 157 

and Hodder's model. Although Tertiary alkalic magmas are not 

associated at the surface with the northern Park Range fluorspar, 

fluorite is present in the nearby molybdenum-containing alkalic stocks 

at Climax and Urad-Henderson (Wallace and others, 1968). Furthermore, Popenoe and others (1970) have speculated that Tertiary plutons 

may have formed in north-central Colorado from the older 1.4-b.y. 

granites, and some Tertiary plutons could occur in the Park Range 

subsurface. 

OTHER ROCK COMMODITIES 

Included under this heading are mica, feldspar, cement rock, aggregate, riprap, and ornamental stone. Sheet mica (muscovite) has been 

quarried from several small pits in pegmatite in Mica Basin and on 

the south ridge of Big Agnes Mountain (fig. 20), and feldspar could 

be concentrated from some of the same deposits. However, the small 

size of the pegmatites and poor grade of these resources, coupled with 

the rugged topography and long distance from market, make it certain that this product will never be important in this area. Possibly 

some of the marble rock units and certainly the lower half of the 

Niobrara Formation are suitable for use as a source of cement rock 

within the confines of the adjacent area. However, the Niobrara Formation is present throughout Colorado and the main factor in its 

utilization as a cement-rock source is a high-volume market nearby. 

Other sources will always be more appropriate than the Niobrara 

within the adjacent area. (However, during 1977, wet cement was 

trucked daily from the Fort Collins area over two high mountain 

passes for use in the Hayden area.) At least four lithologies have been 

used in the area for sized aggregate for concrete construction or dirtroad top-dressing: Precambrian crystalline rock, Cretaceous shale, Tertiary porphyry, and alluvial gravels. One or another is readily available 

outside the adjacent area near any place it is likely to be needed. 

Precambrian bedrock or large erratic boulders in till have been used 

locally for riprap or ornamental stone. Again, the demand is unlikely 

to exceed the exterior supply. 

COAL, OIL, AND GAS 

Hydrocarbon resources have never been searched for within the 

Mount Zirkel Wilderness and adjacent area, and they are certainly 

not present anywhere near the present land surface. However, besides 

coal mines, there are paying oil fields in suitable trapping structures 

in Mesozoic rocks on both sides of the range (northwest of Delaney 
158 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Butte and west of Steamboat Springs) so the geological environment 

may be suitable. If the thrust fault nearly everywhere present on the 

west side of the range could be proven to dip shallowly eastward for 

several miles, this would mean that surface Precambrian rocks could 

overlie subsurface Mesozoic rocks, with the intervening thrust fault 

as a capping seal for any hydrocarbons trapped in underlying Mesozoic 

rocks. But neither oil nor gas has been found in the anticlines nearest 

this thrust, and there has been no incentive to attempt drilling through 

such a hypothetical crystalline caprock. Nor have hydrocarbons ever 

been discovered in seeps anywhere within the wilderness and adjacent area. For the present, then, it should be stated that it is not impossible (just unlikely) that some oil and gas could be trapped locally 

at great(?) depth below the western boundary of the adjacent area. 

GEOTHERMAL RESOURCE APPRAISAL 

No evidence of a significant geothermal resource was found anywhere within the bounds of the Mount Zirkel Wilderness or adjacent 

area, even though a well-known geothermal resource lies just outside 

this area. The external evidence of a possible geothermal resource consists of hot springs, travertine deposited by former hot springs, or 

recent volcanic deposits, such as lava flows or cinder cones. Hot 

springs and travertine deposits are present just outside of the adjacent area. One hot spring, Routt hot spring, is located in Hot Spring 

Creek near the end of the road north of Copper Ridge. A much larger 

- group of hot springs is located along the Yampa River in the village 

of Steamboat Springs just southwest of the southwest corner of the 

area of plate 1. One spring supplies hot water to a local bathing pool, 

but the others are not utilized as a thermal source. There are three 

main areas of active springs, one with numerous small active areas, 

and five areas of mapped travertine deposits, some without modern 

spring activity. These hot springs and travertine deposits occur near 

the intersections of perpendicular normal faults (Snyder, 1977c, 1980c). 

Routt hot spring and the Steamboat Springs group are linked by a 

zone of epidote and chlorite alteration in the bedrock along Copper 

Ridge (Snyder, 1977b, 1980b) and this whole area, a north-south 

elongate zone about 16 by 5 km (10 by 3 mi) should, on present criteria 

(Godwin and others, 1971, p. 6), be considered as suitable for a detailed study of the potential utilization of geothermal energy (Price 

and Arnow, 1974, fig. 24, p. C36). Some limestone near the base of 

the Browns Park Formation in this area may also be hot-spring travertine (this report, p. 44; Snyder 1977b, 1980b). In the Routt hot springSteamboat Springs system, the springs have a maximum surface temperature of 66 °C, an estimated subsurface temperature of 129 °-195 °C, 
EVALUATION OF SURFACE POTENTIAL 159 

a maximum discharge of 250 gallons per minute, and an estimated 

reservoir heat content of 0.2 X 1018 cal (Renner and others, 1975, p. 

32, 33; Grim, 1977; U.S. Geological Survey and Colorado Geological 

Survey, 1977). Water collected from 11 springs in this system was 

found to contain 0.1 to 6.5 mg/L of lithium in 1950, the lowest amount 

from Routt hot spring. Another small area of travertine has been 

mapped on the north side of Delaney Butte (Hail, 1965, pl. 3), but, 

so far as is known, no other travertine deposits or any other active 

hot springs are within the area shown on plate 1. Nor are there any 

recent volcanic deposits or other evidence of magmatic activity recent enough to retain residual heat in the upper crust. The potential 

for any geothermal resource within the Mount Zirkel Wilderness or 

adjacent area appears to be minimal (fig. 1 09). 

WATER 

Liquid water is seldom thought of as a mineral resource, but the 

crystalline solid, snow, from which most Park Range water is derived, 

is more easily considered as such. The fact is that water may be the 

greatest mineral resource of the Mount Zirkel area, renewable at that! 

Because of the great distance to high terrain west and northwest of the 

range, these mountains, despite their lower crestal elevations than the 

Front Range to the east, receive a disproportionately larger share of 

the precipitation from storm systems migrating eastward from the 

Pacific than does the Front Range. Melting snow ensures abundant 

year-round runoff that is consumed by people, animals, and crops in 

numerous ways downstream from the Mount Zirkel Wilderness source 

areas. 

This water is also a potential resource in another way that has never 

been utilized in the northern Park Range. If large retention dams were 

constructed in any of numerous suitable narrow mountain-front canyons (for example, on the Elk River east or west of Hinman Park, on 

the Encampment River near the Wyoming State line, or Red Canyon, 

Big Creek, or Mad Creek near their mouths), the resultant reservoirs 

could be the sources of hydroelectric power, as well as additional irrigation potential and sport and recreational activities. This recounting of the obvious should not be construed as a recommendation that 

retention dams be constructed, but simply as a reminder that the dams 

are feasible and, as such, are part of the total resource potential afforded by the Mount Zirkel area. Park Range water is a mineral 

resource; it is being used and reused all the way downstream now, 

and this will continue in the future. Whatever balance between 

economic and wilderness values is chosen for Mount Zirkel, its water 

resource will doubtless enter into this decision in many ways. 
160 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

"' ::t 

m 

)> 

0 

3:: 

0 

c: 

z 

.... 

)> 

z 

"' 

~Tertiary 

~ Proterozoic 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X ·--··"1111f 111'-

undillerentiated 

- --Adjacent area 

Yq'$ 

TMz 

FIGURE 52.-Anomalous rock Spec Cu (spectrographic copper), Mount Zirkel area. 

Smallest symbol 50-300 ppm; intermediate 500-3,000 ppm; largest 5,000-20,000, 

>5,000, >20,000 ppm. 

.... 

0 "' 

z 
41 • 

EVALUATION OF SURFACE POTENTIAL 161 

~ 

"' X 

)> 

0 

;::. 

0 

c 

z 

_. TMz 

)> 

z 

EX PLANA liON 

G 

B Tertiary 

Proterozoic 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

Yqt; 

TMz 

FIGURE 53.-Anomalous rock AA Cu (atomic absorption copper), Mount Zirkel area. 

Smallest symbol280-2,100 ppm; next to smallest 2,500-15,000 ppm; next to largest 

18,000-146,000 ppm; largest symbol152,000-210,000 ppm. 

.... 

"' 0 

z 
162 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

)> 

0 

~ 

0 

c 

z 

-< 

)> 

z 

EXPLANATION 

B Tertiary and Mesozoic rocks 

EJ Proterozoic Y quartz monzonite~l'if.,(-GifEEN'VILLE of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

W Remaining Proterozoic X. --··.-,if/Iii.' A. 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

' . 

Yq'tJ 

FIGURE 54.-Anomalous stream-sediment Spec Cu (spectrographic copper), Mount 

Zirkel area. Smallest symbol 50 ppm; next to smallest 70 ppm; next to largest 

100-150 ppm; largest symbol 200-300 ppm. 

"' <( 

"-

.... 

"' 0 

z 
"' > 

0 

:;:: 

0 

c 

z 

__, 

> 

z 

EVALUATION OF SURFACE POTENTIAL 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz mornzor1ite:~i~;,!GiVo,NvllLI of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X ·--··c;utnin. 

undifferentiated 

- --Adjacent area 

163 

Yq'&J 

FIGURE 55.-Anomalous stream-sediment AA Cu (atomic absorption copper), Mount 

Zirkel area. Smallest symbol30-35 ppm; next to smallest 40-55 ppm; next to largest 

60-120 ppm; largest symbol 200-250 ppm. 

.... 

"' 0 
164 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

"' J: 

m 

> 

0 

~ 

0 

c: 

z 

... TMz 

> 

z 

EXPLANATION 

~Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

I II I I I I I 1,0 

' 

I 

. 

Yq'&J 

FIGURE 56.-Anomalous rock Spec Pb (spectrographic lead), Mount Zirkel area. 

Smallest symbol 50-300 ppm; intermediate 500-3,000 ppm; largest 5,000-15,000, 

>5,000, >20,000 ppm. 

"' <( 

... 

.... 

"' 0 

z 
EVALUATION OF SURFACE POTENTIAL 

"' 

" X 

"' > 

0 

~ 

0 /il, 

c: 

z 

.... 

> 

z 

"' 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

~ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

WRemoining Proterozoic X ·--··:'illi!/l.f}.. 

undifferentiated 

---Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

165 

' 

I 

. 

Yq~ 

FIGURE 57.-Anomalous rock AA Ph (atomic absorption lead), Mount Zirkel area. 

Smallest symbol 30-120 ppm; next to smallest 130-1,000 ppm; next to largest 

1,300-10,000 ppm; largest 14,000-68,000 ppm. 

"' < 

... 

X 

.... 

0 "' 

z 
166 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

"' 

" 

"' )> 

0 

3: 

0 

c 

z 

-1 

)> 

z 

EXPLANATION ~~~~~~~~~~~~~~~~ ~Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonite~ ~;?GIOEENVILLE of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X ·--··cu/1/ii.•A. 

undifferentiated 

- --Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

KILO~zk:~~\~: 

' 

' 

. 

Yq'&J 

FIGURE 58.-Anomalous stream-sediment Spec Ph (spectrographic lead), Mount Zirkel 

area. Smallest symbol 50 ppm; next to smallest 70 ppm; next to largest 100-150 ppm; 

largest 700 ppm. 

< "" 

0.. 

