GEOLOGICAL SURVEY CIRCULAR 592 

Interpreting Pan-Concentrate 

Analyses of Stream Sediments in 

Geochemical Exploration for Gold 

Interpreting Pan-Concentrate 

Analyses of Stream Sediments in 

Geochemical Exploration for Gold 

By R. P. Fischer and F. 5. Fisher 

G E 0 L 0 G I C A L S U R V E Y C I R C U l A R 592 

Washington 1968 
United States Department of the Interior 

WALTER J. HICKEL, Secretory 

Geological Survey 

William T. Pecora, Director 

First printing 1 968 

Second printing 1969 

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

Introduction- - - - - - - - - - - - - - - - -

Sampling and analytical techniques- - - - -

Sample data and analytical results - - - - -

Consistency of analytical results - - - -

CONTENTS 

Page 

1 

1 

1 

2 

2 

Sample data and analytical results--Continued 

Quantitative compatibility of samples 

with known geologic relations - - - - -

Conclusions - - - - - - - - - - - - - - - - -

Reference cited- - - - - - - - - - - - - - -

ILLUSTRATIONS 

Figure 1. Graph of the range, on a logarithmic scale, of analytical determinations for 

samples listed in tables 2 and 3 that were analyzed as two or three separate 

splits - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2. Map showing sample localities and character of mineralized areas in San Juan 

Mountains, Colo - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

TABLES 

Table 1. Samples from streams draining apparently barren areas - - - - - - - - - - - - - - - - -.-

2. Samples from streams draining weakly mineralized areas that contain only a few 

veins and prospects or small mines - - - - - - - - - - - - - - - - - - - - - - - - - - - -

3. Samples from streams draining well-mineralized areas that contain numerous 

veins and some very productive mines - - - - - - - - - - - - - - - - - - - - - - - - - - -

111 

Page 

2 

2 

2 

Page 

4 

5 

Page 

6 

6 

8 

Interpreting Pan-Concentrate Analyses of Stream Sediments in 

Geochemical Exploration for Gold 

By R. P. Fischer and F. S. fisher 

Abstract 

A study of methods of collecting and processing samples to determine whether or not gold is present in areas of moderate size 

was undertaken in the northwestern part of the San Juan Mountains, 

Colo. As part of this study, 57 samples of pan concentrates were 

taken from streams draining three types of areas: (1) "barren" 

areas, where gold mineralization might be geologically possible 

but no deposits are known, (2) slightly mineralized areas that contain only a few known veins and prospects and small mines, and 

(3) well-mineralized areas that contain numerous veins and some 

very productive mines. The concentrate samples were analyzed 

by the fire-assay-atomic-absorption method. 

Replicate analyses of large samples gave results consistent 

enough to permit placing considerable confidence in the results 

obtained for smaller samples on which only one analysis was made. 

For general field practice, it isnecessarytopan only enough sand 

and gravel to yield about 15 grams of concentrate. 

The analytical results are also quantitatively compatihle with 

known geologic relations and indicate that a few samples from a 

stream are adequate to distinguish between "barren" and mineralized areas and to deter m i n e the relative amount of gold in 

mineralized areas. In other areas of similar gold deposits, data 

of this type should help decide whether more intensive search for 

gold deposits is justified. 

INTRODUCTION 

As part of its Heavy Metals program to appraise 

and enhance domestic resources of mineral raw 

materials that are in short supply, the U.S. Geological 

Survey is studying techniques of geologic sampling and 

their application to mineral exploration. In 1967 a project was started in the northwestern San Juan Mountains, Colo., to study several methods of collecting and 

processing samples in order to determine easily and 

quickly whether or not gold is present in areas of a 

few square miles. One method tried is described here. 

It consisted of panning known amounts of sand and 

gravel from selected streams, weighing the heavymineral concentrates and analyzing them by fire assay 

and atomic absorption. The panning practice used did 

not differ from that of the oldtime prospector, but the 

more sensitive analytical procedure available today 

offers a distinct advantage. Reasonably reproducible 

results that seem to be quantitatively meaningful were 

obtained from 57 samples. This type of s amp 1 in g 

should be usable in other areas where similar gold 

deposits might be present, and the results should help 

decide whether more intensive search for gold deposits might be justified. 

Willard Leedy and Mark Voultsos help~d in the collection and panning of samples in the field. W. D. Goss, 

L. B. Riley, Claude Huffman, Jr., and J. A. Thomas 

of the U.S. Geological Survey did the g:'lld analyses. 

