XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1481
line highlighting the division between low and high CM
samples (grade of 0.1%). The 83 analyzed samples have an
average increase of 14.6% in the delta gold extraction, with
the high CM samples averaging 23.5% and samples with
low CM have an average increase of 10.6%. While the aver-
age of the delta gold extraction is higher for the high carbon
samples, there is no appreciable direct correlation between
the delta gold extractions and the CM concentrations. This
indicates that there may be structurally different types of
CM present with different degrees of gold robbing capacity.
It might also suggest that there are different mechanisms of
enhanced gold extraction in the presence of activated car-
bon because at both lower and higher CM contents there
are a wide range of deltas.
As highlighted in the previous section, past studies
have shown that the degree of disorder of the CM within
a sample can be correlated with its gold robbing capacity
(Helm et al., 2009). The disorder of CM can be classified
into crystalline (well ordered) or amorphous (disordered)
endmembers. To investigate whether the type of CM in
the sample is controlling the delta gold extraction by pro-
ducing gold robbing that can be overcome in the presence
of activated carbon, eight samples with low and high CM
were selected for further characterization. Additionally, the
use of the CM classification for the selected samples was
tested as a proxy for gold robbing with amorphous carbon
expected to experience a stronger gold robbing capacity
while crystalline carbon is expected to have less.
MINERALOGICAL CHARACTERIZATION
The eight head samples selected were initially analyzed by
the Tescan Integrated Mineral Analyzer (TIMA) for modal
mineralogy (Table 2). TIMA uses image segmentation algo-
rithms to detect individual particles and mineral grains. A
combination of back-scattered electron (BSE) signal inten-
sity and spectroscopic data is used to distinguish phases. An
energy dispersive X-ray spectrum (EDS) is then collected
for each segment containing mineral chemistry content
that are summed and used for mineral classification. The
TIMA samples were run through a rotary micro-riffler to
Figure 4. Delta gold extraction (CIL-leach) versus CM in the pyrite concentrate samples

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1481
line highlighting the division between low and high CM
samples (grade of 0.1%). The 83 analyzed samples have an
average increase of 14.6% in the delta gold extraction, with
the high CM samples averaging 23.5% and samples with
low CM have an average increase of 10.6%. While the aver-
age of the delta gold extraction is higher for the high carbon
samples, there is no appreciable direct correlation between
the delta gold extractions and the CM concentrations. This
indicates that there may be structurally different types of
CM present with different degrees of gold robbing capacity.
It might also suggest that there are different mechanisms of
enhanced gold extraction in the presence of activated car-
bon because at both lower and higher CM contents there
are a wide range of deltas.
As highlighted in the previous section, past studies
have shown that the degree of disorder of the CM within
a sample can be correlated with its gold robbing capacity
(Helm et al., 2009). The disorder of CM can be classified
into crystalline (well ordered) or amorphous (disordered)
endmembers. To investigate whether the type of CM in
the sample is controlling the delta gold extraction by pro-
ducing gold robbing that can be overcome in the presence
of activated carbon, eight samples with low and high CM
were selected for further characterization. Additionally, the
use of the CM classification for the selected samples was
tested as a proxy for gold robbing with amorphous carbon
expected to experience a stronger gold robbing capacity
while crystalline carbon is expected to have less.
MINERALOGICAL CHARACTERIZATION
The eight head samples selected were initially analyzed by
the Tescan Integrated Mineral Analyzer (TIMA) for modal
mineralogy (Table 2). TIMA uses image segmentation algo-
rithms to detect individual particles and mineral grains. A
combination of back-scattered electron (BSE) signal inten-
sity and spectroscopic data is used to distinguish phases. An
energy dispersive X-ray spectrum (EDS) is then collected
for each segment containing mineral chemistry content
that are summed and used for mineral classification. The
TIMA samples were run through a rotary micro-riffler to
Figure 4. Delta gold extraction (CIL-leach) versus CM in the pyrite concentrate samples

