Establishment of 

Gold-Quartz Standard GQS- 1 

Establishment of 

Gold-Quartz Standard GQS-1 

By Hugh T. Millard, Jr., John Marinenko, and John E. Mclane 

G E 0 L 0 G I C A L S U R V E Y C I R C U L A R 598 

Woaltingfoft J 969 
United States Department of the Interior 

STEWART L. UDALL, Secretary 

Geological Survey 

William T. Pecora, Director 

FrH on application to the U.S. Geological Surv.y, Washington, D.C. 20242 
CONTENTS 

Page 

Abstract---------------------------------------------------------- 1 

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

Experimental procedures ------------------------------------------- 1 

Preparation of the standard powder-------------------------------- 1 

Instrumental neutron activation analysis (INAA) --------------------- 1 

Radioisotope dilution analysis (RDA) ------------------------------- 2 

Results and discussion--------------------------------------------- 3 

Conclusion-------------------------------------------------------- 4 

References cited--------------------------------------------------- 4 

TABLES 

Page 

Table 1. Values for gold content in the gold-bearing quartz powder 

prior to the aqua regia treatment------------------------- 5 

2. Gold content of the gold-quartz standard GQS-1--------------- 5 

3. Analysis of variance for data from runs 1 (irradiation 1), 

2, and 3------------------------------------------------ 5 

4. Gold content of GQS-1 determined by cyanide leachatomic absorption, fire assay-atomic absorption, 

and neutron activation-fire assay------------------------- 6 

5. Average grain sizes of gold particles in the goldbearing quartz and in GQS-1 as computed from 

the analytical data-------------------------------------- 6 

III 

Establishment of gold-quartz standard GQS-1 

Hugh T. Millard, Jr., John Marinenko, and John E. Mclane 

ABSTRACT 

A homogeneous gold-quartz standard, GQS-1, was prepared from 

a heterogeneous gold-bearing quartz by chemical treatment. The 

concentration of gold in GQS-1 wasdeterminedbyboth instrumental neutron activation analysis and radioisotope dUution analysis to 

be 2.61±0.10parts per million. Analysis of 10 samples of the standard by both instrumental neutron activation analysis and radioisotope dilution analysis failed to reveal heterogeneity within the 

standard. The precision of the analytical methods, expressed as 

standard error, was approximately 0.1 part per million. The analytical data were also used to estimate the average size of gold 

particles. The chemical treatment apparently reduced the average 

diameter of the gold particles by at least an order of magnitude 

and increased the concentration of gold grains by a factor of at 

least 4,000. 

INTRODUCTION 

Frequently, the analyst determining the gold content 

of geologic materials is unable to estimate ·analytical 

precision because homogeneous standards are unavailable. To allow analysts to evaluate the accuracy and 

p r e c i s i o n of procedures for determining the go 1 d 

content we attempted to prepare a homogeneous standard reference material. We required that the standard 

be homogeneous with a maximum coefficient ofvariation of 10 percent for 200-mg (milligram) samples. 

A gold-bearing quartz sample was chosen as the 

starting material because the quartz was readily available in large quantities and contained gold at the parts 

per million concentration level. When this material 

proved to be heterogeneous, we treated it chemically 

in an attempt to redistribute the gold. The concentration of gold in the treated material and the degree of 

homogeneity were evaluated by two different analytical 

techniques. Replicate analyses failed to reveal any 

heterogeneity within the treated material. Variation 

among the results was nearly equal to the precision of 

the analytical method. We were also able to derive 

from the analytical data information concerning the 

average sizes of gold particles in the treated and untreated materials. 

Acknowledgments.-We thank Nelson Hi c k I in g, 

Frederick Simon, and Irving May for help in collecting the quartz sample and F. J. Flanagan for sample 

preparation. A. T. Miesch and Flanagan contributed 

significantly to our understanding of the statistics of 

our measurement. 

EXPERIMENTAL PROCEDURES 

Preparation of the Standard Powder 

Some 120 pounds of gold-bearing quartz was collected from a quartz vein near the entrance to the 

Maryland mine at Great Falls, Md. This material was 

ground to about 200-mesh size by means of the procedures described by Flanagan ( 1967). When the powder 

was found to be heterogeneous with respect to gold, 

sufficient aqua regia was added to the quartz powder 

to make a paste. This paste was dried overnight on a 

steam bath and then was ignited at 900°C. The resulting dry powder was ground in a ball mill, mixed in a 

stainless steel V-blender, and poured into 120 12-ounce 

glass bottles. This material was designated goldquartz standard 1 (GQS-1). 