SAMPLING AND ANALYTICAL TEC~-INIQUES 

All samples were sand and gravel from the upper 

part of the alluvial fill, and at each sample locality 

this material was taken from one or more places along 

the stream where placer gold is apt to accumulate, 

such as the head or foot of stream bars, behind boulders, in moss-covered banks, and in ratural riffles 

on bedrock. The samples were taken to· determine the 

presence of gold in the stream sediments and its relative amount; they were not adequate to determine or 

estimate the gold content of the streamb~d fill. 

Samples were panned in the field in ll- and 14-inch 

gold pans. They were not weighed individually, but it 

was determined that the small pan contain~d about 3,500 

grams (nearly 8 pounds) of sand and gra,·~l when filled 

and the large pan, about 7,000 gramf' (nearly 16 

pounds). Samples ranged in size from those thatfilled 

only one small pan to those th~t filled seven or eight 

pans of both sizes and totaled 40,000 to 50,000 grams, 

or about 1 00 pounds. The samples were concentrated 

by panning until most ofthe light-colored(light weight) 

mineral grains were washed from the pan. Concentrates consisted mostly ofdark-ccloredheavy 

minerals, commonly with some fresh sulfides, mainly 

pyrite. At each locality where twoormor~pans of sand 

and gravel were taken, the concentrates from each pan 

were combined into one sample for anal~·sis. Samples 

of concentrate ranged in weight from a fe·111 grams to as 

much as 775 grams. Some samples were panned by 

one person alone; others, by two, three, cr four people. 

In the 1 a b o r at o r y, concentrate sam pies weighing 

more than about 50 grams were split in a Jones splitter 

to samples of about 50 grams. Using ceramic plates, 

these 50-gram splits were then ground to about 80 to 

100- mesh. If the original concentrate sa-nple was less 

than about 50 grams, the entire sample was ground. If 

the ground sample weighed less than ab:>ut 15 grams, 

the whole sample was analyzed in one run. If the ground 

sample weighed more than about 15 grams, it was poured into a cone-shaped pile on a fla': surface, and 
was spread out rather evenly; enough spatula scoops, 

each containing about 1 gram of sample, were taken 

to make two or three separate splits for analysis, 

usually of about 15 grams each. For each analysis, a 

gold-silver bead was obtained by the standard fireassay method. This bead was dissolved in acid and the 

gold was determined quantitatively by atomic-absorption spectrometry (Huffman and others, 1967). The 

limit of detection is 0.02 part per million (ppm) gold 

for samples of 10-15 grams and is slightlyhigher for 

smaller samples. 

SAMPLE DATA AND ANALYTICAL RESULTS 

Tables 1, 2, and 3 show sample data and analytical 

results. Not much significance is placed on the calculated amount of gold in the field samples beyond its 

order of magnitude-the weight of the field sample was 

only estimated; thus the concentration ratio cannot be 

figured precisely. Furthermore, the amount of gold in 

the concentrate is minimal, because gold can be lost 

in panning; however, the amount that might have been 

lost is not known. On the other hand, considerable 

significance can be placed on the consistency of the 

analytical results and their quantitative compatibility 

with geologic relations. 

Consistency of analytical results 

Because gold is particulate in habit, has a high 

specific gravity, and is malleable, it is commonly 

difficult to grind and mix a sample sufficiently to obtain consistent analytical res u 1 t s between sample 

splits. Splits of the pan concentrates used in this study, 

however, gave reasonably consistent results, as shown 

both by graphic plotting and by statistical analyses. 

The consistency between splits permits placing considerable confidence in the determinations for those 

samples on which only one analysis was made. 

The analytical determinations for the samples listed 

in tables 2 and 3 that were analyzed as two or three 

separate splits are plotted on a logarithmic scale in 

figure 1. For most samples, the logarithmic range 

(le~gth of line) between plotted points is small and is 

about the same for low-grade and high-grade samples. 

For a few low-grade samples (054, 114, and 335), as 

might be reasonably expected, the logarithmic range 

appears I a r g e although the actual differences are 

small-indeed, the happens tan t i a 1 inclusion or 

exclusion of perhaps a single particle of gold in a sample split might make the difference between splits. 

