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A Rapid Method for the Determination of Gold

in Rocks, Ores and Other Geological Materials
by F-AAS and GF-AAS After...

Article in MAPAN-Journal of Metrology Society of India · June 2012

DOI: 10.1007/s12647-012-0012-2

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MAPAN-Journal of Metrology Society of India (June 2012) 27(2):87–95
DOI 10.1007/s12647-012-0012-2

ORIGINAL ARTICLE

A Rapid Method for the Determination of Gold in Rocks, Ores

and Other Geological Materials by F-AAS and GF-AAS After
Separation and Preconcentration by DIBK Extraction
for Prospecting Studies
V. Balaram*, R. Mathur, M. Satyanarayanan, S. S. Sawant, P. Roy,
K. S. V. Subramanyam, C. T. Kamala, K. V. Anjaiah, S. L. Ramesh and B. Dasaram
National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad 500 007,
India

Received: 24 August 2011 / Accepted: 28 October 2011 / Published online: 14 June 2012

Ó Metrology Society of India 2012

Abstract: A solvent extraction method using diisobutyle ketone (DIBK) is designed for the accurate and precise esti-
mation of very low concentrations of gold in rocks, ores and other geological samples. 30 g sample was digested using
aqua regia after roasting and gold content was extracted into DIBK phase consisting of AliquatTM 336 and estimated by
flame atomic absorption spectrometer (F-AAS). Samples having gold concentration \0.1 lg/g were estimated using
graphite furnace atomic absorption spectrometer (GF-AAS). Results of DIBK extraction were compared to those obtained
by other well established methods, such as classical Pb-fire assay and methyl isobutyl ketone (MIBK)-AAS methods.
Comparison was also made with results obtained by the direct determination of gold by inductively coupled plasma mass
spectrometry (ICP-MS) technique. The analytical results for international gold reference materials measured by the
proposed method were in close agreement with those obtained by other well established methods and recommended values.
Detection limits (20 ng/g by F-AAS, 0.1 ng/g by GF-AAS and 0.01 ng/g by ICP-MS) of gold (3 r 9 total procedure
blank) is very low and could be further improved by using high pure acids and other reagents.

Keywords: Determination of gold; Solvent extraction; Atomic absorption spectrometry; Fire-assay method; ICP-MS;
Gold exploration; Bore hole samples

1. Introduction deposits is one of the most attractive problems in geo-

chemistry. These studies require the routine estimation of
Gold occurs at extremely low concentrations in earth’s gold at lg/g and ng/g levels in a variety of rock, soil and
crust with an average concentration of 4–5 ng/g levels. ore samples. Distribution of gold in most geological sam-
Gold is also generally distributed in a heterogeneous ples is not homogeneous as it occurs either as grains of
manner occurring as discrete particles and minerals and native gold of varying greatly in size or as an alloy of gold,
existing in solid solutions in sulfides and silicates, and silver and copper often as tellurides associated with base-
spinels [1]. Rapid and accurate estimation of low concen- metal sulfides and other minerals. The maximum size is
trations of gold in rocks, ores and other geological mate- defined by the mesh number of a sieve, but not absolutely,
rials is required in exploration studies [2]. In addition, the because the oblong or thread-like shape of grains enables
understanding of the origin of gold in Earth’s crust, its even larger grains to pass through the sieve. Hence, the
concentration processes and the formation mechanisms of representativeness of the analytical portion is a problem, as
it is dependent not only on the grain size but also on the
grade of gold in a sample [3]. Because of this uneven
distribution, analyses of small amounts of samples gener-
ally lead to inaccurate estimation of gold. As a result,
larger volumes of samples ranging from 10 to 50 g have to
be taken for analysis. It has been shown that methods using
*Corresponding author, E-mail: balaram1951@yahoo.com

123
88 V. Balaram et al.

