Distribution of Beryllium 

Tin, and Tungsten in the 

Lake George area, Colorado 
Distribution of Beryllium 

Tin, and Tungsten in the 

Lake George area, Colorado 

By C. C. Hawley and W. R. Griffitts 

GEOLOGICAL SURVEY CIRCULAR 597 

Washington J 968 
United States Department of the Interior 

STEWART l. UDALL, Secretary 

Geological Survey 

William T. Pecora, Director 

Free on application to the U.S. Geological Survey, Washington, D.C. 20242 
CONTENTS 

Page 

)lbstract ----------------------------------------------------------------- 1 

Introduction -------------------------------------------------------------- 1 

Outline of mining history--------------------.-------------------------- 1 

Geologic setting ---------------------------------------------------------- 1 

Ore deposits -------------------------------------------------------------- 3 

Geochemical sampling and analyses ---------------------------------------- 5 

)lnomalous areas ------------------------------------------------------ 11 

Boomer mine area -------------------~---------------------------- 11 

Redskin area ----------------------------------------------------- 13 

~ary Lee mine area ------------------------------------------------- 13 

Geology ---------------------------------------------------------- 13 

Geochemistry ----------------------------------------------------- 15 

Tappan Mountain area ------------------------------------------------ 15 

Geology ---------------------------------------------------------- 15 

Ore deposits ------------------------------------------------------ 16 

Significance and suggestions for prospecting ------------------------ 16 

~arksbury Gulch area ----------------------------------------------- 16 

Geology ---------------------------------------------------------- 16 

Geochemical anomaly ---------------------------------------------- 16 

Badger Flats fault-zone anomaly -------------------------------------- 17 

Significance ------------------------------------------------------ 17 

Other areas ---------------------------------------------------------- 17 

Summary and conclusions ------------------------------------------------- 17 

References --------------------------------------------------------------- 18 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map and generalized geologic map of the Lake George area 

and adjacent region ------------------------------------------- 2 

2-5. Geochemical maps showing distribution of elements in stream sediments and soils: 

2. Beryllium --------------------------------------------- 6 

3. Tin --------------------------------------------------- 7 

4. Copper ------------------------------------------------ 8 

5. Lead -------------------------------------------------- 9 

6. Geologic and geochemical map of the ~ary Lee mine area ---------- 10 

7. Geologic map of the Tappan ~ountain area ---------------------- 12 

8. Geologic and geochemical map of the ~arksbury Gulch area ------- 14 

TABLES 

Page 

TABLE 1. ~ain ore metals in mineral deposits of the Lake George and Tarryall 

Springs areas ------------------------------------------------ 4 

2. Semiquantitative spectrographic analyses of veins, greisen, and 

granite, ~ary Lee mine area ---------------------------------- 15 

3. Semiquantitative spectrographic analyses of mineral deposits, Tappan 

~ountain area ------------------------------------------------ 16 

III 
DISTRIBUTION OF BERYLLIUM, TIN, AND TUNGSTEN IN THE 

LAKE GEORGE AREA, COLORADO 

By C. C. HAWLEY and W. R. GRIFFITTS 

Abstract 

Complex ore deposits are spatially associated with 

granitic bodies of Precambrian age in the Lake George 

area, Colorado. They include greisens that contain high 

concentrations of beryllium and subordinate amounts 

of tin, tungsten, and other metals associated with the 

Redskin Granite. Scheelite deposits in calc-silicate 

rocks and greisen deposits near Tappan Mountain that 

contain tin a<nd tungsten minerals are associated with 

the Silver Plume (?) Granite. 

Samples of stream sediments and soils locally show 

anomalous concentrations of beryllium, tin, copper, 

lead, and molybdenum. Some of the areas of anomalous 

concentrations correlate with known deposits; others 

do not, and this fact suggests that further prospecting 

is warranted. 

INTRODUCTION 

The Lake George area and adjacent Tarryall 

Springs area, near Lake George in south-central 

Colorad? (fig. 1), are characterized by many 

small deposits of beryllium, tungsten, and 

fluorite. One of these deposits,· that of the 

Boomer mine, has been a major domestic source 

of beryllium; others have produced small 

amounts of beryllium, tungsten, fluorite, and 

base and precious metals. Previous reports 

have described the beryllium deposits (Sharp 

and Hawley, 1960; Hawley, Sharp, and Griffitts, 

1960; Hawley, 1963, 1968) and the scheelitebearing deposits (Tweto, 1960). 

This report describes geochemical anomalies 

of beryllium, tin, and tungsten found in stream 

sediments, soils, and bedrock and emphasizes 

the spatial association of ore deposits with plutons of the Silver Plume ( ?) Granite and the 

Redskin Granite. 

OUTLINE OF MINING HISTORY 

Deposits containing gold or silver were found 

in the Lake George area as early as 1890 and 

1 

include many of the deposits now known to 

contain beryllium, tungsten, or tin. Although 

some precious metals were produced before 

1900, the area was largely dormant until 

World War I, when some deposits such as the 

Redskin, Boomer, and Apex were reexamined 

for molybdenum. In 1943, scheelite ores were 

discovered (Tweto, 1960) ; small-scale mining 

and prospecting for scheelite continued for a 

few years and were succeeded by reexamination of some prospects for uranium. In 1955, 

beryllium ores were recognized in the Boomer 

mine, and the first important production began. 

The interest caused by the Boomer discovery 

led to discoveries of beryllium-tungsten ores in 

the Mary Lee area and beryllium ores in the 

China Wall cupola, recognition of cassiterite in 

at least three places, and discovery of bertrandite at the Redskin molybdenum prospect. The 

Boomer mine operated almost continuously 

from 1955 until July 1965 and produced an 

estimated 3,000 tons of beryllium ore, including 

678 tons which averaged 8.77 percent BeO 

(Hawley, 1968). Other deposits, including the 

Mary Lee, Redskin, and those of the China 

Wall area, have produced a few tons of beryllium ore. 

The late date of recognition of some of the 

complex ores of the district is significant and 

suggests that future prospecting and exploration may result in the discovery of other minable deposits. 

GEOLOGIC SETTING 

The Lake George are~. and adjacent region 

is underlain mainly by metamorphic and igneous rocks of Precambrian age (fig. 1). The 

metamorphic and older igneous rocks form a 
105 ° 30' 

39°07'30" 

THORPE 

GULCH 

STOCK 

s 

s 

p 

0 

BATHOLITH 

REDSKIN STOCK 

TAPPAN 

MOUNTAIN 

STOCK 

2 MILES 

105 ° 22'30" 

p 

FIGURE !.-Generalized geologic map of the Lake George beryllium area and adjar>ent region, with index map. 

2 
EXPLANATION 

D 

Redskin Granite 

Pikes Peak Granite 

Gabbro and quartz monzonite 

Silver Plume(?) Granite 

D 

Metamorphic and older igneous rocks 

Mainly Idaho Springs Formation andBoulder 

Creek(?) Granodiorite, undivided 

39°07'30" 

Contact 

Dashed betweenjacies of Redskin Granite 

Fault 

Antlclme + -+- Syncline 

Fold axis 

I . 1 Chma Wall 

I cupola 

I 

I 

I 

I 

I 

I 

Boomer 

cupola 0 

I Area of figures 2,3, 4, and 5 

I I L _____________ j 

COLORADO 

Area of_. 

report 

z 

< 

0:: 

m 

~ 

< 

u 

w 

0:: 

0.. 

