GEOLOGICAL SURVEY CIRCULAR 411 

GEOCHEMICAL PROSPECTING WITH 

HEAVY-MINERAL CONCENTRATES 

USED TO LOCATE A TUNGSTEN 

DEPOSIT 

UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

GEOLOGICAL SURVEY CIRCULAR 411 

GEOCHEMICAL PROSPECTING WITH HEAVY-MINERAL CONCENTRATES 

USED TO LOCATE A TUNGSTEN DEPOSIT 

By P. K. Theobald, Jr., and C. E. Thompson 

REPRINTED 1960 

Washington, D. C., 1960 

Free on application to the Geological Survey, Washington 25, D. C. 

GEOCHEMICAL PROSPECTING WITH HEAVY-MINERAL CONCENTRATES 

USED TO LOCATE A TUNGSTEN DEPOSIT 

By P. K. Theobald, Jr., and C. E. Thompson 

CONTENTS 

Page 

Abstract. • • . . . . 1 

Introduction • • • • • • 2 

Proposed technique . • • 2 

Application of proposed technique in the Front 

Range . . • . • . • • . • . • • . • . • • . . 3 

Analytical procedure for tungsten. . 3 

Concentrates from the eastern limit 

of Precambrian crystalline rocks • • 4 

Distribution of tungsten along Clear 

Creek .•.•.••••••••••••••. 6 

Clear Creek and West Fork Clear 

Creek. • • • • . • • • • . . • . . 6 

Application of proposed technique-Continued 

Distribution of tungsten-Continued 

Headwaters of West Fork Clear 

Page 

Creek. • • • • • • • • • • • • • 6 

Clear Creek drainage basin outside 

anomalous area • • • . • • • 6 

Tungsten deposit on Red Mountain • • • . • 9 

Geochemical exploration for 

tungsten .•••.•••••••••. 9 

Metals associated with tungsten . • • 11 

Discussion of method • • 11 

Literature cited • • . • • • . . . . . . • • • • • 13 

ILLUSTRATIONS 

Page 

Figure 1. Tungsten content of concentrates from streams along the east edge of the Front Range, Colo. • • • 5 

2. Tungsten content of concentrates along Clear Creek, Colo • • • . • • • • • . • • . • . • • • • • 7 

3. Tungsten content of concentrates from the headwaters of West Fork Clear Creek, Clear Creek 

County, Colo • . . . • • • • . • • • • • • • • • • . • . • . • . . • • • • • • • • • • • • • • • • 8 

4. Frequency distribution of tungsten content of heavy-mineral concentrates from 73 localities 

from the Clear Creek drainage system, Colo • • • • . • . • • . • • • • • . . • • • • • • • • • 9 

5. Plan and profile of a traverse up the southeast slope of Red Mountain, Clear Creek County, 

Colo., showing analytical data for tungsten and associated elements •••••.••••••.•.• 10 

TABLES 

Table 1. Data on selected elements from spectrographic analyses of heavy-mineral concentrates from 

streams along the east edge of the central part of the Front Range, Colo • • • . • • • • . • • 4 

2. Distribution of tungsten among size fractions and specific-gravity fractions of samples from 

a traverse on Red Mountain • • ·• • . • • • • . • • . • • • • • • • • • • • . . • • • • • • • • . 11 

3. Spectrographic analyses of less than 30-mesh material from a traverse on the southeast slope 

of Red Mountain, Clear Creek County, Colo • • • • • • • . • • •. • • • • • . • • • • • • • • • 12 

4. Replicate tungsten analyses of concentrates obtained by 4 in(,iependent groups at"4 localities 

along the eastern limit of the Front Range 1 Colo ••••••.••••.•..••.•••••••. 13 

ABSTRACT 

Rapid field chemical analysis of heavy-mineral 

concentrates panned from stream gravels provides 

a reconnaissance prospecting technique for many 

of the ore minerals that are resistant to chemical 

and mechanical decay. This technique involves three 

steps: areal reconnaissance by sampling the 

mouths of major streams to locate drainage basins 

with anomalous metal content; tracing an anomaly 

through a drainage basin by sampling the main stream 

arid tributaries, proceeding upstream until the anomaly is terminated; and tracing the metal away from 

the stream to the bedrock source by conventional 

1 

geologic or geochemical prospecting techniques. On 

the eastern slope of the central part of the Front Range., 

Colo., apreviously unsuspected tungsten anomaly 

was traced through the Clear C:r,eek drainage basin 

to West Fork Clear Creek and Woods Creek and was 

isolated in an avalanche slope on the southeast side 

of Red Mountain. The anomaly was traced by chemical analysis of the fine fraction of debris on the avalanche ·slope to a huebnerite deposit near the crest of 

the peak. Despite sampling and analytical problems 

this technique is valuable for locating mineralized 

ground because of its speed and low cost. 
lliTRODUCTION 

Use of the gold pan-or a similar device-for 

prospecting has been a standard technique for centuries (Hill, 1746). The addition of heavy-mineral 

studies to sedimentary petrography and greater interest in the heavy accessory minerals of igneous 

and metamorphic rocks is leading to greater interest 

in and expansion of the technique (Mertie, 1954). 

Geochemical prospecting methods have long been 

sought that will reveal anomalous amounts of metals 

miles from their bedrock source. Analyses of both 

stream water and stream sediment have been used extensively with some success, but the most successful 

regional reconnaissance technique is still the ancient 

process of gold panning. If carefully applied, this 

technique may be expanded so that the concentrates 

obtained include a wide variety of resistant ore minerals that may be traced through a drainage basin to 

their source in the same manner originally used for 

gold prospecting. 

Sigov's (1939) procedure for general heavy-mineral 

prospecting in Russia was based on the mineralogic 

analysis of concentrates panned in an "Asiatic ladle," 

The mineralogic approach has been extensively developed by the Russians and appears as the "schlich" 

methods in Ginzburg's ( 1957) general text for geochemical prospecting. 