sample weight of 5–20 g and aqua regia digestion are 2.2. International Geochemical Gold Reference
appropriate for gold exploration studies [4]. Though the Materials
classical fire assay technique with lead collection requires
only a simple fusion furnace and a microbalance, the whole Rock and ore samples having certified values for gold were
procedure is very cumbersome and requires highly skilled obtained from various international agencies and the details
personal. Flame atomic absorption spectrometer (F-AAS) are provided in Table 4.
and graphite furnace atomic absorption spectrometer have
been successfully used for the estimation of gold in geo- 2.3. Reagents
logical samples [5, 6]. The most commonly used method
for the separation of gold from other elements in aqueous The acids and other reagents used were ExcelarTM grade. In
solution is based on the extraction of chloride complex of the case of MIBK extraction, fresh aqua regia was prepared
gold into isobutyl methyl ketone and the gold content is before each experiment, using a 1:3 mixture of concentrated
then measured by F-AAS or GF-AAS [7]. However, to HNO3 and HCl. Double distilled water (18 X M) was used
eliminate the interference of iron, it is necessary to remove throughout these investigations. DIBK and MIBK were
iron by back extraction. Because of this additional step in distilled before use. In the case of MIBK extraction, the
the analytical methodology, the sample throughput is wash solution was prepared by adding 10 mL concentrated
severely affected. In addition, clear separations are not HCl and 10 mL concentrated HBr into a 500 mL volumetric
always achieved between MIBK phase and aqueous pha- flask and bringing to volume with double distilled water.
ses. A few studies in the recent past [8] indicated that Gold calibration solutions of appropriate concentrations
diisobutyle ketone (DIBK) has gained popularity as an were prepared from a 1,000 lg/mL stock solution obtained
alternative solvent to MIBK, as DIBK facilitates cleaner from M/s MBH Analytical Ltd, Herts, UK. SuperflocTM was
separation and extraction of iron is avoided. This paper obtained from Cytec Industries Inc., USA.
evaluates a rapid procedure for the precise estimation of
gold in as large as 30 g samples (to overcome in-homo- 2.4. Field Geological Samples
geneity problems) by F-AAS and GF-AAS after separation
and pre-concentration of gold using DIBK solvent extrac- Samples of 10 kg each were collected in the field from
tion step. A comparison is also made between different Karnataka, India and brought to the laboratory. The sam-
techniques for gold estimation including those of classical ples are sulfidic banded iron formations sometimes asso-
Pb fire-assay method and also direct estimation of gold in ciated with shales/phyllites underlained by basalts/
aqua regia digested samples by ICP-MS. tronjemite-tonalite gneiss (TTG). The gold was observed to
be distributed in the samples as fine grained dissemina-
tions. The major and minor element chemistry of all the
2. Experimental samples in this study is matching with that of standards
used. Each bulk sample was reduced to 600 g of 260 mesh
2.1. Instrumentation for chemical analysis by following the sample preparation
flow-chart described by Balaram et al. 1997 [11].
For this study, a Model Spectra AA 220 (Varian, Australia)
flame atomic absorption spectrometer and a Model Spectra 2.5. Laboratory Sampling Method
AA 880Z with GTA-100 (Varian, Australia) graphite fur-
nace atomic absorption spectrometer with Zeeman back- After powdering the sample to 260 mesh and homogeni-
ground correction were used. Details of instruments are zation, the sample powder was spread over an area of 4 sq
given elsewhere [9]. The instrumental parameters ft on a polythene sheet to form a layer of uniform thick-
(Tables 1 and 2) were optimized for maximum absorbance ness. Square grids of *2 sq in. were made on this layer of
and the readings were taken between 0 and 0.4 absorbance sample using a clean plastic spatula. To obtain 10–30 g
in both cases. ICP-mass spectrometer (ICP-MS) used was samples, small and uniform amounts of samples were
ELAN DRC II (Perkin-Elmer, US). The instrumental and scooped from each grid.
data acquisition parameters are summarized in Table 3.
Prior to analysis, the X,Y and Z positions of the torch, the 2.6. Sample Decomposition and Extraction of Gold
RF power, nebulizer gas-flow and lens voltages were into DIBK
optimized for obtaining maximum possible sensitivity
using 1 ng/mL multi-element solution containing Be, Mg, Each 30 g sample was transferred into a porcelain crucible
Co, In, Ba, Ce, and Pb in 1 % HNO3. Other details are along with 1 g ammonium nitrate, then mixed thoroughly,
provided in [10]. and roasted for 1 h in a muffle furnace at 650 °C. After

