Handbook of flotation reagents chemistry theory and practice volume 2 flotation of gold PGM and oxide minerals

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Introduction

Volume 2 of the ‘Flotation Reagents Handbook’ is a continuation of Volume 1, and presents
fundamental and practical knowledge on flotation of gold, platinum group minerals and the
major oxide minerals, as well as rare earths.
Rather than reiterating what is well known about flotation of gold, PGMs and oxide
minerals, emphasis has been placed on the separation methods which are not so effective
when using conventional treatment processes. These difficult separation methods are
largely attributed to problems with selectivity between valuable minerals and gangue
minerals, especially in the flotation of oxide ores and base metal oxides, such as copper,
lead and zinc oxide ores.
Literature on flotation of gold, PGMs, rare earths and various oxides is rather limited,
compared to literature on treatment of sulphide-bearing ores. As mentioned earlier, the
main problem arises from the presence of gangue minerals in the ore, which have flotation
properties similar to those of valuable minerals. These minerals have a greater floatability
than that of pyrochlore or columbite. In the beneficiation of oxide minerals, finding a
selectivity solution is a major task.
This volume of the Handbook is devoted to the beneficiation of gold, platinum group
minerals and, most important, oxide minerals. The book contains details on flotation
properties of the major minerals. The fundamental research carried out by a number of
research organizations over the past several decades is also contained in this book.
Commercial plant practices for most oxide minerals are also presented.
The major objective of this volume of the Handbook is to provide practical mineral
processors that are faced with the problem of beneficiation of difficult-to-treat ores, with a

comprehensive digest of information available, thus enabling them to carry out their
development testwork in a more systematic manner and to assist in the control of operating
plants.
This book will also provide valuable background information for researchers, university
students and professors. The book contains comprehensive references of worldwide literature on the subject.
New technologies for most of the oxide minerals included in this volume were developed
by the author.

ix


– 17 –

Flotation of Gold Ores

17.1

INTRODUCTION

The recovery of gold from gold-bearing ores depends largely on the nature of the deposit,
the mineralogy of the ore and the distribution of gold in the ore. The methods used for the
recovery of gold consist of the following unit operations:
1.

2.

3.

4.

The gravity preconcentration method, which is used mainly for recovery of gold from
placer deposits that contain coarse native gold. Gravity is often used in combination
with flotation and/or cyanidation.
Hydrometallurgical methods are normally employed for recovery of gold from
oxidized deposits (heap leach), low-grade sulphide ores (cyanidation, CIP, CIL) and
refractory gold ores (autoclave, biological decomposition followed by cyanidation).
A combination of pyrometallurgical (roasting) and hydrometallurgical route is used
for highly refractory gold ores (carbonaceous sulphides, arsenical gold ores) and the
ores that contain impurities that result in high consumption of cyanide, which have to
be removed before cyanidation.
The flotation method is a technique widely used for the recovery of gold from goldcontaining copper ores, base metal ores, copper nickel ores, platinum group ores and
many other ores where other processes are not applicable. Flotation is also used for
the removal of interfering impurities before hydrometallurgical treatment (i.e. carbon
prefloat), for upgrading of low-sulphide and refractory ores for further treatment.
Flotation is considered to be the most cost-effective method for concentrating gold.

Significant progress has been made over the past several decades in recovery of gold using
hydrometallurgical methods, including cyanidation (CIL, resin-in-pulp), bio-oxidation, etc.
All of these processes are well documented in the literature [1,2] and abundantly described.
However, very little is known about the flotation properties of gold contained in various ores
and the sulphides that carry gold. The sparse distribution of discrete gold minerals, as well
as their exceedingly low concentrations in the ore, is one of the principal reasons for the lack
of fundamental work on the flotation of gold-bearing ores.
In spite of the lack of basic research on flotation of gold-bearing ores, the flotation
technique is used not only for upgrading of low-grade gold ore for further treatment, but

1


2

17.

Flotation of Gold Ores

also for beneficiation and separation of difficult-to-treat (refractory) gold ores. Flotation is
also the best method for recovery of gold from base metal ores and gold-containing PGM
ores. Excluding gravity preconcentration, flotation remains the most cost-effective bene­
ficiation method.
Gold itself is a rare metal and the average grades for low-grade deposits vary between 3
and 6 ppm. Gold occurs predominantly in native form in silicate veins, alluvial and placer
deposits or encapsulated in sulphides. Other common occurrences of gold are alloys with
copper, tellurium, antimony, selenium, platinum group metals and silver. In massive
sulphide ores, gold may occur in several of the above forms, which affects flotation
recovery.
During flotation of gold-bearing massive sulphide ores, the emphasis is generally placed
on the production of base metal concentrates and gold recovery becomes a secondary
consideration. In some cases, where significant quantities of gold are contained in base
metal ores, the gold is floated from the base metal tailings.
The flotation of gold-bearing ores is classified according to ore type (i.e. gold ore, gold
copper ore, gold antimony ores, etc.), because the flotation methods used for the recovery
of gold from different ores is vastly different.

17.2

GEOLOGY AND GENERAL MINERALOGY OF GOLD-BEARING ORES

The geology of the deposit and the mineralogy of the ore play a decisive role in the
selection of the best treatment method for a particular gold ore. Geology of the gold
deposits [3] varies considerably not only from deposit to deposit, but also within the

deposit. Table 17.1 shows major genetic types of gold ores and their mineral composition.
More than 50% of the total world gold production comes from clastic sedimentary deposits.

Table 17.1
Common genetic types of gold deposits
Ore type

Description

Magmatic

Gold occurs as an alloy with copper, nickel and platinum group metals.
Typically contains low amount of gold
Placer deposits, in general conglomerates, which contain quartz, sericite,
chlorite, tourmaline and sometimes rutile and graphite. Gold can be
coarse. Some deposits contain up to 3% pyrite. Size of the gold contained
in pyrite ranges from 0.01to 0.07 μm
This type contains a variety of ores, including(a) gold-pyrite ores, (b) goldcopper ores, (c) gold-polymetallic ores and (d) gold oxide ore, usually
upper zone of sulphide zones. The pyrite content of the ore varies from
3% to 90%. Other common waste minerals are quartz, aluminosilicates,
dolomite etc.
Sometimes are very complex and refractory gold ores. Normally the ores
are composed of quartz, sericite, chlorites, calcite and magnetite.
Sometimes the ore contains wolframite and scheelite