COLORADO 

0 5 M 1 LES SPRINGS 

FIGURE 1.-Continued. 

3 

strongly deformed metamorphic complex which 

includes biotite gneiss and schist of the Idaho 

Springs Formation and amphibolite. Also present are orthogneisses, emplaced about 1.7 billion years ago (Hutchinson and Hedge, 1967) 

and tentatively correlated with the Boulder 

Creek Granodiorite of the Front Range. These 

rocks were intruded about 1.45 billion years ago 

by the Silver Plume and correlative granites 

and subsequently by the Pikes Peak and Redskin Granites slightly more than 1.0 billion 

years ago (Hawley and others, 1966). 

The Silver Plume ( ?) Granite of the area is 

a fine- to medium-grained tan to light-gray 

biotite-muscovite quartz monzonite which 

forms crudely oval stocks. The older gneissic 

rocks adjacent to the Silver Plume ( ?) bodies 

are strongly deformed and are invaded by conformable tongues of the granite (fig. 1). Pegmatitic phases of the granite are common, and 

tactitelike calc-silicate rocks form inclusions 

in the granite or are adjacent to it. Two facies 

of the granite occur in the area and were 

mapped separately in the Tappan Mountain 

area. (fi:g. 7). One is a . fine-grained gneis.sic 

abundantly pegmatitic biotite-muscovite granite, the other, an almost massive medium.-

grained granite .containing tabular potassium 

feldspar crystals. 

The Redskin Granite, the youngest Precambrian rock of the area, formed in the igneous 

episode dominated by the Pikes Peak Granite. 

The Redskin forms the sharply discordant Redskin stock, the Boomer cupola, and small bodies 

not shown on the generalized map (fig. 1). It 

is a pink fine- to medium-grained nearly massive biotite or biotite-muscovite granite whose 

texture ranges from equigranular through 

seriate porphyritic to aplitic. The Redskin 

Granite and, to some extent, the nearby Pikes 

Peak Granite are enriched in trace elements 

and can be termed "tin-granites" (Hawley and 

others, 1966, p. C144). The beryllium deposits 

of the area, ex·cept for a few small pe.gmatite 

deposits, are associated with the Redskin 

Granite. 

ORE DEPOSITS 

Beryllium-bearing greisens associated with 

the Redskin Granite are the most important 

exploited deposits in the area. These deposits 

occur in veins, pipes, and complex bodies con-
centrated especially near the Boomer cupola 

but also near the Redskin mine, the Mary Lee 

mine, and east of the village of Tarryall. In the 

Redskin stock, greisens with low but anomalous 

amounts of beryllium are concentrated opposite 

the mouth of Redskin Gulch and approximately 

1 mile southeast of Redskin Gulch. 

Besides the beryllium-bearing minerals, 

which include beryl, bertrandite, and rare 

euclase (Sharp, 1961), the deposits contain 

trace to locally abundant amounts of argentiferous galena, sphalerite, chalcopyrite, arsenopyrite, molybdenite, wolframite, and cassiterite. 

Pitchblende is present in small amounts in at 

least two deposits. The greisen walls of the 

deposits consist mainly of quartz, muscovite, 

and topaz in widely ranging proportions. 

Where greisen has developed in granitic or 

pegmatitic rocks older than the Redskin or 

Pikes Peak Granites, it is bordered by a conspicuous hematitic halo. 

The ore dep.osits contain a typical traceelement suite for greisen-type deposits: In addition to the metals listed in table 1, the ore 

deposits generally contain anomalous amounts 

of niobium, lithium, and rubidium and locally 

detectable amounts of bismuth and germanium. 

Greisen associated with the beryllium deposits 

TABLE 1.-M a in ore m etals in mineral deposits of the Lake George and Tarry all . Springs areas 

[Analysts: J . C. Hamilton, R . G. Havens, and P. R. Barnett. Analyses, unless noted, are semiquantitative spectrographic and reported in parts per million and in series 0.1, 0.1 5, 0.2, 0.3, 0.5 , 0.7, 1.0, 1.5 ... or by the following symbols: N, not detected; L, detected but below limit of determination ; >. greater than ; <. less than J 

Lab Field N o. No . Ag Be 1 Cu Mo Pb Sm w Zn Description 

Greisen: Boomer mine 

H- 3610 IV- lOa-g N 10 15 N 200 100 N N Quartz-muscovite greisen. H-3611 IV-lOa- y 1.5 50,000 10 N 100 30 N N Quartz-bertranditemuscovite greisen. 293626 C2-d 150 21,000 300 50 >IOO,OOO 50 N 3,000 Galena-bearing greisen. 289731 BO- l 15 22 150 N 3,000 300 >IOO,OOO 300 Topaz-quartz-wolframite 

greisen. 289733 Bl-13 30 20 ,000 700 70 30,000 70 N 3,000 Beryl-quartz-muscovite 

greisen, footwall of sample Bl-14. 

289734 Bl- 14 3 31,000 700 N 700 70 300 300 Beryl vein. 281311 Bl-19 N 44,300 70 N 70 15 N N Do. 281314 Bl-22 N 70 30 N 150 70 N 150 Quartz-muscovite greisen, footwall of sample Bl19. 278782 B2- 4 150 1,500 15,000 150 30,000 70 L 7,000 Sparse sulfides, Boomer vein. H-3243 B2-7- 2 .7 15 300 30 1,500 150 N 1,500 Muscovite-fluorite zone, Boomer vein. 

Greisen: J+S (1), Blue Jay (2), Redskin (3 -7), Minerva J ( 8), Black Prince (9), unnamed locality (10) 

Nu m bers in parentheses r ef er to lo calities in figur e 2 

(1) 289719 J+S- 1- 1 N 17,000 30 N 1,500 150 N 700 Beryllium-bearing greisen. 

(2) 288326 559- BJ-2 L 30 300 30 150 15 150 N Vein material. (3) 288294 560- RS- A 1.5 7,000 15 N 150 70 N 70 Greisen, lower pipe. (4 ) 288295 560- RS-B 7 15,000 150 1,500 300 300 N 70 Greisen, main pipe. 

(5) 288301 RS-M3 150 700 700 7 70,000 70 N 150 Do. 

(6) 288307 RS-M912 150 15 700 70 3,000 150 150 '?0 Do. (7) 288309 RS- M916 7 70,000 150 15,000 300 150 N 70 Bertrandite-molybdenite 

greisen. 

(8) 288315 S60- J-M3 L 300 15 30 70 70 N 70 Greisen. (9) 288323 859- BPr- 150 30 15,000 N 15,000 150 1,500 300 Chalcopyrite-bearing 143b greisen. 

(10)304816 BA- 1006 N 15 N 100 1,000 N 300 Greisenized granite. 