:I: 

1-

"" 0 

z 
40"45' 

"' 

" 

"' )> 

~ 

0 

c:: 

z 

_, 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

5Proterozoic Y quartz monzonite~A~IlfGiREE,IVILLI of Mount Ethel pluton 

0 Proterozoic X gaBbro of 

Elkhorn Mountain 

W Remaining Proterozoic 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

167 

' " 

Yq'f) 

FIGURE 59.-Anomalous stream-sediment AA Ph (atomic absorption lead), Mount 

Zirkel area. Smallest symbol30-35 ppm; next to smallest 40-55 ppm; next to largest 

60-100 ppm; largest 130-570 ppm. 

<( "'

0.. 

:1: 

>-

"' 0 

z 
168 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ 

"' :X: 

"' > 

0 

3: 

0 

c 

z 

.... TMz 

> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

BJ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

-·--Approximate boundary of 

Mount Zirkel Wilderness 

' . 

Yq'ffj 

FIGURE 60.-Anomalous rock Spec Zn (spectrographic zinc), Mount Zirkel area. 

Smallest symbol <100, <200, 100-700 ppm; next to smallest 1,000-7,000 ppm; next 

to largest 10,000 ppm; largest >10,000 ppm. 

< "' 

"-

:X: 

... 

0 "' 

z 
EVALUATION OF SURFACE POTENTIAL 

"' 

"' 

"' > 

0 

~ '!. 

0 ~ 

c 

z 

-4 

)> 

z 

"' 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

5J Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X •u"'.~·'/1/////l. undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

169 

Yq'§J 

TMz 

FIGURE 61.-Anomalous rock AA Zn (atomic absorption zinc), Mount Zirkel area. 

Smallest symbol 30-260 ppm; next to smallest 280-2,500 ppm; next to largest 

2,900-25,000 ppm; largest 40,000-200,000 ppm. 

.... 

"' 0 

z 
170 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

" :X:

"' )o 

0 

~ 

0 

c 

z 

-< 

)o 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz :"~rlZonoit<u~~~feEN'VILLE of Mount Ethel pluton ///,lfl/,ll//i//ii/11'/! 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

' " 

Yq'tJ 

FIGURE 62.-Anomalous stream-sediment Spec Zn (spectrographic zinc), Mount Zirkel 

area. Smallest symbol <200, 200, 300 ppm; next to smallest 500-700 ppm; next to 

largest 1,000-1,500 ppm; largest symbol 2,000-3,000 ppm. 

"" < 

D.. 

J: 

,_ 

"" 0 

z 
40"45' 

m 

)> 

~ 

0 

c 

z 

.... 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

~Tertiary and Mesozoic rocks 

~Proterozoic Y quartz ~orlzonlile~~~~{,:,,ILLE of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X ·--··"'"·.1 .. ,. 1 .•• ._ 

undifferentiated 

---Adjacent area 

- .. -Approximate boundary of 

Mount Zirkel Wilderness 

KllO~~~W#f~ 

171 

' 

! 

. 

Yq'&J 

FIGURE 63.-Anomalous stream-sediment AA Zn (atomic absorption zinc), Mount 

Zirkel area. Smallest symbol125-170 ppm; next to smallest 180-260 ppm; next to 

largest 270-480 ppm; largest 850-2,700 ppm. 

"' <( 

:I: 

>--

"' 0 

z 
172 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

:: 

"" :X: 

"' )> 

0 

"!:: 4> 0 • c: 

z 

... 

)> 

z 

EXPLANATION 

B Tertiary and Mesozoic rocks 

~ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

5J Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- • -,Approximate boundary af 

Mount Zirkel Wilderness 

TMz 

Yq'&J 

FIGURE 64.-Anomalous rock Spec Ag (spectrographic silver), Mount Zirkel area. 

Smallest symbol <0.5, 0.5-3 ppm; next to smallest 5-30 ppm; next to largest 

50-300 ppm; largest 500-3,000 ppm. 

.... 

"' 0 

z 
EVALUATION OF SURFACE POTENTIAL 173 

m 

"' 

m 

> 

0 .... 3: Do£:>_ 0 

c 

z 

-< 

> 

z 

"' 

G 

8 

Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undiHerentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

Yq'&J 

FIGURE 65.-Anomalous rock AA Ag (atomic absorption silver), Mount Zirkel area. 

Smallest symbol 0.5-0.7 ppm; next to smallest 7.5-54 ppm; next to largest 

55-250 ppm; largest 500-2,600 ppm. 

,_ 

"' 0 

z 
17 4 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

)> 

0 

~ 

0 

c 

z 

-4 

)> 

z 

"' 

EXPLANATION 

B Tertiary and Mesozoic rocks 

~Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountcin 

GRemaining Proterozoic X ·--"'";J;/ic·r.•L 

undifferentiated 

- --Adiocent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

' . 

Yq'&J 

FIGURE 66.-Anomalous stream-sediment Spec Ag (spectrographic silver), Mount Zirkel 

area. Smallest symbol <0.5 ppm; next to smallest 0.5-0.7 ppm; next to largest 1 ppm; 

largest 2 ppm. 

"' <( 

0. 

:I: 

>-

"' 0 

z 
0 

l: 

0 

c 

z 

-1 

)> 

z 

EVALUATION OF SURFACE POTENTIAL 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountoin 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

175 

' 

/ 

. 

Yq'&J 

FIGURE 67.-Anomalous stream-sediment AA Ag (atomic absorption silver), Mount 

Zirkel area. Smallest symbol 0.4 ppm; next to smallest 0.5 ppm; next to largest 1 ppm; 

largest symbol 2 ppm. 

"' <( 

0.. 

J: 

,_ 

"' 0 

z 
176 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

s: 

0 

c 

z 

.... 

)> 

z 

8 

~Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

Yq~ 

TMz 

FIGURE 68.-Anomalous rock AA Au (atomic absorption gold), Mount Zirkel area. 

Smallest symbol 0.05-0.3 ppm; next to smallest 0.35-1.5 ppm; next to largest 

3-5.5 ppm; largest 20 ppm. 

.... 

"' 0 

z 
'" 

" 

'" )> 

c 

:;:: 

0 

c 

z 

... 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

EM Remaining Proterozoic X __ -.-!l;.r.'/1,'"-

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

177 

' . 

Yq~ 

FIGURE 69.-Anomalous stream-sediment AA Au (atomic absorption gold), Mount 

Zirkel area. Smaller symbol 0.05-0.1 ppm; larger 0.2 ppm. 

"" <( 

a.. 

J: 

... 

0 

z 
178 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

7< 

"' )> 

0 

~ 

0 

c 

z 

-< TMz 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic 

undifferentiated 

---Adjacent area 

' 

I 

. 

Vq'&J 

"' <( 

.,_ 

,_ 

"' 0 

z 

FIGURE 70.-Anomalous rock Inst Hg (instrumental mercury), Mount Zirkel area. 

Smallest symbol 0.04-0.24 ppm; next to smallest 0.28-0.8 ppm; next to largest 

0.85-5.5 ppm; largest symbol 10->10 ppm. 
EVALUATION OF SURFACE POTENTIAL 

; 

:t 

"' )> 

0 

3: 

0 /::,. 

c 

z 

_, 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X ·---'"'litulfL 

undifferentiated 

---Adjacent area 

---Approximate boundary of 

Mount Zirkel Wilderness 

179 

' . 

Yq'&J 

FIGURE 71.-Anomalous rock Spec Sb (spectrographic antimony), Mount Zirkel area. 

Smallest symbol <100 ppm; next to smallest 100-200 ppm; next to largest 

300-500 ppm; largest 700-1,000 ppm. 

"' <( 

11. 

.... 

"' 0 

z 
180 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ 

"' X 

m 

)> 

0 

~ A 0 

c 

z 

.... 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

' . 

Yq'$ 

FIGURE 72.-Anomalous rock Spec As (spectrographic arsenic), Mount Zirkel area. 

Smallest symbol <200 ppm; intermediate 200-1,500 ppm; largest 2,000-5,000 ppm. 

< "' 

0.. 

:I: 

.... 

0 "' 

z 
~ 

0 

c: 

z 

..... 

> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

181 

' . 

Yq~ 

FIGURE 73.-Anomalous rock Spec W (spectrographic tungsten), Mount Zirkel area. 

Smallest symbol <50 ppm; next to smallest 50-100 ppm; next to largest 150-300 ppm; 

largest 500-1,000 ppm. 

"' "' <( 

0.. 

:r 

... 

"' 0 

z 
182 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

'" 

" :X:

'" > 

0 

~ 

0 

c 

z 

.... TMz 

> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

rn Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

TMz 

Yq'tJ 

FIGURE 74.-Anomalous rock Spec Sn (spectrographic tin), Mount Zirkel area Smallest 

symbol <10, 10, 15 ppm; next to smallest 20-30 ppm; next to largest 50-70 ppm; 

largest 100-150 ppm. 

.... 

"' 0 

z 
)> 

0 

~ 

0 

c 

z 

_. 

)> 

z 

EVALUATION OF SURFACE POTENTIAL 183 

[EJ 

8 Tertiary 

Proterozoic 

EXPLANA 

and 

Y 

Mesozoic 

quartz 

liON 

monzonites 

rocks '~ of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

W Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

---Approximate boundary of 

Mount Zirkel Wilderness 

Yq'&J 

FIGURE 75.-Anomalous stream-sediment Spec Sn (spectrographic tin), Mount Zirkel 

area. Smallest symbol <10 ppm; next to smallest 10-15 ppm; next to largest 

20-30 ppm; largest 50-70 ppm. 

.... 

"" 0 

z 
184 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

"' 

" 

"' )> 

0 

~ 

0 

c 

z 

.... 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic 

undifferentiated 

---Adjacent area 

' . 

Yq~ 

FIGURE 76.-Anomalous rock Spec Cd (spectrographic cadmium), Mount Zirkel area. 

Smallest symbol <20, <50, 20, 30 ppm; next to smallest 50-100 ppm; next to largest 

150-300 ppm; largest 500->500 ppm. 

"' <( 

IL 

:r 

1-

"' 0 

z 
41"00' 

EVALUATION OF SURFACE POTENTIAL 

"' 

" 

"' )> 

0 

:;:: 

0 

c 

z 

-< TMz 

)> 

z 

8 

Ej Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks 

,,~~~~~~~~~~~~~~~~~~ of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

EJ Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

185 

' . 

Yq'&J 

FIGURE 77.-Anomalous rock Spec Bi (spectrographic bismuth), Mount Zirkel area. 

Smallest symbol <10, <20, 10, 15 ppm; next to smallest 20-100 ppm; next to largest 

150-700 ppm; largest 1,000->1,000 ppm. 

"' <( 

0.. 

,_ 

"' 0 

z 
186 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ 

" X 

m 

)> 

0 

~ 

0 

c 

z 

.... 

)> 

z 

8 

E] Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

f---L-rL---Lr--.!.......i----'10 KlLO~i:IJ~ts~;~ 

Yq'&J 

FIGURE 78.-Anomalous rock Spec Ga (spectrographic gallium), Mount Zirkel area. 

Smallest symbol <10, <20, 10 ppm; next to smallest 15-20 ppm; next to largest 

30-50 ppm; largest 70-100 ppm. 

.... 

0 "' 

z 
1Q?OQQ' 

41°00' 

TMz 

EVALUATION OF SURFACE POTENTIAL 187 

13 034 

~ 

20 

10 

45' 

02 --- -· ' 01000-1300 

l 0 14 

\ 

7 \ ZIRKEL 

J) ~ 

{ 

/J 

/) 

15 20 

10 

EXPLANATION 

Tertiary and Mesozoic rocks 

140-4600 

l_~ Yq 

258 ' 

500-600' 

l400-3400' 

TMz 

15,000 -----

25 KILOMETERS 

15 MILES 

Proterozoic Y quartz monzonites of Mount Ethel pluton 

Proterozoic X gabbro of Elkhorn Mountain 

Remaining Proterozoic X rocks undifferentiated 

ppm thorium in rock (blank, unknown) 

ppm uranium 

ppm thorium in stream sediment 

ppm uranium 

FIGURE 79.-Localities of measured thorium and uranium in rocks and mineral 

specimens. 
188 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

)> 

0 

3: 

0 

c 

z 

... 