Ores in clastic
sedimentary rock
Hydrothermal

Metasomatic or scarn

ores


17.3

Flotation Properties of Gold Minerals and Factors Affecting Floatability

3

Table 17.2
Major gold minerals
Group

Mineral

Chemical formula

Impurity content

Native gold and
its alloys

Native gold
Electrum
Cuproauride
Amalgam
Bismuthauride

Au
Au/Ag

Au/Cu
Hg/Au
Au/Bi

0–15% Ag
15–50% Ag
5–10% Cu
10–34% Au
2–4% Bi

Tellurides

Calaverite
Sylvanite
Petzite
Magyazite

AuTe3
(Au,Ag)Te2
(Au,Ag)Te
Au(Pb,Sb,Fe)(S,Te11)

Unstable

Krennerite
Platinum gold
Rhodite
Rhodian gold
Aurosmiride

AuTe2(Pt,Pl)
AuPt
AuRh
AuRh
Au,Ir,Os

Up to 10% Pt
30–40% Rh
5–11% Rh
5% Os + 5–7% Ir

Gold associated
with platinum
group metals

In many geological ore types, several sub-types can be found including primary ores,
secondary ores and oxide ores. Some of the secondary ores belong to a group of highly
refractory ores, such as those from Nevada (USA) and Chile (El Indio). The number of
old minerals and their associations are relatively small and can be divided into the
following three groups: (a) native gold and its alloys, (b) tellurides and (c) gold
associated with platinum group metals. Table 17.2 lists the major gold minerals and
their associations.

17.3 FLOTATION PROPERTIES OF GOLD MINERALS AND FACTORS
AFFECTING FLOATABILITY
Native gold and its alloys, which are free from surface contaminants, are readily floatable
with xanthate collectors. Very often however, gold surfaces are contaminated or covered
with varieties of impurities [4]. The impurities present on gold surfaces may be argentite,
iron oxides, galena, arsenopyrite or copper oxides. The thickness of the layer may be of the
order of 1–5 µm. Because of this, the flotation properties of native gold and its alloys vary

widely. Gold covered with iron oxides or oxide copper is very difficult to float and requires
special treatment to remove the contaminants.
Tellurides, on the other hand, are readily floatable in the presence of small quantities of
collector, and it is believed that tellurides are naturally hydrophobic. Tellurides from
Minnesota (USA) were floated using dithiophosphate collectors, with over 9% gold
recovery.


4

17.

Flotation of Gold Ores

30

Adsorption of xanthate (%)

3
25
20

2

15
10
1
5
0
0

10

20

30

40

50

60

70

80

Conditioning time with xanthate (minutes)

Figure 17.1 Relationship between adsorption of xanthate on gold and conditioning time in the
presence of various concentrations of xanthate.

Flotation behaviour of gold associated in the platinum group metals is apparently the
same as that for the platinum group minerals (PGMs) or other minerals associated with the
PGMs (i.e. nickel, pyrrhotite, copper and pyrite). Therefore, the reagent scheme developed
for PGMs also recovers gold. Normally, for the flotation of PGMs and associated gold, a
combination of xanthate and dithiophosphate is used, along with gangue depressants guar
gum, dextrin or modified cellulose. In the South African PGM operations, gold recovery
into the PGM concentrate ranges from 75% to 80%.
Perhaps the most difficult problem in flotation of native gold and its alloys is the

tendency of gold to plate, vein, flake and assume many shapes during grinding. Particles
with sharp edges tend to detach from the air bubbles, resulting in gold losses. This shape
factor also affects gold recovery using a gravity method.
In flotation of gold-containing base metal ores, a number of modifiers normally used for
selective flotation of copper lead, lead zinc and copper lead zinc have a negative effect on
the floatability of gold. Such modifiers include ZnSO4·7H2O, SO2, Na2S2O5 and cyanide
when added in excessive amounts.
The adsorption of collector on gold and its floatability is considerably improved by the
presence of oxygen. Figure 17.1 shows the relationship between collector adsorption,
oxygen concentration in the pulp and conditioning time [4]. The type of modifier and the
pH are also important parameters in flotation of gold.

17.4

FLOTATION OF LOW-SULPHIDE-CONTAINING GOLD ORES

The beneficiation of this ore type usually involves a combination of gravity concentra­
tion, cyanidation and flotation. For an ore with coarse gold, gold is often recovered by
gravity and flotation, followed by cyanidation of the reground flotation concentrate. In


17.6

Flotation of Carbonaceous Clay-Containing Gold Ores

5

some cases, flotation is also conducted on the cyanidation tailing. The reagent combina­
tion used in flotation depends on the nature of gangue present in the ore. The usual
collectors are xanthates, dithiophosphates and mercaptans. In the scavenging section of

the flotation circuit, two types of collector are used as secondary collectors. In the case
of a partially oxidized ore, auxiliary collectors, such as hydrocarbon oils with sulphidi­
zer, often yield improved results. The preferred pH regulator is soda ash, which acts as a
dispersant and also as a complexing reagent for some heavy metal cations that have a
negative effect on gold flotation. Use of lime often results in the depression of native
gold and gold-bearing sulphides. The optimum flotation pH ranges between 8.5 and
10.0. The type of frother also plays an important role in the flotation of native gold and
gold-bearing sulphides. Glycol esters and cyclic alcohols (pine oil) can improve gold
recovery significantly.
Amongst the modifying reagents (depressant), sodium silicate starch dextrins and low­
molecular-weight polyacrylamides are often selected as gangue depressants. Fluorosilicic
acid and its salts can also have a positive effect on the floatability of gold. The presence of
soluble iron in a pulp is highly detrimental for gold flotation. The use of small quantities of
iron-complexing agents, such as polyphosphates and organic acids, can eliminate the
harmful effect of iron.

17.5

FLOTATION OF GOLD-CONTAINING MERCURY/ANTIMONY ORES

In general, these ores belong to a group of difficult-to-treat ores, where cyanidation
usually produces poor extraction. Mercury is partially soluble in cyanide, which
increases consumption and reduces extraction. A successful flotation method [5] has
been developed using the flowsheet shown in Figure 17.2, where the best metallurgical
results were obtained using a three-stage grinding and flotation approach. The
metallurgical results obtained with different grinding configurations are shown in
Table 17.3.
Flotation was carried out at an alkaline pH, controlled by lime. A xanthate collector with
cyclic alcohol frother (pine oil, cresylic acid) was shown to be the most effective. The use
of small quantities of a dithiophosphate-type collector, together with xanthate was

beneficial.