Quantitative compatibility of samples with known 

geologic relations 

The 57 samples used in this study were taken from 

streams draining three geologic types of groundapparently barren, weak 1 y mineralized, and wellmineralized (fig. 2). The analytical results show a 

quantitative compatibility between the samples and 

their source areas. 

2 

Table 1 lists samples taken from the Middle and West 

Forks of Cimarron Creek. These two drainage areas 

contain no known ore deposits and only a few fractures 

along which hydrothermal alteration was relatively 

weak. All 21 samples, which are concentrates from a 

total of about 600 pounds of sand and gravel, and which 

were analyzed in 42 splits, were reported to contain 

less than the limit of detection, usually< 0.02 ppm gold. 

Calculating these results into the volumes of the field 

samples gives values not exceeding tenths or hundredths of a part per billion (ppb), or O.OOOX to O.OOOOX 

ppm, probably one to two orders of magnitude less than 

crustal abundance. 

Table 2 lists samples from streams that drain areas 

classed as weakly mineralized, in which ve~ns are not 

abundant and only a few prospects or small mines are 

known. Table 3 lists samples from streams draining 

well-mineralized areas that contain numerous veins 

and some very productive mines. Of the 31) samples 

shown on these two tables, all were reported to be 

gold-bearing except one, sample 354 (table 2), which is 

from a stream draining a weakly mineralized area. 

The calculated gold content of the sand and gravel from 

streams draining weakly mineralized areas (table 2) 

ranges from a few ·tenths of a ppb to several ppb, or 

0.0003 to 0.009 ppm. The samples from streE'ms draining well-mineralized areas have calculatedr-old values 

ranging from several ppb to a few hundr1ed ppb, or 

0. 006 to 0. 3 ppm. Gold was reported in the analyses of 

all samples and sample splits, and was o:':>served in 

the field in the pan concentrates in 13 out of 15 samples that were found on analysis to contain a calculated 

gold content of at least 0.01 ppm. It is WC'rth noting 

that 0.01 ppm of gold is equivalent to about 1 cent per 

cubic yard of sand and gravel and is below the limit of 

detection by common analytical methods. Obviously, a 

fairly consistent field recognition of such low go 1 d 

values gives useful information on the spot. 

CONCLUSIONS 

The consistency of replicate an a I y s e s permits 

placing considerable confidence in the sanpling and 

analytical methods used, and the quantitative compatibility with known geologic relations indicates that a few 

samples are adequate to distinguish between "barren" 

and mineralized areas and to determine tte relative 

amount of gold in mineralized areas. In other areas 

where similar gold deposits might be present, the 

analytical results of this type of sampling should be 

useful to determine easily and quickly whe':her more 

intensive search for gold deposits might be justified. 

REFERENCE CITED 

Huffman, Claude, Jr., Mensik, J. D., and Riley, L. B., 

1967, Determination of gold in geologic materials 

by solvent extraction and atomic-absorp':ion spectrometry: U.S. Geol. Survey Circ. 544, f p. 
FIGURES 1, 2 AND TABLES 1-3 
~ 

ADG-055 

016 

017 

331 

329 

054 

060 

114 

0:: 

108 

LLJ 015 

m 332 

:E 

:::> 335 

z 061 

w 312 

_J 

Q.. 349 

~ 351 

<I 

(J) 333 

057 

059 

330 

328 

337 

058 

253 

251 

336 

o----<> 

© 

()-() 

@ 

-------------<>-------o o---<> 

---------------------o 

© '/ 

~ 

© 

----------a------------------o 

o--o 

o---o 

(0'1 0 

0() 

@-o 

<0.02 0.02 0.04 0.07 0.1 0.2 0.4 0.7 1.0 2 4 

GOLn, IN ?!\RTS PER ~J1!LLION 

o One split 

(§)Two splits 

o---o--o 

o-o 

<><X> 

00 

o-o 

o-o-o 

o-o 

7 10 2.0 40 

00 

70 100 

_[igure 1.--Graph of the range, on a logarithmic scale, of analytical determinations for samples listed in tables 2 and 3 that 

were analyzed as two or ~hree separate splits. 
EXPLANATION 

Slightly mineralized 

~ area 

UJ " 

. " 

Well-mineralized area 

Sample 

--- -------, 

§ 

C) 

0 

3 

"tJ 

I:) 

::,. 

q 

"" Q) 

0 5 

I I I I I I 

10 

I 

15 MILES 

I 

Figure 2.--Map showing sample localities and character of mineralized areas in San Juan Mountains, Colo. 