)> 

z 

EXPLANATION 

EJ Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

GM Remaining Proterozoic X. ----, '1//! //.r Aundifferentioted 

---Adjacent area 

- •- Approximate boundary of 

Mount Zirkel Wilderness 

' . 

~ 

FIGURE 80.-Anomalous rock Spec Mo (spectrographic molybdenum), Mount Zirkel 

area. Smallest symbol <2, <5, 2, 3 ppm; next to smallest 5-30 ppm; next to largest 

50-300 ppm; largest 500-1,500 ppm. 

"' <( 

:r 

.... 

0 

z 
m 

" ::t 

rn 

)> 

0 

~ 

0 

c 

z 

.... 

)> 

z 

V> 

EVALUATION OF SURFACE POTENTIAL 189 

5J 

8 

Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X - --.c, 1 ..- 1 ,.-,.-1 _

1_,_ 

undifferentiated 

---Adjacent area 

Yq'&J 

FIGURE 81.-Anomalous stream-sediment Spec Mo (spectrographic molybdenum), 

Mount Zirkel area. Smallest symbol <5-5 ppm; next to smallest 7-10 ppQ1; next to 

largest 15-20 ppm; largest 30-50 ppm. 

>-

"' 0 

z 
190 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

"' 

" 

"' )> 

0 

~ 

0 

c: 

z 

.... 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

~ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

B Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

- .. -Approximate boundary of 

Mount Zirkel Wilderness 

' 

I 

. 

Yq'&J 

FIGURE 82.-Anomalous rock Spec Nb (spectrographic niobium), Mount Zirkel area. 

Smallest symbol 20 ppm; next to smallest 30 ppm; next to largest 50-70 ppm; largest 

100-150 ppm. 

< "' 

0.. 

... 

"' 0 

z 
41°00' 

s:: 

0 

c 

z 

..... 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

~Tertiary and Mesozoic rocks 

GJ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

~Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

191 

Yq'&J 

FIGURE 83.-Anomalous stream-sediment Spec Nb (spectrographic niobium), Mount 

Zirkel area. Smallest symbol20 ppm; intermediate 30-50 ppm; largest 70-100 ppm. 

0 
192 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

3: 

0 

c 

z 

.... 

> 

z 

EXPLANATION 

~Tertiary and Mesozoic rocks 

m Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

5J Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

' 

f 

. 

Yq'$ 

FIGURE 84.-Anomalous rock Spec La (spectrographic lanthanum), Mount Zirkel area. 

Smallest symbol 50-70 ppm; next to smallest 100-150 ppm; next to largest 

200-300 ppm; largest 500 ppm. 

"' < 

0.. 

J: 

.... 

"' 0 

z 
s: 

0 

c 

z 

.... 

)> 

z 

EVALUATION OF SURFACE POTENTIAL 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MILES 

193 

£'., ' . 

Yq~ 

TM% 

FIGURE 85.-Anomalous stream-sediment Spec La (spectrographic lanthanum), Mount 

Zirkel area. Smallest symbol 100 ppm; next to smallest 150 ppm; next to largest 

200 ppm; largest 300 ppm. 

"' <( 

"-

:I: 

.... 

"' 0 

z 
40"45' 

194 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

)> 

c 

s:: 

0 

c 

z 

.... 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

KILO~fi~ol~~r~ 

' . 

Yq~ 

FIGURE 86.-Anomalous rock Spec Y (spectrographic yttrium), Mount Zirkel area. 

Smallest symbol 50-70 ppm; next to smallest 100-150 ppm; next to largest 

200-300 ppm; largest 500 ppm. 

"' < 

a.. 

.... 

"' 0 

z 
)> 

0 

;;:: 

0 

c 

z 

.... 

)> 

z 

EVALUATION OF SURFACE POTENTIAL 

EXPLANATION 

~Tertiary and Mesozoic rocks 

Ej Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

195 

' 6 

0 

' 

Yq~ 

FIGURE 87.-Anomalous stream-sediment Spec Y (spectrographic yttrium), Mount 

Zirkel area. Smallest symbol 70 ppm; next to smallest 100-150 ppm; next to largest 

200 ppm; largest symbol 300 ppm. 

"' <( 

0.. 

1-

"' 0 

z 
196 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

"' 

" 

"' )> 

0 

~ 

0 

c 

z 

.... TMz )> 

z 

"' 

8 

~Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic" «><~~/1/!///J'L undifferentiated 

- --Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

10 KILO,METERS~r{;>;(/,-~,7', 

I,· ·,·'iII 

5 MILES 

Yq'&J 

TMz 

FIGURE 88.-Anomalous rock Spec Cr (spectrographic chromium), Mount Zirkel area. 

Smallest symbol 100-200 ppm; next to smallest 300-700 ppm; next to largest 

1,000-1,500 ppm; largest symbol 2,000-3,000 ppm. 

.. 

0 "' 

z 
EVALUATION OF SURFACE POTENTIAL 

" :I: 

"' )> 

s:: 

0 

c 

z 

..... 

)> 

z 

EX PLANA l iON 

8 Tertiar y and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

KILO ~k1~~~} 

197 

' . 

Yq!J 

FIGURE 89.-Anomalous stream-sediment Spec Cr (spectrographic chromium), Mount 

Zirkel area. Smallest symbol 500 ppm; next to smallest 700 ppm; next to largest 

1,000-1,500 ppm; largest 2,000->5,000 ppm. 

< "" 

.. 

... 

"" 0 

z 
198 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

45' 

41°QQ' 

• 0.01 Damfino 

45' 

TMz 

TMz 

10 15 20 25 KILOMETERS 

10 15 MILES 

EXPLANATION 

Tertiary and Mesozoic rocks 

Proterozoic Y quartz monzonites of Mount Ethel pluton 

Proterozoic X gabbro of Elkhorn Mountain 

Remaining Proterozoic X rocks undifferentiated 

• .. Measured Pt +Pd (ppm) locality Wap1t1 

0 .03 

FIGURE 90.-Localities of measured platinum and palladium. 
)> 

Cl 

;;: 

0 

c 

z 

..... 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

B Tertiary and Mesozoic rocks 

[1iJ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

B Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

199 

TMz 

FIGURE 91.-Anomalous rock Spec Co (spectrographic cobalt), Mount Zirkel area. 

Smallest symbol 50-70 ppm; intermediate 100-150 ppm; largest 200 ppm. 

X 

>-

"' 0 
200 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

> 

0 

3: 

0 

c 

z 

.... 

> 

z 

VI 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

E) Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic 

undifferentiated 

- --Adjacent area 

5 MILES 

' . 

Yq'D 

FIGURE 92.-Anomalous stream-sediment Spec Co (spectrographic cobalt), Mount 

Zirkel area. Smaller symbol 50 ppm; larger symbol 70 ppm. 

< "' 

Q.. 

:r 

.... 

0 "' 

z 
EVALUATION OF SURFACE POTENTIAL 

~ 

"' :t: 

rn 

)> 

~ .[:., 

0 

c: 

z 

.... 

)> 

z 

"' 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

- --Adjacent area 

201 

Yqf) 

FIGURE 93.-Anomalous rock Spec Ni (spectrographic nickel), Mount Zirkel area. 

Smallest symbol 20-30 ppm; next to smallest 50-100 ppm; next to largest 

150-300 ppm; largest symbol 500-700 ppm. 

.... 

"' 0 

z 
202 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

"' )> 

0 

3: 

0 

c 

z 

_. 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

0 Proterozoic X gabbro of 

Elkhorn Mountain 

GRemaining Proterozoic X -----.-.:t,•iillic 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

5 MilES 

' -

Yq'tJ 

FIGURE 94.-Anomalous stream-sediment Spec Ni (spectrographic nickel), Mount Zirkel 

area. Smallest symbol 50 ppm; next to smallest 70 ppm; next to largest 100 ppm; 

largest 150-300 ppm. 

"' < 

:t: 

.... 

"' 0 

z 
m 

" 

;:: 

0 

c 

z 

-I 

~ 

z 

EVALUATION OF SURFACE POTENTIAL 

40"45'~ I EXPLANATION 

8 Tertiary and Mesozoic rocks 

~Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

c:J Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

203 

' \,Yq 

\: 

\· 

Yqi;l 

FIGURE 95.-Anomalous rock Spec Ba (spectrographic barium), Mount Zirkel area. 

Smallest symbol 3,000 ppm; intermediate 5,000 ppm; largest >5,000 ppm. 

"' <( 

>-

"' 0 

z 
204 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ 

0 

c: 

z 

.... 

)> 

z 

"' 

E) 

8 

Proterozoic 

Tertiary 

EXPLANATION 

and 

Y 

Mesozoic 

quartz monzonites 

rocks '~ of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

Yq'$ 

FIGURE 96.-Anomalous rock Spec Be (spectrographic beryllium), Mount Zirkel area. 

Smallest symbol 5-7 ppm; intermediate 10-15 ppm; largest 20-30 ppm. 

.... 

"' 0 

z 
"' X 

"' )> 

0 

;,:;: 

0 

c 

z 

-< 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

5J Proterozoic Y quartz monzonites 

of Mount Ethel pi uton 

W Proterozoic X gabbro of 

Elkhorn Mountain 

WRemaining Proterozoic X ·--··,'.'J/.,, .. 11,_ 

undifferentiated 

---Adjacent area 

-·-Approximate boundary of 

Mount Zirkel Wilderness 

205 

' . 

Yq'tJ 

FIGURE 97.-Anomalous stream-sediment Spec Be (spectrographic beryllium), Mount 

Zirkel area. Smaller symbol 5 ppm; larger 7 ppm. 

"' <( 

0.. 

t-

"' 0 

z 
40"45' 

206 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

> 

0 

'!:: 

0 

c 

z 

-< 

> 

z 

EXPLANATION 

~Tertiary and Mesozoic rocks 

EJ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X . --···ci.' Ji,, 1 _ •• L 

undifferentiated 

---Adjacent area 

' . 

Yq'&J 

FIGURE 98.-Anomalous rock Spec Sc (spectrographic scandium), Mount Zirkel area. 

Smallest symbol 20 ppm; next to smallest 30 ppm; next to largest 50 ppm; largest 

70-100 ppm. 

"' <( 

>-

"' 0 

z 
40"45' 

rn 

)> 

0 

~ 

0 

c 

z 

-< 

)> 

z 

EXPLANATION 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

207 

Yq'&J 

FIGURE 99.-Anomalous stream-sediment Spec Sc (spectrographic scandium), Mount 

Zirkel area. Smaller symbol 50 ppm; larger 70 ppm. 

"' <( 

1-

"' 0 
208 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

" :X: 

m 

)> 

0 

" t::. 

0 

c 

z 

.... 

)> 

z 

V> 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

~ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X . --··,., 1111111 ,_ 

undifferentiated 

---Adjacent area 

' . 

Yq'$ 

FIGURE 100.-Anomalous rock Spec Sr (spectrographic strontium), Mount Zirkel area. 

Smallest symbol1,000 ppm; next to smallest 1,500 ppm; next to largest 2,000 ppm; 

largest >5,000 ppm. 

"' <( 

... 

:X: 

... 

"' 0 

z 
EVALUATION OF SURFACE POTENTIAL 

"' ,. 

0 

~ 

0 

c: 

z 

... 

,. 

z 

EXPLANATION 

~Tertiary and Mesozoic rocks 

Ej Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount Zirkel Wilderness 

209 

~ ' . 

Yq~ 

FIGURE 101.-Anomalous stream-sediment Spec Sr (spectrographic strontium), Mount 

Zirkel area. Smaller symbol 500 ppm; larger 700 ppm. 