Calc-silicate deposits and fluorite veins 

278778 TR- 53 N 70 7 30 30 15 3,000 N D116498 T3-SJ N 10 1 10 N N N N Diopside-rich gneiss. D12!l286 T2-17 N 1.5 50 N N 30 2<5 N Garnet-epidote-vesuvianite 

rock. D128287 T4- 220 N 3 7 7 10 15 2 45 700 Garnet-calcite rocks. 2888275 S60- 27 L 150 7 N 70 700 L 150 Calc-silicate rock. 

Tweto (1960~ table 3, 20 500 30 20 20 <IOO <200 Composite sample, calc- analysis 3) silicate rock. Tweto (1960, table 3, < I 50 10 200 10 <IO <IOO <200 Do. 

analysis 4) 

293635 BA- 583 3 3 20 N N 150 N N Fluorite vein. 

288269 S60-35 3 1.5 700 N N 30 N L Fluorite vein, Jacob Kolle vein. 

288268 S60 - 17 1.5 1.5 150 1,500 30,000 N N L Fluorite vein, Silver Dollar vein. 

Limits of determination ------------ .5 5 5~10 10 10 100 200 

1 Semiquantitative spectrographic or morin-fluorescent. 2 Dithiol spectrophotometric method by J. A. Thomas and J. E. Troxel. 

4 
generally contains from about 30 to 300 parts 

per million (ppm) tin, or about two to 20 times 

more than the Redskin Granite, which itself 

contains about five times as much tin as most 

granite (Hawley and others, 1966, p. C145). 

The tin content of the greisen is rarely as much 

as 1,000 ppm. 

Greisen of a slightly different type occurs at 

the northeast end of the Tappan Mountain 

stock of Silver Plume ( ?) Granite. The greisen 

is a quartz-muscovite variety, has less beryllium but possibly more tin and tungsten than 

greisen of the Redskin type, and does not have 

associated hematitic alteration. Cassiterite, 

wolframite, scheelite, pyrite, and copperbearing sulfides are present locally. Analyses 

of representative greisens associated with Silver Plume ( ?) Granite are given in the discussion of the Tappan Mountain area (table 3). 

The scheelite deposits are in calcium-rich 

metamorphic rocks, mainly in the southern and 

southwestern part of the area (fig. 1). With a 

few exceptions, the deposits are in discontinuous belts (Tweto, 1960, p. 1413) near or in roof 

pendants of metamorphic rocks in the Silver 

Plume(?) Granite. Individual deposits are 

lenses or pods, generally in clusters. The deposits are complex mineral<)gically, but most 

contain diopside, garnet, cliiwzoisite, vesuvianite, epidote·, quartz, and calcite·. Besides scheelite, the principal metal-bearing minerals are 

bornite, chalcopyrite, molybdenite, manganiferous silicates, and sphalerite. The trace-element 

suite in the scheelite deposits is somewhat 

similar to that of the greisen deposits, but 

concentrations of tungsten and molybdenum 

generally exceed those of beryllium and tin; 

bismuth (not shown in table 1) is generally 

present. 

Vein deposits of flu-orite, barite, and precious 

and base metals also .occur in the area. The 

fluorite deposits are small but are fairly numerous in the Redskin Granite in a northwestwardtrending belt passing through Redskin Gulch. 

They locally contain galena and copper minerals 

but generally have only very minute contents 

of beryllium (t~ble 1). The vein deposits are 

younger than the beryllium-bearing greisens 

but probably formed during the same period of 

magmatic activity. They are spatially associated with the Redskin-Pikes Peak igneous 

5 

series. Furthermore, the abundance of fluorite 

in both the granitic host and the veins and the 

similar rare earth contents (not given in table 

1) of the fluorite ores and certain facies of the 

granite suggest a genetic relation between 

them. 

GEOCHEMICAL SAMPLING AND ANALYSES 

Stream-sediment samples, some soil samples, 

and abundant rock materials were collected by 

the authors and by W. N. Sharp. The streamsediment samples consisted of sand, silt, and 

clay-sized materials, most of them collected 

from the courses of intermittent streams. Soil 

samples, collected on traverses at 50-foot intervals across or near the Badger Flats fault zone, 

were predominantly of silt-sized material with 

intermixed residual rock fragments. They were 

collected at an average depth of about 6 inches. 

The rock materials were as fresh as it was 

possible to obtain and came from outcrops, 

mine workings, and mine or prospect dumps. 

Beryllium determinations were made by the 

morin-ftuorescence method or by spectrograph. 

Comparisons made between the two methods on 

samples of granite used for background determination (Hawley and others, 1966, table 5) 

show very close agreement ; comparisons made 

on sieved stream-sediment samples suggest an 

average positive bias towards the spectrographic method, although in most cases the 

morin-fluorescence analysis is within one subgroup of the spectrographic determination, that 

is, within one numerical value in the series 1, 

1.5, 2, 3, 5, 7. The disagreement does not affect 

the values enough to discredit any anomalous 

area, especially since most anomalies are also 

defined by copper, lead, or tin. 

Most of the stream-sediment and soil samples 

were sieved to -100 mesh or -200 mesh and 

the fine portions analyzed. Comparisons were 

made between analyses of unscreened pulverized samples and tile sieved splits. Except for 

beryllium in s~mples from just below the 

Boomer mine, discussed later, the finer portions 

contain greater amounts of metals, as shown by 

data on 20 samples frorp the Redskin Gulch area: 

Content, in parts per million 

Element Sieved Pulverized 

split sample 

Be_________________________________ 16 11 

Cu_________________________________ 11 6 Nb________________ _______ __________ 66 39 

Pb______________________ ______ _____ 44 33 Sn __________ __ 27 16 
R. 7 3 W . 

105 ° 30' 27'30" 

39°07'30"r-~~-------------,----~--~r.~~--~~~~---.-r~~~~--~~~--------------------~~-m~~ 

R. 72 W . 

T . 11 S 

5' 

\ 

\ 

\ 

· . \ 

~~ \ 

) 

Q Q 

0 Q 

0 

Q 

0 Q 

0 

• Scheelite 

Base from U.S. Geological Survey 

1:24,000 Tarryall, 1956 

Redskin Granite 

~ 

~ 

Pikes Peak Granite 

Silver Plume(?) Granite 

D 

Other rocks, undivided 

Contact 

Fault or barren vein 

Dashed where inferred 

z 

<( 

a:: 

CD 

~ 

<( 

u 

w 

a:: 

Cl. 

:eQ 

0 

0 0 

0 

0 0 

Q 

• • 

EXPLANATION 

:·:;·.=.:. 9 

Greisenized rocks 

Number shoum in table 1 

Quartz vein with greisenized walls 

Vein locally contains beryl, wolframite, 

and cassiterite. Dashed where inferred 

------- Fluorite or barite vein 

Dashed where inferred 

Vein containing ---uranium minerals 

Scheelite 

Scheelite 

Approximate location of scheelite occurrence 

or scheelite prospect area 

0 

~2 

~ 

3-5 • 7-10 

(i)20 

~ 15 

Stream-sediment sample locality 

Showing beryllium concentration, 

in parts per million 

2· 

~ 

Soil-sample traverse 

Showing average beryllium concentration; 

in parts per million 

13~· 

rw--! ~ ~ 0 . " z (J 

UJ ;::: 

::0 "' 

0: " ... ~ 

~ 

APPROXIMATE MEAN 

DECLINATION , 1968 

FIGURE 2.--Geochemical map showing distribution of beryllium in stream sediments and soils. 

