1600 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Ag and Pb in the high-Mn ore but rather Ag and Zn recov-
ery trends appear to follow one another. The Ag in the high
Mn ore is recovered to both the Pb (22.0%) and Zn con-
centrates (45.4%). The high recovery of Ag to the high-
Mn Zn concentrate may be due to a function of the poor
galena liberation and the galena association with sphalerite,
as shown in Figure 3.
Silver Mineralogy in Flotation Pb and Zn Concentrates
The distribution of Ag-bearing minerals in the Pb and
Zn concentrates is presented in Figure 5. The amount of
Ag-bearing particles within the concentrates is considerably
low given the concentrate Ag grades (a total 67 particles
detected). The ‘Ag in galena’ and ‘Ag in sphalerite’ catego-
ries are interpreted to represent micro Ag-bearing minerals
hosted in galena and sphalerite, respectively and not solid
solution-hosted Ag, since SEM-WDS indicated no detect-
able Ag within galena or sphalerite solid solution above the
detection limit. The ‘Ag-Si’ phase most likely represents
micro inclusions of Ag-bearing minerals hosted within sili-
cates. Argentite, sternbergite and ‘Ag in galena’ are the main
hosts of Ag in the high-Mn Pb concentrate. In the low Mn
ore concentrates, Ag mainly occurs as native Ag and argen-
tite. In the low-Mn Zn concentrate, Ag occurs as native
Ag, argentite and malinowskite. There are also significant
proportions of ‘Ag in galena’ grains within Pb concentrates,
and more native Ag present in the low-Mn concentrates.
A preliminary calculation of the Ag distribution suggests
that Ag cannot solely be hosted as discrete Ag minerals
within these samples (represented as a preliminary calcula-
tion given the low number of Ag-particle counts). It is pos-
sible that additional silver may occur within nano/micro
discrete Ag minerals that cannot be accurately detected
by SEM, or in solid solution within BMS. Although this
was undetected by SEM-WDS analysis of the two primary
ore minerals, galena and sphalerite, an alternative analysis
technique such as laser ablation inductively coupled plasma
mass spectrometry (LA-ICP-MS) with significantly lower
detection limits would be able to determine the Ag trace
element concentrations in all sulphides in the ore. The
study from Quinteros et al. (2015) on the flotation of a
different complex Zn-ore, showed up to 2936 ± 686 ppm
Ag in pyrite. If pyrite were to be a significant host of Ag
at Gamsberg, alternative flowsheet options would have to
be investigated to recover it given that pyrite is currently
rejected on site.
Back-scattered electron (BSE) images and accompa-
nying EDS data for selected Ag-bearing minerals in the
Pb and Zn concentrates are illustrated in Figure 6 to pro-
vide an indication of the particle characteristics that were
observed across the sample set. Figure 6a illustrates a fine-
grained freibergite particle present in the high-Mn Pb con-
centrate which is associated with an exposed galena particle
associated with pyrrhotite. The Ag content in freibergite is
14.1 wt.%, which is around the Ag content in other frei-
bergite grains observed in the samples. Unliberated freiber-
gite particles associated with pyrite and chalcopyrite were
also observed in this concentrate. Figure 6b illustrates a
0 2 4 6 8 10 12 14 16 18 20 22
0
10
20
30
40
50
60
70
80
90
100
Time (min)
High-Mn Ag
High-Mn Zn
High-Mn Pb
High-Mn Fe
High-Mn C
C Pb Zn
0 2 4 6 8 10 12 14 16 18 20 22
0
10
20
30
40
50
60
70
80
90
100
Time (min)
Low-Mn Ag
Low-Mn Zn
Low-Mn Pb
Low-Mn Fe
Low-Mn C
C Pb Zn
A B
Figure 4. Cumulative elemental recovery vs time following sequential flotation for the low-Mn (a) and high-Mn (b) ores.