Instrumental Neutron Activation Analysis (INAA) 

Splits amounting to 0.2 g (gram) of the gold-quartz 

standard 1 were divided into two equal portions, which 

were sealed in separate polyethylene snap-cap vials. 

Flux monitors were prepared by weighing two drops 

of a 92-J.1g (micrograms) Au per ml (milliliter) or one 

drop of a 5-J.1g Au per ml standard gold solution onto 

100 mg of spectrographic-grade quartzpowder. These 

monitors were also sealed in polyethylene snap-cap 

vials. The sample and monitor vials were placed in a 

polyethylene irradiation bucket in a cylindrical array 

such that the portions of each sample would occupy 

symmetrical positions in the neutron flux. The array 

was irradiated 4 minutes in the nuclear reactor at the 

Naval Research Laboratory, Washington, D.C. At 30-

second intervals, the bucket was raised, rotated arbitrarily, and lowered into the reactor to randomize 

the orientation of the array in the neutron flux. 

After irradiation, the 24Na activity was allowed to 

decay several days, and the 198Au was counted in a 

3- by 3-inch Nai well detector. Gamma-spectra were 

collected in a 256-channel analyzer with a resolution 
of 10 Kev(kilo electron volts)perchannelover a period of 8 days. The area under the 412-Kev photopeak 

was measured and the concentration of gold in GQS-1 

calculated by the equation: 

%QS-l: 

AcQS-1 

A -.§. 

w -§_ c 

-.§ 

w ·-p• -GQS-1 .§ 

(1) 

where C . =GQS-1 = concentration of gold in GQS-1 (JJg 

per g), 

c 

-.s._ = concentration of gold in the standard 

gold solution (JJg per ml), 

AcQS- 1 = counting rate for GQS-1, in counts 

per minute ( cpm), 

~ = counting rate for the flux monitor 

(cpm), 

Y:!...§ = weight of the standard gold solution 

(g), 

j¥GQS-1 =weight of GQS-1 (g), 

p 

.§ = density of the standard gold solution 

(g per ml). 

Radioisotope Dilution Analysis (RDA) 

Ten-gram samples of the gold-quartz standard 

were weighed in degreased glass beakers. To these, 

10-ml portions of aqua regia were added to make a 

paste. Gold standards were prepared by pipetting 1.00 

ml of a 10.0 JJg Au per ml standard gold solution into 

separate degreased glass beakers. One ml of a 0.05 

microcurie per ml 198Au radio-tracer solution (< 0.1 

JJg Au per ml) was added to each sample paste andgold standard. The beakers were covered and heated 

and their contents stirred occasionally for 1 hour on 

a steam bath. An additional 20 ml of aqua regia was 

added to each beaker, the beakers were heated for half 

an hour, and the supernatants above the quartz were 

decanted. The residues were washed several times 

with a total of 30 ml 6.!;:! HCl and the washes were then 

combined with the supernatants. The supernatants and 

gold-standard solutions were evaporated to dryness 

and the residues dissolved in 1 ml aqua regia and 

diluted to 50 ml with 0. 51;:! HCI. Each so 1 uti on was 

then poured through an SB- 2 anion exchange disk (H. 

Reeve Angel and Co.) and the disk w a s h e d with 100 

ml of water. 

The disks for the samples and gold standards were 

counted in a 3- by 3-inch Nal well detector and the 

counting rates were compared to radio-tracer standards prepared by weighing 2-drop portions of the 

198 Au radio-tracer solution onto anion exchange disks. 

2 

The yields of gold on the disks from the GQS-1 samples and gold standards were calculated by the equation: 

(2) 

where Y -.!. : yield of gold from GQS-1 or from the 

gold standards, 

~ = counting rate for GQS-1 or the gold standards (cpm), 

l!.rs • counting rate for the radio-tracer standard (cpm), 

~s = weight of the radio-tracer standards (g), 

P .I§ • density of the radio-tracer solution (g 

per ml), 

Yrs = volume of the radio-tracer solution(ml). 