6 
T. 11 S 

5' 

0 

0 

0 

0 

0 00 

0 0 0 0 Scheelite 

Base from U.S. Geological Survey 

1:24,000 Tarryall, 1956 

Redskin Granite 

Pikes Peak Granite 

Silver Plume(?) Granite 

D 

Other rocks, undivided 

Contact 

Fault or barren vein 

Dashed where inferred 

z 

<X: 

0:: 

rn 

~ 

<X: 

u 

w 

0:: 

(}_ 

0 

0 

27'30" R 72 W 

~oo 

0 

0 0 

0 0 

0 0 0 

0 d o-· 0 

0 0 

!!__adge~ o ---""o-----

EXPLANATION 

Greisenized rocks 

Quartz vein with greisenized walls 

Vein locally contains beryl, wolframite, 

and cassiterite. Dashed where inferred 

---- Fluorite or barite vein 

Dashed where in/erred 

Vein containing ---uranium minerals 

Scheelite 

Scheelite 

Approximate location of scheelite occurrence 

or scheelite prospect area 

25' 

o Q • al50 

:5 10 15-20 30-50 ?.70 

R 71 W 

105°22'30" 

Stream-sediment sample iocality 

Showing tin concentration, 

in parts 'JH!T million 

< 10 

1==::1 

Soil-sample traverse 

Showing average tin concentration, 

in parts per million 

13ls" 

:!J >- ;; 

< 

APPROXI MATE MEAN 

DECLI NATION, 1968 

FIGURE 3.-Geochemical map showing distribution of tin in stream sediments and soils. 

7 
R. 73 W . 

105 ° 30' 27'30" R. 72 W. 25' 

R 71 W 

105°22'30 " 

39 ° 07' 30" r-----..;;-r---~---.--, -_-__ -r--..-:-T"?I":l'77""--;"~...-;-:--:-nr--;;:----:--/-:--~;:r-:------,--~---;\-/:---:-?">""':TII~ 

~ee'-'"-.e .t>OTarryall 

r. 11 s. 

5' 

so· . \ 

'___/' 

~----- --.- ' 

0 

e 

0 

0 

0 00 

0 0 0 0 

Base from U.S. Geologica I Survey 

1:24 ,000 Tarryall, 1956 

I(: ~I Redskin Granite 

Pikes Peak Granite 

Silver Plume(?) Granite 

D 

Other rocks, undivided 

Contact 

Fault or barren vein . 

Dashed where inferred 

z 

<( 

0:: 

aJ 

~ 

<( 

u 

w 

0:: 

0.. 

e 

0 

e 

~oO 00 

0 

0 0 

e 0 0 

e e• 

0 

.. -el e e 

... -

0 

0 

!!._adger ·--......__....-

EXPLANATION 

Greisenized rocks 

Quartz vein with greisenized walls 

Vein locally contains beryl, wolframite, 

and cassiterite. Dashed where inferred 

Fluorite or barite vein 

Dashed where inferred 

---- Vein containing uranium minerals 

Scheelite 

Scheelite 

Approximate location of scheelite occurrence 

or scheelite prospect area 

0 

< 50 

e 

50-70 • 

100 

Stream-sediment sample locality, 

Showing copper cOttCe?ttration, 

in parts per million 

~140 

Soil-sample traverse 

Slwwin{J average copper concentration, 

in parts per million 

13~· 

I ,_ 

.... :s 

W

:z: 

g; 

z 

w 

:::> 

~ 

~ 

APPROXIMATE MEAN 

DECLINATION. 1968 

FIGURE 4.-Geochemical map showing distribution of copper in stream sediments and soils. 

8 
R. 73 W. 

105 ° 30' 

39°07'30" 

T . 11 S. 

5' 

\ 

\ 

\ 

·. \ 

~~ \ 

) 

Q 0 

0 0 

0 

0 

0 0 0 

Q 0 0 0 

Sche lite 

Base from U.S. Geological Survey 

1:24,000 Tarryall , 1956 

Redskin Granite 

Pikes Peak Granite 

Silver Plume(?) Granite 

D 

Other rocks, undivided 

Contact 

Fault or barren vein 

Dashed where inferred 

z 

~ 

0:: 

Ill 

~ 

~ 

u 

w 

0:: 

11. 

27'30" R. 72 W 25' 

' 

~ 

\\ 

, 

Q 

"-/I \ / 

I --..... I 

--.·~ 

0 0 

Q 

Q 0 

0 0 0 

0 _.r) e Q 

o- · 

Q 

0 

!!_adger e ·- -~ 

EXPLANATION 

Greisenized rocks 

Quartz vein with greisenized walls 

Vein locally contains beryl, wolframite, 

and cassiterite. Dashed where inferred 

Fluorite or barite vein 

Dashed where inferred 

---- Vein containing uranium minerals 

Scheelite 

Scheelite 

Approximate location of scheelite occurrence 

or scheelite prospect area 

'\.\I \ I I I 

R 71 W 

105°22'30" 

0 ~ • il ,200 

20-30 50-70 100 2. 150 

Stream-sediment sample locality 

Showing lead concentration, 

in parts per million 

Soil-sample traverse 

Showing average lead concentration, 

in parts per million 

3~0 

0 ~w·--f ., 

z () w ;::: 

:::> "' "' ., .... "' ; 

APPROXI MATE MEAN 

DECLINATI ON, 1968 

FIGURE 5.-Geochemical map showing distribution of lead in stream sediments and soils. 

9 
I I 

+ --------------------~~~--~-------------------+-

APPR OXI MATE A~ 

DECLINATION, 1968 

rg 

rg 

"' \ 

I 

I 

r'(t-/ '-"~'!; 

1 

J 

/ 

/-

/-

1 

/ o---Tv 

' ' " ...... 

50 

~ 

ics'j 

,~ 

. .. . '----- .. . --·(f) ~ien _J.u.lch 

~/: ;··· __.-··· I -spring 

1~~ ~ ~ 

HAPPY THOUGHT Greisen pipe~· / ~ ) 

2 2 MINE TENNESSEE/ MINE A 

T. 11 S. .,:.ta \ 1 2 .~_... .. ...-

' ~~ ;~~- ) rfa 

"".v~-=--='-_,......f ... : 5~\ ' --

X 

tics 

.. . ---···----

.v.vr ~ ..(P (5 \ "~-<' ,~ ,'=~ _.., 

;y 5 .r / 1 ' "'" " / 

\\ . 1 , 4.1.. ' 5 t._e) -\ ,_-......_. ~~~ ~ ICS a,) ~ \ 53 80 "~ . · '*~X 80, 

-- ,t 1 Ma)-·~/· · ~ :· l 72 ~~'\_ \'~ r~" 

~.\ ' ,..~ 8 0 y 'i, / ~'=:,_ -=~~ }"Jf- ~ · ~ 5 0 MARY L~E J1F\ <I II ~ ·· ~===""'~:-.""'~":':" >< 

di• / I 10 

CD 

Mo 

/ 

. 

