XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1597
tailings were dried overnight and weighed. All flotation
tests were conducted in duplicate. The flotation products
were then assayed for Cu, Pb, Zn, Fe, Al, Ca, S and Ag
using a two-acid microwave digestion method (HNO3 and
HF) and inductively coupled plasma optical emission spec-
troscopy (ICP-OES) at Scientific Services. The analysis of
the samples was carried out using a Spectro Acros ICP-OES
with a plasma power at 1400 W, pump speed set at 30 rpm,
coolant flow at 14 L/min, auxillary flow at 2.1 L/min, and
nebulizer flow at 0.8 L/min. Recoveries and grades of Ag,
Zn, Pb, Fe and C within the successive C, Pb and Zn flota-
tion concentrates were determined.
Mineralogy
A 300 g representative aliquot of each milled sample was
wet screened to +53, +25/–53, +10/–25 and –10 µm size
fractions, dried and split to 4 g for quantitative evaluation
of minerals by scanning electron microscopy (QEMSCAN)
analysis using a FEI QEMSCAN 650F instrument operat-
ing at 25 kV and 10 nA. Each sized sample was prepared
as two 30 mm diameter polished blocks using carbon black
and a resin-hardener mixture before carbon coating, and
then run using the QEMSCAN bulk mineralogical analy-
sis (BMA) and trace mineral search (TMS) routines. Even
though samples were analyzed on a size-by-size basis, the
reconstituted (bulk) results are reported. The BMA and
TMS routines were performed using between 2–4 µm
pixel size and 211×–425× magnification. Mineralogy was
also conducted on the Pb and Zn batch flotation concen-
trates. For each sample, the two Pb concentrate samples
were combined and the four Zn concentrate samples were
combined. QEMSCAN blocks for the four samples were
prepared as 30 mm polished sections of unsized samples.
Seven blocks were prepared for the Pb concentrates, and
ten blocks for the Zn concentrates. The TMS routine
was conducted to search for discrete Ag-minerals within
the samples (21 surfaces for Pb concentrate samples and
30 surfaces for Zn concentrate samples). The overall Ag
counts for the Ag-bearing minerals are low, therefore, the
results are considered more qualitative. Scanning electron
microscope (SEM)—backscattered electron (BSE) images
were captured for most of the Ag-bearing minerals, and
energy dispersive spectroscopy (EDS) was conducted on
the grains. The EDS Ag data presents the average Ag con-
tent amongst three spots per grain. False colour field images
of two coarse 70 mm by 70 mm polished blocks (denoted
high-Mn PEO_Po and low-Mn), which have been analysed
as part of a previous study, have also been included in this
work (Molifie et al. 2021).
Each sized feed sample was also submitted for X-ray
fluorescence spectrometry (XRF) at the Gamsberg analyti-
cal laboratories. Unsized feed samples were submitted for
quantitative X-ray diffraction (XRD) using a Bruker D8
Advance diffractometer with a LynxEve detector at UCT
to validate the QEMSCAN data. Phase identification was
done in the Bruker EVA software and quantification using
the Rietveld refinement method in the Bruker TOPAS soft-
ware. Good correlation between the QEMSCAN and XRD
datasets was observed giving confidence in the QEMSCAN
mineralogy.
One 30 mm QEMSCAN block per sample was sub-
mitted for scanning electron microscopy-wavelength dis-
persive spectroscopy (SEM-WDS) using a ZEISS EVO
MA 15 EDS/WDS SEM instrument at the Centre for
Analytical Facilities (CAF) at Stellenbosch University
to determine whether Ag occurs in solid solution within
galena and sphalerite. SEM-WDS detected no measurable
Ag hosted in solid solution within galena or sphalerite. The
Ag may be present in a concentration below the detection
limit of 0.01 wt.%.
RESULTS AND DISCUSSION
Mineralogy and Chemistry
The bulk mineral grades within the high-Mn and low-Mn
ores are presented in Figure 1. The sphalerite grade is 33.0
wt.% in the high-Mn ore and 15.0 wt.% in the low-Mn ore.
The low-Mn ore is the only ore containing notable galena
(1.5 wt.%), whereas the galena content in the high-Mn ore
is less than 1 wt.%. Minor zincite, gahnite (grouped under
Zn oxides) and plumbogummite (under phosphates) are
present in both ores. Pyrite, quartz and mica are the major
gangue minerals present in these ores, although the high-
Mn ore also has significantly more pyrrhotite compared to
the low-Mn ore, whereas the low-Mn ore contains more
pyrite.
False colour field images for the high-Mn PEO_Po and
low-Mn samples are provided in Figure 2a and 2b, respec-
tively, to provide an indication of the unbroken particle
textures of these ores. The high-Mn PEO_Po end member
sample was chosen for presentation because it contributed
70% to the high-Mn ore. In the high-Mn PEO_Po sample,
there is a slight foliation in the quartzitic region which is
defined by mica. The sphalerite is coarse-grained, anhedral
and mainly associated with pyrrhotite and quartz. In the
quartzitic regions of the low-Mn ore, there is a rock folia-
tion also defined by mica. Fine-grained pyrite occurs in the
more foliated regions of the ore, whereas the pyrite in non-
foliated regions is coarse-grained. Sphalerite in the low-Mn
ore is anhedral and much more fine-grained (d50=372 µm)
tailings were dried overnight and weighed. All flotation
tests were conducted in duplicate. The flotation products
were then assayed for Cu, Pb, Zn, Fe, Al, Ca, S and Ag
using a two-acid microwave digestion method (HNO3 and
HF) and inductively coupled plasma optical emission spec-
troscopy (ICP-OES) at Scientific Services. The analysis of
the samples was carried out using a Spectro Acros ICP-OES
with a plasma power at 1400 W, pump speed set at 30 rpm,
coolant flow at 14 L/min, auxillary flow at 2.1 L/min, and
nebulizer flow at 0.8 L/min. Recoveries and grades of Ag,
Zn, Pb, Fe and C within the successive C, Pb and Zn flota-
tion concentrates were determined.