In the United States, mineralogic analysis of 

concentrates has been used extensively in the search 

for placer deposits. Recently, W. C. Overstreet 

(oral communication) has used mineralogic data acquired from heavy-mineral concentrates panned from 

alluvium to outline certain general features of the 

metamorphic rocks in an area of 4, 000 square miles 

in the southeastern Piedmont province. During this 

and subsequent work, he has supplemented the mineralogic analyses with spectrographic and chemical analyses for elements whose ore minerals may be easily 

overlooked. 

Complete mineralogic analysis of concentrates 

is both slow and costly; it is rarely used on a large 

scale except in the U.S.S.R. Other methods currently 

.in use where the ore mineral sought is not conspicuous 

are selective staining of mineral grains and spectrographic analyses of the concentrates. Sigov (1939) 

gives staining methods for scheelite and cassiterite 

but points out that spectrographic analyses are cheaper than using a stain. Visual estimation of the proportion of a mineral in a stained concentrate usually 

leads to overestimation. 

Spectrographic analyses are probably best used 

for initial reconnaissance. The method gives reliable 

estimates of many elements with a single analysis, 

is relatively cheap and fast, and requires only a small 

sample (20-50 milligrams). Its chief disadvantages 

are the lack of portability of the equipment for an 

analysis at each locality, the time consumed for 

completion of single analyses, and the poor sensitivity for several elements (notably zinc and tungsten). 

Rapid field chemical analyses of the concentrates allow anomalously high concentrations of metals 

to be detected and followed when the ore minerals 

2 

are inconspicuous owing to their appearance, small 

grain size, or low level of concentration. This rapid 

technique has led to the discovery of a deposit of huebnerite, the manganese-rich end member of the wolframite series, near the crest of Red Mountain in the 

western part of the Clear Creek drainage basin, Clear 

Creek County, Colo. The tungsten anomaly was first 

found along the eastern limit of the Front Range more 

than 45 miles downstream from the deposit. 

PROPOSED TECHNIQUE 

Rapid field chemical analyses developed for use 

in geochemical prospecting for specific elements in 

soils offer an ideal method to overcome the problems 

encountered in techniques used to date. The most 

rapid of these, the so-called cold tests, are not suitable because the elements are too tightly fixed in 

oxide, sulfide, or silicate minerals; but any of the 

specific tests that will effect solution of the ore minerals are acceptable. 

The proposed prospecting technique is based on 

the premise that any ore deposit at ·the bedrock 

surface, even if covered by soil, colluvium, or alluvium, is providing sediment to the drainage system 

within which it occurs. Many of the ore minerals 

have a high specific gravity and are resistant to chemical and mechanical decay. These will travel into 

the drainage system and will be concentrated with 

other heavy miner?J.s. They will persist for many 

miles downstream from the source, and samples 

taken from heavy-mineral-rich gravels in streambeds and terraces near the mouths of streams should 

include minerals from any ore deposits drained by 

the streams. 

Samples are taken from gravels in preference 

to other stream sediments, because gravels have 

the greatest proportion and variety of heavy minerals. 

Usually a gravel bar or riffle in the stream bed can 

be found in which more than 50 percent of the material is greater than one-quarter of an inch in mean 

diameter. The sample i~ shoveled fro.m such a bar, 

and pebbles and cobbles are removed. The remaining material, which has a median diameter in the 

coarse sand or granule range, is panned. Samples 

of approximately the same size are taken at each 

locality, and the heavy minerals are concentrated 

by panning. Only a crude approximation of the 

proportion of heavy minerals is made, since this 

is a function of the sediment type and the environment of deposition. During the present work a 

single, heaping 12-inch pan of gravel, weighing 

about 10 kilograms, was taken and concentrated at 

each locality. The weight of the concentrate below 

the junction of Clear Creek with West Fork Clear 

Creek, in the unglaciated area, generally ranged 

from 50 to 100 grams and was a function of the 

amount of magnetite and ilmenite. Above this junction, in the glaciated area, concentrates rarely exceeded 10 grams and were often less than 1 gram. 

The smallest concentrates were obtained from the 

gravels in,cataracts flowing down the steep glaciated 

valley walls. 

Magnetite was removed from each sample 

with a hand magnet before analysis. For tungsten, 

this procedure removes any contamination due to 
tungsten steels, and it would be well to retain this step 

when other metals used in ferroalloys are being sought. 

The first series of analyses in an area is intended 

only to outline specific streams for further study. 

Streams 10-50 miles long seem the optimum size for 

the initial reconnaissance; each of these is sampled at 

its mouth, and the concentrates are analyzed. On the 

basis of this preliminary work, a figure may be selected for a given element above which a value is considered 

anomalous and below which a value is considered "background." An anomalous value in the initial analysis is 

checked with a few samples near the original locality. 

If confirmed, the anomaly is followed upstream, samples of gravels being collected from the mouth of each 

major tributary and from the main stream just above 

this tributary until the source area of the metal is 

located. 

Concentrates are packaged and labeled for laboratory study after the field analysis is completed. 

Selected analyses are checked by more precise laboratory methods, and additional chemical or spectrographic analyses are made as desired. The concentrates are then available for mineralogic studies. 

Because most of the grains in the concentrate contain 

only one mineral, several separations using heavy 

liquids (we have used both bromoform, specific 

gravity 2. 9, and methylene iodide, specific gravity 

3. 3) and electromagnetic separators will provide a 

series of smaller concentrates each of relatively 

simple mineralogy. 

APPLICATION OF PROPOSED TECHN1QUE IN THE 

FRONT RANGE 

An area in the east-central part of the Front 

Range, Colo. , was chosen to test the technique in the 

field. The initial samples were taken from five 

streams at the eastern limit of Precambrian crystalline rocks from Bear Creek on the south to Boulder 

Creek on the north (fig. 1). A tungsten anomaly on 

Clear Creek was then traced through the drainage 

basin, and a reconnaissance of the entire drainage 

basin was made. Application of the technique resulted 

in the discovery of a huebnerite deposit in the western 

part of the drainage basin. 