17.6

FLOTATION OF CARBONACEOUS CLAY-CONTAINING GOLD ORES

These ores belong to a group of refractory gold ores, where flotation techniques can be
used to (a) remove interfering impurities before the hydrometallurgical treatment process
of the ore for gold recovery, and (b) to preconcentrate the ore for further pyrometallur­
gical or hydrometallurgical treatment. There are several flotation methods used
for beneficiation of this ore type. Some of the most important methods are described
below.


6

17.

Flotation of Gold Ores

Feed
Grind 1
Classification 1
Classification 2

Grind 2

Scalp Float

Classification

Flotation 1
Cleaner

Classification
Grind 3
Flotation 2

Cleaner 1
Cleaner 2
Cleaner 3

Final tailing

Concentrate to smelter

Figure 17.2 Flotation flowsheet developed for the treatment of gold-containing mercury–antimony
ore.

Table 17.3
Gold recovery obtained using different flowsheets [5]
Product

Single-stage grind-flotation
Two-stage grind-flotation
Three-stage grind-flotation

% Recovery in concentrate

Tailing assays (%, g/t)

Au

Ag

Sb

As

S

Au

Ag

Sb

As

S

88.1
92.2
95.3

89.2
91.8
95.2

72.9
93.4

95.7

68.4
78.7
81.2

70.1
81.2
85.7

1.7
1.0
0.7

5.0
4.1
2.2

0.04
0.015
0.005

0.035
0.022
0.015

0.38
0.27
0.19

17.6

Flotation of Carbonaceous Clay-Containing Gold Ores

17.6.1

7

Preflotation of carbonaceous gangue and carbon

In this technique, only carbonaceous gangue and carbon are recovered by flotation, in
preparation for further hydrometallurgical treatment of the float tails for gold recovery.
Carbonaceous gangue and carbon are naturally floatable using only a frother, or a combi­
nation of a frother and a light hydrocarbon oil (fuel oil, kerosene, etc.). When the ore
contains clay, regulators for clay dispersion are used. Some of the more effective regulating
reagents include sodium silicates and oxidized starch.

17.6.2

Two-stage flotation method

In this technique, carbonaceous gangue is prefloated using the above-described
method, followed by flotation of gold-containing sulphides using activator–collector
combinations. In extensive studies [6] conducted on carbonaceous gold-containing
ores, it was established that primary amine-treated copper sulphate improved gold
recovery considerably. Ammonium salts and sodium sulphide (Na2S · 9H2O) also have
a positive effect on gold-bearing sulphide flotation, at a pH between 7.5 and 9.0. The
metallurgical results obtained with and without modified copper sulphate are shown in
Table 17.4.

17.6.3

Nitrogen atmosphere flotation method

This technique uses a nitrogen atmosphere in grinding and flotation to retard oxidation
of reactive sulphides, and has been successfully applied on carbonaceous ores from
Nevada (USA). The effectiveness of the method depends on (a) the amount of carbo­
naceous gangue present in the ore, and (b) the amount and type of clay. Ores that are
high in carbon or contain high clay content (or both) are not amenable for nitrogen
atmosphere flotation.

Table 17.4
Effect of amine-modified CuSO4 on gold-bearing sulphide flotation from carbonaceous refractory ore
Reagent used

CuSO4 + xanthate
Amine modified
CuSO4 + xanthate

Product

Gold sulphide concentrate
Gold sulphide tail
Head
Gold sulphide concentrate
Gold sulphide tail
Head

Weight

(%)

30.11
69.89
100.00
26.30
73.70
100.00

Assays (%, g/t)
Au

S

9.63
1.86
4.20
13.2
0.85
4.10

4.50
0.49
1.70
5.80
0.21
1.68

% Distribution
Au

69.1
30.9
100.0
84.7
15.3
100.0

S
79.7
20.3
100.0
90.8
9.2
100.0


8

17.

17.7

Flotation of Gold Ores

FLOTATION OF GOLD-CONTAINING COPPER ORES

The floatability of gold from gold-containing copper gold ores depends on the nature and
occurrence of gold in these ores, and its association with iron sulphides.
Gold in the porphyry copper ore may appear as native gold, electrum, cuproaurid and
sulphosalts associated with silver. During the flotation of porphyry copper-gold ores,

emphasis is usually placed on the production of a marketable copper-gold concentrate
and optimization of gold recovery is usually constrained by the marketability of its
concentrate.
The minerals that influence gold recovery in these ores are iron sulphides (i.e. pyrite,
marcasite, etc.), in which gold is usually associated as minute inclusions. Thus, the iron
sulphide content of the ore determines gold recovery in the final concentrate. Figure 17.3
shows the relationship between pyrite content of the ore and gold recovery in the copper
concentrate for two different ore types. Most of the gold losses occur in the pyrite.
The reagent schemes used in commercial operations treating porphyry copper–gold ores
vary considerably. Some operations, where pyrite rejection is a problem, use a dithiopho­
sphate collector at an alkaline pH between 9.0 and 11.8 (e.g. OK Tedi/PNG Grasberg/
Indonesia). When the pyrite content in the ore is low, xanthate and dithiophosphates are
used in a lime or soda ash environment.
In more recent years, in the development of commercial processes for the recovery of
gold from porphyry copper–gold ores, bulk flotation of all the sulphides has been empha­
sized, followed by regrinding of the bulk concentrate and sequential flotation of copper–
gold from pyrite. Such a flowsheet (Figure 17.4) can also incorporate high-intensity
conditioning in the cleaner–scavenger stage. Comparison of metallurgical results using
the standard sequential flotation flowsheet and the bulk flotation flowsheet are shown in
Table 17.5. A considerable improvement in gold recovery was achieved using the bulk
flotation flowsheet.

Gold recovery in Cu cleaner conc. (%)

100

80

60
1

40
2

20

0
0

1

2

3 4 5 6 7 8
Pyrite content of ore (%)

9

10

Figure 17.3 Effect of pyrite content of the ore on gold recovery in the copper–gold concentrate at
30% Cu concentrate grade (1: ore from Peru; 2: ore from Indonesia).