"' <( 

0.. 

:t: 

I-

"' 0 

z 
210 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

" 

m 

)> 

0 

~ 6 

0 

c 

z 

-< 

)> 

z 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

G Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

5 MILES 

' . 

Yq'&J 

FIGURE 102.-Anomalous rock Spec V (spectrographic vanadium), Mount Zirkel area. 

Smallest symbol 30-70 ppm; next to smallest 100-150 ppm; next to largest 

200-300 ppm; largest 500-700 ppm. 

"' <( 

.... 

"' 0 

z 
41°00' 

~ 

"' X 

m 

)> 

0 

3:: 

0 

c 

z 

_. 

)> 

z 

EXPLANAUON 

EVALUATION OF SURFACE POTENTIAL 

8 Tertiary and Mesozoic rocks 

EJ Proterozoic Y quartz monzonites 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

G Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

---Approximate boundary of 

Mount Zirkel Wilderness 

211 

' 

I 

. 

YqjjJ 

FIGURE 103.-Anomalous stream-sediment Spec V (spectrographic vanadium), Mount 

Zirkel area. Smallest symbol 300 ppm; intermediate 500 ppm; largest 700 ppm. 

"" <( 

.... 

"" 0 

z 
212 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

~ 

"' :%: 

m 

,. 

0 

l: 

0 

c 

z 

-1 

,. 

z 

"' 

EXPLANATION 

EJ Tertiary and Mesozoic rocks 

[Ej Proterozoic Y quartz monzonif!!_ 

of Mount Ethel pluton 

G Proterozoic X gabbro of 

Elkhorn Mountain 

~Remaining Proterozoic X ·--··.-; 111;itfJ.. 

undifferentiated 

- --Adjacent area 

' . 

Yq'&J 

FIGURE 104.-Anomalous stream-sediment Spec Zr (spectrographic zirconium), Mount 

Zirkel area. Smallest symbol 500 ppm; next to smallest 700 ppm; next to largest 

1,000 ppm; largest >1,000 ppm. 

"' <( 

a.. 

::c 

,_ 

0 "' 

z 
EVALUATION OF SURFACE POTENTIAL 213 

40' 106'52'30" 

45' ~~~~----~--~~~~--~~~-r~~---------.~~--~~~~~ 

00" 

40' 

37' 

30" 

6 7 8 KILOMETERS 

EXPLANATION 

Post-Precambrian rocks-Mainly Tertiary 

and Mesozoic sedimentary rocks 

Proterozoic Y rocks of Mount Ethel 

pluton 

Proterozoic X metamorphic wall rocks 

Thin section without visible fluorite 

• Thin section with <0.5 percent fluorite 

• Thin section with >0.5 percent fluorite 

FIGURE 105.-Association of interstitial fluorite with rocks of the Mount Ethel pluton. 

Geophysical Appraisal 

By JEFFREY J. DANIELS, U.S. GEOLOGICAL SURVEY 

MINERAL RESOURCES OF THE MOUNT ZIRKEL 

WILDERNESS AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

U.S. GEOLOGICAL SURVEY BULLETIN 1554-D 
CONTENTS 

Page 

Introductory note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 

Magnetic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 

Interpretation of aeromagnetic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 

ILLUSTRATION 

Page 

FIGURE 106. Diagram of geophysical models of anomalies M1, M2, and M5 220 

TABLE 

Page 

TABLE 12. Magnetic susceptibility values for selected rocks . . . . . . . . . . . . 218 

216 
MINERAL RESOURCES OF THE MOUNT ZIRKEL WILDERNESS 

AND NORTHERN PARK RANGE VICINITY, 

JACKSON AND ROUTT COUNTIES, COLORADO 

GEOPHYSICAL APPRAISAL 

By JEFFREY J. DANIELS, U.S. GEOLOGICAL SURVEY8 

INTRODUCTORY NOTE 

Aeromagnetic surveys were made in the Mount Zirkel region by the 

U.S. Geological Survey in 1965 (U.S. Geological Survey, 1970) and 

1972 (U.S. Geological Survey, 1981) as a part of the North Park 

aeromagnetic survey. The 1965 and 1972 surveys were flown at 

altitudes of 13,000 and 12,000 ft, respectively, above sea level. The 

base datum for the 1965 survey was 52,725 gammas. The 1972 survey 

was adjusted to this datum by adding 1,140 gammas to all map values. 

Results of these surveys are presented as a total-intensity magnetic 

map (pl. 1). The values on the map are the total magnetic intensities 

minus 52,725 gammas. Corrected values range from 3,100 gammas 

in the southern part of the adjacent area to 3,900 gammas in the northwestern part. Additionally, an induced polarization survey is available 

for the Hahns Peak area (Young and Segerstrom, 1973, p. 12). 

MAGNETIC PROPERTIES 

Table 12 shows magnetic susceptibility values for selected samples 

from pertinent rock units within the wilderness. The localities of these 

samples are indicated on plate 1. Because most of the samples were 

not oriented, the direction and intensity of remanent magnetization 

8Present address (1987) Department of Geology and Mineralogy, Ohio State University, Columbus, OH 43210. 

217 
218 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

TABLE 12.-Magnetic susceptibility values for selected rocks in the Mount Zirkel region 

[.uCGS, micro-centimeter·gram·second units; to convert to current SI unit, multiply ,.CGS value by 4 1r) 

Sample Susceptibility Sample Susceptibility Sample Susceptibility 

No. ( CGS units) No. ( CGS units) No. ( CGS units) 

1018 2,330 1006 21.5 1243 165 

"Cl () (/) 

~ 1411 421 .,., ;..J 1077 29.9 1244 213 ol (/) 

Q) -~ -~ ~ 

(/) :> 1501-A 2,407 .--i..C 1080 8,592 0 1707 88 0 .,., Q) () •;j Jo-< (/) "" (/) ..0 ;:l 1685 2,990 1657 19.8 ol 1708 8.69 ..0 Jo-< s ol ;..J Jo-< 

b!l~ 1765 926 975 6,119 0 1782 57.2 .,., ~ 

~.~ 1781 2,847 987 56.7 ,.,. 1919 142 Ul Jo-< 

..04-< ,.,. ol 

ol 1927 156 () 988-A 34.0 "" 1961 8.08 ~ s 0 

Jo-< 

.--i 1985 2,500 () 989 10.7 ~ 1979 19.1 .,., 0 

554 l ,858 ~ 1014 5. 39 Jo-< 1980 12.5 ol >Q 

() 

555 1,703 .--i 1029 5. 92 1983 8.98 (/) 0 Q) :> ;..J 984 127 ol 1065 6.69 19 1,620 .,., ;..J 

~ Q) 

~ 985 141 s 1148 54.5 22 605 ~ "Cl 0 1066 40 ~ 1285 678 226 4,160 s ol 

N 1067 199 :;., 1298 624 1691 2,381 ;..J Jo-< 

Jo-< 

ol 1068 51 ~ 1693 2,058 ;:l ~ 

cr Q) (/) 1290 14 s 1388 25.4 1808 44.9 .,., Q) 

:;., "Cl :> 1525 133 Q) 1643 80.3 .,., 1813 2,035 ..0 (/) (/) 

~ ;:l 

.... 1676 9.12 Q) 1849 18.2 t: 1819 70.8 .--i s ~ 

1827 204 .,., 1896 2,120 ~ 

ol :;., 

437 3,839 .,., 1854 38.9 Jo-< 1958 13.3 N Jo-< ol 

;..J ..0 .,., Jo-< 522 48 8 1970 55.2 ;..J 

ol Ul Jo-< 

;:l Q) () Q) 

cr<-J 524 4,271 Q) E-< .,., Jo-< 

. ~ 

:>-.o 1023 834 "" • N Jo-< 

..0 ~ Q) 

0 1097 512 ..;- s -5 

0 .--i 

could not be determined. The Precambrian mafic and ultramafic intrusive rocks have the highest magnetic susceptibilities as a group, 

but individual measured highs were from chloritized pelitic schist (No. 

1080) and a gedrite gneiss (No. 975), both volumetrically minor. With 

the further exception of two hornblende gneisses (Nos. 1285, 1298), 

the rest of the Precambrian metasediments and metavolcanics gave 

low susceptibilities. The two highest measurements of the 1. 7-b.y. 

quartz monzonites (Nos. 554, 555) are from Buffalo Mountain south 

of the Mount Ethel pluton. Similarly, the two highest susceptibility 

measurements on the 1.4-b.y. quartz monzonites (Nos. 437, 524) are 

near each other east of Swamp Park and on the flanks of anomaly M1 

(pl. 1). Four Tertiary intrusives containing olivine (Nos. 226, 1691, 

1693, 1896) averaged 2,680 susceptibility units, and six of more intermediate or silicic composition (Nos. 19, 22, 1808, 1813, 1819, 1958) 

averaged 732 susceptibility units. Four unaltered Browns Park 
GEOPHYSICAL APPRAISAL 219 

sediments averaged 144 susceptibility units, whereas six red-oxidized 

Browns Park sediments (Nos. 1708, 1961, 1979, 1980, 1983) averaged 

24 units. 

INTERPRETATION OF AEROMAGNETIC DATA 

The magnetic map generally reflects the surface and subsurface 

geology of this region, with topography having very little influence 

on the magnetic anomalies. Positive anomalies, related to intrusives, 

dominate the magnetic character of the area. Prominent evidence for 

faulting is in the northern part of the map area (about long 106°50' 

W.). Northerly magnetic trends in this region may be caused either 

by faulting (for example, east of Silver City basin and west of Black 

Mountain) or by the large intrusive indicated by anomaly M4 (pl. 1). 

The prominent magnetic lineament that extends S. 60° W. from the 

northeast comer of the mapped area is apparently controlled by a zone 

of 1.7-b.y. quartz monzonite intrusives. 

Anomaly M4 has a magnetic intensity of 600-700 gammas. This 

anomaly is almost certainly caused by the highly magnetic gabbro 

of Elkhorn Mountain. The northeastern extension of anomaly M4 accurately mirrors the northeastern extension of the gabbro of Elkhorn 

Mountain. Having anomaly M4 centered on the western exposed part 

of the gabbro batholith suggests that the gabbro body extends west 

and southwest under Tertiary cover by an amount roughly equal to 

its exposed mass. Gabbro inclusions in the City Mountain Tertiary 

intrusive 4. 7 km (2. 9 mi) southwest of the beginning of cover support 

this conclusion. Likewise, with this area exhibiting the largest quantity of red-altered Browns Park sediments, the contribution of the Tertiary cover to anomaly M4 must be minimal. No relation is apparent 

between this anomaly and topography. The gabbro of Elkhorn Mountain apparently also accounts for a gravity high on the Bouguer gravity map of Colorado (Behrendt and Bajwa, 1974). 

Anomalies M1 and M2 are of special interest owing to their position in relation to the Mount Ethel pluton. Model studies indicate that 

the main source of these anomalies is at depth. A cross section (A-A') 

of the anomaly and a three-dimensional model are shown on figure 

106. Talwani's three-dimensional magnetics modeling program was 

used to generate the model. The estimated depths of M 1 and M2, determined by Thalens Depth Rule (De Ridder, 1972), are 0.73 km (2,400 ft) 

and 0.91 km (3,000 ft) below the surface, which are considerably less 

than the depths determined from the model studies. However, as De 

Ridder pointed out, depths determined from ''rules-of-thumb'' are only 

approximate values. The model assumes a susceptibility contrast of 
220 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

1-

CJ) 

<( 

~ 

~ 

200 

~ 100 

~ 10,000 

u. 

~- 15,000 

:r 

1-

~ 20,000 

Cl 

Depth extent = oo 

I Width = 13,200 ft 

II Width = 10,560 ft 

Ill Width = 7290 ft 

FIGURE 106 (above and facing page).-Cross sections of three-dimensional 

prismatic models for anomalies Ml and M2 (profile A-A') and M5 (profileB-B1. 