123
A Rapid Method for the Determination of Gold in Rocks 89

120 Table 1 Operating parameters of F-AAS

Percent Extraction of Gold into DIBK

110
Wavelength 248.2 nm
100
Lamp current 4 mA
90
Slit width 1 nm
80
Flame type Air-acetylene
70
Air flow-rate 3.50 L/min
60
50
Acetylne flow-rate 1,50 L/min
40
(both for MIBK and DIBK)
30 Solvent uptake rate 2.5 ml/min
20 Measurement time 5.0 s.
10 Background correction D2 Lamp
0 Sampling mode Manual
0 1 2 3 4 5 6 7 8 9 10 11 12
pH

Fig. 1 The effect of pH on the extraction of gold using DIBK

Table 2 Operating parameters of GF-AAS with Zeeman background
correction

roasting, the samples were transferred to 250 mL glass Step Temp (oC) Hold time
beakers and 30 ml of conc. HNO3 and 70 ml of conc. HCl Dry 100 °C 55 s
were added to each sample and each beaker was covered Ash 700 °C 9.0 s
with a watchglass and heated on a hotplate for nearly 2 h. Atomize 2600 °C 4.0 s.
The beakers were removed from the hot plate when the Background correction Zeeman
acid volume comes down to nearly 20 ml to ensure that Measurement mode Peak hight
bulk of the nitric acid is evaporated since nitric acid
Argon flow rate 3 L/min
impedes the gold extraction. Further, if evaporated to
Sample volume 10 ll
dryness, gold may be reduced to lower valency state and
Wavelength 242.8 nm
can not be extracted into DIBK phase. 10 ml of 1 % Su-
Slit width 1 mm
perflocTM solution was added to assist solids settling, and
EHT 300 v
mixed thoroughly and the contents were poured into a
Lamp current 10 mA
200 ml volumetric flask and the volume was made and
Sampling mode Automix
poured back into the beaker. Nearly after 30 min, the solids
settled down. Then 30 ml clear solution is transferred to a
125 mL separating funnel followed by the addition of 5 ml
of 1 % AliquatTM in DIBK into the separating funnel and filled with the respective organic solvent (either DIBK or
shaking of the funnel for 5 min in each case. It was found MIBK) before starting the analysis work. In the case of GF-
that gold is extracted quantitatively over a broad range of AAS analysis, TritonTM X-100 solution was utilized for
pH measured after extraction (i.e. pH 2.5–5.0) as indicated emulsification of the organic solution.
in Fig. 1. After allowing the phases to clearly separate, the In both F-AAS and GF-AAS techniques, the calibrations
DIBK layer containing the Au contents of the sample were were performed using the international geochemical
transferred into 10 ml glass vial with a screw cap and taken gold reference samples. The calibrations for F-AAS and
for AAS measurements. G-FAAS are presented in Fig. 2a, b. Since the calibration
standards and the samples were prepared identically, there
2.7. AAS Measurements and Calibrations Using would be a one-to-one correlation between calibration
International Gold Geochemical Reference standards and samples.
Samples
2.8. ICP-MS Measurements
Absorbance measurements were made at the 242.8 nm
wavelength using D2 background correction in the case of After making the aqua regia digested sample to 200 ml,
F-AAS and Zeeman correction in the case of GF-AAS. The appropriate volume of the sample solution was taken in a
operating parameters (Tables 1, 2) were optimized to get volumetric flask and diluted appropriately to make a final
maximum absorbance for gold in the working range. In the solution of 0.02 % with respect to total dissolved solids
case of F-AAS, the nebulizer spray chamber reservoir was (TDS). 103Rh at an overall concentration of 20 ng/ml was

123
90 V. Balaram et al.