17.7

Flotation of Gold-Containing Copper Ores

Flotation feed

9

Bulk scavenger

Bulk rougher

Regrind
High-intensity
conditioning

Cu-Au rougher

Cu-Au cleaner 1

Cu-Au
scavenger

Combined tailing

Cu-Au cleaner 2
Cu-Au cleaner 3
Cu-Au cleaner concentrate

Figure 17.4

Bulk flowsheet used in the treatment of pyritic copper–gold ores [8].
Table 17.5

Comparison of metallurgical results using conventional and bulk flotation flowsheets on ore
from peru
Flowsheet used

Conventional
(sequential Cu/Au)
Bulk
(Figure 17.4)

Product

Cu/Au concentrate
Cu/Au tail
Head
Cu/Au concentrate
Cu/Au ail
Head

Weight (%)

2.28
97.72
100.00
2.32
97.68
100.00

Assays (%, g/t)

% Distribution

Au

S

Au

S

27.6
0.031
0.66
27.1
0.032
0.66

32.97
0.23
0.98
36.94
0.14
0.96

95.4
4.6
100.0
95.2
4.8
100.0

76.7
23.3
100.0

85.8
14.2
100.0

During beneficiation of clay-containing copper-gold ores, the use of small quantities of
Na2S (at natural pH) improves both copper and gold metallurgy considerably.
In the presence of soluble cations (e.g. Fe, Cu), additions of small quantities of organic
acid (e.g. oxalic, tartaric) improve gold recovery in the copper concentrate.
Some porphyry copper ores contain naturally floatable gangue minerals, such as chlor­
ites and aluminosilicates, as well as preactivated quartz. Sodium silicate, carboxy methylcellulose and dextrins are common depressants used to control gangue flotation.
Gold recovery from massive sulphide copper–gold ores is usually much lower than that of
porphyry copper–gold ores, because very often a large portion of the gold is associated with
pyrite. Normally, gold recovery from these ores does not exceed 60%. During the treatment
of copper–gold ores containing pyrrhotite and marcasite, the use of Na2H2PO4 at alkaline pH
values depresses pyrrhotite and marcasite, and also improves copper and gold metallurgy.


10

17.

17.8

Flotation of Gold Ores

FLOTATION OF OXIDE COPPER–GOLD ORES

Oxide copper–gold ores are usually accompanied by iron hydroxide slimes and various
clay minerals. There are several deposits of this ore type around the world, some of
which are located in Australia (Red Dome), Brazil (Igarape Bahia) and the Soviet Union

(Kalima). Treatment of these ores is difficult, and even more complicated in the
presence of clay minerals.
Recently, a new class of collectors, based on ester-modified xanthates, have been
successfully used to treat gold-containing oxide copper ores, using a sulphidization
method. Table 17.6 compares the metallurgical results obtained on the Igarape Bahia ore
using xanthate and a new collector (PM230, supplied by Senmin in South Africa).
The modifier used in the flotation of these ores included a mixture of sodium silicate and
Calgon. Good selectivity was also achieved using boiled starch.

17.9

FLOTATION OF GOLD–ANTIMONY ORES

Gold–antimony ores usually contain stibnite (1.5–4.0% Sb), pyrite, arsenopyrite, gold
(1.5–3.0 g/t) and silver (40–150 g/t). Several plants in the United States (i.e. Stibnite/
Minnesota and Bradly) and Russia have been in operation for some time. There are two
commercial processes available for treatment of these ores:
1.

2.

Selective flotation of gold-containing sulphides followed by flotation of stibnite with
pH change. Stibnite floats well in neutral and weak acid pH, whereas in an alkaline
pH (i.e. >8) it is reduced. Utilizing this phenomenon, gold-bearing sulphides are
floated with xanthate and alcohol frother in alkaline medium (i.e. pH > 9.3) followed
by stibnite flotation at about pH 6.0, after activation with lead nitrate. Typical
metallurgical results using this method are shown in Table 17.7.
Bulk flotation followed by sequential flotation of gold-bearing sulphides, and
depression of stibnite. This method was practiced at the Bradly concentrator (USA)
Table 17.6

Effect of collector PM230 on copper/gold recovery from Igarape Bahia oxide copper/gold ore [8]
Reagent used

Product

Weight (%)

Assays
(%, g/t)
Au

Na2S = 2500 g/t
PAXa = 200 g/t
Na2S = 2500 g/t
PAXa/PM230 (1:1) = 200 g/t
a

PAX = potassium amyl xanthate.

Copper Cl concentrate
Copper tail
Feed
Copper Cl concentrate
Copper tail
Feed

9.36
90.64
100.00

10.20
89.80
100.00

%
Distribution
S

33.3
14.15
1.61
1.46
4.65
2.65
39.5
21.79
0.61
0.42
0.61
0.42

Au

S

67.0
50.0
33.0
50.0
100.0 100.0

88.0
85.5
12.0
14.5
12.0
14.5


17.10

Flotation of Arsenical Gold Ores

11
Table 17.7

Metallurgical results obtained using a sequential flotation method
Product

Weight (%)

Gold concentrate
Stibnite concentrate
Tailing
Feed

2.34
4.04
93.62
100.00

Assays (%, g/t)

% Distribution

Au

Ag

Sb

Au

Ag

Sb

42.3
6.2
0.65
1.86

269.3
559.8
18.7
46.4

20.0
51.0
0.7
3.2

53
13
34
100.0

13
51
36
100.0

15
64
21
10.0

Courtesy of stibnite plant (Minnesota, 1976).

Table 17.8
Plant metallurgical results obtained using a bulk flotation method
Product

Weight (%)

Gold concentrate
Antimony concentrate
Middlings
Bulk concentrate
Tailing
Feed

1.80
1.80
0.50
4.10
95.90
100.00

Assays (%, g/t)

% Distribution

Au

Ag

Sb

Au

Ag

Sb

91.1
13.0
46.6
51.7
0.6
2.7

248.8
684.2
248.8
440.0
3.1
21.0

1.5
51.3
20.0
29.0
0.2
1.3

61.0
9.0
8.6
78.6
21.4
100.0

31.3
58.6
6.0
85.9
14.1
100.0

2.0

75.0
8.0
85.0
15.0
100.0

Courtesy of the Bradly concentrator (USA).

and consisted of the following steps: (a) bulk flotation of stibnite and gold-bearing
sulphides at pH 6.5 using lead nitrate (i.e. Sb activator) and xanthate, (b) the bulk
concentrate is reground in the presence of NaOH (pH 10.5) and CuSO4, and the goldbearing sulphides are refloated with additions of small quantities of xanthate, (c)
cleaning of the gold concentrate in the presence of NaOH and NaHS. The plant
metallurgical results employing this method are shown in Table 17.8.
Recent studies conducted on ore from Kazakhstan have shown that sequential flotation
using thionocarbamate collector gave better metallurgical results than those obtained with
xanthate.