Susceptibility contrast equals 2,000 J.LCGS units; to convert to current standard 

SI unit, multiply J.LCGS value by 4 1r. I-III are like artificial rock masses having 

assigned susceptibility. Horizontal distances not drawn to scale. 

2,000 ~-tCGS units9 between the "body" and the surrounding rock. A 

lower contrast would yield a shallower depth. The quartz monzonite 

porphyry (sample 437) or more mafic granodioritic rocks, like sample 

551 (Snyder, 1978, table 5), are likely candidates (in terms of geology 

and volume) to have caused the 2,000 ~-tCGS contrast. Quartz monzonite porphyry forms a highly irregular carapace around the north 

and west sides of the Mount Ethel pluton and could account not only 

for anomaly M1 but also for M3 and several anomalies between. 

Anomaly M3 also lies on the edge of the Mount Ethel pluton and has 

a Thalen-depth estimate of less than 1.16 km (3,800 ft) below the surface. The sources of anomalies M1, M2, and M3 all extend to depths 

9 J.ICGS units were the standard units when this report was prepared. To convert J.ICGS units to the current, SI 

unit, multiply J.ICGS value by 4 ..-. 
(/) 

<( 

~ 

~ 

200 

~ 100 

GEOPHYSICAL APPRAISAL 221 

0~------------------------------------------~ 

1- 5000 

UJ 

UJ 

u.. 

~ 10,000 

~ 15,000 a.. 

UJ 

0 20,000 

Depth extent = oo 

Width = 5280 ft 

of several kilometers. Anomaly M2 is also within the quartz monzonite 

porphyry carapace, but it happens to coincide with the surface exposure of a 1.6-km-long (1-mi-long) inclusion of a more mafic plutonic 

phase of dark granodiorite. 

A cross section (B-B') and the model generated for anomaly M5 are 

also shown on figure 106. The depth of this source as indicated by 

this model is 1.5 km (5,000 ft) below the surface. The susceptibility 

contrast assumed for this anomaly is also 2,000 t-tCGS units. The 

anomaly is centered on Big Agnes Mountain where felsic gneisses, 

pelitic schists, and granites are complexly interlayered and interfolded 

and many smaller intrusive bodies of pegmatite and ultramafic rock 

also occur. The anomaly is consistent with an ultramafic intrusive 

source at depth but could also be explained by a subsurface Tertiary 

intrusive. 

From a minerals exploration point of view, anomalies M1 through 

M5 are all of interest. A pluton-country rock contrast associated with 

magnetic highs is a potentially mineralized area. Also, the faults east 

of anomaly M4 could give rise to mineralization. All of these are near 

the margin of the adjacent area, except M5, which is squarely in the 

center of the Mount Zirkel Wilderness. 
222 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

SUMMARY EVALUATION OF 

MINERAL RESOURCE POTENTIAL 

By GEORGE L. SNYDER, U.S. GEOLOGICAL SURVEY 

There is a good possibility of a substantial mineral resource underlying part of the Mount Zirkel Wilderness and adjacent area. Water is 

ubiquitous, abundantly utilized, and renewable-the only renewable 

mineral resource. Fluorite is the main nonrenewable surface resource 

that is presently mineable, largely in the Crystal district overlapping 

the wilderness boundary and on Delaney Butte. Other possible subsurface mineral resources are less certain but could be much more 

valuable. (In the following discussion a surface resource is defined as 

one exposed in bedrock at the ground surface or buried beneath a thin 

layer of soil or rock, whereas a subsurface resource is defined as that 

enclosed in bedrock as much as several miles deep but capable of being utilized by man from surface workings, if it can be found.) 

Potential surface mineral resources, shown on figure 109A, are based 

on observations in surface outcrops or prospect pits or on geochemical 

anomalies in surface rocks or stream sediments. Many are described 

in greater detail in the preceding sections on mine appraisal and 

geochemical appraisal, in tables 5, 6, and 8, and on figures 52-104. 

Geochemical maxima are highlighted on figures 107 and 108. Most 

areas are small and scattered, mainly near the fringes of the wilderness 

or adjacent area, but some, for example the Gilpin district (figs. 3, 

14, 36), are squarely in the center of the most scenic part of the 

wilderness. The high fluorite potential and active geothermal areas 

are based on field observations, whereas the moderate base- and 

precious-metal potential, low uranium-thorium potential, and low 

platinum-chromium potential are based on geochemical anomalies. 

Potential subsurface mineral resources, shown on figure 109B, are 

untested but could be substantial; they are based partly on figure 

109A and partly on both a detailed knowledge of local geology and 

a broad knowledge of distant but geologically similar producing 

mineral provinces. There is a moderate to high subsurface fluorite 

potential anywhere within the steep-sided 1.4-b.y. Mount Ethel pluton 

(fig. 105), where the common interstitial fluorite (Snyder, 1978) could 

have been easily concentrated along joint sets, fault planes, or fault 

breccia zones that penetrated these rocks. Three belts of high copperlead-zinc-silver-gold potential are shown on figure 109B, controlled 

by the bedrock geochemical anomalies and mines of figure 1 09A and 

the northeastward grain of both the mapped geologic units and some 
SUMMARY EVALUATION 223 

geophysical lineaments. (Some stream-sediment geochemistry suggests that the southern two belts may merge with each other.) Ores 

in the northern two of these three belts would all be within 3.2 km 

(2 mi) of the contact of a 1.7-b.y. granite body, which might have served 

as the concentrating engine for the ore elements; most ores in the 

southern belt seem to have been controlled by calc-silicate or marble 

beds as favorable replacement horizons. The judgment that there is 

high potential for a deeply buried base- and precious-metal sulfide 

deposit within these geochemically favorable belts is based on the 

::: 

" ; 

}> 

0 

3: 

0 As c 

z 

.... 

}> 

z 

V> 

\: 

YqiJ 

>-

"' 0 

z 

FIGURE 107.-Locations of high concentrations of selected elements in rock, Mount Zirkel 

area. For specifics, see individual element maps and tables. AA, analysis by atomic absorption; S, analysis by spectrometry. 
224 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

" :I: 

"' )> 

Sr 0 

i: 

0 

c 

z 

... 

)> 

z 

V> 

EXPLANATION 

8 Tertiary and Mesozoic rocks 

m Proterozoic Y quartz monzonites AA + .. 

of Moun! Ethel pluton ~~ G Proterozoic X gabbro of . · 

Elkhorn Mountain · 

~Remaining Proterozoic X 

undifferentiated 

---Adjacent area 

- •-Approximate boundary of 

Mount ZirKel Wilderness 

KllO~f~Wffjt~ 

Sr 

' -

YqiJ 

FIGURE 108.-Locations of high concentrations of selected elements in stream sediment, 

Mount Zirkel area. For specifics, see individual element maps and tables. AA, analysis 

by atomic absorption; S, analysis by spectrometry. 

knowledge that many such massive sulfide deposits occur throughout 

the world in marine metasediments and metavolcanics of this (1.8 b.y.) 

age; for example, Mount Isa and Broken Hill, Australia; the Kidd 

Creek mine at Timmins, Ontario; McArthur River, Canada; Outukumpu, Finland; the United Verde mine at Jerome, Ariz., and therecent Exxon and Bear Creek finds in Wisconsin. Two areas of low 

platinum-chromium potential are indicated on figure 109B. One, based 

on the largest peridotite intrusive on the ridge between Lone Pine 

"' "' o( 

0.. 

J: 

... 

0 "' 

z 
SUMMARY EVALUATION 225 

Creek and Bear Creek, is here extended north to include the high cobalt 

and chromium stream-sediment anomalies measured on streams 

issuing from beneath rock glaciers between Ute Lake and Twin Lake. 

The other, essentially the area of the gabbro of Elkhorn Mountain, 

is included for completeness. Funnel-shaped layered gabbro bodies 

this size throughout the world are known to have a potential for 

magmatically segregated platinum-chromium ores. Here, there is 

no geological or geochemical indication of such magmatically 

segregated gabbroic layering, so the potential for a buried resource 

is judged to be low. Three low-potential uranium-thorium areas are 

indicated near the boundaries of the wilderness or adjacent area on 

figure 109B, and another is included within the molybdenum-potential 

area near the Crystal district. All of these are based on uranium, 

thorium, beryllium, niobium, or lanthanum geochemical anomalies. 

Though the potential is low, a large low-grade Rossing-type deposit 

beneath the indicated areas might be economically leachable. A linear 

belt of low molybdenum potential is shown from the Gilpin district 

through the Crystal district to east of Steamboat Springs. Based mainly on anomalous instrumental mercury, this belt nevertheless includes 

some anomalous molybdenum, the fluorite veins of the Crystal district 

and some uranium and thorium maxima; the northern part of the belt 

also includes aeromagnetic anomalies M3 and M5, which have no ready 

explanation in the surface geology and could be revealing the tops 

of deeply buried Tertiary intrusive pipes. Such a geochemical suite 

characterizes molybdenum-bearing carapaces near the tops of Tertiary 

porphyry vertical cylindrical intrusives in the Western United 

States-for example, the Climax and Henderson deposits in Colorado. 

Although no Tertiary intrusives occur at the surface in this part of 

the Park Range, such rocks are present both southeast and northwest 

of this geochemical belt. It may be pertinent to note that neither of 

the recently discovered valuable molybdenum deposits at Mount 

Emmons, Crested Butte, Colo., or Pine Grove, Utah, were exposed 

at the surface or had much of a geochemical anomaly. Although the 

potential for a similar Park Range deposit is judged to be low, the 

implications of such a deposit beneath the wilderness would be profound. A moderate geothermal potential is indicated in a north-south 

zone enclosing Steamboat Springs, but this is outside of the adjacent 

area. There is no potential for coal at all, and only low potential for 

oil and gas, largely in undrilled thrust-faulted Precambrian areas 

overlying apparently dry Mesozoic anticlines near the western boundary of the adjacent area. Other commodities or elements of possible 

economic interest are known to be present but in concentrations far 

smaller than would justify mining. 
226 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

m 

r 

7' 

:I: 

m 

)> 

Cl 

EL 

Dl 

10 15 

10 

EXPLANATION 

High fluorite potential 

Moderate Cu-Pb-Zn-Ag-Au potential 

Low U-Th potential 

Low Pt-Cr potential 

Active geothermal area 

Adjacent area 

20 25 KILOMETERS 

15 MILES 

Approximate boundary of Mount Zirkel Wilderness 

I 

1-

a:: 

0 

z 

= 

FIGURE 109 (above and facing page).-Map of Mount Zirkel Wilderness and adjacent area, showing areas of A, surface, and B, subsurface mineral resource potential. (Entire area has high water-resource potential.) 
40"30' B 

SUMMARY EVALUATION 

WYOMING ---------

10 15 

10 

EXPLANATION 

20 

Moderate (locally high) fluorite potential 

High Cu-Pb-Zn-Ag-Au potential 

Low U-Th potential 

Low Pt-Cr potential 

Low(?) Mo potential 

Moderate geothermal potential 

Adjacent area 

25 KILOMETERS 

15 MILES 

Approximate boundary of Mount Zirkel Wilderness 

227 

~ 

a: 

<( 

Cl. 

I 

fa: 

0 

z 
228 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Except for water, no large high-grade economically interesting 

mineral deposits are present anywhere at the surface in the study area. 

However, subeconomic surface deposits outlined by this report could 

guide others in more detailed searches for valuable subsurface 

resources, a step encouraged by the Congress of the United States 

in the Mining and Minerals Policy Act of 1970 (Osborn, 1974, p. 16, 17). 