(a) 0.6 2.9. MIBK-AAS Method of Gold Estimation

0.5 GAu-18
10 g of each sample was digested using aqua regia. Gold
was extracted into 10 ml of MIBK and determined by
0.4
Absorbance

F-AAS as described by [7].

0.3
2.10. Pb Fire-Assay Method of Gold Estimation
0.2
GAu-17
The method is widely used all over the world not only for
0.1
GAu-16 analyzing gold but also platinum and palladium. It permits
GAu-15
0 use of large sample (*20 g) which is necessary because of
0 2 4 6 8 10 12 uneven distribution of gold. In these investigations, gold
Concentrations (ng/g) was determined using the procedure described by Kall-
mann and Wobart, 1970 [12].
(b) 0.7 GAu-14

0.6 GAu-7

0.5 3. Results and Discussion

Absorbance

0.4
Solvent extraction methods in favorable circumstances
0.3 combine a high degree of selectivity with the ability to
concentrate minute amounts of a particular element from a
0.2
complex matrix to a concentration level at which it can be
0.1 GAu-1 estimated reliably using an analytical technique or a pro-
GAu-8 cedure. The organic medium in the extraction of gold
0
0 20 40 60 80 100 120 consists of Aliquat 336 in DIBK. Aliquat 336 is a long chain
Concentrations (ng/g) in quaternary amine (tri-capril mono-methylammonium
chloride). Aliquat 336 forms a stable complex with gold and
Fig. 2 Calibration curves of a F-AAS and b GF-AAS generated by 100 % of gold content will be extracted into the organic
the use of international gold geochemical reference samples
phase. It is found that gold extraction is 100 % over a large
range of pH (2.5–5.0) (Fig. 1). The gold content of the
organic phase can be accurately determined by atomic
Table 3 Operating parameters of ELAN DRC II ICP-MS absorption spectrometry. Table 5 presents gold data
RF Power 1100 W obtained on some international gold geochemical reference
Argon gas-flow samples by DIBK extraction method in comparison with
Nebulizer 0.90 L/min certified values.
Auxiliary 1.20 L/min
Plasma 15.00 L/min 3.1. Comparison of MIBK and DIBK Extraction
Lens voltage 7.5 v Methods
Data acquisition mode Peak hopping
Dwell time 50 ls Although, both extraction techniques have several features
Sweeps per reading 40 in common such as, sample roasting and aqua regia diges-
Replicates 6 tion, DIBK procedure has got certain definite advantages
over MIBK procedure. DIBK method can be applied to large
quantities of samples (*30 g). The major advantage of
DIBK extraction over MIBK extraction is, cleaner separa-
used as an internal standard. Rinsing with 5 % HNO3 in tions are achieved and that co-extraction of iron is avoided.
water in between samples was extended to 5 min in order Thus the additional step of back-extraction of iron is avoided,
to reduce uncertainties introduced through instrumental which is vital especially when larger number of samples are
memory. In case of ICP-MS measurements also, calibration to be analyzed as a part of any exploration study. The data
was carried out using a solution of identically prepared presented in Table 6 show, both extraction techniques can
international geochemical gold reference material. provide accurate data when properly applied.

123
 Table 4 Details of international gold reference materials
Sample Sample type Source

GAu 8 Medium grained biotite granite Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 9 Deluvia soil derived from granite Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 10 Soil from a Carline-type gold ore district Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 11 Stream sediment from an epithermal auriferous sulfide mineralized ore district Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 12 Stream sediment from an epithermal auriferous sulfide mineralized ore district Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 13 Soil with micrograined gold Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 14 Soil from carbonate rock with micrograined gold Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 15 Soil over auriferous polymetallic sulfide deposit Institute of geophysical and geochemical exploration, Langfang, Hebei 102849. China
A Rapid Method for the Determination of Gold in Rocks

