1596 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
be present as nano/micro inclusions, such as freibergite as
fine as 5 µm enclosed in galena or tiny inclusions of 5 µm
Ag-bearing minerals such as acanthite in sphalerite (Riley,
1974 Wu et al. 2018). If the Ag at Gamsberg is to be prof-
itably recovered, it is critical to determine how this relates
to Zn and Pb flotation recovery. Preferential recovery of
Ag to the Pb circuit has been observed in studies of similar
ores (Galant, 2015 Tiu et al. 2021). Silver has therefore
been observed to have an affinity to Pb (Ag-Pb substitu-
tion in galena, Ag minerals association with galena, and the
recovery of Ag to the Pb circuit) and whether this affinity
between Ag and Pb occurs in the South African Gamsberg
deposit will be of interest.
The purpose of this study is to determine the distri-
bution of Ag in the Gamsberg ore, from both mineralogi-
cal and flotation perspectives. The Gamsberg operation is
managed as eastern and western sectors based on orebody
geometry, grade distribution, geometallurgical character-
ization, and Zn distribution. This segregation is in place to
optimize consistent blended ore stability and feed charac-
teristics to the plant for optimal setup of plant processing
conditions of sphalerite recovery. This study investigates
the East pit ore at Gamsberg, which includes metapelite
(PEO) and magnetite pyroxene ores (MPO). All ores at
Gamsberg are further subdivided into two key geometal-
lurgical domains, one differentiating the degree of ore oxi-
dation (fresh vs transitional), and the other based on Mn
grades (high-Mn vs low-Mn) (Price et al. 2023). The study
investigates the Ag distribution within the fresh ‘degree of
oxidation’ at high- and low-Mn grades.
MATERIALS AND METHODS
Sampling and Sample Preparation
Representative samples of the different ores were sampled
directly from the Gamsberg East pit and delivered to the
University of Cape Town (UCT) for further processing. All
analytical work was performed at UCT unless otherwise
indicated. A summary of the sample details, including the
ore type and lithologies is provided in Table 1. The litholo-
gies are denoted magnetite pyroxene ores (MPO), pyrrho-
tite-dominated pelitic ore (PEO_Po) and pyrite-dominated
pelitic ore (PEO_Py). The material was crushed using a
jaw crusher (Terminator JLT1AL) at UCT and the mate-
rial passed through a 2.8 mm screen. Any top-size material
was reintroduced into the crusher. Samples were repre-
sentatively split using a 10-way rotary splitter into sample
sizes suitable for milling 1 kg for fLMn_Py (denoted ‘low-
Mn’). Sample fHMn_MPO was subsampled to 300 g and
combined with 700 g of high-Mn PEO_Po to give a total
of 1 kg blended ore (Table 1). The ratio of the MPO and
PEO_Po samples were 30:70, consistent with the ore blend
used at Gamsberg. The blended fresh sample was denoted
‘high-Mn’.
Batch Flotation Tests
The batch flotation tests were conducted on the two ore
samples denoted high-Mn and low-Mn. Each 1 kg sample
was milled in a 1 kg stainless steel rod mill (6 rods – 25 mm
× 285 mm, 8 rods – 20 mm × 285 mm, and 6 rods – 16 mm
× 285 mm) for 5 minutes to obtain a grind of ~60% pass-
ing 75 µm. Flotation tests were conducted in a 3 L Barker
bench flotation cell at an impeller speed of 1200 rpm and
an airflow rate of 5 L/min. The froth height was maintained
at 15 to 20 mm using in-house synthetic plant water. Two
feed samples were drawn from the cell before the com-
mencement of the experiments. Recoveries and grades of
Ag, Zn, Pb, Fe and C within the successive C, Pb and Zn
flotation concentrates were determined. Carbon flotation
is undertaken initially to remove C-bearing minerals (pre-
dominantly graphite) from the samples. For carbon flota-
tion, the pH was adjusted to 8.0–9.0 using lime. Sodium
cyanide at 90 g/t and Hydrofroth 8490 at 60 g/t was con-
ditioned for two and one minutes, respectively. The air was
then turned on and the concentrate collected for a total of
30 seconds. The pH was then adjusted to 8.5–9.0 for Pb
flotation. Sodium normal propyl xanthate (SNPX) at 20
g/t and Hydrofroth 8490 at 10 g/t was used. Two Pb con-
centrates were collected for two minutes each. For Zn flota-
tion, the pH was adjusted to 10.2–10.5. Copper sulphate
(CuSO4) at 1000 g/t, SNPX at 40 g/t and Hydrofroth 8490
at 60 g/t were added and conditioned for five, two and one
minutes, respectively. Four Zn concentrates were collected
for one, three, five and eight minutes, respectively. Tailings
samples were drawn after the C, Pb and Zn flotation steps.