~ 90 l VEIN Cassiteritebearing JL'l'l ,lfl _:-·:. -x_ ~ 11/ ~ II PARK COUNTY 

;y 7 IIC~ ( X ·. ' 80 ~r / ~ v~in' /f . · • , I{ HIGHWAY 77 

/j ~ """ I X 6f 15 15 I. / ; II sm ..,~ · r \ ;. ~0\. l 6 -~""~ ~ 10 /!• 'l' . ;1-_ ics l X .. - 9 " ,_- ~~ 9 

\ It ~~ 0<\ LITTLE JOHN- ,~~==~"" II'( 

II ,l II 

II 

II 

II 

\I 

II 

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ICS \ X VEIN .-.~ =:=:fit.~ . ~~· 1TT~~~~OHN 1 

r, (f) ~~ .• • -- •• 70 68).. 

\ ~ ,/ 75 ~ fT . . ............... . . . /\ ~s~ .;t 12 ... ____.... .· · 

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--·~\ \ : 1\ 

II 

II 

\1 X 

--~----,--__;;:o;_ ____ "'' ,;' _;"--~-" ~----------------- + - -<'~~;~:MER MINE VIA 

IL___+ 

It 

I; BOOMER MINE VIA 

Jl BADGER FLATS / ¥ BADGER I" LA TS ROAD 

Base from U.S. Geological Survey 

1:24,000 Tarryall: 1956 

EXPLANATION 

I ~Tv I 

Welded tuff 

[±J 

Redskin Granite 

rfa,fine-grained ara1tite aplite; • . rp, medium-grained seriate porph11ritic 

granite; ,., medium-graimd equigra1tular granite 

} ~~

wa:: J-< 

z 

< 

·a:: 

m 

~ 

< u 

w 

a:: 

0.. 

500 0 500 

Silver Plume(?) Granite 

Medium-araimd araniu 

1~4 Calc-silicate rock 

Locall11 with scheeliu 

D 

Granitic gr.eiss and biotite 

&'J1ei88 undivided 

FIGURE 6.-Geologic and geochemical map of the Mary Lee mine area. 

10 

1000 FEET 

z 

< 

a:: 

m 

~ 

< 

u 

w 

a:: 

0.. 
75 

Contact, showing dip 

Dashed where in/erred or uradatiofml 

Inferred fault or barren vein 

90 ( 0 ' ... ...,.._....,.__ 

Vein, showing dip 

Dashed where in/erred 

Greisenized rocks 

1!1 >--< X >-

Shaft Trench Pit Adit or 

incline 

4 A 

Vein Rock 

Sample location, table 2· 

Geochemical symbols 

Slwwinq '1netal concentration, 

in parts per million 

Sn .. < 10 a·_-_-_""D S_3 

10 (:::) 5 

15 -~~~· 7 

20 C•:::i) 10 

Value shown if ~30 Value shown if 2: 15 .1 .Ag 

Example: Be=5, Sn=20, Ag= 1 

FIGURE 6.-Continued. 

11 

ueocnem1ca1 aa"!;a Ior S"!;rea.m anu :sou :sarnples for beryllium, tin, copper, and lead are 

summarized on four maps (figs. 2-5). Additional data on some areas are given on more 

detailed geologic maps (figs. 6-8). These four 

elements are enriched in the greisen deposits 

and to some extent in the calc-silicate deposits. 

Beryllium, copper, and lead were detected in 

most samples; their lower limits of determination were respectively, 1, 5, and 10 ppm. Tin was 

not detected in most samples from streams 

draining the terrane of older rocks but was 

generally detected in streams draining the 

Redskin stock; the lower limit of detection was 

10 ppm. Tungsten was not detected in any 

sample of stream sediment, probably because 

the lower limit of detection was high (100 

ppm). Molybdenum was detected in only a few 

samples which are cited at appropriate places 

in the text or on detailed maps. _ 

On the geochemical maps the analyses are 

grouped in four ranges: 

Element 

Be ----------

Sn ----------

Cu ----------

Pb ----------

Values, in parts per million, for indicated ranges 

2 4 

~2 3-5 7-10 (~ 15, value shown) 

~10 15- 20 30-50 (~ 70, value shown) 

<50 50-70 100 (~150, value shown) 

20-30 50-70 100 (~150, value shown) 

These ranges reflect approximate frequency 

distribution of the analyses but also, to some 

extent, the analytical method or reporting interval and variations in regional background. 

For example, the Redskin stock contains an 

average of about 6 ppm beryllium and 15 ppm 

tin, the schist and older granitic terrane probably about 3 ppm or less beryllium and less 

than 3 ppm tin. Hence a geochemical map based 

on the schist background would suggest that 

all samples from the Redskin Granite terrane 

are quite noticeably anomalous. 

ANOMALOUS AREAS 

Boomer Mine Area 

Anomalous values of copper, lead, and beryllium occur in a small area near the Boomer 

mine, the main beryllium deposit of the area. 

Replicate analyses of stream-sediment samples 

near the mine show beryllium concentrations of 

as much as 20 ppm in crushed samples compared with the maximum of 10 ppm in sieved 
,\ 

230 feet \\ :; 

N. 75° W. to 1 j' 

corner sec. I 1 

25-24 // 

19-30 /..~. 

I ·:·· I I 

I I 

I I 

~45 

_L Sample locality 

~-- . 6 50 .'<?.' 

.·.0 

.: ... <:· ., . . . ::() 

·.': ~:.:·.·: ._ ... ·.·. ' .. 

~ 

I~": g 0 :z z () w ;:: 

"' "' :z "' .... ;; 

~ 

I / 

I I 

\ \ 

APPROXIMATE MEAN 

OECLINATION, 1968 

0 

\ \ 

\ \ 

\ \ 

50 100 

·f1· 

. BJ' 

~33 

200 FEET 

Enlarged area in northwest corner 

of section 30 

23 

Base from U.S. Geological Survey 1:24,000 

Tarryall, 1956, and Hackett Mountain, 1956 

/ 

FIGURE 7.-Geologic map of the Tappan Mountain area. 

12 

105°22'30" 

10 ~ 

~4/ 

~ 

8P 

68 
EXPLANA·, ION 

EJ 

Welded tuff 

0 

Redskin Granite 

Granite-aplite 

8 

Granite pegmatite 

~ 

Silver 

~ Plume(?) Granite 

sm, medium-grained granite 

sf, fine-grained gneissic granite 

Idaho Springs Formation 

ics, calc-silicate rock, locally with scheelite 

i, migmatitic lYWtite-muscovite gneiss 

Contact 

Dashed where inferred 

.£5 

Fault or barren vein, showing dip 

___.l_9 

Strike and dip of foliation 

_ ,o 

Direction and plunge of lineation 

May be combined with foliation symbol 

C'o· 

H 

w 

1-

z 

<( 

0::: 

[J) 

~ 

<( 

u 

w 

0::: 

a.. 