GAu 16 Poor ore from altered sandstone gold deposit Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 17 Ore from altered pelitic siltstone gold deposit Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
GAu 18 Rich ore from hydrothermal metasomatic gold deposit in shattered fault belt Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 102849. China
Ox 2 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 4 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 5 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 8 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 9 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 11 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
Ox 12 Sodium feldspar with minor quantities of gold bearing quartz Rock Labs Ltd., Auckland, New Zealand
S2 Sodium feldspar with minor quantities of gold bearing quartz and iron pyrites Rock Labs Ltd., Auckland, New Zealand
KH 1 Sodium feldspar with minor quantities of gold bearing quartz and iron pyrites Rock Labs Ltd., Auckland, New Zealand
WG 2 Siliceous oxidized gold ore containing finely disseminated gold Rock Labs Ltd., Auckland, New Zealand
BND 3401.01 High-grade gold geochemical reference material National Physical Laboratory, New Delhi
All other samples used in this study are field samples containing bore hole, open mine and underground mine samples collected from Karnataka, India. These samples include sulfidic-banded
iron formations, quartz veins, quartz-bearing volcanic rocks, shaly sulfidic-banded iron formations and enriched ores
91

123
92 V. Balaram et al.

Table 5 Values of gold in Chinese gold reference samples by DIBK- numbers of samples are being analyzed as a part of an
AAS method exploration study in a limited time.
Sample Concentration of Au
DIBK-AAS methoda Certified value [19] 3.3. Sample Digestion
GAu-8 0.60 ± 0.05 ng/gb 0.5 ± 0.2 ng/g
GAu-9 1.51 ± 0.18 ng/gb 1.5 ± 0.1 ng/g
Samples have to be ground to -200 mesh before
b application of any sample decomposition methods. Aqua
GAu-10 5.51 ± 0.27 ng/g 5.3 ± 0.2 ng/g
regia (HCl:HNO3, 3:1) and HBr-Br2 (0.5 % Br2 in 9 M
GAu-11 11.02 ± 1.40 ng/gb 11.3 ± 0.4 ng/g
HBr2) attacks are the two oxidizing acid leaches that are
GAu-12 21.11 ± 2.50 ng/gb 21.5 ± 1.0 ng/g
b in common use for the extraction of Au from geological
GAu-13 48.72 ± 2.90 ng/g 50.0 ± 2.0 ng/g
materials: [13]. Some workers ([11], [14]) preferred use
GAu-14 105.19 ± 8.40 ng/gb 100.0 ± 3.0 ng/g
of HF during decomposition of the sample to recover Au
GAu-15 290.26 ± 17.43 ng/gb 300.0 ± 20 ng/g
completely. Majority of the cases significant differences
GAu-16 1.11 ± 0.13 lg/gc 1.09 ± 0.03 lg/g
are not observed in the extraction efficiency of gold
GAu-17 3.09 ± 0.30 lg/gc 3.14 ± 0.06 lg/g
when HF was added to the reaction mixture. However,
GAu-18 10.27 ± 0.84 lg/gc 10.00 ± 0.20 lg/g
there have been several published reports [15–18] that
a
Average of three values aqua regia attack is virtually completely efficient in
b
by GF-AAS solubilizing Au from geological samples, particularly
c
by F-AAS when the attack is made after roasting the sample at
650 o C.