The anion exchange disks were irradiated 5 minutes 

in the Naval Research Laboratory nuclear reactor and 

counted in a 3- by 3-inch Nal well detector. The 198Au 

412-Kev photopeak areas were corrected for activity 

due to the 198Au radio-tracer and the amount of gold 

in GQS-1 was calculated by the equation: 

A Y W -GQS-1 --:&. -~ 

~GQS-1 =A 

-.§. .YGQS-1 . ~QS-1, (3) 

where W -.§. • weight of gold from the standard gold 

solution (JJg), 

.Y§. = yield of gold from the gold standards, 

YGQS-1 = yield of gold from GQS-1, 

and the other symbols have the same meaning as in 

equation 1. 

The quartz residues remaining from the treatment of 

GQS-1 were washed several times with 6N HCl and 

water and then dried. To determine the quantity of 

unleached gold in these residues, portions of each were 

weighed out and irradiated along with untreated samples of GQS-1. After counting of the i r radiated 

samples, the corrected concentration of gold in GQS-1 

was calculated using the equation: 

1 AcQS-1 

c_ GQS-1 =A -A ~GQS-1 (4) 

~S-1 -r 

1 -

where .C. GQS-1 = corrected concentration of gold in 

GQS-1 (JJg per g), 

hcQS-1 = counting rate for the untreated GQS1 (cpm), 

~ = counting rate for the residue ( cpm), 

CGQS-1 = concentration of gold in GQS-1. 
RESULTS AND DlSCUSSIO~ 

The homogeneity of the original untreated goldbearing quartz was estimated by determining gold in 

randomly selected 15-g samples by the fire assayatomic absorptio:1 technique of Huffman, Mensik, and 

Riley ( 1967). The results shown in table 1 indicate that 

this sample was extremely heterogeneous and, therefore, not suitable for use as a standard reference 

material. 

Results obtained by the two independent techniques 

chosen to evaluate the gold content and homogeneity of 

GQS-1 are given in table 2. Every lOth bottle of the 

first 100 12-ounce sample bottles wastakenformeasurement. Separate sets of samples were weighed for 

each run. Run 1 was irradiated twice using separately 

prepared flux monitors for each irradiation in an attempt to evaluate the precision of the INAA technique. 

The coefficient of variation for run 1 was 5 percent. 

Two factors which might introduce error into the 

INAA techniqLie are; 

I. Self-shielding of the neutron flux by the large amounts of gold in the flux monitors, 

2. Radiocontam1nation of the 198Au photopeak in the 

GQS-1 spectra. 

Both of these effects would increase the value for 

gold in GQS-1. The flux monitors contained 0. 2-9 l1g 

of gold. Other experiments indicated that the sp·=cific 

activities ( cpm per g Au) produced in monitors containing from 0.04 to 4 l1g gold varied by less than 2 

percent. Therefore, the first effect should be negligible. In any case, the flux monitors in run 2 contain-ed 

the same amount of gold as GQS-1 and the effect of 

self-shielding should have been the same in both. 

The presence of radiocontamlnation under the 198 Au 

photopeak can be detected by energy discrimination and 

half-life disc r 1m in at ion. Spectra taken with a high 

resolution Ge(Li) detector yielded a value of 412±5 

Kev for the I98Au gamma peak (literature value= 412 

Kev). No significant contamination peaks were observed 

within the energy range covered ::>y the Nai detector. 

To :neasure the half-life, the decay of 1 98Au in one 

sample of GQS-1 was followed for a period of 1 0 days. 

The measured half-life was 2. 7+0.1 days (literature 

value= 2. 7 days). Therefore, anyradiocontaminantfor 

198Au ln the GQS-1 samples must have a half-life in 

the range of 2.6-2.8 days, an energy in the range of 

402-422 Kev, and must be produced in high yield by 

neutron bombardment. The only nuclide that fulfills 

these requirements is 191Ft with a 3.0-day half-life 

and a 410-Kev gamma energy. However, other more 

abundant gammas from 191pt, which should be present 

at 352, 361, and 540 Kev, weremissingfrom the spectra and, therefore, a significant 191 Pt contamination 

was not present. 

The RDA results may be in errorowingto contamination of the GQS-1 samples by gold during the analysis 

or to failure to equilibrate the gold in the standards 

or GQS-1 samples with the radiogold spike. Contami3 

nation as a source of error is unlikely. A reagent 

blank carried through the same procedure at the same 

time showed less than 0. OS percent of the gold present 

in the samples. An attempt was made to eliminate the 

second source of error by adding the radiogold as 

soon as possible after the aqua regia to prevent loss 

of gold on the container wails before equilibration. 

