SIST ISO 10378:2016

INTERNATIONAL ISO
STANDARD 10378
Third edition
2016-02-15
Copper, lead and zinc sulfide
concentrates — Determination of gold
and silver — Fire assay gravimetric
and flame atomic absorption
spectrometric method
Concentrés de sulfure de cuivre, de plomb et de zinc — Dosage de
l’or et de l’argent — Méthode gravimétrique par essai au feu et
spectrométrie d’absorption atomique dans la flamme
Reference number
ISO 10378:2016(E)
©
ISO 2016

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ISO 10378:2016(E)

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ISO 10378:2016(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Principle . 2
3.1 General . 2
3.2 Fusion . 2
3.3 Cupellation . 2
3.4 Parting . 2
3.5 Retreatment . 2
3.6 Correction for blank contamination . 2
4 Reagents . 2
5 Apparatus . 4
6 Sample . 5
6.1 Test sample . 5
6.2 Test portion . 5
7 Procedure. 6
7.1 Number of determinations . 6
7.2 Trial fusion . 6
7.3 Blank tests . 6
7.4 Charge preparation . 6
7.5 Primary fusion . 7
7.6 Cupellation . 8
7.7 Retreatment of residues . 8
7.8 Determination of gold in the primary bead . 9
7.9 Determination of gold and silver in secondary beads and blanks, and of silver in prills .10
7.10 Determination of silver in the parting solution .11
8 Expression of results .12
8.1 Mass fraction of gold .12
8.2 Mass fraction of silver .13
9 Precision .14
9.1 Expression of precision .14
9.2 Method for obtaining the final result (see Annex H) .15
9.3 Precision between laboratories .15
9.4 Check of trueness .17
9.4.1 General.17
9.4.2 Type of certified reference material (CRM) or reference material (RM) .18
10 Test report .18
Annex A (normative) Procedure for the preparation and determination of the mass of a
predried test portion .19
Annex B (normative) Trial fusion .21
Annex C (normative) Blank determination .22
Annex D (normative) Inquartation .23
Annex E (normative) Determination of vaporization loss of silver during the
cupellation process .24
Annex F (normative) Sulfuric acid — Parting .25
Annex G (normative) Determination of impurities in parting solutions and washings .27
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ISO 10378:2016(E)

Annex H (normative) Flowsheet of the procedure for the acceptance of analytical values for
test samples (see 9.2) .31
Annex I (informative) Flowsheet of the method .32
Annex J (informative) Roasting method .33
Annex K (informative) Guide to the preparation of dilutions for the determination of silver
in parting solutions and residues .34
Annex L (informative) Derivation of precision equations .35
Bibliography .50
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ISO 10378:2016(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
This third edition cancels and replaces the second edition (ISO 10378:2005), in which 6.2 has been
technically revised and the warning notice in A.3.1 has been updated.
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ISO 10378:2016(E)

Introduction
This International Standard describes a method for the determination of the mass fraction of gold
and silver in copper, lead, and zinc sulfide concentrates. This International Standard was prepared
to enable laboratories to determine the mass fraction of gold and silver in suitable samples using
instrumental methods.
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INTERNATIONAL STANDARD ISO 10378:2016(E)
Copper, lead and zinc sulfide concentrates —
Determination of gold and silver — Fire assay gravimetric
and flame atomic absorption spectrometric method
WARNING — This International Standard may involve hazardous materials, operations,
and equipment. It is the responsibility of the user of this International Standard to establish
appropriate health and safety practices and determine the applicability of regulatory limitations
prior to use.
1 Scope
This International Standard specifies a fire assay gravimetric and flame atomic absorption
spectrometric method for the determination of the mass fraction of gold and silver in copper, lead, and
zinc sulfide concentrates as follows.
— Copper concentrates
The method is applicable to the determination of mass fractions of gold from 0,5 g/t to 300 g/t and
of mass fractions of silver from 25 g/t to 1 500 g/t in copper sulfide concentrates containing mass
fractions of copper from 15 % to 60 %.
— Lead concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 25 g/t and
of mass fractions of silver from 200 g/t to 3 500 g/t in lead sulfide concentrates containing mass
fractions of lead from 10 % to 80 %.
— Zinc concentrates
The method is applicable to the determination of mass fractions of gold from 0,1 g/t to 12 g/t and
of mass fractions of silver from 10 g/t to 800 g/t in zinc sulfide concentrates containing mass
fractions of zinc up to 60 %.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4787, Laboratory glassware — Volumetric instruments — Methods for testing of capacity and for use
ISO 9599, Copper, lead and zinc sulfide concentrates — Determination of hygroscopic moisture in the
analysis sample — Gravimetric method
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ISO 10378:2016(E)