Clear Creek heads at the Continental Divide 

in the west-central part of the Front Range, 

Colo. , and follows a generally eastward course 

to join the South Platte River just north of Denver, east of the Front Range. The major part 

of the drainage basin is underlain by Precambrian crystalline rocks that constitute most of 

the Front Range. About a quarter of the way 

downstream from its head, the stream crosses 

the Front Range mineral belt. The richest part 

of the mineral belt, which is drained by Clear 

Creek and its tributary North Clear Creek includes a group of base- and precious-metal 

districts, generally free of tungsten mineralsthe Alice, North Gilpin, Central City, Empire, 

Lawson-Dumont, Idaho Springs, Silver Plume, 

and Argentine mining districts described by 

Lovering and Goddard (1950, pl. 4). Small 

pockets of scheelite have been prospected at 

several localities, but none of these is economically important. 

The upper reaches of the stream pass over 

glacial drift, and the valleys are broad and generally 

flat floored and steep walled. Within this glaciated 

area, resistant rock shoulders interrupt the valleys, and the streams plunge past these impediments in cataracts commonly confined to narrow, 

deep gorges. The most impressive of the cataracts are just above the junction of Woods Creek 

(fig~ 2) with the West Fork of Clear Creek, on 

both streams, and just above Georgetown and 

South Clear Creek and Clear Creek. Similar rapid, 

confined reaches are on both Clear Creek and the 

West Fork of Clear Creek just above their junction, 

where the streams breach the lowest conspicuous 

moraines. 

Below the junction of the West Fork of Clear 

Creek and Clear Creek, the stream enters a. series 

of canyons that, in general, become deeper and 

more sinous to the east. At Golden the stream 

leaves the crystalline rocks and the canyon anct 

follows an open valley carved in sedimentary 

rocks to its junction with the South Platte River. 

The streams flowing parallel to Clear 

Creek-Bear Creek on the south, and Coal 

Creek, Ralston Creek, South Boulder Creek, 

and Boulder Creek on the north-have similar 

topographic and geologic relations. With the 

exception of Boulder Creek, however, they do 

not penetrate the mineral belt. Boulder Creek 

drains the Boulder County tungsten, Grand 

Island, Magnolia, and Gold Hill districts. 

Analytical Procedure for Tungsten 

The method used to determine tungsten at 

the sample site is a modification of the method developed by. F. N. Ward (1951). As portability and speed are more important than precision when prospecting with heavy minerals, 

much of the equipment was changed or eliminated, although the same reagents. were used. 

A lucite scoop drilled to hold 0. 6 gram of 

flux on one end and 0. 25 gram of soil or 

concentrate on the other was used instead of 

a balance. Culture tubes scored at various 

volumes were used in place of pipettes. 

Neither filtration of the sample nor use of 

a hot-water bath was needed in this simplified procedure. No standard solution or standard series used for estimation of unknowns 

was necessary. A bunsen-type burner using 

light-weight disposable tanks of liquefied petroleum was preferred to the gasoline stove recommended by Ward. 

The procedure follows: Part of the concentrate is taken directly from the gold pan 

and dried, and 0. 25 gram is measured with 

the scoop and transferred to a 16- by 150-millimeter culture tube. The flux is added, and 

the sample and flux are sintered over the 

burner. The sodium tungstate formed during 

the sinter is dissolved with 5 milliliters of 

water, and a aliquot is transferred to another 
culture tube after the residue has settled. This 

aliquot is diluted to 5 milliliters; the stannous 

chloride and potassium thiocyanate solutions are 

are added; and the tube and contents are warmed. The 

tube is cooled; the potassium thiocyanate solution and 

isopropyl ether are added; and the tube is shaken to 

extract the yellowish-green tungsten thiocyanate complex into the ether layer. A little experience is necessary to be able to estimate the tungsten content by the 

intensity of the color without reference to standards; 

but artificial standards may be made, or the culture 

tubes containing the complex may be carried from one 

locality to the next to make a direct comparison of the 

color intensity. 

Molybdenum, where present, produces an ambercolored thiocyanate that masks the tungsten color. 

This interference can usually be eliminated by the 

procedure outlined by Ward (1951, p. 3). Differences 

in sulfur content from sample to sample can be detected 

from the black gummy sinter formed if sulfur is present. 

Concentrates from the Eastern Limit of Precambrian 

Crystalline Rocks 

A segment of the east slope of the Front Range 

in Colorado extending from Bear Creek on the south of 

Boulder Creek on the north was chosen to test the 

technique. The initial reconnaissance samples were 

taken at the eastern limit of the Precambrian crystalline rocks on Bear Creek, Clear Creek, Coal Creek, 

South Boulder Creek, and Boulder Creek. The relation of these streams to the Front Range mineral belt 

was known, and maximum variation in metal content 

was expected. Bear Creek and Coal Creek, which\do 

not intersect the mineral belt, were expected to provide an estimate of background, South Boulder Creek 

drains a relatively weakly mineralized part of the 

mineral belt and was expected to have intermediate 

metal content. Clear Creek drains the central, baseand precious-metal-rich segment of the belt, and 

Boulder Creek drains the tungsten-rich part of the 

mineral belt. These streams were expected to be 

rich in metal, with maximum tungsten content on 

Boulder Creek. A lower tungsten content was expected 

on South Boulder Creek. 

Magnetite-free heavy-mineral concentrates from 

each of these streams were analyzed spectrographically by E. F. Cooley and U. Oda, of the U. S. Geological Survey, and field chemical determinations were 

made for tungsten and lead. The results of the spectrographic analyses for 11 of the 28 elements determined are in table 1, and the tungsten contents are 

shown on figure 1. 

The tungsten content of the sample from Boulder 

Creek is so great that contamination was suspected 

from the mill at Tungsten. Terrace gravel in a roadcut was sampled to check the value obtained in the 

stream, and the drop from 5, 000 parts per million in 

the stream to 200 ppm in the terrace apparently reflects the contamination. Both of these values have 

been repeated in other field samples. Compared with 

the 40, 20, and 60 ppm in concentrates from Bear, 

Coal, and South Boulder Creeks, either of the values 

from Boulder Creek is anomalous, particularly as the 

60 ppm on South Boulder Creek probably reflects 

tungsten minerals from the southern part of the Tungsten district, and small pockets of scheelite are contributing tungsten to the other two streams. 