.u.s 

Quartz vein with greise~ized walls, showing dip 

Locally contains wolframite, scheelite, and pyrite 

Greisenized rocks 

4 

Sample locality, table 3 

)( 0 

Prospect pit 

ED >-< 

Trench 

-< 

Adit 

1!1"'] 

Shaft 

FIGURE 7.-Continued. 

13 

samples. The values of lead and copper are as 

high as 200 ppm in the sieved portion but are 

only 30-50 ppm in crushed material. Additional 

data on the mine, including some suggestions 

for prospecting, are included in other reports 

on the beryllium deposits of the area (Hawley, 

1963, 1968). 

Redskin Area 

The area drained by Redskin Gulch and 

lower Spud Gulch is strongly anomalous in 

beryllium, lead, copper, and tin. Anomalous 

metal concentrations are to be expected because the berylliferous Redskin and Minerva 

greisen pipes are in the area. The highest concentration (300 ppm), however, was in a sample 

collected topographically above these pipes, 

which suggests that an undiscovered deposit 

may occur nearby. The rather high concentrations of metals in Redskin Gulch and Spud 

Gulch are very striking when compared to the 

low concentration of beryllium below the Boomer deposit; hence, it is possible that larger or 

richer deposits than those discovered thus far 

could exist in the Redskin Gulch area. Undiscovered beryllium deposits almost certainly are 

in the adjacent Spud Gulch drainage, as indicated by beryllium values of as much as 50 ppm 

in stream-sediment samples. 

Samples taken from two intermittent streams 

southeast of the mouth of Redskin Gulch show 

copper concentrations similar to those in Redskin Gulch (fig. 4) ; therefore, the drainage 

areas of these streams may also be favorable 

for prospecting. 

MARY LEE MINE AREA 

Geology 

The Mary Lee mine area (fig. 6), about 1 mile 

east of the Boomer mine, is underlain partly 

by Redskin Granite and partly by older igneous 

and metamorphic rocks. Local layers and lenses 

of calc-silicate gneiss ar~ distinguished on the 

map because they have been prospected for 

scheelite. 

Three facies were distinguished in the Redskin Granite: a medium-grained equigranular· 

facies, which is predominant; granite-aplite, 

which forms a lobate cap on the granular rocks 

near the center of the section; and a seriate 

porphyritic granite, which forms a local border 

zone in the northeast part. Exposures in the 
39°05' 

105°30' R. 73 W. R. 72 W. 

s 70 

.-)-

13 

acs 1 acs 

Mark~~~(. ___ 1 • .,.___.i) . .. . - // '/ 

', 

' 

70 

........................ ____ .--

14 

~ 45 

gp'O acs 

~ 

0-<acs ___ , 

"'35 

'\gp 

s 

Base from U.S. Geological Survey 

1:24,000, Tarryall, 1956 

Granite pegmatite 

Silver PlumeG) Granite 

Amphibolite, locally altered to 

calc-silicate rock 

ib 

0 

~s~~ acs 

? ~ acs rl!!l.' \. J 

" 

EXPLANATION 

Hornblendit.e 

Idaho Springs Formation 

z 

<( 

cr 

III 

~ 

<( 

u 

w 

cr 

a. 

APPROXIMATE M EAN 

DEC LI NATION, 1968 

Geochemical symbols 

Showing metal concentration, 

in parts per million 

Mo 8e 

< 10 o=:::=D :S2 

10 3-5 

20 7 

Concentration 

shown if ?10 

Tin concentration 

given, if detected 

-7 .f' -7 

h-7 / 

- h-Yr .. . .:;::..:;::.- :::>~· 

/J r __...... ... ~ \ -::::-~ . · · 200 ppm Sn 

..., -r ~.~ in pulverized 

7 -.;::; -,::;./ sample; <10 ppm 

· • in -200 mesh 

1 MILE 

Contact 

Dashed where i71,{erred 

.-<53 

Pyritic vein, showing dip 

~ X >-'-< 

Shaft Prospect pit Trench 

Mostly scheelite prospects 

FIGURE 8.-Geologic and geochemical map of the Marksbury Gulch area. 

14 
Mary Lee mine show that the granite-aplite 

lobe continues to the southeast for at least a 

short di~tance in the subsurface and that the 

lobe is inferred to extend outward even farther, 

possibly below the zone of veins which are 

oriented at about right angles to the trend of 

the lobe. 

Greisen occurs in a pipe at the Happy 

Thought mine, in irregular masses and veins at 

the Tennessee mine, and along the walls of the 

steep northeast-striking Mary Lee and Little 

John veins and other shorter veins. Beryl, the 

main beryllium 1nineral of the area, is present 

locally at the Tennessee, Mary Lee, and Little 

John deposits, where it is associated with 

quartz, topaz, and wolframite. Cassiterite has 

been found in one vein (noted in fig. 6) and 

probably occurs at locality 4 (table 2). Galena 

and sphalerite occur at the Happy Thought 

deposit and probably in small amounts in most 

of the veins. Table 2 is a compilation of the 

available analyses of vein and bedrock samples 

of the area. 

Geochemistry 

Stream sediments from the Mary Lee area 

are locally anomalous in beryllium and tin, and 

some samples have detectable molybdenum. 

The high concentrations of beryllium (as much 

as 15 ppm) and tin (as much as 50 ppm) correlate fairly well with known veins or suspected 

faults such as the inferred north-northwesttrending fault west of the Mary Lee vein. Detectable molybdenum was found only near calcsilicate rocks. 

TAPPAN MOUNTAIN AREA 

Greisen bodies and veins containing discrete 

tin and tungsten minerals or noticeable 

amounts of these metals as detected by chemical analysis are concentrated in a small area 

east and southeast of the top of Tappan Mountain (fig. 7). 

Geology 

The Tappan Mount~in area is underlain by 

the Silver Plume ( ?) Granite and by biotite 

gneiss of the Idaho Springs Formation which 

in turn contains widely scattered lenses of calcTABLE 2.-Sem.iquantitative spectrographic analyses of veins, greisen, and granite, Mary Lee m.ine area 

[Analysts: U. Oda, E. F. Cooley, and J. C. Hamilton. Results reported in parts per million and in series 0.1, 0.15, 0.2, 0.3, 0.7, 1.0, 1.5 ... or by the following symbols: N, not detected; L det,ected but below limit of determination; >. greater than] 

Sample 

locality Lab. Field No. No. No. Ag Be Cu Mo Pb Sn w Zn Description 

1 289735 HT-1 N 70 150 75 300 150 N 700 Greisen. 289736 HT-2 3 30 700 15 3,000 70 300 L Greisen, topaz-bearing. 289737 HT-3 3 15 300 15 700 150 N 700 Greisen. HT-1 HT-1 N 3 150 N 200 30 N 700 Do. HT-2 HT-2 N 7 300 10 500 50 N 500 Do. 

HT-3 HT-3 N 7 2,000 N 5,000 300 N 1,500 Do. HT-4 HT-4 N 15 2,000 N 5,00€1 N N 2,000 Do. HT-5 HT-5 30 2 3,000 50 5,000 N N 300 Do. 2 Tenn-1 Tenn-1 N 5,000 15 N 50 30 N 200 Quartz-beryl vein. 3 288013 BA-385B N 15 300 N 700 1fi0 N N Greisen. 