REFERENCES CITED 

Abbott, J. T., 1972, Rb-Sr study of isotopic redistribution in a Precambrian mylonitebearing shear zone, northern Front Range, Colorado: Geological Society of America 

Bulletin, v. 83, no. 2, p. 487-493. 

Adams, J. W., 1964, Pegmatite minerals, in Mineral and water resources of Colorado: 

Washington, U.S. Government Printing Office, p. 169-173. 

Amstutz, G. C., 1964, Introduction to Developments in sedimentology, volume 2 of 

Sedimentology and ore genesis: Amsterdam, Netherlands, Elsevier, p. 1-7. 

Anderson, C. A., and Creasey, S.C., 1958, Geology and ore deposits of the Jerome area, 

Yavapai County, Arizona: U.S. Geological Survey Professional Paper 308, 185 p. 

Anderson, C. A., and Nash, J. T., 1972, Geology of the massive sulfide deposits at Jerome, 

Arizona-A reinterpretation: Economic Geology, v. 67, p. 845-863. 

Antweiler, J. C., 1966, Isotopic evidence of Precambrian episodes of mineralization in 

Colorado: Geological Society of America Abstracts for 1965, Special Paper 87, p. 270, 

271. 

Antweiler, J. C., Doe, B. R., and Delevaux, M. H., 1972, Lead isotope and other evidence 

on the bedrock source of placer gold at Hahns Peak, Colorado: Economic Geology, 

v. 67, p. 302-314. 

Atwood, W. W., Jr., 1937, Records of Pleistocene glaciers in the Medicine Bow and Park 

Ranges [Wyoming and Colorado]: Journal of Geology, v. 45, no. 2, p. 113-140. 

Ball, M. W., and Stebinger, Eugene, 1910, Eastern part of the Little Snake River coal 

field, Wyoming: U.S. Geological Survey Bulletin 381, p. 186-213. 

Barclay, C. S. V., 1968, Geology of the Gore Canyon-Kremmling area, Grand County, 

Colorado: U.S. Geological Survey Open-File Report. 

Barnwell, W. W., 1955, The geology of the south Hahns Peak district: Laramie, Wyo., 

University of Wyoming M.A. thesis, 91 p. 

Bass, N. W., Eby, J. B., and Campbell, M. R., 1955, Geology and mineral fuels of parts 

of Routt and Moffat Counties, Colorado: U.S. Geological Survey Bulletin 1027-D, 

250 p. 

Beekly, A. L., 1915, Geology and coal resources of North Park, Colorado: U.S. Geological 

Survey Bulletin 596, 121 p. 

Behrendt, J. C., and Bajwa, L. Y., 1974, Bouguer gravity map of Colorado: U.S. 

Geological Survey Geophysical Investigations Map GP-895. 

Behrendt, J. C., and Popenoe, Peter, 1969, Basement structure contour map of North 

Park-Middle Park basin, Colorado: American Association of Petroleum Geologists 

Bulletin, v. 53, no. 3, p. 678-682. 

Behrendt, J. C., Popenoe, Peter, and Mattick, R. E., 1969, A geophysical study of North 

Park and the surrounding ranges, Colorado: Geological Society of America Bulletin, 

v. 80, p. 1523-1528. 

Bernard, A. J., 1973, A review of processes leading to the formation of mineral deposits 

in sediments, in Amstutz, G. C., and Bernard, A. J., eds., Ores in sediments: International Union of Geological Sciences, ser. A, no. 3, p. 16. 
REFERENCES CITED 229 

Beroni, E. P., and Derzay, R. C., 1955, The uranium deposits of the Fish Creek district, 

Colorado, in Guidebook to the geology of northwest Colorado: Intermountain 

Association of Petroleum Geologists and Rocky Mountain Association of Geologists, 

p. 123. 

Beroni, E. P., and McKeown, F. A., 1952, Reconnaissance for uraniferous rocks in northwestern Colorado, southwestern Wyoming, and northeastern Utah: U.S. Geological 

Survey Trace Elements Investigations Report 308-A, 41 p. 

Blackstone, D. L., Jr., 1977, Independence Mountain thrust fault, North Park basin, 

Colorado: Laramie, Wyo., University of Wyoming Contributions to Geology, v. 16, 

no. 1, 15 p. 

Boyle, R. W., 1970, The source of metals and gangue elements in hydrothermal deposits, 

in Pouba, Zdenek, and Stemprok, Miroslav, eds., Problems of hydrothermal ore 

deposition: International Union of Geological Sciences, ser. A, no. 2, p. 3-6. 

Brady, B. T., 1975, Map showing fluorspar deposits in Colorado: U.S. Geological Survey 

Mineral Investigations Resources Map MR-70, 10 p. 

Brobst, D. A., and Pratt, W. P., 1973a, Summary of United States mineral resources: 

U.S. Geological Survey Circular 682, 19 p. 

Brobst, D. A., and Pratt, W. P., eds., 1973b, United States mineral resources: U.S. 

Geological Survey Professional Paper 820, 722 p. 

Buckner, D. L., 1977, Ribbon forest development and maintenance in the central Rocky 

Mountains of Colorado: Boulder, Colo., University of Colorado Ph. D. thesis, 239 p. 

Buffler, R. T., 1967, The Browns Park Formation and its relationship to late Tertiary 

geologic history of the Elkhead region, northwestern Colorado-south central Wyoming: Berkeley, Calif., University of California Ph. D. thesis; available Ann Arbor, 

Mich., University Microfilms, Inc., 215 p. 

Christensen, A. L., 1942, Igneous geology of the Elkhead Mountains, Colorado: Berkeley, 

Calif., University of California Ph. D. thesis, 180 p. 

Clark, S. P., Jr., Peterman, Z. E., and Heier, K. S., 1966, Abundances of uranium, thorium 

and potassium, in Handbook of physical constants: Geological Society of America 

Memoir 97, p. 521-541. 

Colton, R. G., Halligan, J. A., Patterson, P. E., and Anderson, L. W., 1975, Preliminary 

map of landslide deposits, Craig 1 ox 2° quadrangle, Colorado: U.S. Geological 

Survey Mineral Investigations Field Studies Map MF-700. 

Crawford, R. D., Wilson, K. M., and Perini, V. C., Jr., 1920, Some anticlines of western 

Colorado: Colorado Geological Survey Bulletin 23, 61 p. 

de la Montagne, John, 1955, Cenozoic history of the Saratoga valley area, Wyoming 

and Colorado: Laramie, Wyo., University of Wyoming Ph. D. thesis, 140 p. 

De Nault, K. J., 1967, Geology and distribution of copper, lead, and zinc in streams 

and soil-Broadway mine area, Carbon County, Wyoming: Laramie, Wyo., University of Wyoming M.S. thesis, 38 p. 

DeRidder, Edward, 1972, The relative accuracy of some magnetic depth determination 

techniques: Golden, Colo., Colorado School of Mines M.S. thesis T-1488, 78 p. 

Divis, A. F., 1975, The geology and geochemistry of the Sierra Madre Mountains, Wyoming: San Diego, Calif., University of California Ph. D. thesis. 

___ 1976, Geology and geochemistry of Sierra Madre Range, Wyoming: Quarterly 

of the Colorado School of Mines, v. 71, no. 3, 127 p. 

___ 1977, Isotope studies on a Precambrian geochronologic boundary, Sierra Madre 

Mountains, Wyoming: Geological Society of America Bulletin, v. 88, p. 96-100. 

Doe, B. R., 1978, The application of lead isotopes to mineral prospect evaluation of 

Cretaceous-Tertiary magmatothermal ore deposits in the Western United States 

[abs.]: Association of Exploration Geochemists, Seventh International Geochemists 

Exploration Symposium, Program, p. 35-37. 
230 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Ebbett, B. E., 1970, Geologic maps of the Singer Peak, Encampment, Red Mountain, 

and Bridger Peak quadrangles: Laramie, Wyo., Geological Survey of Wyoming open· 

file maps. 

Eckel, E. B., 1961, Minerals of Colorado-A 100-year record: U.S. Geological Survey 

Bulletin 1114, 399 p. 

Fenneman, N. M., and Gale, H. S., 1906, The Yampa coal field, Routt County, Colorado: 

U.S. Geological Survey Bulletin 297, 96 p. 

Fenton, M.D., 1965, The geology of parts of Mad Creek, Clark, Floyd Peak quadrangles, 

Routt County, Colorado: Laramie, Wyo., University of Wyoming M.S. thesis, 39 p. 

Ferris, C. S., Jr., 1964, Petrology and structure of the Precambrian rocks southeast of 

Encampment, Wyoming: Laramie, Wyo., University of Wyoming Ph. D. thesis. 

Gabelman, J. W., 1976, Strata-binding mineralization processes, in Wolf, K. H., ed., 

Handbook of strata-bound and strataform ore deposits, volume 4, Tectonics and 

metamorphism: Amsterdam, Netherlands, Elsevier, p. 31-73. 

Gale, H. S., 1906, Hahns Peak gold field: U.S. Geological Survey Bulletin 285, p. 28-34. 

__ 1909, Coal fields of northwestern Colorado and northeastern Utah: U.S. Geological 

Survey Bulletin 341, p. 283-315. 

__ 1910, Coal fields of northwestern Colorado and northeastern Utah: U.S. Geological 

Survey Bulletin 415, 265 p. 

George, R. D., and Crawford, R. D., 1909, Hahns Peak region, Routt County, Colorado: 

Colorado Geological Survey 1st Report, p. 189-229. 

Godwin, L. H., Haigler, L. B., Rioux, R. L., White, D. E., Muffler, L. J.P., and Wayland, 

R. G., 1971, Classification of public lands valuable for geothermal steam and 

associated geothermal resources: U.S. Geological Survey Circular 647, 18 p. 

Goldschmidt, V. M., 1954, Geochemistry: London, Oxford University Press, 730 p. 

Graff, Paul, 1973, The areal geology of the West Fork Lake quadrangle, northern Colorado: De Kalb, Ill., Northern Illinois University M.S. thesis, 59 p. 

__ 1978, Geology of the lower part of the Early Proterozoic Snowy Range Supergroup, 

Sierra Madre, Wyoming, with chapters on Proterozoic regional tectonics and 

uraniferous quartz-pebble conglomerates: Laramie, Wyo., University of Wyoming 

Ph. D. thesis, 85 p. 

Grim, P. J., 1977, [Map of] Geothermal energy resources of the Western United States: 

National Geophysical and Solar-Terrestrial Data Center, National Oceanic and Atmospheric Administration. 

Grout, F. F., Worcester, P. G., and Henderson, Junius, 1913, Reconnaissance of the 

geology of the Rabbit Ears region, Routt, Grand and Jackson Counties, Colorado: 

Colorado Geological Survey Bulletin 5, pt. 1, 57 p. 

Grutt, E. W., Jr., and Whalen, J. F., 1955, Uranium in northern Colorado and southern 

Wyoming, in Guidebook to the geology of northwest Colorado: Intermountain 

Association of Petroleum Geologists and Rocky Mountain Association of Geologists, 

p. 126-129. 

Hail, W. J., Jr., 1965, Geology of northwestern North Park, Colorado: U.S. Geological 

Survey Bulletin 1118, 133 p. 

__ 1968, Geology of southwestern North Park and vicinity, Colorado: U.S. Geological 

Survey Bulletin 1257, 119 p. 

Hedge, C. E., Houston, R. L., Tweto, Ogden, Reid, R. R., Harrison, J. E., and Peterman, Zell, 1977, The Precambrian of the Rocky Mountain region: Geological Society of America Abstracts with Programs, v. 9, no. 7, p. 1010. 

Hewett, G. C., 1889, The northwestern Colorado coal region: American Institute of Mining Engineers Transactions, v. 17, p. 375-380. 