5 
Table I.--Samples from s~reams 

Sample Field sample I Concentrate ~nalyzed 

Concentrate Concentration (weillht in llrams) 

No. Weight in grams ratio Split 1 I Split 2 

West Fork Cimarron Creek 

ADG-047 10,000 26.77 380 IS 11.77 

049 7,000 18.3S 380 10 8.3S 

oso 7,000 36.31 200 IS 21.31 

OS! 7,000 24.27 280 12 12.27 

109 40,000 77S.8 so IS IS. 

110 so,ooo 89.8 sso IS 15. 

111 40,000 483.1 80 IS IS. 

112 3,500 40.2 90 IS IS. 

113 20,000 219.4 90 IS 15. 

Middle Fork Cimarron Creek 

041 7,000 142.7 so 15 IS 

042 7,000 96.8 70 IS IS 

043 7,000 3.8 1,800 3.8 

044 7,000 33.68 200 IS 10 

052 14,000 359.0 40 IS IS 

229 40,000 278.7 140 15 IS 

230 3,SOO 28.90 120 15 13.90 

231 1S,OOO 16.47 900 10 6.47 

232 20,000 19.68 1,000 10 9.68 

233 3,500 19.04 180 10 9.04 

234 20,000 186.2 110 lS 15 

23S 3,SOO 64.1 60 IS IS 

Table 2 --Samples from streams draining weakly mineralized areas 

Concentrate analyzed 

(weight in grams) 

Sample No. Sample locality Field sample Concentrate Concentration Spllt 1 I Spll t 2 

Welght 1n grams ratio 

Cimarron Creek drainage area 

ADG-055 Cimarron Creek 14,000 266.9 50 15 15 

054 East Fort 17,000 270.1 60 15 15 

Uncompahgre River drainage area 

060 Cow Creek 14,000 214.5 60 15 15 

114 ------do------ 40,000 460.6 90 15 15 

015 De.xter Creek 14,000 17.22 800 10 7.22 

016 ------do------ 7,000 53.5 130 15 15 

017 ------do------ 9,000 59.7 150 15 15 

108 ------do------ 40,000 265.3 150 15 15 

Animas River drainage area 

351 South Fork 

Mineral Creek 8,000 19.73 420 10 9.73 

352 ------do-_: ____ 8,000 3.00 2,500 3.00 

354 ------do------ 8,000 124.9 60 15 15 

356 ------do------ 8,000 14.28 550 14.28 

San Miguel River drainage area 

331 Mill Creek 16,000 103.9 150 15 15 

332 Lake Fork 25,000 46.60 550 15 15 

335 ------do------ 16,000 34.23 480 15 10 

Dolores River drainage area 

329 Barlow Creek 20,000 43.5 460 15 15 

!/Gold was recognized visually in the pan. 

6 
draining apparently barren areas 

Concentrate Gold content in parts per million 

Sample analyzed-Con. Concentrate I Field 

No. (weight in grams) Spl1t 1 I Split 2 ( Split 3 I Average l sample Solit 3 (c~lculated) 

West Fork C1marron Creek 

ADG-047 <0.02 <0.02 <0.02 <0. oooox 

049 <.02 <.02 <.02 <.OOOOX 

050 <.02 <.02 <.02 <.OOOOX 

05i <.02 <.02 <.02 <.OOOOX 

:i09 <.02 <.02 <.02 <.OOOX 

110 <.02 <~02 <.02 <.OOOOX 

111 <.02 <.02 <.02 <.OOOX 

112 <.02 <,02 <.02 <.OOOX 

113 <.02 <.02 <.02 <.OOOX 

Middle Fork Cimarron Creek 

041 <0.02 <0.02 <0.02 <O.OOOX 

042 <.02 <.02 <.02 <.OOOX 

043 <.05 <.OS <.OOOOX 

044 8.68 <.02 <.02 <0.02 <.02 <.OOOOX 

052 <.02 <.02 <.02 <.OOOX 

229 <.02 <.02 <.02 <.OOOX 

230 <.02 <.02 <.02 <,OOOX 

231 <.02 <.04 <,03 <.OOOOX 

232 <.02 <,02 <.02 <.OOOOX 

233 <.02 <.02 <,02 <,OOOX 

234 <.02 <.02 <.02 <,OOOX 

235 <.02 <.02 <.02 <,OOOX 

that contain only a few veins and prospects or small mines 

Gold content in parts per million 

Field 

Sample No. Concentrate analyzed--Con. Concentrate sample 

(weight in grams) 