3.4. Comparison with Pb Fire-Assay Method

Table 6 A comparison of gold concentrations (lg/g) obtained in a
few field samples from Karnataka, India by F-AAS using both MIBK Pb fire-assay method was employed to effect the separation
and DIBK separation and preconcentration method and pre-concentration of Au prior to the analysis of gold by
Sample Concentration of Au (lg/g) F-AAS. The classical fire-assay method is used widely all
over the world and it is generally accepted as the most
MIBK-FAASa DIBK-FAASa
dependable analytical method for the determination of Au.
VB-1 0.09 ± 0.01 0.01 ± 0.01 The fusion flux is generally varied to make it applicable to
VB-2 1.39 ± 0.08 1.28 ± 0.09 different types of samples [20]. This technique involves the
VB-3 0.35 ± 0.02 0.39 ± 0.02 dissolution of Ag collection bead formed through cupel-
VB-4 0.03 ± 0.01 0.04 ± 0.01 lation in an acid mixture of HNO3 and HCl. Small varia-
VB-5 4.30 ± 0.34 3.73 ± 0.11 tions in the results may be due to the errors introduced at
VB-6 0.24 ± 0.02 0.28 ± 0.01 fire-assay stage, rather than during the measurement step
VB-7 0.95 ± 0.02 1.19 ± 0.06 by F-AAS, since the analyte has been separated from
VB-8 1.62 ± 0.06 1.75 ± 0.14 potential interferences arising from matrix. A comparison
VB-9 2.76 ± 0.12 2.83 ± 0.12 of the gold concentrations obtained by fire-assay with
VB-10 0.23 ± 0.01 0.20 ± 0.01 F-AAS finish are presented in Table 7, 8, 9 and 10 with
a
those obtained by DIBK and MIBK extraction methods and
Average of three determinations, sample are oxide and sulfide faces
ICP-MS on a set of field samples. No significant differ-
banded iron formations
ences are observed between the results obtained by dif-
ferent methods and in fact, the agreement is very good.

3.2. Effect of the Concentration of HCl in Sample

Solution on the Extraction of Gold 4. Conclusion

An HCl concentration of about 1 M was found to give Both MIBK and DIBK extraction have the advantage over
maximum extraction even greater than 99 % efficiency conventional fire-assay methods and save labor and mate-
with 1 min optimum shaking time. It was also found that rial expense, and can be operated by less trained techni-
even 20 % change in HCl concentration (v/v), there was no cians. On the other hand DIBK extraction procedure is
significant change in the extraction efficiency of gold. This superior to MIBK extraction procedure as some interfer-
feature will ensure accurate data particularly when large ence is caused by high contents of iron in the MIBK phase

123
A Rapid Method for the Determination of Gold in Rocks 93

Table 7 Gold concentrations

Sample MIBK-FAAS methoda DIBK-FAAS methodb ICP-MS methodc Certified value
(lg/g)d in a few tailing samples
determined by different Tailing sample-1 0.66 ± 0.005 0.52 ± 0.05 0.61 ± 0.04 –
extraction methods by AAS in
comparison with those obtained Tailing sample-2 0.41 ± 0.05 0.36 ± 0.04 0.37 ± 0.03 –
by ICP-MS method Tailing sample-3 0.26 ± 0.03 0.34 ± 0.03 0.30 ± 0.03 –
Tailing sample-4 0.33 ± 0.03 0.44 ± 0.04 0.40 ± 0.04 –
Tailing sample-5 0.30 ± 0.02 0.35 ± 0.03 0.37 ± 0.04 –
Tailing sample-6 0.36 ± 0.03 0.45 ± 0.03 0.39 ± 0.03 –
Tailing sample-7 0.27 ± 0.03 0.26 ± 0.03 0.30 ± 0.03 –
Tailing sample-8 0.37 ± 0.04 0.36 ± 0.03 0.40 ± 0.03 –
Tailing sample-9 0.38 ± 0.03 0.34 ± 0.04 0.31 ± 0.03 –
Tailing sample-10 0.61 ± 0.05 0.65 ± 0.05 0.66 ± 0.05 –
Tailing sample-11 0.99 ± 0.08 0.93 ± 0.02 0.96 ± 0.08 –
Tailing sample-12 1.05 ± 0.07 1.01 ± 0.08 0.97 ± 0.07 –
a
10 g Sample OX-5 (Standard) 1.03 ± 0.09 1.05 ± 0.08 1.01 ± 0.07 0.97
b
30 g sample OX-9 (Standard) 0.45 ± 0.02 0.44 ± 0.05 0.43 ± 0.04 0.43
c
0.02% Solution taken from OX-11 (Standard) 2.94 ± 0.14 2.81 ± 0.15 2.90 ± 0.11 2.88
DIBK procedure after aqua OX-12 (Standard) 6.60 ± 0.27 6.89 ± 0.34 6.71 ± 0.26 6.86
regia digestion S-2 (Standard) 1.45 ± 0.08 1.38 ± 0.07 1.20 ± 0.08 1.35
d
Average of three S-3 (Standard) 0.68 ± 0.07 0.65 ± 0.05 0.69 ± 0.04 0.6
determinations