The 300 ppm on Clear Creek is above the concentration found in the terrace on Boulder Creek and 

an order of magnitude above what is considered to be 

a high background established on the other streams. 

Although small scheelite prospects are scattered 

throughout the Clear Creek drainage basin, these 

should not contribute more to Clear Creek than similar small deposits contribute to the adjoining streams. 

The anomalous value was repeated in additional samples nearby. Clear Creek, therefore, provided an 

unexplained anomaly to be traced to its source. 

The spectrographic analyses (table 1) bore out, 

out, in general, the expectations from panning 

and field chemical analysis. The base and 

precious metals-lead, zinc, silver, copper-are 

highest in the concentrate from Clear Creek. 

The relatively high lead, zinc, and copper 

concentrations on Bear Creek are somewhat 

surprising, but may reflect small sulfidebearing veins in the vicinity of Idledale, 

only 2 miles upstream from the sample locality. The high tin content of the concentrate from Clear Creek does not come from 

any known deposits. One possible explanation 

is that the tin comes from the same source 

as the tungsten, but this remains as an 

anomaly that should be checked further. Molybdenum varies only slightly, considerably less 

than was expected. The molybdenite is probably comminuted during vigorous stream 

transport to very fine cleavage flakes which 

because of their habit and size are not concentrated with the other heavy minerals. Manganese, cobalt, nickel, and cadmium are included as examples of elements that did not 

show appreciable variation. The significance of the chromium variation is not 

known. 

Table 1.--Data on selected elements ~rom spectrographic analyses o~ heavy-mineral concentrates ~rom streams along the 

east edge o~ the central par·t o~ the Front Range, Colo. 

[Analyses in parts per million, by E. F. Cooley and U. Oda, U. S. Geological Survey] -

Creeks Pb Zn Ag Cu Sn Mo Mn Co Ni Cr Cd 

Bear-------------------------- 100 500 <2 150 70 15 >10,000 )0 20 )00 50 

Clear------------------------- 500 10,000 70 700 100 )0 >10,000 50 )0 700 <50 

Coal--------------------~----- 100 < 200 <2 50 50 20 10,000 )0 20 700 70 

South Boulder----------------- 70 < 200 <2 )0 20 20 7,000 )0 )0 1,500 50 

Boulder: 

Stream-------------------- 70 < 200 <2 )0 50 10 7,000 20 )0 500 <50 

Terrace------------------- 50 < 200 <2 50 )0 20 10,000 )0 )0 1,000 70 

4 
CJ1 

EXPLANATION ,; 

' t?o ~ ~. 

(' 040 

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Sample locality with 

tungsten content of concentrate 

(ppm) cu ( • "" 

il 

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.~ ( o" o L.-

( 

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L 

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0 5 10 Miles )t r~ • Berthoud / 1 

Pass ' 

r--, ;'/,...__,,.._,/ .Jones I' 11. -- Passl 

2; i, 

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§) 

CJ ' L"'lond ,, ~ \...- , ... ,..-\ / _/1 0 

Pass ,~ L.~ 

,--c--1' / 

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Figure 1. -Tungsten content of concentrates from streams along the east edge of the Front Range, Colo. 
Distribution of Tungsten along Clear Creek 

The anomalous tungsten value at the eastern 

limit of the Precambrian rocks on Clear Creek was 

checked at the original locality, and also by a pair of 

samples within the next few miles upstream. The 

6 analyses ranged only from 200 to 400 ppm of tungsten, 

confirming the lack of v ~riation of the anomaly. These 

and subsequent tungsten analyses were made by the 

rapid field technique, though some analyses were confj_rmed in the laboratory. 

Clear Creek and West Fork Clear Creek 

The anomaly was traced upstream by samples 

being taken at the mouths of major tributaries and at 

more widely scattered localities along the main 

stream (fig. 2). By the end of the first day in the 

field at this stage of prospecting, the anomaly had 

been traced as far as Empire. On part of a second 

day the anomaly was traced onto Woods Creek where 

the tungsten content of the concentrate increased 

abruptly to 1, 000 ppm. 

The anomaly was initially attributed to scheelite, 

as this mineral was conspicuous when the samples 

were checked with an ultraviolet light. Upstream, however, the amount of scheelite decreased while the anomaly remained unchanged. By splitting the concentrates 

in a strong electromagnetic field, wolframite and 

scheelite were separated, and their relative importance 

was estimated. At the mouth of Clear Creek, 20 percent 

of the anomaly results from huebnerite and 80 percent 

results from scheelite. The initial anomaly is, therefore, principally the result of scheelite whose ma~:o. 

source remains unknown. Since the scheelite content 

of the concentrates gradually decreases upstream, it 

is likely that the scheelite is gradually accumulating 

downstream from a large number of small deposits. 

Conversely, the huebnerite content of the ,concentrates 

gradually increases upstream, accounting for 20 percent of the tungsten at the mouth, 50 percent above 

the Fall River, 80 percent at Empire, and 100 percent 

on Woods Creek. 

Headwaters of West Fork Clear Creek 

The extreme tungsten content, 1, 000 ppm, at the 

mouth of Woods Creek, coupled with the high of 150 ppm 

on the West Fork of Clear Creek above Woods Creek 

prompted more detailed sampling in this area. (See 

figure 3.) The first sample, from the tailings pond 

of the Urad molybdenum mine, eliminated the molybdenum deposit as the major source of tungsten, though 

the tailings do contain some huebnerite. A sample from 

the first tributary, Ruby Creek, also contained anomalous tungsten, but not as much as in the main stream 

above Ruby Creek. The three low samples on the m~ 

stream and tributaries upstream from Ruby Creek gave 

an upstream limit for the anomaly. The known molybdenite deposit on the slopes of Red Mountain, the huebnerite in the Urad mine tailings, and intense alteration 

of the country rocks made the southeast side of Red 

Mountain seem the likely source for the tungsten; so 

the next sample was taken about halfway between Ruby 

Creek and the most head ward sample, below an avalanche slope at the southwest end of Red Mountain. 