17.10

FLOTATION OF ARSENICAL GOLD ORES

There are two major groups of arsenical gold ores of economical value. These are the
massive base metal sulphides with arsenical gold (i.e. the lead–zinc Olympias deposit,
Greece) and arsenical gold ores without the presence of base metals. Massive, base metal


12

17.

Flotation of Gold Ores

arsenical gold ores are rare, and there are only a few deposits in the world. A typical
arsenical gold ore contains arsenopyrite as the major arsenic mineral. However, some
arsenical gold ores, such as those from Nevada in the USA (Getchel deposit), contain
realgar and orpiment as the major arsenic-bearing minerals. Pyrite, if present in an arsenical
gold ore, may contain some gold as minute inclusions.
Flotation of arsenical gold ores associated with base metals is accomplished using a
sequential flotation technique, with flotation of base metals followed by flotation of goldcontaining pyrite/arsenopyrite. The pyrite/arsenopyrite is floated at a weakly acid pH with a
xanthate collector.
Arsenical gold ores that do not contain significant base metals are treated using a bulk
flotation method, where all the sulphides are first recovered into a bulk concentrate. In case
the gold is contained either in pyrite or arsenopyrite, separation of pyrite and arsenopyrite is
practiced. There are two commercial methods available. The first method utilizes arseno­
pyrite depression and pyrite flotation, and consists of the following steps:
1.

2.

Heat the bulk concentrate to 75°C at a pH of 4.5 (controlled by H2SO4) in the
presence of small quantities of potassium permaganate or disodium phosphate. The
temperature is maintained for about 10 min.
Flotation of pyrite using either ethyl xanthate or potassium butyl xanthate as collector.
Glycol frother is also usually employed in this separation.

This method is highly sensitive to temperature. Figure 17.5 shows the effect of tempera­
ture on pyrite/arsenopyrite separation. In this particular case, most of the gold was
associated with pyrite. Successful pyrite/arsenopyrite separation can also be achieved
with the use of potassium peroxy disulphide as the arsenopyrite depressant.
The second method involves depression of pyrite and flotation of arsenopyrite. In this

method, the bulk concentrate is treated with high dosages of lime (i.e. pH > 12), followed

Pyrite/arsenopyrite recovery (%)

100
Pyrite
80
60
40
Arsenopyrite
20
0
0

20
40
60
Heating temperature (°C)

80

Figure 17.5 Effect of temperature on separation of pyrite and arsenopyrite from a bulk pyrite/
arsenopyrite concentrate.


17.11

Flotation of Gold From Base Metal Sulphide Ores

13

by a conditioning step with CuSO4 to activate arsenopyrite. The arsenopyrite is then floated
using a thionocarbamate collector.
Separation of arsenopyrite and pyrite is important from the point of view of reducing
downstream processing costs. Normally, roasting or pressure oxidation followed by cya­
nidation is used to recover gold.

17.11

FLOTATION OF GOLD FROM BASE METAL SULPHIDE ORES

Very often lead-zinc, copper-zinc, copper-lead-zinc and copper-nickel ores contain signifi­
cant quantities of gold (i.e. between 1 and 9 g/t). The gold in these ore types is usually
found as elemental gold. A large portion of the gold in these ores is finely disseminated in
pyrite, which is considered non-recoverable. Because of the importance of producing
commercial-grade copper, lead and zinc concentrates, little or no consideration is given
to improvement in gold recovery, although the possibility exists to optimize gold
recovery in many cases. Normally, gold recovery from base metal ores ranged from 30%
to 75%.
In the case of a copper-zinc and copper-lead-zinc ore, gold collects in the copper
concentrate. During the treatment of lead-zinc ores, the gold tends to report to
the lead concentrate. Information regarding gold recovery from base metal ores is
sparse.
The most recent studies [9] conducted on various base metal ores revealed some
important features of flotation behaviour of gold from these ores. It has been demonstrated
that gold recovery to the base metal concentrate can be substantially improved with the
proper selection of reagent schemes. Some of these studies are discussed below.
17.11.1

Gold-containing lead-zinc ores

Some of these ores contain significant quantities of gold, ranging from 0.9 to 6.0 g/t (i.e.
Grum/Yukon, Canada; Greens Creek, Alaska; and Milpo, Peru). The gold recovery from
these ores ranged from 35% to 75%. Laboratory studies have shown that the use of high
dosages of zinc sulphate, which is a common zinc depressant used in lead flotation, reduces
gold floatability significantly. The effect of ZnSO4 · 7H2O addition on gold recovery in the
lead concentrate is illustrated in Figure 17.6.
In order to improve gold recovery in the lead concentrate, an alternative depressant to
ZnSO4 · 7H2O can be used. Depressant combinations such as Na2S + NaCN, or Na2SO3 +
NaCN, may be used. The type of collector also plays an important role in gold flotation of
lead-zinc ores. A phosphine-based collector, in combination with xanthate, gave better gold
recovery than dithiophosphates.
17.11.2

Copper-zinc gold-containing ores

Gold recovery from copper-zinc ores is usually higher than that obtained from either a leadzinc or copper lead-zinc ore. This is attributed to two main factors: when selecting a reagent


17.

Gold recovery in Lead concentrate (%)

14

Flotation of Gold Ores

70
Greens Creek ore
(Alaska)

60
50
40

Grum ore Yukon
(Canada)

30
20
10
0
0

100

200

300

400

500

ZnSO4 · 7 H2O (g/t)

Figure 17.6

Effect of ZnSO4 additions on gold recovery from lead–zinc ores.

scheme for treatment of Cu-Zn ores, there are more choices than for the other ore types,
which can lead to the selection of a reagent scheme more favourable for gold flotation.
In addition, a non-cyanide depressant system can be used for the treatment of these ores,
which in turn results in improved gold recovery. This option is not available during
treatment of lead-zinc ores. Table 17.9 shows the effect of different depressant combina­
tions on gold recovery from a copper-zinc ore.
The use of a non-cyanide depressant system resulted in a substantial improvement in
gold recovery in the copper concentrate.