3 Principle
3.1 General
Fire assaying for the determination of gold and silver comprises a series of steps to separate firstly the
precious metals from most of the associated metals, followed by separation of the gold from silver and
other metals pre-concentrated into a precious-metal alloy.
The stages that comprise the determinations are described in 3.2 to 3.6 inclusive.
3.2 Fusion
The samples are fused in a crucible after mixing with a litharge-based flux which, under reducing
conditions, collects the precious metals in a metallic lead button.
3.3 Cupellation
The base metals present in the lead button are substantially separated from the precious metals by
oxidizing fusion. Cupellation produces a bead largely comprising a silver-gold alloy with small quantities
of other metals.
3.4 Parting
Gold is separated from the primary bead by treatment with nitric acid. The gold prill is weighed. Gold
prills having a mass less than 50 μg are dissolved in aqua regia and the gold is determined by atomic
absorption spectrometry (AAS). Silver is determined in the parting solution by AAS.
3.5 Retreatment
All residues are retreated to maximize the recovery of gold and silver. The addition of collectors for
either gold or silver is not required, as both metals are present in sufficient amounts to be readily
visible after the cupellation stage. The second bead is dissolved in acids followed by analysis of both
metals by AAS.
3.6 Correction for blank contamination
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents
without the test portion.
4 Reagents
During the analysis, use only reagents of recognized analytical grade and water that complies with
grade 2 of ISO 3696.
4.1 Sodium carbonate, anhydrous.
4.2 Litharge (PbO), assay grade having a mass fraction of gold of less than 0,01 g/t and a mass fraction
of silver of less than 0,2 g/t.
4.3 Silica, precipitated.
4.4 Potassium nitrate or sodium nitrate
NOTE If sodium nitrate is used, the masses specified for potassium nitrate will have to be modified:
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ISO 10378:2016(E)

85,0
gofKNO ×= gofNaNO
33
101,1
4.5 Flour
4.6 Borax, fused anhydrous sodium tetraborate (borax glass powder).
4.7 Nitric acid, concentrated (ρ 1,42 g/ml), chloride concentration <0,5 μg/ml.
20
4.8 Nitric acid, diluted 1+1.
Slowly add 500 ml of concentrated nitric acid (4.7) to 500 ml of water, while stirring.
4.9 Lead, foil, having a mass fraction of gold of less than 0,01 g/t and a mass fraction of silver of less
than 0,2 g/t.
4.10 Silver, of minimum purity 99,99 %.
4.11 Hydrochloric acid (ρ 1,16 g/ml to 1,19 g/ml).
20
4.12 Thiourea, 10 g/l solution.
Add 1 g of thiourea to 100 ml of water.
4.13 Aqua regia
Mix three parts of hydrochloric acid (4.11) with one part of nitric acid (4.7). Prepare freshly as required.
4.14 Standard solutions
Standard solutions should be prepared at the same ambient temperature as that at which the
determinations will be conducted.
4.14.1 Silver, standard stock solution A (500 μg of Ag/ml).
Weigh 0,500 0 g of silver metal to the nearest 0,1 mg. Transfer to a 100 ml beaker, add 20 ml of diluted
nitric acid (4.8), and warm to dissolve. Cool and add 20 ml of concentrated nitric acid (4.7). Transfer to
a 1 000 ml volumetric flask, fill up with water nearly to the mark, mix and cool to room temperature;
then fill up exactly to the mark and mix again.
4.14.2 Silver, standard solution B (50 μg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask, fill up
with water nearly to the mark, mix and cool to room temperature; then fill up exactly to the mark
and mix again.
Prepare a fresh solution per batch.
4.14.3 Gold, standard solution (1 000 μg of Au/ml).
Weigh 1,000 g of gold metal to the nearest 0,1 mg. Transfer to a 200 ml beaker, add 25 ml of aqua regia
solution (4.13), and warm to dissolve. Cool and transfer to a 1 000 ml volumetric flask. Add 75 ml of
hydrochloric acid (4.11), fill up nearly to the mark with water, mix and cool to room temperature; then
fill up exactly to the mark and mix again.
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ISO 10378:2016(E)