Table 8 Concentration of gold

Concentration of gold (lg/g)
(lg/g) obtained in gold
reference materials by MIBK- Sample DIBK-FAAS methoda MIBK-FAAS methoda Certified valueb lg/g
FAAS and DIBK-FAAS
methods in comparison with OX-2 1.40 ± 0.02 1.41 ± 0.03 1.42 ± 0.02
certified values OX-4 0.97 ± 0.03 0.98 ± 0.04 0.96 ± 0.003
OX-8 0.19 ± 0.01 0.17 ± 0.02 0.186 ± 0.008
OX-9 0.48 ± 0.4 0.49 ± 0.05 0.465 ± 0.012
OX-11 2.92 ± 0.25 2.93 ± 0.12 2.94 ± 0.03
a OX-12 6.59 ± 0.39 6.56 ± 0.46 6.60 ± 0.08
Average of six values
b S-2 1.57 ± 0.14 1.55 ± 0.15 1.53 ± 0.03
Certificate of Analysis for
Gold Reference Materials, KH-1 0.87 ± 0.08 0.87 ± 0.09 0.85 ± 0.02
Rocklabs, Auckland, New WG-2 1.39 ± 0.12 1.36 ± 0.11 1.38 ± 0.03
Zealand, 1997, 1998, 1999
c BND 3401.01c 12.22 ± 0.82 12.19 ± 0.90 12.1 ± 0.70
[21]

in the organic phase if not washed sufficiently with wash detection limits and very high throughputs achieved for
solution. Two technicians can complete 50 effective gold estimation in the proposed method, it is suitable for
determinations including two check standards and three the geochemical mapping and prospecting studies on a
repeats taken at random from the batch in a working day regional scale and also for basic research. The method
using DIBK method. The method does not need highly described above has definitely improved the effectiveness
trained staff or sophisticated instrumentation. of gold prospecting studies undertaken by the Geochem-
Data obtained in this work show that DIBK extraction istry Group of National Geophysical Research Institute,
method is much superior to MIBK extraction for the esti- Hyderabad, in some parts in India and Madagascar in the
mation of gold from geological materials. Due to very low recent past.

123
94 V. Balaram et al.

Table 9 Comparison of gold

Samplea Lead fire-assay MIBK-FAAS value DIBK-FAAS value ICP-MS value
concentrations (lg/g) by
GF-AAS finishb
different popular analytical
techniques with those obtained AA-11/1 0.31 ± 0.03 0.28 ± 0.03 0.29 ± 0.04 0.26 ± 0.02
by DIBK-FAAS procedure
AA-5/1 3.19 ± 0.18 2.98 ± 0.23 3.20 ± 0.16 3.09 ± 0.20
AA-9/1 0.42 ± 0.03 0.38 ± 0.04 0.37 ± 0.05 0.40 ± 0.04
AA-12/5 0.45 ± 0.03 0.38 ± 0.04 0.41 ± 0.04 0.42 ± 0.03
SL2C-21 0.20 ± 0.03 0.21 ± 0.03 0.18 ± 0.02 0.18 ± 0.02
SL3C-21 0.11 ± 0.02 0.10 ± 0.01 0.11 ± 0.01 0.11 ± 0.01
SL2T-221 1.43 ± 0.07 1.50 ± 0.18 1.47 ± 0.15 1.45 ± 0.16
SL2T-241 1.45 ± 0.09 1.39 ± 0.12 1.50 ± 0.12 1.47 ± 0.11
SL2T-311 0.14 ± 0.02 0.12 ± 0.01 0.13 ± 0.01 0.12 ± 0.01
SL2T-341 0.35 ± 0.03 0.30 ± 0.02 0.39 ± 0.03 0.32 ± 0.02
SL3T-151 0.07 ± 0.01 0.05 ± 0.01 0.07 ± 0.01 0.08 ± 0.01
SL3T-221 0.47 ± 0.03 0.43 ± 0.04 0.50 ± 0.05 0.51 ± 0.04
HMT-2041 1.33 ± 0.11 1.29 ± 0.15 1.25 ± 0.15 1.32 ± 0.15
HMT-2051 0.50 ± 0.05 0.47 ± 0.04 0.45 ± 0.05 0.45 ± 0.05
a
Field samples from HMT-3091 0.03 ± 0.01 0.02 ± 0.01 0.03 ± 0.01 0.03 ± 0.01
Karnataka, India
b
HMT-5093 0.37 ± 0.03 0.36 ± 0.03 0.35 ± 0.03 0.39 ± 0.04
[7]