4 288003 BA-190 N 3 150 N N 1,500 N N Quartz vein, greisenized walls. 5 288153 ML-2 N 15 30 N 70 15 N 300 7.0-ft. chip, shear zone. 288154 ML-3 N 3 15 N 70 30 N 300 Vein. H3238 ML-4-2 1 7 150 N 700 70 N 300 Greisen on wall of ML-4-3. H3239 ML-4-3 3 15 700 70 1,500 7 N 700 Quartz-topaz vein. 

H3240 ML-4-4 1.5 7 700 15 1,500 70 N 300 Greisen on wall of ML-4-3. ML-1 ML-1 10 10 150 150 >10,000 150 10,000 1,000 Quartz-wolframite vein. ML-2 ML-2 1 20 500 100 5,000 N N 700 Greisen. ML-3 ML-3 30 70 10,000 100 >10,000 15 N >10,000 Vein. ML-4 ML-4 N 5 30 N 50 N 150 N Greisen. 

6 287994 BA-62 7 3 150 N 1,500 30 N 300 Vein. 7 288015 BA-470A N 150 150 7 1,500 70 N N Beryl-bearing, veinlets. 288016 BA-470B 3 7 300 30 3,000 70 N L 1.0-ft. chip across zone of BA-470A. 8 288017 BA-473 N 7 30 N 15 70 N N Greisen. 9 288011 BA-351A N 15 7 N N 300 N N Do. 

10 289726 BA-352 N 15,000 30 15 300 70 N N Quartz-beryl fluorite vein. 11 288014 BA-408 N 7 7 N N 150 N L Greisen 12 288336 BA-399 7 7 150 15 700 150 1,500 N Do. 13 288008 BA-336 N 15 15 N 15 300 N N Do. A 278794 BA-ll N 7 15 7 70 N N N Granite-aplite. B 278793 BA-10 1.5 7 70 7 70 30 N N Do. 

Limits of determination ____ ________ __ 5-10 10 10 10 100 200 

15 
silicate rock. The Inain body of Silver Plume ( ?) 

Granite is the northeast part of the Tappan 

Mountain stock. The northwest flank of the 

stock dips northwest at about 20°-50°, or about 

parallel to the foliation of the adjacent biotite 

gneiss. The southeast flank of the stock is 

poorly exposed ; it probably also dips northwest, but at a high angle. The northeast end 

of the stock is blunt and probably plunges to 

the northeast at a moderately high angle beneath the biotite gneiss country rock. Smaller, 

mainly concordant bodies of Silver Plume ( ?) 

occur on both the northwest and southeast 

flanks of the stock. 

Faults, locally mineralized, strike northeast 

and dip steeply northwest or southeast. 

Ore Deposits 

The mineralized bodies of the area are veins 

and irregular greisen masses noticeably clustered at the blunt end of the Tappan Mountain 

stock. Mineralized rock is very abundant as is 

emphasized by a sketch map of part of the area. 

(See inset, fig. 7.) Greisen and probably related quartz masses and veins are also exposed 

in prospect pits or shallow mine workings to 

the northeast. 

The deposits contain discrete concentrations 

of scheelite, wolframite, and pyrite (Lucky Boy 

mine), copper-stained pyrite (loc. 3), and cassiterite at the locality shown in the northeast 

corner of figure 5. Rocks in fault zones are also 

locally greisenized and contain fluorite. Tin, 

ranging in amounts from traces to as much as 

700 ppm, and one high concentration of tungsten (1000 ppm) were found in random grab 

samples of greisenized materials (table 3). 

Significance and Suggestions for Prospecting 

The greisen at Tappan Mountain is spatially 

related to the Silver Plume(?) Granite rather 

than the Redskin Granite. The strong localization of the greisen at the nose of the stock and 

the northeasterly fracture pattern suggest that 

greisenization continues at depth along the 

plunge direction of the stock; the intensity of 

mineralization indicates that further exploration of the area is justified. Placer concentrations of wolframite or cassiterite can be inferred 

to be present in the drainages below the greisen 

occurrences. 

MARKSBURY GULCH AREA 

Geology 

The Marksbury Gulch area, on the southeast 

flank of the Thorpe Gulch stock of Silver 

Plume(?) Granite (fig. 8), is underlain by the 

granite, by biotite gneisses of the Idaho Springs 

Formation, and by numerous bodies of amphibolitic rocks that have locally been converted 

to tungsten-bearing calc-silicate rocks. The 

amphibolitic rocks occur in lens-shaped masses 

in the biotite gneiss and in roof pendants engulfed in the granite. 

Geochemical Anomaly 

One sample of stream sediment in Marksbury 

Gulch contains 150 ppm tin and 20 ppm molybdenum. Molybdenum (10 ppm) was detected in 

several othe,r samples from the area and probably is associated with mineralized calc-silicate 

bodies. The occurrence of tin-rich stream sediment near the contact of the ,granite body suggests that mineralized rock may occur near 

that contact. Tin (200 ppm) was also found in 

the pulverized split of a sample from O'Brien 

TABLE 3.-Semiquantitative spectrographic analyses of mineral deposits, Tappan Mountain area 

[Analysts: A. L. Sutton and J. C. Halllilton. Analyses reported in parts per million aJH], i_n i?~ri!?S Q.J, 0.15, 0.2, 0.3, 0.5, 0.7, 1.0, 1.5 ... or by the following symbols: N, not detected; L, detected but below limit of determination] · 

Sample 

locality Lab Field No. No. No. Ag ne Cn Mo Pb Sn w Zn Description 

278768 TR-35 N 7 70 30 15 700 N N All samples except '1'1-235 are greisen. 2 D114212 '1'1-207 10 30 500 7 300 150 N N 3 D114211 '1'1-206 10 3 3,000 20 1,000 10 1,000 700 Copper-stained greisen. 4 Dl14214 '1'1-235 N 3 200 N N N N N Calc-silicate rock. 5 D114209 '1'1-173 N 5 100 N N 100 N N 

6 Dl14226 Tl-239 N 7 50 N 100 150 N N 

8 288285 860-62 N 7 100 N L 300 N N 9 D114213 Tl-230 N 2 100 N 1.") 300 N N 

--------- I Tl-202 N 10 3 N N 100 N N 

Limits of determination __________ 0.5 1 5 5-10 10 100 200 

16 
Gulch but was not detected in the sieved portion; it is thus suspected that at least one 

cassiterite grain was present in the original 

sample. 

BADGER FLATS FAULT-ZONE ANOMALY 

An anomalous area about 11,4 miles southsoutheast of the Boomer mine is suggested by 

the presence of a maximum of 15 ppm beryllium and a copper concentration averaging 140 

ppm in a series of soil samples, and of detectable tin in one sample. The area is alined along 

the Badger Flats fault, a pregreisen structure 

(Hawley, Sharp, and Griffitts, 1960) which 

strikes north-northwest and can be traced for 

more than 4 miles across the Badger Flats. 