This sample, at 80 ppm, was higher than the upstream 

sample, but not comparable with the sample above 

Ruby Creek. The stream distance to Ruby Creek was 

6 

split, and the sample taken from just below another 

prominent avalanche slope, this time near the middle 

of Red Mountain. This sample contained more than 

1,-000 ppm tungsten. To confirm the suspected source 

on Red Mountain, a concentrate was panned from the 

rubble at the base of the avalanche slope. The result 

was similar to but more intense than that in the adjoining stream. The concentrate was taken back to the laboratory, and the analysis confirmed at greater than 

1 percent tungsten. 

The headwaters of West Fork Clear Creek seem 

to drain a generally tungsten-rich area. Tungsten 

mineralization on the slopes of Red Mountain is verified not only by the major anomaly but also by the 

80 ppm on Woods Creek half a mile upstream from the 

anomaly, and by the 200 ppm in the stream draining 

north along the west side of Red Mountain. The several high-tungsten samples-the 100 ppm on Ruby Creek 

(fig. 3), 140 ppm on the small tributary of West Fork 

Clear Creek below the junction with Woods Creek (fig. 3), 

and 200 ppm on a small stream north of West Fork 

Clear Creek directly opposite the 200 ppm at the west 

end of Red Mountain (fig. 3) must be taken to indicate 

extensions of the tungsten-rich area outward from Red 

Mountain proper. An 800 ppm on a small tributary (not 

shown on any illustration) at Empire (fig. 2) may be 

within this area. 

The effect in the stream concentrates of the molybdenite deposit at the Urad mine is confined to the immediate neighborhood of the deposit. As little as 15 ppm 

of molybdenum could be recognized by its interference 

with the tungsten analysis, and this was noted in only 

3 of the samples. One of these, containing 16 ppm, was 

near the head of Fall River (fig. 2). The sample at the 

mouth of Woods Creek has the largest concentration of 

molybdenum-more than 1, 000 ppm. This is due in 

large part to contamination by tailings from the Urad 

mill; the concentrate from the tailings contains conspicuous molybdenite. The other molybdenum-rich 

concentrate, 30 ppm, is from Woods Creek just above 

Ruby Creek. This may also be contamination-from 

an abandoned tramway that extended down the slope 

from the upper workings ()f the Urad in.ine and crossed 

the creek just above the sample locality. Three other 

concentrates from Ruby Creek and the tributaries of 

West Fork Clear Creek north of Red Mountain contain 

less than 4 ppm of molybdenum. 

Clear Creek Drainage Basin Outside Anomalous Area 

Samples were taken from North Clear Creek, Fall 

River, Chicago Creek, South Clear Creek, and the headwaters of Clear Creek to gain information on the distribution of tungsten in the entire drainage basin and to 

provide samples for future studies. In all, 73 samples 

were collected, concentrated, and analyzed for tungsten. 

The frequency distribution of tungsten contents (fig. 4) 

serves to establish background for Clear Creek more 

definitely. The distribution curves are undoubtedly 

biased in favor of the high values, because of selective 

sampling within the anomaly. Indeed, if samples from 

the main stream of Clear Creek and the headwaters of 

West Fork Clear Creek are eliminated, only 3 values 

remain. in the 100- to 200-ppm range. One of these 

three is a concentrate from a small intermittent stream 

south of Idaho Springs that is just south of the sample at 

the mouth of Chicago Creek and forms a fifth branch in 

the middle of the stream with four branches {fig. 2); 
-.:J 

-t~''"l)'t"'"'E.!o 

EXPLANATION 

040 

Sample locality with 

tungsten content of concentrate 

(ppm) 

Figure 2. -Tungsten content of concentrates along Clear Creek, Colo. 

il 

DENVER 

• 

0 5Miles 
,-s ,~ .. 

I 

\ 

r--\ 

} 

I ~I 

I 

,1/ Jones (I' Pass 

EXPLANATION 

080 

Sample locality with 

tungsten content of concentrate 

(ppm) 

__ ,..... __ _ 

Dirt rood 

0 I Mile 

Hassell 

Lake 

Figure 3. -Tungsten content of concentrates from the headwaters of West Fork Clear Creek, Clear Creek County, Colo. 

the other two are from the main stream of Clear Creek 

just below Georgetown, and from the major forked 

tributary to Clear Creek about 4 miles above Silver 

Plume (Quayle Creek). 

Most values above 100 ppm are from samples on 

tributaries of West Fork Clear Creek in and adjoining 

the anomaly. The highest value not in the anomaly, 

800 ppm, is on a small stream that enters West Fork 

Clear Creek from the north in the town of Empire 

(fig. 2). This is the only value in excess of 200 ppm 

that is not part of the principal anomaly. It represents 

an area that deserves further investigation, but which 

will be difficult to prospect because of the extreme 

disturbance of the stream and adjoining slopes by 

placer and lode mining. 

8 

The frequency distribution serves best to 

establish that the analyses we have considered in 

following the principal anomaly represent only the 

high end of a strongly skewed distribution. True 

background is 20 ppm or less, supporting the 

expectation expressed in the preceding section 

that with the exception of Coal Creek samples 

from all the streams display enrichment of tungsten. For a complete study of tungsten distribution 

in this area, sources should be sought for all samples containing 40 ppm or more. Indeed, the 

tungsten anomaly produced by wolframite alone at 

the mouth of Clear Creek is only 60 ppm, and 

this has been shown in this report to be a valid 

anomaly. 
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~ 

• Q. 

• . :: 

c 

-; 

E 

::I 

0 

~ ~ ~ ~ ~ g ~ ~ ~ ~ ~ ~ g v 0 0 0 0 0 0 0 g 

100 

90 

80 

70 

60 

50 

0 

Tungsten content of concentrates (ppm) 

~ ~ ~ ~ 0 ~ ~ ~ ~ ~ ~ 0 0 0 0 0 0 0 0 g 

Tungsten content of concentrates (ppm) 

Figure 4.-Frequency distribution of tungsten content 

of heavy-mineral concentrates from 73 localities 

from the Clear Creek drainage system, Colorado. 