Hill, J. J., 1969, Petrology and structure of the Precambrian rocks of the Park Range 

of north-central Colorado: Eugene, Oreg., University of Oregon M.S. thesis, 75 p. 
REFERENCES CITED 231 

Hills, F. A., Gast, P. W., Houston, R. S., and Swainbank, I. G., 1968, Precambrian 

geochronology of the Medicine Bow Mountains, southeastern Wyoming: Geological 

Society of America Bulletin, v. 79, p. 1757-1784. 

Hills, F. A., and Houston, R. S., 1979, Early Proterozoic tectonics of the Central Rocky 

Mountains, North America: Laramie, Wyo., University of Wyoming Contributions 

to Geology, v. 17, no. 2, p. 89-109. 

Hills, R. C., 1893, Coal fields of Colorado: U.S. Geological Survey Mineral Resources 

of the United States, 1892, p. 319-365. 

Houston, R. S., and others, 1968, A regional study of rocks of Precambrian age in that 

part of the Medicine Bow Mountains lying in southeastern Wyoming-with a chapter 

on the relationship between Precambrian and Laramide structure: Wyoming 

Geological Survey Memoir 1, p. 1-167. 

Houston, R. S., and Ebbett, B. E., 1977, Geologic map of the Sierra Madre and western 

Medicine Bow Mountains, southeastern Wyoming: U.S. Geological Survey Map 

MF-827. 

Houston, R. S., Karlstrom, K. E. [incorrectly listed as Karl E. Strom on cover], and 

Graff, P. J., 1979, Progress report on the study of radioactive quartz-pebble conglomerate of the Medicine Bow Mountains and Sierra Madre, southeastern Wyoming [incorrectly listed as southeastern Montana on cover]: U.S. Geological Survey 

Open-File Report 79-1131, 43 p. 

Houston, R. S., Schuster, J. E., and Ebbett, B. E., 1975, Preliminary report on the 

distribution of copper and platinum group metals in mafic igneous rocks of the Sierra 

Madre, Wyoming: U.S. Geological Survey Open-File Report 75-85, 129 p. 

Huang, Chi-I, 1970, Cataclastic rocks in the Little Beaver Creek area, Carbon County, 

Wyoming: Laramie, Wyo., University of Wyoming M.S. thesis, 63 p. 

Hunter, J. M., 1955, Geology of the north Hahns Peak area, Routt County, Colorado: 

Laramie, Wyo., University of Wyoming M.A. thesis, 77 p. 

Izett, G. A., 1975, Late Cenozoic sedimentation and deformation in northern Colorado 

and adjoining areas, in Cenozoic history of the Southern Rocky Mountains: 

Geological Society of America Memoir 144, p. 179-209. 

Izett, G. A., and Barclay, C. S. V., 1973, Geologic map of the Kremmling quadrangle, 

Grand County, Colorado: U.S. Geological Survey Geologic Quadrangle Map 

GQ-1115. 

Izett, G. A., Cobban, W. A., and Gill, J. R., 1971, The Pierre Shale near Kremmling, 

Colorado, and its correlation to the east and the west: U.S. Geological Survey Professional Paper 684-A, p. A1-A19. 

Izett, G. A., Denson, N. M., and Obradovich, J.D., 1970, K-Ar age of the lower part 

of the Browns Park Formation, northwestern Colorado: U.S. Geological Survey Professional Paper 700-C, p. C150-C152. 

Jensen, M. L., and Bateman, A.M., 1979, Economic mineral deposits, 3d edition: New 

York, John Wiley, 593 p. 

Johnson, R. B., Jr., 1979, Structural and stratigraphic controls on Precambrian Pb-ZnCu type mineralization at the Greenville mine, Clark, Colorado: Geological Society 

of America Abstracts with Programs, v. 11, no. 6, p. 275. 

King, Clarence, 1878, Report of the geological exploration of the fortieth parallel, v. I, 

Systematic geology: U.S. Army Professional Papers of the Engineer Department, 

No. 18, 803 p. 

Kucera, R. E., 1962, Geology of theY ampa district, northwest Colorado: Boulder, Colo., 

University of Colorado Ph. D. thesis, 675 p. 

Lackey, L. L., 1965, Petrography of metavolcanic and igneous rocks of Precambrian 

age in the Huston Park area, Sierra Madre, Wyoming: Laramie, Wyo., University 

of Wyoming M.A. thesis, 78 p. 
232 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Lamarre, A. L., and Hodder, R. W., 1978, Distribution and genesis of fluorite deposits 

in the Western United States and their significance to metallogeny: Geology, v. 6, 

no. 4, p. 236-238. 

Larson, E. E., Ozima, Minoru, and Bradley, W. C., 1975, Late Cenozoic basic volcanism 

in northwestern Colorado and its implications concerning tectonism and the origin 

of the Colorado River system, in Cenozoic history of the Southern Rocky Mountains: 

Geological Society of America Memoir 144, p. 155-178. 

Larson, T. G., 1955, Stratigraphy of the Steamboat Springs area, Colorado, in Intermountain Association of Petroleum Geologists (and Rocky Mountain Association of 

Geologists) Guidebook, 6th Annual Field Conference, 1955: p. 10, 11. 

Lovering, T. S., 1963, Epigenetic, diplogenetic, syngenetic, and lithogene deposits: 

Economic Geology, v. 58, p. 315-331. 

Madden, D. H., 1977 a, Exploratory drilling in the Coalmont coal field, Jackson County, 

Colorado: U.S. Geological Survey Open-File Report 77-887, 138 p. 

__ 1977b, Exploratory drilling in the McCallum coal field, Jackson County, Colorado: 

U.S. Geological Survey Open-File Report 77-788, 80 p. 

Madole, R. F., 1982, Surficial geologic map of the Craig %0 X1 o quadrangle, Moffat and 

Routt Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series 

Map I-1346. 

Malan, R. C., 1957, Geology of uranium occurrences in North and Middle Parks, Colorado: Guidebook to the geology of North and Middle Parks Basin, Colorado; Rocky 

Mountain Association of Geologists, p. 126-136. 

McCallum, M. E., 1968, Cenozoic history of the East-Central Medicine Bow Mountains, 

Wyoming: Mountain Geologist, v. 5, no. 2, p. 69-81. 

McConnell, M.D., 1960, The geology of the Clark-Hinman Park area, Routt County, 

Colorado: Laramie, Wyo., University of Wyoming M.A. thesis, 71 p. 

McDowell, F. W., 1966, Potassium-argon dating of Cordilleran intrusives: New York, Columbia University Ph. D. thesis, p. 6, 221. 

Merry, R. D., 1963, Precambrian geology, shear zones and associated mineral deposits 

of the Hog Park area, Carbon County, Wyoming: Laramie, Wyo., University of Wyoming M.S. thesis, 73 p. 

Millard, H. T., 1976, Determination of uranium and thorium in U.S.G.S. standard rocks 

by the delayed neutron technique, in Flanagan, F. J., ed., Descriptions and analyses 

of eight new U.S.G.S. rock standards: U.S. Geological Survey Professional Paper 840, 

p. 61-65. 

Miller, W. R., 1971, Geology of the Indian Rocks area, Carbon County, Wyoming, with 

particular reference to the evolution of mafic dikes: Laramie, Wyo., University of 

Wyoming M.S. thesis, 40 p. 

Morse, J. G., and Curtin, M. S., 1977, CERI Colorado energy resources handbook, volume 

3, Uranium: Golden, Colo., Colorado School of Mines, 68 p. 

Murphy, R. W., 1958, Geology of the Slavonia-Diamond Park area, Routt County, Colorado: Laramie, Wyo., U Diversity of Wyoming M.A. thesis, 54 p. 

Oriel, S. S., 1954, Thctonic map of Colorado, in The oil and gas fields of Colorado: Denver, 

Colo., Rocky Mountain Association of Geologists, pl. 1. 

Osborn, E. F., 1974, Our mineral resource problem and what we can do about it (Edward 

H. Draus memorial lecture, Ann Arbor, Mich., University of Michigan, September 12, 

1974): Carnegie Institution of Washington Geophysical Laboratory Paper 1652, 17 p. 

Osterwald, F. W., and Dean, B. G., 1958, Preliminary tectonic map of northern Colorado 

and northeastern Utah showing the distribution of uranium deposits: U.S. Geological 

Survey Mineral Investigations Field Studies Map MF-130. 

__ 1961, Relation of uranium deposits to tectonic pattern of the central Cordilleran 

foreland: U.S. Geological Survey Bulletin 1087-I, p. 337-390. 
REFERENCES CITED 233 

Park, G. M., 1977, Oil potential of Mesozoic sediments beneath the Independence Mountain thrust fault, North Park, Colorado, in Explm::ation frontiers of the Central and 

Southern Rockies: Rocky Mountain Association of Geologists, 1977 Symposium, 

p. 61-66. 

Parsons, H. F., and Liddell, C. A., 1903, Coal and mineral resources of Routt County: 

Colorado School of Mines Bulletin 1, no. 4, p. 47-59. 

Peterman, Z. E., and Hedge, C. E., 1967, Precambrian history of the Front Range and 

adjacent areas, Colorado, in Geochronology of Precambrian stratified rocks: 

Geochronology Commission, I.U.G.S., Can&da Geological Survey, and Department 

of Geology, Alberta University, p. 77-78. 

Peterman, Z. E., Hedge, C. E., and Braddock, W. A., 1968, Age of Precambrian events 

in the northeastern Front Range, Colorado: Journal of Geophysical Research, v. 73, 

no.6, p.2227-2296. 

Popenoe, Peter, Brinkworth, G. L., Worl, R. G., and Behrendt, J. C., 1970, Geophysical 

lineations in north-central Colorado and their possible relationship to Tertiary 

plutonic activity: Geological Society of America Abstracts, v. 2, no. 5, p. 343. 

Price, Don, and Arnow, Ted, 1974, Summary appraisals of the Nation's ground-water 

resources-Upper Colorado region: U.S. Geological Survey Professional Paper 813-C, 

40 p. 

Read, T. T., 1903, Nodular-bearing schists near Pearl, Colorado: Journal of Geology, 

v. 11, p. 493-497. 

Renner, J. L., White, D. E., and Williams, D. L., 1975, Hydrothermal convection systems, 

in Assessment of geothermal resources of the United States, 1975: U.S. Geological 

Survey Circular 726, p. 5-57. 

Ridge, J. D., 1976, Origin, development, and changes in concepts of syngenetic ore 

deposits as seen by North American geologists, in Wolf, K. H., ed., Handbook of 

strata-bound and stratiform ore deposits, volume 1, Classifications and historical 

studies: Amsterdam, Netherlands, Elsevier, p. 183-297. 

Ridgely, N.H., 1971, Precambrian rocks in the Blackhall Mountain area, Carbon County, Wyoming: Laramie, Wyo., University of Wyoming M.S. thesis, 50 p. 

Ritzma, H. R., 1949, Geology along the southwest flank of the Sierra Madre, Carbon 

County, Wyoming: Laramie, Wyo., University of Wyoming M.A. thesis, 77 p. 

Rollins, J. F., 1952, Stratigraphy and structure of the Sheep Mountain area, in North 

Park, Jackson County, Colorado: Lincoln, Nebr., University of Nebraska M.S. thesis, 

106p. 

Ryan, Star ley, 1976, Pearl-A forgotten mountain jewel: Denver Post Empire Magazine, 

September 26, 1976, p. 12-15. 

Sangster, D. F., and Scott, S.D., 1976, Precambrian, strata-bound, massive Cu-Zn-Pb 

sulfide ores of North America, in Wolf, K. H., ed., Handbook of strata-bound and 

stratiform ore deposits, volume 6, Cu, Zn, Pb and Ag deposits: Amsterdam, 

Netherlands, Elsevier, p. 129-222. 