Labels are given to show the domains of sequential C, Pb and Zn flotation. Error bars represent the standard error between
duplicate floats
Recovery
(%)
Recovery
(%)
Ag and Pb in the high-Mn ore but rather Ag and Zn recov-
ery trends appear to follow one another. The Ag in the high
Mn ore is recovered to both the Pb (22.0%) and Zn con-
centrates (45.4%). The high recovery of Ag to the high-
Mn Zn concentrate may be due to a function of the poor
galena liberation and the galena association with sphalerite,
as shown in Figure 3.
Silver Mineralogy in Flotation Pb and Zn Concentrates
The distribution of Ag-bearing minerals in the Pb and
Zn concentrates is presented in Figure 5. The amount of
Ag-bearing particles within the concentrates is considerably
low given the concentrate Ag grades (a total 67 particles
detected). The ‘Ag in galena’ and ‘Ag in sphalerite’ catego-
ries are interpreted to represent micro Ag-bearing minerals
hosted in galena and sphalerite, respectively and not solid
solution-hosted Ag, since SEM-WDS indicated no detect-
able Ag within galena or sphalerite solid solution above the
detection limit. The ‘Ag-Si’ phase most likely represents
micro inclusions of Ag-bearing minerals hosted within sili-
cates. Argentite, sternbergite and ‘Ag in galena’ are the main
hosts of Ag in the high-Mn Pb concentrate. In the low Mn
ore concentrates, Ag mainly occurs as native Ag and argen-
tite. In the low-Mn Zn concentrate, Ag occurs as native
Ag, argentite and malinowskite. There are also significant
proportions of ‘Ag in galena’ grains within Pb concentrates,
and more native Ag present in the low-Mn concentrates.
A preliminary calculation of the Ag distribution suggests
that Ag cannot solely be hosted as discrete Ag minerals
within these samples (represented as a preliminary calcula-
tion given the low number of Ag-particle counts). It is pos-
sible that additional silver may occur within nano/micro
discrete Ag minerals that cannot be accurately detected
by SEM, or in solid solution within BMS. Although this
was undetected by SEM-WDS analysis of the two primary
ore minerals, galena and sphalerite, an alternative analysis
technique such as laser ablation inductively coupled plasma
mass spectrometry (LA-ICP-MS) with significantly lower
detection limits would be able to determine the Ag trace
element concentrations in all sulphides in the ore. The
study from Quinteros et al. (2015) on the flotation of a
different complex Zn-ore, showed up to 2936 ± 686 ppm
Ag in pyrite. If pyrite were to be a significant host of Ag
at Gamsberg, alternative flowsheet options would have to
be investigated to recover it given that pyrite is currently
rejected on site.
Back-scattered electron (BSE) images and accompa-
nying EDS data for selected Ag-bearing minerals in the
Pb and Zn concentrates are illustrated in Figure 6 to pro-
vide an indication of the particle characteristics that were
observed across the sample set. Figure 6a illustrates a fine-
grained freibergite particle present in the high-Mn Pb con-
centrate which is associated with an exposed galena particle
associated with pyrrhotite. The Ag content in freibergite is
14.1 wt.%, which is around the Ag content in other frei-
bergite grains observed in the samples. Unliberated freiber-
gite particles associated with pyrite and chalcopyrite were
also observed in this concentrate. Figure 6b illustrates a
0 2 4 6 8 10 12 14 16 18 20 22
0
10
20
30
40
50
60
70
80
90
100
Time (min)
High-Mn Ag
High-Mn Zn
High-Mn Pb
High-Mn Fe
High-Mn C
C Pb Zn
0 2 4 6 8 10 12 14 16 18 20 22
0
10
20
30
40
50
60
70
80
90
100
Time (min)
Low-Mn Ag
Low-Mn Zn
Low-Mn Pb
Low-Mn Fe
Low-Mn C
C Pb Zn
A B
Figure 4. Cumulative elemental recovery vs time following sequential flotation for the low-Mn (a) and high-Mn (b) ores.
Labels are given to show the domains of sequential C, Pb and Zn flotation. Error bars represent the standard error between
duplicate floats
Recovery
(%)
Recovery
(%)