Tungsten Deposit on Red Mountain 

The tungsten deposit has not been found in place; 

however, the anomaly has been traced up the slope of 

Red Mountain to a point where huebnerite is conspicuous 

in the float and the talus itself could be considered marginal ore. 

Geochemical Exploration for Tungsten 

The steep talus-covered southeast slope of Red 

Mmmtain offers a challenge to any form of prospecting. 

Because of the heavy cover by lateral moraine and talus, 

standard geologic methods yield little beyond generalized 

conclusions. Geochemical methods based on residual 

soils are not applicable; not only has everything on the 

slope been transported, but the mer~ act of climbing 

the talus dislodges a startling quantity of debris. Two 

avenues of attack appear promising: deep-rooted plants 

may penetrate the surficial debris and accumulate metals 

9 

from the underlying bedrock, and avalanche and landslide debris on the avalanche slopes could, with caution, be substituted for residual soils. The latter was 

chosen because the stream anomaly had been traced 

into this material. 

The tungsten-rich avalanche slope is a narrow, 

almost treeless 30° chute rarely more than a few 

hundred feet wide and with more than 1, 500 feet of 

relief. It has a crudely cirquelike head just south of 

the main crest of Red Mountain. From this oversteepened somewhat broadened head, the chute changes 

little in width, slope, or direction for a vertical distance of 1, 000 feet. At its base, the chute widens, 

and the slope becomes more gentle. Below the oversteepened segment, m'ost of the chute is covered by 

a long narrow cone of poorly sorted angular debris 

that probably is a rock slide. The slide surface flattens 

at the base of the chute and continues up the oppo'sing 

slope for a short distance to terminate in an arcuate 

ridge of rubble concave northwestward to'#ard Red 

Mountain. Woods Creek has cut a _gorge 20-40 feet 

deep through the lowest part of the slide. 

Lateral moraine, conspicuous in other parts of 

the valley, apparently was removed before the slide 

debris accumulated, for the fragments in the slide 

are of local derivation and lack the rounded or 

smoothed forms characteristic of the morainal material. Material at a given locality in the slide could 

have come only from a bedrock source upslope from 

the slide or covered by the slide. Upslope from a 

metal source in a covered vein, the anomaly could be 

expected to drop off abruptly only if the vein crossed 

the slide at right angles and perpendicular to the 

general slope-at this place, trending northeastward . 

A traverse was made on the avalanche slope 

with these conditions in mind. Samples were taken 

at 200-foot intervals up the slope, and the vertical 

distance between sample sites was determined with 

a hand level. The average horizontal distance between localities is about 175 feet. The first sample 

taken at the base of the slope coincides with the last 

sample taken during work along the stream described 

in the preceding section. The straight course and 

nearly constant 30° slope are evident in the plan and 

profile of the traverse (figs. 5 and 6). 

The samples were screened to pass 30 mesh, 

and part of the fine fraction was analyzed for tungsten 

at the site. The· unused part of the fine fraction was 

saved for spectrographic analysis. 

The first sample taken at the base of the slope 

contains 150 ppm of tungsten (table 2 and fig. 5) compared with 1 percent (10, 000 ppm) in the concentrate, 

indicating a concentration ratio of about 70 to 1 during 

panning. For the next 1, 000 feet up the slope, the 

tungsten content of the "soil" gradually increases to 

300 ppm. Two hundred feet beyond this point, at 

locality 7, the "soil" contains more than 0.1 percent 

(1, 000 ppm) tungsten. The value for all samples 

above locality 7-1,200 feet of traverse-was above 

0.1 percent, and the value was still high where the 

traverse was stopped. 

Semiquantative spectrographic methods are sufficiently sensitive to be used for tungsten in all the 

samples upslope from locality 5, and both field chemical 
1-' 

0 

I ... ~ 

Plan of 

traverse 

0 

0 

o:t_ 

Profile of traverse 

Approximate altitude 

0 

0 

o_ 

0 

0 

10 

Q I I I I I I I I I I I I 

13 

0 

0 

0 

rt) 

Tungsten (ppm) 

0 

0 

0 

N 

0 

0 

10 

0 

0 

Q 

0 

0 

10 0 

I.-

r 

0 

0 

0 

Spectrographic analyses (ppm) 

Molybdenum 

0 

0 

10 0 

0 

0 

Tin 

10 0 

L.....-..-.J 

Lanthanum 

0 0 

~ ~ 0 

L-.1....J 

--' 

-. Niobium 

0 0 

~ ~ 0 

1.......1-..J 

---y-I lr-r---!1 ------rl· I I I ----~~n~ ---Jn11T11II1- ,- 111 _ 1 

! -- J -'~ A" '\ .--- - ~-----!.:!..<·-.. ,- 1 .- ...t'I:.U I 

"' . \ -, --.,._....,----, 'I A -

12\. ~ ~ --{!, ' 12 -- -\ -, - " <------y 

_A - /'";0/d 'c, ,.31..-1.-1----1111 I J 

m- ~ ==---t-----l..l~~'~,I:~r--· ~ j 1 r-------'f 

~-~ -' '\ I 

no ~c.~ \! ' \ - -------...!. .. '<'/ '0/-'\. J. -T 

·..------ ;._ s;;.;;;,;;;;p;;:,-_....-~ r--J ----l - ...------ ~· I -- l l 

T'7 ---\ - - }r-_ I ' 

I ,, -,---

re • ---r,----- - --11------rr-. ..--- ~ ~ \'t= - _;.,_ L- • 

, ~ I. - \, ~ ~ -

Woods Creek Woods Creek 

Horizontal and vertica I scale 

0 500 1000 Feet 

Figure 5.-Plan and profile of a traverse up the southeast slope of Red Mountain, Clear Creek County, Colo., showing analytical data for tungsten and associated elements. 
and spectrographic data are available for this part of 

the traverse (fig. 5). Agreement between the 2 methods 

is excellent below 500 ppm. Above 1, 000 ppm the 

curves do not agree so well, but there is unanimity 

in the richness of this part of the traverse; only at 

locality 8 do the 2 methods disagree as much as 3 reporting steps. Both methods report a six-step, logarithmic breakdown for each order of magnitude (10, 

15, 20, 30, 50, 70). The tungsten content of the upper 

part of the traverse is more than an order of magnitude 

above that of the lower part, and the tungsten content 

of the lower part of the traverse is at least an order 

of magnitude above background. Thus the anomaly 

is firmly established by both analytical methods. 