Mineralogy
A 300 g representative aliquot of each milled sample was
wet screened to +53, +25/–53, +10/–25 and –10 µm size
fractions, dried and split to 4 g for quantitative evaluation
of minerals by scanning electron microscopy (QEMSCAN)
analysis using a FEI QEMSCAN 650F instrument operat-
ing at 25 kV and 10 nA. Each sized sample was prepared
as two 30 mm diameter polished blocks using carbon black
and a resin-hardener mixture before carbon coating, and
then run using the QEMSCAN bulk mineralogical analy-
sis (BMA) and trace mineral search (TMS) routines. Even
though samples were analyzed on a size-by-size basis, the
reconstituted (bulk) results are reported. The BMA and
TMS routines were performed using between 2–4 µm
pixel size and 211×–425× magnification. Mineralogy was
also conducted on the Pb and Zn batch flotation concen-
trates. For each sample, the two Pb concentrate samples
were combined and the four Zn concentrate samples were
combined. QEMSCAN blocks for the four samples were
prepared as 30 mm polished sections of unsized samples.
Seven blocks were prepared for the Pb concentrates, and
ten blocks for the Zn concentrates. The TMS routine
was conducted to search for discrete Ag-minerals within
the samples (21 surfaces for Pb concentrate samples and
30 surfaces for Zn concentrate samples). The overall Ag
counts for the Ag-bearing minerals are low, therefore, the
results are considered more qualitative. Scanning electron
microscope (SEM)—backscattered electron (BSE) images
were captured for most of the Ag-bearing minerals, and
energy dispersive spectroscopy (EDS) was conducted on
the grains. The EDS Ag data presents the average Ag con-
tent amongst three spots per grain. False colour field images
of two coarse 70 mm by 70 mm polished blocks (denoted
high-Mn PEO_Po and low-Mn), which have been analysed
as part of a previous study, have also been included in this
work (Molifie et al. 2021).
Each sized feed sample was also submitted for X-ray
fluorescence spectrometry (XRF) at the Gamsberg analyti-
cal laboratories. Unsized feed samples were submitted for
quantitative X-ray diffraction (XRD) using a Bruker D8
Advance diffractometer with a LynxEve detector at UCT
to validate the QEMSCAN data. Phase identification was
done in the Bruker EVA software and quantification using
the Rietveld refinement method in the Bruker TOPAS soft-
ware. Good correlation between the QEMSCAN and XRD
datasets was observed giving confidence in the QEMSCAN
mineralogy.
One 30 mm QEMSCAN block per sample was sub-
mitted for scanning electron microscopy-wavelength dis-
persive spectroscopy (SEM-WDS) using a ZEISS EVO
MA 15 EDS/WDS SEM instrument at the Centre for
Analytical Facilities (CAF) at Stellenbosch University
to determine whether Ag occurs in solid solution within
galena and sphalerite. SEM-WDS detected no measurable
Ag hosted in solid solution within galena or sphalerite. The
Ag may be present in a concentration below the detection
limit of 0.01 wt.%.
RESULTS AND DISCUSSION
Mineralogy and Chemistry
The bulk mineral grades within the high-Mn and low-Mn
ores are presented in Figure 1. The sphalerite grade is 33.0
wt.% in the high-Mn ore and 15.0 wt.% in the low-Mn ore.
The low-Mn ore is the only ore containing notable galena
(1.5 wt.%), whereas the galena content in the high-Mn ore
is less than 1 wt.%. Minor zincite, gahnite (grouped under
Zn oxides) and plumbogummite (under phosphates) are
present in both ores. Pyrite, quartz and mica are the major
gangue minerals present in these ores, although the high-
Mn ore also has significantly more pyrrhotite compared to
the low-Mn ore, whereas the low-Mn ore contains more
pyrite.
False colour field images for the high-Mn PEO_Po and
low-Mn samples are provided in Figure 2a and 2b, respec-
tively, to provide an indication of the unbroken particle
textures of these ores. The high-Mn PEO_Po end member
sample was chosen for presentation because it contributed
70% to the high-Mn ore. In the high-Mn PEO_Po sample,
there is a slight foliation in the quartzitic region which is
defined by mica. The sphalerite is coarse-grained, anhedral
and mainly associated with pyrrhotite and quartz. In the
quartzitic regions of the low-Mn ore, there is a rock folia-
tion also defined by mica. Fine-grained pyrite occurs in the
more foliated regions of the ore, whereas the pyrite in non-
foliated regions is coarse-grained. Sphalerite in the low-Mn
ore is anhedral and much more fine-grained (d50=372 µm)