An analysis of variance was carried out for runs 1 

(irradiation 1 ), 2, and 3 using the model, YcR = 11 + 

a.C. +S.R + E:CR· This model employs a two-way classification in which the two criteria are independent and 

there is one observation per cell (Beyer, 1966, p. 106 ). 

The subscript £ refers to the column of data (that is, 

the analytical method), R refers to the row of data 

(the bottle), the YcR 1 s are the measured gold concentrations, l1 is the-grand mean of all the YCR1 s, the 

a.C' s and 8 R 1 s are the column and row effects, and 

the e: CR1 s are the residual effects. a. c is a fixed 

effect because the analytical methods are not a random 

effect produced by variation among bottles (the individual bottles are assumed to be homogeneous). The 

presence of both fixed and random effects makes this 

a "mixed" model. Table 3 shows the results of the 

analysis of variance. The F test was used to evaluate 

the significance of the mean squares for the column 

and row effe~ts as compared to the residual effects. 

The variation among columns is highly significant 

(0.001 < P <0.005, where f is the probability of occurrence for this ratio of column effect mean square to 

residual mean square); the variation among rows is 

negligible (P >0. 2). Stated differently, these analytical 

methods fail to detect any significant heterogeneity 

among the bottles. 

Although heterogeneity among the bottles could not 

be demonstrated in this test, some degree of heterogeneity almost certainly exists. Its detection, however, 

will require the use of an analytical method with considerably better precision than the precision of the 

methods now available. The precision of the methods 

used in this test is about+0.10ppm (parts per million) 

(standard error). Unless- the precision of the method 

used is considerably better than this, the determinations made on a group of bottles should vary little 

more or no more than repeated determinations on the 

same bottle. 

The gold content of GQS- 1 ·has also been measured 

by other analytical techniques. The results are summarized in table 4. These values are in ex c e I I en t 

agreement with those obtained by INAA and RDA. 

It should be noted that the estimated gold content of 

the gold-bearing quartz (table 1) was only one-tenth 

that of GQS-1 (tables 2, 4). About 100mg of gold would 

have had to have been added to account for this increase. Such a level of contamination is extremely 

unlikely. One explanation for the apparent increase 

in content may lie in the particle size-frequency distribution. If most of the gold in the gold-bearing quartz 

was contained in relatively few large grains which 

were not included in the samples taken for analysis, 
then the aqua regia treatment would have made the 

gold content of these grains available for analysis in 

GQS-1. The difficulty of obtaining accurate values for 

gold in heterogeneous materials is apparent, and the 

estimate given in table 1 is thought to be low. 

It is instructive to estimate the average sizes of the 

gold particles in the gold-bearing quartz and in GQS-1. 

Wickman ( 1963) and Wilson ( 1964) published mathematical treatments of this problem. They assumed that 

the gold grains are equivoluminal and distributed within the sample binomially. If the number of grains is 

large, the distribution approximates the normal or 

Gaussian distribution; if the numher is small, the distribution approximates the Poisson distribution. Considering the precision of our data, the method used by 

DeGrazia and Haskin (1964) is adequate to estimate 

the size of the gold particles. They assume a uniform 

particle size and apparently assume a Poisson distribution of the grains. Table 5 shows the computed 

grain diameters and number of grains of gold before 

and after the aqua regia treatment. According to these 

calculations, the aqua regia treatment reduced the 

average diameter of the gold particles by at least an 

order of magnitude and increased the concentration of 

gold grains by at least a factor of 4,000. 

CONCLUSION 

We have succeeded in preparing and calibrating a 

gold-quartz standard which contains about 2.61 ppm 

4 

gold. The coefficient of variation, 5 percent, is well 

within our goal of 10 percent for 200-mg samples, and 

thus, this standard reference material should be useful for the evaluation of analytical techniques for gold. 

The concentration of gold grains in this material is 

greater than 2,200 per g and the average diameter of 

the grains is less than 5 l.l • 

REFERENCES CITED 

Beyer, W. H., ed., 1966, CRC handbook of tables for 

probability and statistics: Cleveland, Chemical 

Rubber Co., 502 p. 

DeGrazia, A. R., and Haskin, Larry, 1964, On the gold 

contents of rocks: Geochim. et Cosmochim. Acta, 

v. 28, no. 5, p. 559-564. 

Flanagan, F. J., 1967, U.S. Geological Survey silicate 

rock standards: Geochim. et Cosmochim. Act a, 

v. 31, no. 3, p. 289-308. 