The tungsten distribution within the samples was 

determined by splitting each sample into two size fractions-less than 32 mesh but greater than 200 mesh, and 

less than 200 mesh-and separating the coarser of these 

into two specific-gravity fractions by means of bromoform (table 2). The bromoform (sp gr 2. 9) concentrate 

is similar to that produced in the gold pan although less 

dense-the separation in the pan is nearer a specific 

gravity of 3. 5(Theobald, 1957). The tungsten anomaly 

is produced by the concentration of huebnerite grains 

in the size range greater than 200 mesh. Inspection of 

the concentrates indicates that average grain size of the 

huebnerite is less than 100 mesh though near that size 

but that most of the huebnerite grains are attached to or 

included in quartz fragments whose average size is near 

50 mesh. More than 60 percent of the tungsten is in the 

heavy coarse fraction in most of the samples even though 

this fraction constitutes less than 10 percent of all the 

sample and is usually less than 5 percent of the sample. 

The contribution of the fine fraction to the total 

tungsten content of the samples never exceeds 30 ppm 

and is least in the richest samples. It probably results 

from very fine-grained huebnerite that is somewhat 

more concentrated toward the base of the slope. The 

light coarse fraction varies in its contribution to the 

total tungsten content from less than 20 ppm along 

the lower part of the traverse to more than 1, 000 ppm 

at the upper end of the traverse. This relatively constant increase in the proportion of the tungsten in the 

light fraction is most readily explained by the lack of 

comminution necessary to release huebnerite from 

quartz in the upper part of the slope and may be taken 

as direct evidence of proximity to the source. 

Huebnerite was separated by gravity, and by 

electromagnetic and chemical means, from a composite of the heavy coarse fractions described above. 

It was not possible toobtain 100 percent purity, but 

contaminants were limited to about 5 percent, mostly 

of interlocking quartz grains. Analysis of the concentrate yields an Fe: Fe +lvfu ratio of 0.16, indicating 

huebnerite, the manganese-rich end member of the 

wolframite series. 

Metals Ass0ciated with Tungsten 

A group of elements with related variation is 

indicated by examination of spectrographic data from 

the traverse on the southeast slope of Red Mountain 

(fig. 5 and table 3). This group includes molybdenum 

and tin, common associates of wolframite-series 

minerals in ore deposits, and manganese, a major 

constituent of huebnerite. 

The molybdenum increases upslope from 30 ppm 

to 700 ppm in a manner almost identical with the tungsten. Unlike the tungsten, the molybdenum is principally found in the!200-mesh:fraction of the samples, 

presumcbly as finely divided cleavage flakes of molybdenite. The tin is thought to be in cassiterite, which 

is concentrated with the huebnerite in the heavy coarse 

fraction of the samples. The huebnerite itself is rich 

in tin. 

DISCUSSION OF METHOD 

Analyzing heavy-mineral COIJ.centrates from 

stream gravels is an excellent technique for locating 

and tracing anomalies of those metals whose ore 

minerals are of high specific gravity and are resistant 

to chemical and mechanical attack. The chemical 

and mineralogic data obtained ate valuable in predicting 

the general characteristics of the deposits sought and 

the general characteristics and distribution of heavy 

accessory minerals in the country rocks. The technique is simple, but interpretations must be tempered 

Table 2.---Distribution of tungsten among size fractions and specific gravity fractions of samples from a traverse 

Red Mountain 

[Heavy fractions· analyzed spectrographically by E. F. Cooley, U. S. Geologies! Survey, the remaining analyses by 

chemical method] 

1 Computed Bulk less than 200 mesh Greater than 200 mesh bulk Sample tungsten Light fraction Heavy fraction tur1gsten site analysis Weight Tungsten Weight Tungsten Weight Tungsten analysis (ppm) percent (ppm) percent (ppm) percent (ppm) (ppm) 

1 ------- 150 81.3 40 17.6 20 1.1 7,000 110 

2 ------- 8o 74.2 20 24.2 40 1.6 5,000 100 

3 ------- 175 77.3 <20 21.4 60 1.3 5,ogo 90 

4 ------- 60 74.0 <20 24.2 8o 1.8 5,000 120 

5 ------- 200 58.1 20 37.6 160 4.:; 10,000 500 

6 ------- 200 90.6 20 6.3 100 :;.1 5,000 170 

7 ------- 300 58.6 40 35.0 600 6.4 10,000 900 

8 ------- 600 45.8 40 48.3 400 5.9 7,000 600 

9 ------- 2,000 17.0 40 74.7 600 8.:; >10,000 >1,200 

10 ------- 2,000 29r5 60 62.0 600 8.5 >10,000 >1,200 

11 ------- 3,ooo 24.7 20 66.7 BOG 8.6 10,000 1,400 

12 ------- 1,200 18.1 20 71.4 1,600 l~ >10,000 >2,000 

!separation with bromoform at about sp gr 2.9. 

11 
1-' 

N 

Table ).---Spectrographic analyses of less than 30-mesh material from a traverse on the southeast slope of Red Mountain, Clear Creek County, Colo. 