4.14.4 Gold and silver, standard solution (100 μg of Au/ml + 50 μg of Ag/ml).
Pipette 10,00 ml of silver standard stock solution A (4.14.1) into a 100 ml volumetric flask. Add 40 ml
of hydrochloric acid (4.11). Pipette 10,00 ml of gold standard solution (4.14.3) into the volumetric flask.
Fill up nearly to the mark with water, mix and cool to room temperature; then fill up exactly to the
mark and mix again.
4.15 Calibration solutions
Calibration solutions should be prepared at the same ambient temperature as that at which the
determinations will be conducted.
4.15.1 Gold/silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 5,00 ml, and 10,00 ml of gold and silver standard solution (4.14.4) into a
series of 100 ml one-mark volumetric flasks.
Add 40 ml of hydrochloric acid (4.11) to each flask, fill up nearly to the mark with water, mix and cool to
room temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 μg of Au/ml, 1,00 μg of Au/ml, 2,00 μg of Au/ml, 5,00 μg of Au/ml, and
10,00 μg of Au/ml; and 0,0 μg of Ag/ml, 0,50 μg of Ag/ml, 1,00 μg of Ag/ml, 2,50 μg of Ag/ml, and 5,00 μg
of Ag/ml, and shall be freshly prepared.
4.15.2 Silver calibration solutions
Pipette 0,0 ml, 1,00 ml, 2,00 ml, 4,00 ml, 6,00 ml, 8,00 m,l and 10,00 ml of silver standard solution B
(4.14.2) into a series of 100 ml volumetric flasks. Add 10 ml of nitric acid (4.7), fill up nearly to the mark
with water, mix and cool to room temperature; then fill up exactly to the mark and mix again.
These solutions contain 0,0 μg of Ag/ml, 0,50 μg of Ag/ml, 1,00 μg of Ag/ml, 2,00 μg of Ag/ml, 3,00 μg of
Ag/ml, 4,00 μg of Ag/ml, and 5,00 μg of Ag/ml, and shall be freshly prepared.
Contamination by gold and silver impurities in the reagents is corrected for by fusing the reagents
without the test portion.
5 Apparatus
5.1 Assay crucible furnace, with a maximum required operating temperature of 1 200 °C.
5.2 Muffle furnace, with a maximum required operating temperature of 1 100 °C. Temperature
indication, automatic temperature control, and controlled air flow are preferable.
5.3 Assay crucibles, made of fire clay, of nominal capacity 200 ml to 600 ml, capable of withstanding
corrosion by the samples and fluxes at 1 100 °C.
The crucible shall be of such a size that the charge does not fill the crucible to a depth greater than 3/4
the depth of the crucible.
5.4 Cupels, made of magnesium oxide, or bone-ash cupels having a nominal capacity of 50 g of molten
lead.
The inside bottom of the cupel shall be concave, as recommended in the fire assay texts referred to in
the Bibliography.
5.5 Conical mould, made of cast iron, of sufficient capacity to contain all of the molten lead plus slag
from the crucible fusion.
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ISO 10378:2016(E)