Scott, R. W., 1961, Geology of Rabbit Ears Pass area, Jackson and Grand Counties, 

Colorado: Laramie, Wyo., University of Wyoming M.A. thesis, 73 p. 

Segerstrom, Kenneth, and Kirby, S. H., 1969, Tuffaceous epiclastic breccia and sandstone near Hahns Peak, Colorado, and their genetic implications, in Geological 

Survey research 1969: U.S. Geological Survey Professional Paper 650-B, 

p. B19-B22. 

Segerstrom, Kenneth, and Young, E. J ., 1972, General geology of the Hahns Peak and 

Farwell Mountain quadrangles, Routt County, Colorado: U.S. Geological Survey 

Bulletin 1349, 63 p. [1973]. 

Shawe, D. R., 1976, Geology and resources of fluorine in the United States: U.S. 

Geological Survey Professional Paper 933, 99 p. 
234 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

Shawe, D. R., 1979, Comment and reply on Distribution and genesis of fluorite deposits 

in the Western United States and their significance to metallogeny: Geology, v. 7, 

no. 3, p. 115-116. 

Sheridan, D. M., and Raymond, W. H., 1977, Preliminary data on some Precambrian 

deposits of zinc-copper-lead sulfides and zinc spinel (gahnite) in Colorado: U.S. 

Geological Survey Open-File Report 77-607, 27 p. 

Short, B. L., 1958, A geologic and petrographic study of the Ferris-Haggarty mining 

area, Carbon County, Wyoming: Laramie, Wyo., University of Wyoming M.A. thesis, 

138 p. 

Smith, J. B., 1974, The mineral industry of Colorado, in U.S. Bureau of Mines Minerals 

Yearbook, 1974, volume 2: p. 143-163. 

Snyder, G. L., 1977a, Geologic map of the northernmost Park Range and southernmost 

Sierra Madre, Jackson and Routt Counties, Colorado: U.S. Geological Survey OpenFile Report 77-188. 

__ 1977b, Geologic map of the central part of the northern Park Range, Jackson and Routt Counties, Colorado: U.S. Geological Survey Open-File Report 

77-187. 

__ 1977 c, Geologic map of the northernmost Gore Range and southernmost northern 

Park Range, Grand, Jackson, and Routt Counties, Colorado: U.S. Geological Survey 

Open-File Report 77-189. 

___ 1978, Intrusive rocks northeast of Steamboat Springs, northern Park Range, Colorado, with a section on Geochronology by C. E. Hedge: U.S. Geological Survey 

Professional Paper 1041, 42 p. 

__ 1980a, Geologic map of the northernmost Park Range and southernmost Sierra 

Madre, Jackson and Routt Counties, Colorado: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-1113. 

___ 1980b, Geologic map of the central part of the northern Park Range, Jackson 

and Routt Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations 

Series Map I-1112. 

__ 1980c, Geologic map of the northernmost Gore Range and southernmost northern 

Park Range, Grand, Jackson, and Routt Counties, Colorado: U.S. Geological Survey 

Miscellaneous Investigations Series Map I-1114. 

Snyder, G.L., Brandt, E.L., and Smith, V.C., 1987, Precambrian petrochemistry of the 

northern Park Range, Colorado, and its implications for studies of crustal derivation: U.S. Geological Survey Professional Paper 1343, 116 p. 

Snyder, G. L., Hopkins, R. T., Jr., Domenico, J. A., Frisken, J. G., and Mitchell, J., 

1981, Analyses of rock and stream sediment samples from the Mount Zirkel 

Wilderness and northern Park Range vicinity, Jackson and Routt Counties, Colorado: U.S. Geological Survey Open-File Report 81-186, 85 p. 

Solomon, M., 1976, "Volcanic" massive sulphide deposits and their host rocks-A review 

and an explanation, in Wolf, K. H., ed., Handbook of strata-bound and stratiform 

ore deposits, volume 6, Regional studies and specific deposits: Amsterdam, 

Netherlands, Elsevier, p. 21-77. 

Spencer, A. C., 1903a, Mineral resources of the Encampment copper region, Wyoming: 

U.S. Geological Survey Bulletin 213, p. 158-162. 

___ 1903b, Reconnaissance examination of the copper deposits at Pearl, Colorado: 

U.S. Geological Survey Bulletin 213, p. 163-169. 

__ 1904, The copper deposits of the Encampment district, Wyoming: U.S. Geological 

Survey Professional Paper 25, 107 p. 

Stanton, R. L., 1972, Ore petrology: New York, McGraw-Hill, 713 p. 

Steven, T. A., 1954, Geology of the Northgate fluorspar district, Colorado: U.S. Geological 

Survey Mineral Investigations Field Studies Map MF-13. 
REFERENCES CITED 235 

Steven, T. A., 1956, Cenozoic geomorphic history of the Medicine Bow Mountains near 

the Northgate fluorspar district, Colorado: Colorado Scientific Society Proceedings, 

v. 17, no. 2, p. 35-55. 

__ 1957, Metamorphism and the origin of granitic rocks, Northgate district, Colorado: U.S. Geological Survey Professional Paper 274-M, p. 335-377. 

__ 1960, Geology and fluorspar deposits, Northgate district, Colorado: U.S. 

Geological Survey Bulletin 1082-F, p. 323-422. 

Sullivan, C. J., 1958, The origin of massive sulphide ores, in Gill, J. E., Symposium 

on the genesis of massive sulphide deposits: Canadian Mining and Metallurgical 

Bulletin 570, p. 613-619. 

Taylor, R. B., Theobald, P. K., and Izett, G. A., 1968, Mid-Tertiary volcanism in the 

central Front Range, Colorado, in Cenozoic volcanism in the southern Rocky Mountains: Colorado School of Mines Quarterly, v. 63, no. 3, p. 39-50. 

Theobald, P. K., Jr., and Thompson, C. E., 1968, Platinum and associated elements at 

the New Rambler mine and vicinity, Albany and Carbon Counties, Wyoming: U.S. 

Geological Survey Circular 607, 14 p. 

Todd, D. K., 1970, The water encyclopedia: Port Washington, N.Y., Water Information Center, Inc., 559 p. 

Turekian, K. K., and Wedepohl, K. H., 1961, Distribution of the elements in some major units of the earth's crust: Geological Society of America Bulletin, v. 72, 

p. 175-192. 

Tweto, Ogden, 1960, Scheelite in the Precambrian gneisses of Colorado: Economic 

Geology, v. 55, p. 1406-1428. 

__ 1968, Geologic setting and interrelationships of mineral deposits in the mountain province of Colorado and south-central Wyoming, in part 5 of Ore deposits of 

the United States, 1933-1967: Colorado Rockies, p. 551-588. 

__ 1975a, Laramide (late Cretaceous-early Tertiary) orogeny in the Southern Rocky 

Mountains, in Cenozoic history of the Southern Rocky Mountains: Geological Society 

of America Memoir 144, p. 1-44. 

__ 197 5b, Preliminary geologic map of the Craig 1 o X 2 o quadrangle, northwestern 

Colorado: U.S. Geological Survey Mineral Investigations Field Studies Map MF-666. 

__ 1976a, Geologic map of the Craig 1 o X 2° quadrangle, northwestern Colorado: 

U.S. Geological Survey Miscellaneous Investigations Map 1-972. 

___ 1976b, Preliminary geologic map of Colorado: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-788. 

___ 1977a, Tectonic history of west-central Colorado, in Exploration frontiers of the 

Central and Southern Rockies: Rocky Mountain Association of Geologists, 1977 

Symposium, p. 11-22. 

__ 1977b, Nomenclature of Precambrian rocks of Colorado: U.S. Geological Survey 

Bulletin 1422-D, 22 p. 

__ 1977c, Tectonic map of the Rio Grande rift system in Colorado: U.S. Geological 

Survey Open-File Report 77-750. 

Tweto, Ogden, Bryant, Bruce, and Williams, F. E., 1970, Mineral resources of the Gore 

Range-Eagles Nest Primitive Area and vicinity, Summit and Eagle Counties, Colorado: U.S. Geological Survey Bulletin 1319-C, 127 p. 

Tweto, Odgen, and Sims, P. K., 1963, Precambrian ancestry of the Colorado mineral 

belt: Geological Society of America Bulletin, v. 74, p. 991-1014. 

U.S. Geological Survey, 1970, Aeromagnetic survey of North Park and vicinity, northcentral Colorado: U.S. Geological Survey Open-File Report, 1 sheet, scale 

1:125,000. 

__ 1975, Mineral resource perspectives, 1975: U.S. Geological Survey Professional 

Paper 940, 24 p. 
236 MOUNT ZIRKEL WILDERNESS AND NORTHERN PARK RANGE 

U.S. Geological Survey, 1978, Aeromagnetic survey of North Park and vicinity, Colorado: U.S. Geological Survey Open-File Report 78-112, 1 sheet, scale 1:125,000. 

U.S. Geological Survey and Colorado Geological Survey, 1977, Energy resources map 

of Colorado. 

Van Alstine, R. E., 1964, Fluorspar, in Mineral and water resources of Colorado: 

Washington, U.S. Government Printing Office, p. 160-165. 

__ 1976, Continental rifts and lineaments associated with major fluorspar districts: 

Economic Geology, v. 71, no. 6, p. 977-987. 

Vanderwilt, J. W, 1947, Mineral resources of Colorado: Colorado Mineral Resources 

Board, 54 7 p. 

Wakefield, L. W., 1952, Geology of the Boetcher [sic] Ridge-Sheep Mountain-Delanos 

Butte area, North Park, Colorado: Boulder, Colo., University of Colorado M.S. thesis, 

74 p. 

Wallace, S. R., Muncaster, N. K., Jonson, D. C., MacKensie, W. B., Bookstrom, A. A., 

and Surface, V. E., 1968, Multiple intrusion and mineralization at Climax, Colorado, 

in Ridge, J. D., ed., Ore deposits in the United States 1933-1967: New York, 

American Institute of Mining, Metallurgical and Petroleum Engineers, p. 605-640. 

Walters, R. F., 1953, Geology of the Independence Mountain area, North Park, Colorado: Laramie, Wyo., University of Wyoming M.A. thesis, 64 p. 

Walton, D. S., 1963, The geology of Slater Park, Routt County, Colorado, and the 

stratigraphy of the Lewis Shale, northern Routt County, Colorado: Golden, Colo., 

Colorado School of Mines M.S. thesis, 164 p. 

Warner, L.A., 1978, The Colorado Lineament-A middle F:ecambrian wrench fault 

system: Geological Society of America Bulletin, v. 89, p. 161-171. 

Wellborn, R. E., 1977, Struchtral style in relation to oil and gas exploration in North 

Park-Middle Park basin, Colorado, in Exploration frontiers of the Central and 

Southern Rockies: Rocky Mountain Association of Geologists, 1977 Symposium, 

p. 41-60. 

Welsh, J. E., 1951, Geology of the Sheep Mountain-Delaney Butte area, North Park, 

Colorado: Laramie, Wyo., University of Wyoming M.A. thesis, 51 p. 

Wied, 0. J., 1960, Geology of the Encampment area, Carbon County, Wyoming: Laramie, 

Wyo., University of Wyoming M.S. thesis, 52 p. 

Wood, H. B., 1974, Fluorspar and cryolite, in U.S. Bureau of Mines Minerals Yearbook, 

1974, volume 1: p. 565-587. 

Woodmansee, W. W., 1974, Uranium, in U.S. Bureau of Mines Minerals Yearbook, 1974, 

volume 1: p. 1327-1349. 

Young, E. J., and Segerstrom, Kenneth, 1973, A disseminated silver-lead-zinc sulfide 

occurrence at Hahns Peak, Routt County, Colorado: U.S. Geological Survey Bulletin 

1367, 33 p. 

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