[Analyses in parts per million, by E. F. Cooley and U. Oda, U. S. Geological Survey] 

Locality Element 1 2 3 4 5 6 7 8 9 10 11 12 

W--------------- <100 <100 <100 <100 200 150 300 2,000 1,000 1,500 2,000 3,000 

Mo-------------- 30 30 30 30 30 150 150 200 500 500 700 150 

Sn-------------- 20 10 15 10 100 150 200 300 200 500 300 500 

La-------------- 50 50 50 50 50 70 70 200 200 200 200 150 

Nb-------------- <50 <50 <50 <50 <50 <50 <50 70 100 100 100 70 

Si-------------- 300,000 200,000 300,000 70,000 150,000 200,000 300,000 500,000 500,000 >500,000 >500,000 500,000 

Ti-------------- 2,000 1,500 1,500 1,000 1,000 1,500 1,500 3,000 3,000 2,000 3,000 2,000 

Mn-------------- 5,000 1,000 1,000 1,000 1,000 1,500 2,000 2,000 2,000 2,000 2,000 2,000 

Mg-------------- 5,000 3,000 3,000 2,000 2,000 3,000 3,000 3,000 2,000 2,000 2,000 2,000 

Ni-------------- 7 5 7 <5 <5 <5 <5 <5 <5 <5 <5 <5 

Cr-------------- 20 20 30 10 10 20 20 20 10 10 10 10 

Ba-------------- 500 300 300 200 150 200 200 500 150 150 150 100 

Sr-------------- 50 30 50 30 30 50 30 30 10 10 15 15 

Pb-------------- 300 150 200 150 200 500 700 3,000 1,000 700 700 700 

Cu-------------- 30 20 50 10 15 50 50 50 50 30 30 20 

Ag-------------- <1 <1 <1 <1 1 1 1 1.5 1 1 1 1 

13 

3,000 

300 

500 

150 

70 

500,000 

2,000 

2,000 

1,500 

<5 

10 

70 

<10 

700 

20 

1 
with both geologic and chemical lmowledge. The greatest value will be obtained from the data when the work 

is either performed or carefully evaluated by men 

experienced in the fields of geology and chemistry. 

The anomaly due to huebnerite along the lower 

part of Clear Creek would probably have been overlooked 

had not the scheelite been present to enhance the total 

tungsten content of the samples. However, the huebnerite content of the initial samples is anomalous, and 

the tungsten content due to huebnerite is equally anomalous above Idaho Springs, and probably throughout the 

anomaly. 

Sampling errors can be great because the technique is based on the appearance of anomalies in detritus; 

that is, the metal determined by the chemist is present 

in discrete mineral grains that are richer in the element 

than the remainder of the grains. The average grain 

size of the concentrates analyzed is near 80 mesh, so 

that a few grains more or less of the metal-carrying 

mineral may make a sizable difference in the analytical 

result, particularly if the anomaly is of low magnitude. 

For this reason, interpretations should not be based on 

single determinations, and critical or questionable 

samples should be checked by completely new samples. 

The greatest variation of this type encountered while 

sampling Clear Creek was on West Fork Clear Creek 

just above Empire, where the original field analysis, 

800 ppm, was reduced to 300 ppm on more careful 

splitting of the concentrate for analysis in the laboratory. 

At two other localities analytical results of 150 and 

300 ppm in the field were reduced to 40 and less than 

20 ppm respectively by more careful sample preparation 

in the laboratory. None of these affected the rate of 

progress while following the anomaly, and all were 

conspicuous erratic values. At the mouth of Woods 

Creek the combination of high sulfur, molybdenum 

interference, and possibly a sampling error led to a 

low field estimate of 400 ppm tungsten. This is the 

only example of the reverse error, and it did not affect 

the tracing of the anomaly. 

The initial reconnaissance data was repeated by 

three different groups of people, none of whom were 

familiar either with gold panning or with the analytical 

procedure. The variation in these four independent 

analyses (table 4) is negligible. When the sampling 

problem is realized, these results are surprisingly 

uniform. 

The unusual assemblages of minerals and elements 

that are found in heavy-mineral concentrates may require revision of analytical methods. The example 

of molybdenum's inter-ference with the tungsten determination is but one of many such combinations. This 

Table 4.--Replicate tungsten analyses of concentrates 

obtained by 4 independent groups at 4 localities along 

the eastern limit of the Front Range, Colo. 

Tungsten content (ppm) Creek Field laboratory 

l 2 3 4 

Bear----------------- <20 20 <20 4o 

Clear---------------- 200 200 4oo 300 

Coal----------------- <20 <20 20 20 

Boulder: 

Stream------------- >400 >4000 >4000 5000 

Terrace------------ 300 300 300 300 

13 

interference was never completely removed from the 

sample at the mouth of Woods Creek, but it was successfully avoided in the samples above the Urad mill. 

A combination of interferences prevent successful 

chemical determination of the tin content of the 

concentrates. 

The advantages of the technique are the mobility 

of the field team and the speed with which an anomaly 

may be traced and the source located. One man can 

easily carry the equipment and reagents necessary 

to make over 100 determinations for tungsten. If a 

geologist and a chemist work as a team, the analyses 

at no time need be more than one sample behind a 

collection. Such a team accomplished the initial 

reconnaissance, traced the anomaly along Clear Creek, 

isolated the anomaly on Woods Creek, and traced the 

anomaly to the huebnerite source on Red Mountain in 

only 5 days. 

LITERATURE CITED 

Ginzburg, A. I., 1957, Experimental development of 

theoretical and basic geochemical methods of 

prospecting for ores of non-ferrous and rare metals: 

Moscow [ in Russian J, [Translation by V. P. Soboloff, 

in press]. 

Hill, John (translator), 1746, History of stones by 

Theophrastus, 300 B. C. ( ?): London, printed for 

c. Davis, 211 p. 

Lovering, T. S., and Goddard, E. N., 1950, Geology 

and ore deposits of the Front Range, Colorado: U. S. 

Geol. Survey Prof. Paper 223. 

Mertie, J. B., Jr., 1954, Thegoldpan: aneglected 

geological tool: Econ. Geology, v. 49, no. 6, 

p. 639-651. 

Sigov, A. P., 1939, Prospecting by heavy mineral 

studies: Transactions of the Ural Scientific Research 

Inst. of Geol., Prospecting and Econ. Mineralogy 

and Sverdlovsk Mining Inst., no. 4, abstracted by 

H. E. Hawkes, U. S. Geol. Survey open-file report. 

Theobald, P. K. , Jr. , 1957, The gold pan as a quantitative geologic tool: U. S. Geol. Survey Bull. 1071-A, 

p. 1-54. 

Ward, F. N., 1951, A field method Jor the determination of tungsten in soils: U. s. Geol. Survey Circ. 119. 

INT.-DUP. SEC., lAS!!.. D.C.