5.6 Analytical balance, sensitive to 1 mg.
5.7 Microbalance, sensitive to 1 μg or less.
5.8 Ordinary laboratory glassware, washed free of chlorides.
5.9 Volumetric glassware, of class A complying with ISO 385, ISO 648, and ISO 1042, and used in
accordance with ISO 4787.
5.10 Atomic absorption spectrometer (AAS), equipped with background correction and a glass bead
in the spray chamber.
5.11 Inductively coupled plasma (ICP) atomic emission spectrometer.
5.12 Pulverizer.
5.13 Hotplate.
6 Sample
6.1 Test sample
Prepare an air-equilibrated test sample in accordance with ISO 9599.
NOTE A test sample is not required if predried test portions are to be used (see Annex A).
6.2 Test portion
Taking multiple increments, extract a test portion from the test sample in such a manner that it is
representative of the whole contents of the dish or tray. Weigh to the nearest 1 mg approximately 10 g
to 20 g of the test sample. At the same time as test portions are being weighed for analysis, weigh test
portions for the determination of hygroscopic moisture in accordance with ISO 9599.
NOTE 1 The precision of determination of the mass of contained gold in a lot is the sum of sampling and
analytical precision. The presence of particulate gold in a concentrate contributes to imprecision of the analytical
component of total precision. When it has been established that the presence of particulate gold in a concentrate
causes unacceptable imprecision, the following mixing and sampling methods are recommended.
a) Mix the sample by either of the following preferred mixing methods as described in ISO 12743:2006:
— 15.3.2 c), strip mixing;
— 15.3.2 e), riffle, or rotary divider.
Mixing methods in items a), b), and d) in ISO 12743:2006, 15.3.2 are not recommended.
b) Extract a test portion from the test sample using either of the following methods described in ISO 12743:2006:
— 15.4.1 a), rotary sample division;
— 15.4.1 f), ribbon division.
Methods in items b) to e) and g) in ISO 12743:2006, 15.4.1 are not recommended.
Alternatively, the method specified in Annex A may be used to prepare predried test portions directly
from the laboratory sample.
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ISO 10378:2016(E)

If a mass fraction of arsenic above 2 % is present in the sample, this element should be removed by
following the procedure in Annex J; otherwise, interference with the cupellation stage may occur.
NOTE 2 If the mass fraction of copper is greater than 30 %, a 10 g or 15 g test portion is preferable (see the
fourth paragraph of 7.4).
For lead concentrates, the test portion should be 10 g to ensure an adequate supply of lead.
7 Procedure
7.1 Number of determinations
Carry out the determinations at least in duplicate, as far as possible under repeatability conditions, on
each test sample.
NOTE 1 Repeatability conditions exist where mutually independent test results are obtained with the same
method on identical test material in the same laboratory by the same operator using the same equipment, within
short intervals of time.
NOTE 2 In the case where the ratio of silver to gold does not exceed 2,5 to 1 and the procedure specified in
7.10 is carried out for the silver determination, separate determinations for gold and silver will be necessary (see
Annex D). Four test portions, therefore, are required, i.e. two for determinations of gold and two for silver.
NOTE 3 Annex I contains a flowsheet of the method.
7.2 Trial fusion
Carry out a trial fusion as described in Annex B, to ensure that the mass of the lead button is between
30 g and 45 g.
7.3 Blank tests
Carry out a reagent blank test as described in Annex C in parallel with the analysis, using the same
quantities of all reagents, with the addition of sufficient flour (4.5) to the flux to give a lead button of
between 30 g and 45 g. Omit the test portion and the potassium nitrate. The total blank should not
exceed 5 μg of gold or 100 μg of silver.
7.4 Charge preparation
Determine the mass of potassium nitrate (4.4) and flour (4.5) required in the charge, as indicated by
the trial fusion (see Annex B), and include this reagent in the flux mixture. Typical masses of the flux
components for copper, lead, and zinc concentrates are shown in Tables 1 to 3 respectively.
Thoroughly mix the test portion with a flux.
Intimate mixing of flux components and the test portion is very important. All flux components should
be in a finely divided state with a preferred particle size of less than 0,5 mm.
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ISO 10378:2016(E)

Table 1 — Typical masses of flux components for copper concentrates
Mass
Flux components
g
Sodium carbonate (4.1) 30
Litharge (4.2) 210
Silica (4.3) 25
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 20
If the mass fraction of copper is greater than 30 %, the mass of litharge should be 30 times that of
copper plus 35 g for the lead button. Alternatively, a 10 g or 15 g test portion can be used while retaining
the flux composition given in Table 1. If there are difficulties experienced in achieving a fluid melt, the
amount of silica recommended in Table 1 can be reduced to 19 g, while including 6 g borax.
Table 2 — Typical masses of flux components for lead concentrates
Flux components Mass, g
Sodium carbonate (4.1) 30
Litharge (4.2) 100
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test portion 10
Table 3 — Typical masses of flux components for zinc concentrates
Flux components Mass, g
Sodium carbonate (4.1) 30
Litharge (4.2) 120
Silica (4.3) 10
Borax (4.6) 10
Potassium nitrate (4.4) —
Flour (4.5) —
Test p
...