1 I I Split 3 I Average 

(calculated) 

Sol it 3 Split Split 2 

Cimarron Creek drainage area 

ADG-055 <0.02 0.04 0.03 0.0006 

054 15 .l <.02 0.3 .l .002 

Uncompahgre River drainage area 

060 0.3 0.2 0.2 0.003 

114 15 <.02 .4 <0.02 .l .002 

015 • 5 • 5 . 5 • 0 0.06 

016 .05 .03 .04 .0003 

017 .06 .06 .06 .0004 

108 . 4 .4 .4 .003 

Animas River drainage area 

351 3. 2 2.9 3.0 lo.oo7 

352 1.3 1.3 .0005 

354 <.02 <.02 <.02 <.OOOX 

356 5.1 5.1 .009 

San Miguel River drainage area 

331 .08 0.1 0.09 0.0006 

332 16.60 . 3 . 7 . 5 . 5 .001 

335 9.23 .07 <.02 • 8 • 3 .0006 

Dolores River drainage area 

329 0.2 0.2 0.2 0.0004 

7 
Table 3.--Samples from streams draining well-mineralized areas 

Field sample !concentrate 

Concentrate 

analyzed 

Sample No. Sample locality Concentration (wei£ht in £rams) 

We1ght 1n grams ratio Split 1 I Split 2 

Lake Fork of Gunnison River drainage area 

ADG-061 Lake Fork s,ooo 2S.79 190 12 13.79 

Animas River drainage areas 

248 Cement Creek--- 8,000 11.49 700 11.49 

249 Placer Gulch--- 8,000 5.41 1,500 5.41 

2SO ------do------- 8,000 4.46 1,800 4.46 

2Sl ------do------- 16,000 1S.72 1,000 10 S.72 

253 ------do------- 8,000 1S.73 soo 10 S.73 

254 ------do------- 8,000 8.23 1,000 8.23 

ass ------do------- 8,000 1.35 6,000 1.3S 

30S Brown Gulch, 8,000 S.62 1,400 S.62 

(North Fork 

Mineral Creek). 

312 Mineral Creek-- 3,500 21.21 170 12 9.21 

349 Middle Fork 16,000 S1.4 320 15 lS 

Mineral Creek. 

San Miguel River drainage area 

OS7 San Miguel River, lS,OOO 39.14 380 15 15 

bench. 

059 ------do------- 15,000 65.0 240 15 15 

058 San Miguel River 15,000 65.5 320 15 15 

330 ------do------- 25,000 103.6 240 15 1S 

336 ------do------- 8,000 32.02 240 15 17.02 

337 ------do------- 16,000 107.4 150 15 15 

328 South Fork, San 2S,OOO 98.4 260 15 lS 

Miguel River. 

333 Howard Fork, South 16,000 43.22 380 15 15 

Fork, San Miguel 

River. 

334 ------do------- 12,000 12.04 1,000 12.04 

.!/Gold was recognized visually in the pan, 

8 
that contain numerous veins and some very productive mines 

Gold content in parts per million 

Concentrate analyzed--Con. 

____ _iwe~&h!.~in_~2r~a~m~s~•)~------+-~~~,---r-~~~C~o~n~c~e~n~t~r~a~t~e~~~~--~~~~ Split 3 Split l 1 Spllt z 1 Spl1t 3 1 Average 

15 

9.14 

15 

15 

13.22 

Lake Fork of Gunnison River drainage area--Continued 

0.7 0.9 

Animas River drainage areas--Continued 

98 

41 

32 

52 

40 

45 

71 

9.3 

1.3 

2 

San Miguel 

9 

18 

43 

23 

71 

25 

23 

6 

River 

5.8 

54 

47 

.9 

1 

drainage 

13 

16 

39 

19 

67 

29 

22 

5 

9 

1 

area--Continued 

17 

47 

22 

5 

0.8 

98 

41 

32 

53 

44 

45 

71 

9.3 

1.1 

1.3 

13 

17 

43 

21 

69 

27 

22 

5 

5.8 

Field 

sample 

(calculated) 

0.004 

.006 

.044 

!/ 0. 03 

1/ T/.01 

- .2 

1/"09 

rr 3 

rr 2 

- .09 

!l.o1 

.006 

GPO 881 728