Table 17.9
Effect of different depressant combinations on gold recovery to the copper concentrate from lower
zone Kutcho Creek ore
Depressant system

Product

Weight (%) Assays (%, g/t)
Au

ZnSO4, NaCN, CaO Cu concentrate
3.10
pH 8.5 Cu, 10.5 Zn Zn concentrate
5.34
Tailings
91.56
Feed
100.00
3.05
Na2SO3, NaHS, CaO Cu concentrate
pH 8.5 Cu, 10.5 Zn Zn concentrate

5.65
Tailings
91.30
Feed
100.00
Courtesy of Esso Canada Resources.

Ag

% Distribution
Sb

Au

Ag

Sb

20.4
26.2 330
45.1 85.6
2.8
1.20 0.61 55.4
4.6
3.4
82.2
0.77 0.11 0.58 50.3 11.0 15.0
1.4
0.95 3.60 100.0 100.0 100.0
32.5 28.1

2.80 68.3 87.4
2.3
1.20 0.55 54.8
4.7
3.2
84.6
0.43 0.10 0.52 27.0
9.4
13.1
1.45 0.98 3.66 100.0 100.0 100.0


17.12

Conclusions

17.11.3

15

Gold-containing copper-lead-zinc ores

Because of the complex nature of these ores, and the requirement for a relatively complex
reagent scheme for treatment of this ore, the gold recovery is generally lower than that
achieved from a lead-zinc or copper-zinc ore. One of the major problems associated with
the flotation of gold from these ores is related to gold mineralogy. A large portion of the
gold is usually contained in pyrite, at sub-micron size. If coarse elemental gold and
electrum are present, the gold surfaces are often coated with iron or lead, which can result
in a substantial reduction in floatability.
The type of collector and flowsheet configuration play an important role in gold

recovery from these ores. With a flowsheet that uses bulk Cu–Pb flotation followed by
Cu–Pb separation, the gold recovery is higher than that achieved with a sequential
Cu–Pb flotation flowsheet. In laboratory tests, and Aerophine collector type, in
combination with xanthate, had a positive effect on gold recovery as compared to
either dithiophosphate or thionocarbamate collectors. Table 17.10 compares the metal­
lurgical results obtained with an Aerophine collector to those obtained with a dithio­
phosphate collector.
Because of the complex nature of gold-containing Cu–Pb–Zn ores, the reagent schemes
used are also complex. Reagent modifiers such as ZnSO4, NaCN and lime have to be used,
all of which have a negative effect on gold flotation.

17.12

CONCLUSIONS

The flotation of gold-bearing ores, whether for production of bulk concentrates for further
gold recovery processes (i.e. pyrometallurgy, hydrometallurgy) or for recovery of gold to
base metal concentrates, is a very important method for concentrating the gold and
reducing downstream costs.
The flotation of elemental gold, electrum and tellurides is usually very efficient, except
when these minerals are floated from base metal, massive sulphides.
Flotation of gold-bearing sulphides from ores containing base metal sulphides present
many challenges and should be viewed as flotation of the particular mineral that contains
gold (i.e. pyrite, arsenopyrite, copper, etc.), because gold is usually associated with these
minerals at micron size.
Selection of a flotation technique for gold preconcentration depends very much on the
ore mineralogy, gangue composition and gold particle size. There is no universal method
for flotation of the gold-bearing minerals, and the process is tailored to the ore character­
istics. A specific reagent scheme and flowsheet are required for each ore.
There are opportunities in most operating plants for improving gold metallurgy. Most of

these improvements come from selection of more effective reagent schemes, including
collectors and modifiers.
Perhaps the most difficult ores to treat are the clay-containing carbonaceous sulphides.
Significant progress has been made in treatment options for these ores. New sulphide
activators (i.e. amine-treated CuSO4, ammonium salts) and nitrogen gas flotation are
amongst the new methods available.


16

Table 17.10
Effect of collector type on Cu–Pb–Zn–Au metallurgical results from a high-lead ore, Crandon (USA)
Collector

30 g/t xanthate
20 g/t dithiophosphate 3477

30 g/t xanthate
20 g/t aerophine 3418A

Cu concentrate
Pb concentrate
Zn concentrate
Tailing
Feed
Cu concentrate
Pb concentrate
Zn concentrate
Tailing
Feed

Weight (%)

2.47
1.80
13.94
81.79
100.00
2.52
1.92
13.91
81.65
100.00

Assays (%, g/t)

% Distribution

Au

Cu

Pb

Zn

Au

Cu

Pb

Zn

22.4
2.50
1.10
0.71
1.33
31.3
2.80
0.90
0.41
1.30

25.5
0.80
0.60
0.089
0.80
26.1
0.90
0.50
0.093
0.82

1.20
51.5
0.80
0.28

1.30
1.10
51.1
0.72
0.30
1.35

4.50
8.30
58.2
0.52
8.80
5.00
9.20
58.5
0.44
8.80

41.6
3.4
11.5
43.5
100.0
60.6
4.1
9.6
25.7
100.0

78.6

1.8
10.4
9.1
100.0
80.1
2.1
8.5
9.3
100.0

2.3
71.3
8.6
17.8
100.0
2.1
72.5
7.4
18.0
100.0

1.3
1.7
92.2
4.8
100.0
1.4
2.0
92.5
4.1

100.0
17.

Courtesy of Exxon coal.

Product

Flotation of Gold Ores


References

17

REFERENCES
1. Kudryk, V., Carigan, D.A., and Liang, W.W., Precious Metals, Mining Extraction and Processing.
AIME, 1982.
2. Martins, V., Dunne, R.C., and Gelfi, P., Treatment of Partially Refractory Gold Ores, Randol Gold
Forum, Australia, 1991.
3. Baum, W., Mineralogy as a Metallurgical Tool in Refractory Ore, Progress Selection and
Optimization, Randol Gold Forum, Squaw Valley, 1990.
4. Fishman, M.A., and Zelenov, B.I., Practice in Treatment of Sulphides and Precious Metal Ores,
Izdatelstro Nedra (Russian), Moscow, Vol. 5, pp. 22–101, 1967.
5. Sristinov, N.B., The Effect of the Use of Stage Grinding in Processing of Refractory ClayContaining Gold Ore, Kolima, No. 1, pp. 34–40, 1964.
6. Bulatovic, S.M., and Wyslouzil, D.M., Proceedings of the 2nd International Gold Symposium,
Flotation Behaviour of Gold During Processing of Porphyry Copper-Gold Ores and Refractory
Gold-Bearing Sulphides, Lima, Peru, 1996.
7. Bulatovic, S.M., Evaluation of New HD Collectors in Flotation of Pyretic Copper-Gold Ores from
B.C. Canada, Internal R&D Report LR029, 1993.
8. Bulatovic, S.M., An Investigation of the Recover of Copper and Gold from Igarape Bahia Oxide

Copper-Gold Ores, Report of Investigation LR4533, 1997.
9. Bulatovic, S.M., An Investigation of Gold Flotation from Base Metal Lead-Zinc and Copper-Zinc
Ores, Interim Report LR049, 1996.