Table 10 Comparison of gold concentrations in borehole samples by different popular analytical techniques at different laboratories with those
obtained by DIBK-F-AAS procedure
S. No. Borehole Gold concentration (lg/g)
sample no.
MSPL, Hospet Pb fire NGRI, Hyderabad Shiva lab, Bangalore DIBK F-AAS
assay- F-AAS Pb fire-assay ICP-MS Method
MIBK Pb fire assay
F-AAS F-AAS

1. S-101 3.20 ± 0.20 3.17 ± 0.28 4.34 ± 0.19 3.06 ± 0.16 3.21 ± 0.21
2. S-102 0.35 ± 0.02 0.36 ± 0.02 0.30 ± 0.02 0.36 ± 0.02 0.35 ± 0.03
3. S-103 1.30 ± 0.09 1.34 ± 0.10 1.38 ± 0.06 1.38 ± 0.07 1.36 ± 0.09
4. S-107 3.40 ± 0.17 3.42 ± 0.44 3.49 ± 0.26 3.22 ± 0.19 3.37 ± 0.16
5. S-107a 1.40 ± 0.06 1.42 ± 0.09 1.44 ± 0.08 1.33 ± 0.08 1.41 ± 0.08
6. S-201 0.30 ± 0.02 0.22 ± 0.01 0.31 ± 0.02 0.26 ± 0.02 0.28 ± 0.22
7. S-201a 4.80 ± 0.19 5.11 ± 0.25 5.44 ± 0.32 4.95 ± 0.24 5.09 ± 0.22
8. S-202 1.30 ± 0.08 1.74 ± 0.12 1.94 ± 0.07 1.52 ± 0.12 1.69 ± 0.10
9. S-203 0.10 ± 0.01 0.03 ± 0.01 0.05 ± 0.01 0.04 ± 0.01 0.07 ± 0.01
a
Sample at a different depths

Acknowledgments The authors thank the Director, National Geo- [3] E.H. Clifton, R.E. Hunter, F.J. Swanson and R.L. Philips,
physical Research Institute, Hyderabad, for permitting the publication Sample Size and Meaningful Gold Analysis, U.S. Geol. Surv.
of this paper. PR and CTK thank CSIR, New Delhi, for providing RA Prof. Pap. 625-C, (1969) 17p.
fellowships. The National Physical Laboratory, New Delhi, is thanked [4] E. Kontas Ed.; Analytical Methods for Determining Gold in
for providing high-grade gold geochemical reference material (BND Geological Samples. Report of Investigation, Geological Survey
3401.01). of Finland, (1993) p. 43.
[5] C.E. Thompson, H.M. Nakagawa and G.H. Van Sickle, Rapid
Analysis of Gold in Geological Materials: US Geological Sur-
vey, Prof. Pap. 600-B, (1968) B130–B132.
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