About 11;3 miles south-southeast of the Boomer 

mine, rocks in the fault zone exposed in a 

trench are greisenized and contain fluorite, pyrite, and as much as 300 ppm tin~ 

Significance 

A possibility exists that the Boomer cupola 

of Redskin Granite was localized partly by preexisting fault structures related to the Badger 

Flats fauit, which occurs about a quarter of a 

mile to the west. Granitic bodies similar to the 

Boomer cupola but not yet exposed by erosion 

may be present along this fault zone. If present, 

a clue to their location might be provided by 

the geochemical anomalies, which may have 

formed by leakage into the faults from concealed mineral deposits. 

OTHER AREAS 

Anomalous concentrations of metals were 

also found in some isolated samples or in small 

groups of samples. A stream-sediment sample 

containing the highest content of tin found in 

the area (300 ppm) came from a locality in the 

Redskin stock northwest of Redskin Gulch, 

far from known greisen deposits. This sample 

also showed a high concentration of niobium 

(300 ppm) and zirconium (700 ppm). Niobium 

is known to be an associate of tin. The high 

concentrations of tin, niobium, and zirconium 

were probably caused -by placer concentration 

of the heavy minerals. 

Anomalous contents of tin were also found 

locally, in the Thorpe Gulch drainage· and in the 

first main drainage southeast of Redskin Gulch. 

These values, plus the anomalous concentra17 

tions of tin in O'Brien Gulch, seem to suggest 

that tin (cassiterite), like gold, tends to occur 

in nuggets and that whether or not any split 

of a sample contains a particle will depend on 

the number and grain size of the particles. 

This in turn suggests that if a systematic survey for tin is carried out in the area, the heavy 

minerals should be concentrated prior to sample 

splitting. 

Anomalous concentrations of tin and beryllium have also been found in reconnaissance of 

the adjacent McCurdy Mountain quadrangle 

north of the Lake George· area. A stream-sediment sample from a tributary to Hay Creek 

at a point 5,850 feet N. 35° W. from South 

Tarryall Peak contained 20 ppm beryllium, 700 

ppm lanthanum, 200 ppm tin, and 3,000 ppm 

zirconium in a -80 mesh split and 5 ppm beryllium, 200 ppm lanthanum, 30 ppm tin, and 

200 ppm zirconium in a pulverized split. Greisen 

float was noted in two intermittent drainages 

at the north edge of the quadrangle. One stream 

is the southeastward-trending portion of Refrigerator Gulch; the second stream is 1,200 

feet to the west, at the same approximate altitude. The occurrences in the McCurdy Mountain quadrangle are in terrain underlain by the 

Pikes Peak Granite. 

SUMMARY AND CONCLUSIONS 

Complex polymetallic deposits of greisen and 

contact-metasomatic type occur in the Lake 

George area and adjacent regions and are associated with the Redskin, Silver Plume ( ?) and 

perhaps Pikes Peak Granites. 

Known beryllium-bearing deposits at the 

Boomer mine, in the Redskin Gulch area, and 

in the Mary Lee mine area are reflected in 

anbmalous concentrations of one or more of the 

metals beryllium, lead, copper, and tin in 

stream-sediment samples. Especially in the Redskin Gulch area, anol1lalous metal concentrations in drainages above or a way from known 

deposits suggest that other deposits exist. Anomalous concentrations of tin found west of the 

Mary Lee vein may be related to veins in or 

near an inferred northwestward-striking fault 

structure. 

Anomalous concentrations of metals found 

in stream-sediment samples or bedrock samples from the Marksbury Gulch and Tappan 
Mountain areas, respectively, are believed to 

be related to mineralization associated with the 

Silver Plume ( ?) Granite, and contacts of the 

granite in both areas are favorable for prospecting. Mineralization is strongly controlled by the 

lobate northeastern projection of the Tappan 

Mountain stock, and this area deserves more 

surface prospecting and possibly drilling. 

The main economic deposit of the area, at 

the Boomer mine, is of the classic cupola type, 

occurring in the upper part of a small granite 

plug (Hawley, 1968). The plug is barely unroofed, and similar bodies could exist in the 

area; possibly such an area is about 114 miles 

south of the Boomer cupola, where anomalous 

concentrations of metals were noted in some 

stream sediments, soils, and fault-zone materials along the Badger Flats fault. 

Finally, it should be pointed out that the 

recognition of ore association with the Silver 

Plume ( ?) Granite indicates that all three 

major Precambrian granite series of the Colorado Front Range-Boulder Creek at about 1.7 

billion years, Silver Plume at about 1.45 billion years, and Pikes Peak-Redskin at slightly 

more than 1 billion years-are now known to 

have associated metallic mineralization; Antweiler (1966) has already reported isotopic 

evidence of mineralization at 1.7 and 1.0 billion 

years. This in turn suggests that the mineral 

potential of Precambrian rocks of Colorado and 

adjacent regions should be reevaluated. 

18 

REFERENCES 

Antweiler, J. C., 1966, Isotopic evidence of Precambrian episodes of mineralization in Colorado 

[abs.]: Geol. Soc. America Spec. Paper 87, p. 

270-271. 

Hawley, C. C., 1963, Geology of the Pikes Peak Granite 

and associated ore deposits, Lake George beryllium 

area, Park County, Colorado: U.S. Geol. Survey 

open-file rep., 283 p. 

---1968, Geology and beryllium deposits of the 

Lake George (or Badger Flats) beryllium area, 

Park and Jefferson Counties, Colorado: U.S. Geol. 

Survey Prof. Paper 608-A (in press). 

Hawley, C. C., Sharp, W. N., and Griffitts, W. R., 1960, 

Premineralization faulting in the Lake George 

area, Park County, Colorado, _in Geological Survey 

research 1960: U.S. Geol. Survey Prof. Paper 

400-B, p. B71-B73. 

Hawley, C. C., Huffman, Claude, Jr., Hamilton, J. C., 

and Rader, L. F., Jr., 1966, Geologic and geochemical features of the Redskin Granite and 

associated rocks, Lake George beryllium area, 

Colorado, in Geological Survey research 1966: U.S. 

Geol. Survey Prof. Paper 550-C, p. C138-C147. 

Hutchinson, R. M., and Hedge, C. E ., 1967, Depth-zone 

emplacement and geochronology of Precambrian 

plutons, central Colorado Front Range [abs.]: 

Geol. Soc. America, Rocky Mountain Sec., 20th 

Ann. Mtg., Natl. Assoc. Geology Teachers, Southwest Sec., Golden, Colo., Program, p. 40-41. 

Sharp, W. N., 1961, Euclase in greisen pipes and 

associated deposits, Park County, Colorado: Am. 

Mineralogist, v. 46, nos. 11-12, p. 1505-1508. 

Sharp, W. N., and Hawley, C. C., 1960, Bertranditebearing greisen, a new beryllium ore, in the Lake 

George district, Colorado, in Geological Survey research 1960: U.S. Geol. Survey Prof. Paper 400-B, 

p. B73-B74. 

Tweto, Ogden, 1960, Scheelite in the Precambrian 

gneisses of Colorado: Econ. Geology, v. 55, no. 7, 

p. 1406-1428.