– 18 –

Flotation of Platinum Group Metal Ores

18.1

INTRODUCTION

In chemical terms the six main platinum group elements (PGE), ruthenium, rhodium,
palladium, osmium, iridium and platinum, belong to the group VIII transition metals, to
which also belong iron, nickel and cobalt. These elements have long been considered, when
grouped with gold and silver, as ‘precious metals’. This, in fact, is misleading because the
mineralogy and geochemistry of silver and gold do not correlate with that of PGE.
Also, in literature, there are two terms of reference, including PGE and platinum group
minerals (PGM). From a flotation point of view, PGM is the more common term. There­
fore, the term PGM will be used in this text.
The chemical similarity between the six PGE and iron, nickel and cobalt accounts for the
fact that they tend to concentrate together as a result of geological processes. This is quite
important not only for the formation of PGM ores, but also for beneficiation.

18.2

MINERALS AND CLASSIFICATION OF PGM ORES

There are over 100 different platinum group minerals. Some of the most common PGM are

shown in Table 18.1. The stoichiometry of most of the PGM named [1] is known, but
because these minerals are subject to a wide range of element substitution, as indicated in
Table 18.1, there is little consistency between an ideal formula for the individual minerals
and compositions of the given minerals from various locations.
In general, PGM are concentrates in the crust found in two different ways: (a) by
leaching the metal-rich lava (mantle) deposited into the crust, which is known as chemical
weathering, especially in a hot climate where silica and magnesia are leached away. This
leaves a residue enriched in iron and nickel, which contains the PGM elements; and (b)
melting a portion of the mantle may give rise to ultramafic or basalic lava, which is then
squeezed upwards as a result of pressure within the earth to intrude the crust or extrude lava
on the surface. This magma is not particularly rich in nickel or PGM; however, because of
their siderophile nature [2], the group VIII metals are also chalcophile in nature, that is they
prefer to form bonds with sulphur than oxygen.

19


20

18.

Flotation of Platinum Group Metal Ores

Table 18.1
List of platinum group minerals and their compositions
PGM

Ideal formula

Other elements present

Anduoite
Arsenopalladinite
Atheneite
Atokite
Borovskite
Braggite
Cooperite
Daomanite
Erlichamanite
Froodite
Genkinite
Geversite
Guanglinite
Hollingworthite
Hongshlite
Iravsite
Iridium
Isoferroplatinum
Kotulskite
Majakite
Monochelite
Nigglite
Omelite
Osmium
Palarstanide
Palladium
Platiniridium
Rhodium
Ruthenium

Ruthenosmiridium
Sperrilite
Temagamite
Uvantserite
Vysotaskite
Xingzhongite
Zvyagintsevite

RuAs2
Pd8As2.5Sb0.5
(PdHg)3As
PdSn
Pd8SbTe4
(PtPd)S
PtS
PtCuAsS2
OsS2
PdBi2
(PtPd)4Sb3
PtSb2
Pd3As
RhAsS
Pt(Cu)
IrAsS
Ir
Pt3Fe
PtTe
PtNiAs
PtTe3
PtSn

OsAs2
Os
Pd8(SnAs)3
Pd
(IrPt)
Rh
Ru
(IrOsRu)
PtAs2
PdHgTe3
Pd(BiPb)2
PdS
(IrCuRh)S
Pd3Pb

(RuOsIr)As
(PdCu)AsSb
(PdHgAuCu)AsSb
(PdPt)Sn
(PdPtNiFe)SbBiTe
(PtNiPd)S
(PtNiPd)S
(PtCuAs)S
(OsRhIrPdRu)S
(PdPt)Bi
(PtPdRhNiCu)SbAsBi
Pt(SbBi)
(Pd)As
(RhPdPtIr)AsS
(Pt)Cu

(IrRuRhPt)AsS
(IrPtFeOsRhPdNi)
(PtFeCuNi)
(PdPt)(TeBiSb)
(PdNiAs)
PtPd(TeBi)
(PtBiSb)Sn
(OsRuFeNiIrCo)As
(OsIrRuPt)
(PdPtAuCu)(AsSnSb)
PdHg
(IrPtFeOsCuNi)
RhPt
RuIrRhOsPdFe
(IrRuOsPtRhFeNiPd)
(Pt)(AsSb)
(Pt)HgTe)Bi
Pd(BiPb)
(PdFePt)
(IrCuRhFePbPtOs)S
(PdPtFeNiCu)Pb

These sulphide deposits are able to concentrate these metals by a factor of
100–1000 ppm and form PGM deposits, together with precious metals, nickel and copper.
Almost always the PGM deposits contain nickel minerals.
The PGM deposits can be classified into the following two groups: (a) PGM-dominated
deposits and (b) nickel–copper-dominated deposits. Of major interest concerning this
chapter will be the PGM-dominated deposits. The flotation of copper–nickel-containing
PGM was discussed in Volume I of this book.

18.3

Description of PGM-Dominated Deposits

18.3

21

DESCRIPTION OF PGM-DOMINATED DEPOSITS

According to the processing characteristics of PGM-dominated deposits, they can be
divided into the following three groups: (a) Morensky type, (b) hydrothermal deposits
and (c) placer deposits. Each type of deposit is briefly described below.
18.3.1

Morensky-type deposits

The Morensky-type deposits can be found in very large bodies of basaltic magma, which
were intruded into stable continental rock. An example includes the Busheld Complex in
South Africa and the Great Dyke of Zimbabwe. Mineralization similar to the above is also
found in the Stillwater Complex in Montana, USA.
The Busheld Complex consists of varieties of ore types, including high-chromium ores,
ore with floatable gangue minerals and small but significant quantities of ultrafine slimes
that are important from a processing point of view.
The Stillwater Complex consists of a sequence of differential layers of mafic and
ultramafic rocks, which extend for a strike length of up to 40 km and has a maximum
exposed thickness of about 7.4 m [3]. There are several mineralization zones at the Stillwater Complex, including a PGM-rich zone and a low-grade zone. The Stillwater ore that is
processed nowadays contains olivine, plagioclase, as well as plagioclase-brauzite, all of
which are naturally hydrophobic gangue minerals.