All flotation products, including feed, concentrates and
Table 1. Summary of the East Pit sample details. Lithologies are denoted MPO- magnetite pyroxene ores, PEO_
Po- pyrrhotite-dominated pelitic ore and PEO_Py- pyrite-dominated pelitic ore
Degree of Oxidation Ore Type Lithologies Sample Name
Fresh
High-Mn
MPO (30% or 300 g) +fHMn_mix (referred to as’ High-Mn’) PEO_Po (70% or 700 g)
Low-Mn PEO_Py fLMn_Py (referred to as ‘Low-Mn’)
be present as nano/micro inclusions, such as freibergite as
fine as 5 µm enclosed in galena or tiny inclusions of 5 µm
Ag-bearing minerals such as acanthite in sphalerite (Riley,
1974 Wu et al. 2018). If the Ag at Gamsberg is to be prof-
itably recovered, it is critical to determine how this relates
to Zn and Pb flotation recovery. Preferential recovery of
Ag to the Pb circuit has been observed in studies of similar
ores (Galant, 2015 Tiu et al. 2021). Silver has therefore
been observed to have an affinity to Pb (Ag-Pb substitu-
tion in galena, Ag minerals association with galena, and the
recovery of Ag to the Pb circuit) and whether this affinity
between Ag and Pb occurs in the South African Gamsberg
deposit will be of interest.
The purpose of this study is to determine the distri-
bution of Ag in the Gamsberg ore, from both mineralogi-
cal and flotation perspectives. The Gamsberg operation is
managed as eastern and western sectors based on orebody
geometry, grade distribution, geometallurgical character-
ization, and Zn distribution. This segregation is in place to
optimize consistent blended ore stability and feed charac-
teristics to the plant for optimal setup of plant processing
conditions of sphalerite recovery. This study investigates
the East pit ore at Gamsberg, which includes metapelite
(PEO) and magnetite pyroxene ores (MPO). All ores at
Gamsberg are further subdivided into two key geometal-
lurgical domains, one differentiating the degree of ore oxi-
dation (fresh vs transitional), and the other based on Mn
grades (high-Mn vs low-Mn) (Price et al. 2023). The study
investigates the Ag distribution within the fresh ‘degree of
oxidation’ at high- and low-Mn grades.
MATERIALS AND METHODS
Sampling and Sample Preparation
Representative samples of the different ores were sampled
directly from the Gamsberg East pit and delivered to the
University of Cape Town (UCT) for further processing. All
analytical work was performed at UCT unless otherwise
indicated. A summary of the sample details, including the
ore type and lithologies is provided in Table 1. The litholo-
gies are denoted magnetite pyroxene ores (MPO), pyrrho-
tite-dominated pelitic ore (PEO_Po) and pyrite-dominated
pelitic ore (PEO_Py). The material was crushed using a
jaw crusher (Terminator JLT1AL) at UCT and the mate-
rial passed through a 2.8 mm screen. Any top-size material
was reintroduced into the crusher. Samples were repre-
sentatively split using a 10-way rotary splitter into sample
sizes suitable for milling 1 kg for fLMn_Py (denoted ‘low-
Mn’). Sample fHMn_MPO was subsampled to 300 g and
combined with 700 g of high-Mn PEO_Po to give a total
of 1 kg blended ore (Table 1). The ratio of the MPO and
PEO_Po samples were 30:70, consistent with the ore blend
used at Gamsberg. The blended fresh sample was denoted
‘high-Mn’.
Batch Flotation Tests
The batch flotation tests were conducted on the two ore
samples denoted high-Mn and low-Mn. Each 1 kg sample
was milled in a 1 kg stainless steel rod mill (6 rods – 25 mm
× 285 mm, 8 rods – 20 mm × 285 mm, and 6 rods – 16 mm
× 285 mm) for 5 minutes to obtain a grind of ~60% pass-
ing 75 µm. Flotation tests were conducted in a 3 L Barker
bench flotation cell at an impeller speed of 1200 rpm and
an airflow rate of 5 L/min. The froth height was maintained
at 15 to 20 mm using in-house synthetic plant water. Two
feed samples were drawn from the cell before the com-
mencement of the experiments. Recoveries and grades of
Ag, Zn, Pb, Fe and C within the successive C, Pb and Zn
flotation concentrates were determined. Carbon flotation
is undertaken initially to remove C-bearing minerals (pre-
dominantly graphite) from the samples. For carbon flota-
tion, the pH was adjusted to 8.0–9.0 using lime. Sodium
cyanide at 90 g/t and Hydrofroth 8490 at 60 g/t was con-
ditioned for two and one minutes, respectively. The air was
then turned on and the concentrate collected for a total of
30 seconds. The pH was then adjusted to 8.5–9.0 for Pb
flotation. Sodium normal propyl xanthate (SNPX) at 20
g/t and Hydrofroth 8490 at 10 g/t was used. Two Pb con-
centrates were collected for two minutes each. For Zn flota-
tion, the pH was adjusted to 10.2–10.5. Copper sulphate
(CuSO4) at 1000 g/t, SNPX at 40 g/t and Hydrofroth 8490
at 60 g/t were added and conditioned for five, two and one
minutes, respectively. Four Zn concentrates were collected
for one, three, five and eight minutes, respectively. Tailings
samples were drawn after the C, Pb and Zn flotation steps.
All flotation products, including feed, concentrates and
Table 1. Summary of the East Pit sample details. Lithologies are denoted MPO- magnetite pyroxene ores, PEO_
Po- pyrrhotite-dominated pelitic ore and PEO_Py- pyrite-dominated pelitic ore
Degree of Oxidation Ore Type Lithologies Sample Name
Fresh
High-Mn
MPO (30% or 300 g) +fHMn_mix (referred to as’ High-Mn’) PEO_Po (70% or 700 g)
Low-Mn PEO_Py fLMn_Py (referred to as ‘Low-Mn’)