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

1967, Determination of gold in geologic materials 

by solvent extraction and atomic-absorption spectrometry: U.S. Geol. Survey Circ. 544, 6 p. 

Wickman, F. E., 1963, The amount of material necessary for a trace element analysis: Arkiv Mineralogi 

och Geologi, v. 3, no. 6, p. 131- 1 39. 

Wilson, A. D., 1964, The sampling of silicate rock 

powders for chemical analysis: The Analyst, v. 89, 

no. 1 054, p. 18-30. 
Table 1.--Values for gold content. in parts per million. in the 

gold-bearing quartz powder prior to the aqua regia treatment 

[Analyses by Leo Mei and Carroll Burton by the fire assay-atomic 

absorption method on 15-gram samples] 

Gold content--------------------------

Mean and standard error--------------- Standard deviation-------------------- ~oefficient of variation percent------

0.18, 0.17, 0.44, 0.46, 

0.23, 0.42 

0.32+0.06 

0.14-

44 

Table 2.--Gold content, in parts per million, of the gold-quartz standard GQS-1 

[Analyses by H. T. Millard, Jr., by instrumental neutron activation analysis (INAA) and radioisotope dilution analysis (RDA)] 

GQS-1 

bottle No. 

10--------------------------

20--------------------------

30--------------------------

40--------------------------

50--------------------------

60--------------------------

70--------------------------

80--------------------------

90--------------------------

100--------------------------

Irradiation 1 

2.58 

3.01 

2.77 

2.69 

2.80 

2.65 

2.62 

2.59 

2.65 

2.60 

Mean and standard error---- 2.70!0.04 

Standard deviation--------- .13 

Coefficient of variation--percent--4.8 

INAA (0.2-gram samples) 

Run 1 

Irradiation 2 

2.67 

3.08 

2.75 

2.69 

2.85 

2.69 

2.67 

2.64 

2.63 

2.64 

2.73+0.04 - .14 

5.1 

Run 2 

2.66 

2.61 

2.56 

2.52 

2.69 

2.54 

2.58 

2.54 

2.55 

2.54 

2.58+0.02 - . 06 

2.2 

Grand mean and standard deviation = 2.64+0.10 ppm 

RDA (10-gram 

samples 

Run 3 

2.50 

2.45 

2.55 

2.61 

2.55 

2.61 

2.56 

2.39 

2.63 

2.47 

2.53+0.02 - .08 

3.1 

Table 3.--Analysis of variance for data from runs 1 (irradiation 1), 2, and 3 

Sum of Degrees of Mean 

Source of variation sguares freedom sguare F test 

Column, or method, effects----- 0.143 2 o. 071 8.20 

Row, or bottle, effects-------- .086 9 .010 1.09 

Residual effects--------------- .157 18 .009 

Total--------------------- .386 29 

5 
Table 4.--Gold content, in parts per million, of GQS-1 

[Cyanide leach-atomic absorption and fire assay-atomic absorption (Denver) an- alyses by Claude Huffman. Fire assay-atomic absorption (Washington) analyses 

by P. J. Aruscavage, and neutron activation-fire assay analyses by J. J. 

Rowe and Frederick Simon (Washington). Numbers in parentheses are number of 

samples] 

Sample size 

Type of analysis (grams) 

Cyanide leach-atomic absorption- 15 (4) 

Fire assay-atomic absorption 

(Denver)---------------------- 15 (4) 

Fire assay-atomic absorption 

(Washington)------------------ 15 (2) 

Neutron activation-fire assay--- 0.1 (10) 

Gold content 

2.60, 2.63, 

2.68, 2.65 

2.64, 2.65, 

2.65, 2.64 

2.61, 2.47 

2.71, 2.15, 

2.22, 2.40, 

2.30, 2.02, 

2.23, 3.00, 

2.77, 2.72 

Average 

gold content 

2.64 

2.65 

2.54 

2.45 

Table 5.--Average grain sizes of gold particles in the gold-bearing quartz 

and in GQS-1 as computed from the analytical data 

Gold-bearing 

quartz (before 

aqua regia 

treatment---------

GQS-1 (after aqua 

regia treatment)--

Coefficient 

of 

variation 

(percent) 

45 

<5 

Sample 

size 

(grams) 

15 

.1 

6 

Grain 

diameter 

(microns) 

70 

<5 

Number of grains--

per gram 

0.33 

>2,200 

3 

per em 

0.9 

>6,000 

GPO 869·127