Another similar origin deposit is Lac des Illes in Canada. This complex is apparently
contrary to a somewhat general rule in that of intrusion and is regarded as Archean age and
may be therefore intruded prior to the Kenora origin into a technically unstable
environment.
18.3.2

Hydrothermal deposits

An example of a hydrothermal deposit is the New Rambler deposit, described by McCal­
lum et al. [4] in the Medicine Bow Mountains in south-western Wyoming, USA, which
contains a significant amount of PGM. The ore occurs in irregular pods that are hydrothermally decomposed into metadiorite and metagabbro zones. Pyroxenite and peridotite
are reported to be intersected at a depth beneath the ore zone. All have been affected by
supergene alteration. The main sulphides in the ore include pyrite, chalcopyrite, pyrrhotite,
covellite and marcasite with associations of electrum, pentlandite and PGM.
There is no evidence that the depth may be a result of an alteration in the original
concentration of magmatic sulphides. It may be a result of concentration of hydrothermal
solutions.
18.3.3

Placer deposits

The eluvial and alluvial PGM deposits have been processed in the Soviet Union, Canada,
Columbia and the United States. Most of these deposits are associated with Alaskan-type
ultrafamic rocks, which are, themselves, enriched in PGM, in particular, in the vicinity of


22

18.

Flotation of Platinum Group Metal Ores

concentration of chromite and with alpine ultrafamic bodies. As a process of weathering,
there is a marked change in Pt/(Pt–Pd) ratio as compared to the source becoming greatly
increased in the former due to the greater ease with which Pd dissolves and is removed in a
weathering enrichment. Examples of this include the placer related to the Norilsk sulphide
deposits and deposits found in Ural region USSR.

18.4 EFFECT OF MINERALOGY ON RECOVERY OF PLATINUM GROUP
MINERALS
The recovery of PGM minerals is a subject which has received very little attention in
published literature. This is mainly due to the fact that major PGM producers are sur­
rounded by secrecy, therefore, neither commercial processes nor research work on recovery
of PGM is publically available.
Long-term research work conducted by a number of research organizations and data
collected from a number of operating plants are summarized in this chapter.
From a processing point of view, PGM-containing ores can be divided into three general
groups as follows:
1.
2.
3.

ores amenable to gravity preconcentration,
ores amenable to flotation and
ores that can only be treated using a hydrometallurgical route.

18.4.1

Ores amenable to gravity preconcentration

The most important features of these ores are (a) the valuable constituents occur as minerals
of high density, (b) they do not have middlings and (c) the grain-size distribution falls in a
region where a gravity technique can be adopted successfully.
Ore types where gravity preconcentration is used include Alaskan-type deposits, alluvial
and fossil placer deposits.
In the Alaskan-type deposits, the principal PGM minerals include Pt–Fe alloys, isoferro­
platinum (Pt2Fe) and platiniridium (Ir,Pt). There are several producing plants that process
these ores, mainly in rural mountain areas (USSR).
The alluvial deposits were treated in the early 20th century. The PGM in these deposits
occur as alloys, usually as Pt rich in the form of loose grains and nuggets. These deposits
have been mined in a number of countries, including Russia, Columbia and South Africa.
Although there is a comprehensive review of the placer deposits [5], very little is known
about PGM recovery using a gravity preconcentration method. Some of these deposits
contain clay minerals, which require pretreatment before preconcentration. It should be
mentioned that the PGM ores from Alaska contain magnetite, which is removed before
gravity preconcentration.
The fossil placer deposits are in fact gold-bearing conglomerates that carry small
amounts of PGM, together with gold, uranium and other heavy minerals. However, studies
conducted revealed that some of the fossil placer deposits contain about 22 PGM species,
including Ir–Os–Ru alloys, sperrylite and isoferroplatinum.


18.5

Copper-Nickel and Nickel Sulphide Deposits with PGM as a By-Product

23

There are several operating mines that recover PGM and gold from fossil placer deposits,
some of which include Witwatersrand and Geduld mines in South Africa.

18.4.2

Ores amenable to flotation

Classification of the ores amenable to flotation
Based on flotation processing characteristics, these ores can be divided into the following
major groups:
(a) PGM sulphide-dominated deposits. In these deposits, PGM are in general
associated with base metal sulphides, as grain boundaries between sulphides and
silicates. In some cases, the PGM may be present in solid solution with sulphides.
From these deposits, PGM are recovered in a bulk Cu/Ni/Co/PGM concentrate that
is further processed using pyrometallurgical techniques. In many cases these
ore types contain floatable non-opaque gangue minerals, including talc, chlorites,
etc.
(b) PGE-dominated deposits. This in fact is a term for stratiform deposits containing
sparse sulphides and PGM concentration in a range between 5 and 30 g/t. These ores
are typified by the Morensky Reef of the Bushveld Complex in South Africa.
Mineralization of a similar type is found in the Stillwater Complex in Montana,
USA. These deposits are characterized by a variety of different gangue minerals
and high content of PGM sulphide minerals, such as cooperate (PtS), braggite
[(PtPd)S] and vysotskite (PdS). Note that these minerals are rare and non-existent
in most PGM-bearing copper-nickel sulphide deposits. Typical deposits that belong to
this group include the Morensky Reef (South Africa), the Stillwater Complex (USA)
and Lac des Illes (Canada).

18.5

COPPER-NICKEL AND NICKEL SULPHIDE DEPOSITS WITH PGM
AS A BY-PRODUCT

Prior to discovery of the PGM Morensky Reef deposit, copper-nickel deposits in Ontario,
Canada, and the Norilsk (USSR) were the principal sources of PGM production. However,
about 40% of the world’s production of PGM comes from different Cu–Ni deposits.
The major deposits from this group are discussed in the following sections.
18.5.1

The Sudbury area in Ontario, Canada

Mineralogical examination of these ores [8] revealed a variety of PGM and their associa­
tions. The michenerite (PdBiTe) and sperrylite (PtAs2) are the most common platinum/
palladium minerals for many deposits in the Sudbury region. Other minerals of economic
value found in these deposits are moncheite (PtTe2), froodite (PdBi2), inszwaite (PtBi2),
iravsite (IrAsS), niggliite (PtSn) and mertiate (PdSb3). Most of these minerals are liberated
at a relatively coarse size (40–200 μm).