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1482 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
obtain a 2 gram sub-split of the material. Each sample was
then mixed with carbon, mounted in epoxy resin, polished,
and carbon-coated for analysis.
Pyrite was the dominant sulfide in the head samples,
with concentrations ranging from 3–13%, with trace to
minor amounts (≤ 2%) of sphalerite and galena detected.
Sulfide quantities are greater in samples 1 through 4, how-
ever, the analysis indicates similar sulfur deportment results
throughout the suite, with pyrite accounting for an average
of 87% of the sulfur in the samples.
The eight head samples sized at –2 mm were subse-
quently analyzed by TIMA and laser ablation inductively
coupled plasma mass spectrometry (LA-ICP-MS) for gold
deportment. TIMA results represent visible gold occur-
rences (≥0.3 µm) followed by LA-ICP-MS for solid solution
gold 0.3 µm). TIMA’s Bright Phase Search (BPS) method
was used for gold characterization. The BPS method will
scan particles with grains that lie in a selected grey level
range. The grey levels selected for the scans were near-white
to white, to detect high atomic number minerals, such as
gold. LA-ICP-MS analyses were made using an Applied
Spectra RESOlution-SE 193 nm excimer laser ablation
instrument coupled with an Agilent 8900 ICP-MS. Samples
were ablated in a helium atmosphere using 12–30 µm laser
spots or 12 µm line scans. Table 3 shows the distribution of
gold in pyrite as visible or solid solution gold, along with
carbon and gold robbing characteristics. Carbon content
and gold robbing capacity are based on chemical analyses
completed on the samples. LA-ICP-MS analyzed sulfides
in the sample for submicron gold. Sulfides analyzed include
pyrite, galena, sphalerite, and arsenopyrite. Distinct mor-
phologies were analyzed for the dominant sulfide (pyrite)
which included coarse, porous, microcrystalline, and dis-
seminated. No discernible trends were evident in the gold
content among the different pyrite morphologies. The gold
content within all the sulfides analyzed in the sample was
summed up and used to determine solid solution gold.
The samples were subsequently characterized by man-
ual scanning electron microscopy (SEM) and Raman spec-
troscopy to characterize the physical properties of the CM
in the polymetallic ore deposit. The head samples were
received at –2 mm and stage crushed to –600 µm to maxi-
mize carbon liberation from gangue minerals while preserv-
ing the carbon grain size. Due to the fine-grained nature
of the CM, samples were screened to –150 µm and run
through a rotary micro-riffler to obtain a 20 g split.
The concentration of CM in the eight samples varies
from very low (0.01%) to higher (0.53%). Sample splits
were run through a heavy liquid density separation to
increase the concentration of CM by removing the sulfides
Table 2. Modal Mineralogy of the eight selected head samples
Mineral Mass, %1 2 3 4 5 6 7 8
Gold Phases 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
Silver Phases 0.01 0.001 0.001 0.001 0.001 0.01 0.001 0.001
Galena 1.08 0.12 0.04 0.03 0.83 1.14 0.49 0.60
Sphalerite 2.08 1.10 0.14 1.84 0.57 1.66 0.59 1.12
Pyrite 6.37 11.84 13.42 10.05 4.21 5.96 6.20 3.43
Arsenopyrite 0.001 0.04 0.07 0.05 0.34
Copper Sulfosalts 0.04 0.2 0.14 0.41 0.01 0.06 0.01 0.001
Other Sulfide and Sulfosalts 0.03 0.01 0.01 0.00 0.05 0.03 0.02 0.01
Non-Sulfide Gangue 90.40 86.74 86.26 87.67 94.29 91.08 92.65 94.49
Total 99.99 100.00 100.00 100.00 99.99 100.00 99.99 100.00
Table 3. Gold distribution, relative carbon content and gold robbing classification of the eight selected head samples
Sample ID Visible Gold, %Solid Solution Gold, %Carbon Content
Gold Robbing
Classification
1 79.5 20.5 Low Non
2 87.8 12.2 Low Non
3 63.6 36.4 Low Non
4 95.1 4.9 Low Non
5 37.5 62.5 High Highly
6 64.1 35.9 High Highly
7 16.2 83.8 High Highly
8 33.3 66.7 High Highly

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Extracted Text (may have errors)

1482 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
obtain a 2 gram sub-split of the material. Each sample was
then mixed with carbon, mounted in epoxy resin, polished,
and carbon-coated for analysis.
Pyrite was the dominant sulfide in the head samples,
with concentrations ranging from 3–13%, with trace to
minor amounts (≤ 2%) of sphalerite and galena detected.
Sulfide quantities are greater in samples 1 through 4, how-
ever, the analysis indicates similar sulfur deportment results
throughout the suite, with pyrite accounting for an average
of 87% of the sulfur in the samples.
The eight head samples sized at –2 mm were subse-
quently analyzed by TIMA and laser ablation inductively
coupled plasma mass spectrometry (LA-ICP-MS) for gold
deportment. TIMA results represent visible gold occur-
rences (≥0.3 µm) followed by LA-ICP-MS for solid solution
gold 0.3 µm). TIMA’s Bright Phase Search (BPS) method
was used for gold characterization. The BPS method will
scan particles with grains that lie in a selected grey level
range. The grey levels selected for the scans were near-white
to white, to detect high atomic number minerals, such as
gold. LA-ICP-MS analyses were made using an Applied
Spectra RESOlution-SE 193 nm excimer laser ablation
instrument coupled with an Agilent 8900 ICP-MS. Samples
were ablated in a helium atmosphere using 12–30 µm laser
spots or 12 µm line scans. Table 3 shows the distribution of
gold in pyrite as visible or solid solution gold, along with
carbon and gold robbing characteristics. Carbon content
and gold robbing capacity are based on chemical analyses
completed on the samples. LA-ICP-MS analyzed sulfides
in the sample for submicron gold. Sulfides analyzed include
pyrite, galena, sphalerite, and arsenopyrite. Distinct mor-
phologies were analyzed for the dominant sulfide (pyrite)
which included coarse, porous, microcrystalline, and dis-
seminated. No discernible trends were evident in the gold
content among the different pyrite morphologies. The gold
content within all the sulfides analyzed in the sample was
summed up and used to determine solid solution gold.
The samples were subsequently characterized by man-
ual scanning electron microscopy (SEM) and Raman spec-
troscopy to characterize the physical properties of the CM
in the polymetallic ore deposit. The head samples were
received at –2 mm and stage crushed to –600 µm to maxi-
mize carbon liberation from gangue minerals while preserv-
ing the carbon grain size. Due to the fine-grained nature
of the CM, samples were screened to –150 µm and run
through a rotary micro-riffler to obtain a 20 g split.
The concentration of CM in the eight samples varies
from very low (0.01%) to higher (0.53%). Sample splits
were run through a heavy liquid density separation to
increase the concentration of CM by removing the sulfides
Table 2. Modal Mineralogy of the eight selected head samples
Mineral Mass, %1 2 3 4 5 6 7 8
Gold Phases 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
Silver Phases 0.01 0.001 0.001 0.001 0.001 0.01 0.001 0.001
Galena 1.08 0.12 0.04 0.03 0.83 1.14 0.49 0.60
Sphalerite 2.08 1.10 0.14 1.84 0.57 1.66 0.59 1.12
Pyrite 6.37 11.84 13.42 10.05 4.21 5.96 6.20 3.43
Arsenopyrite 0.001 0.04 0.07 0.05 0.34
Copper Sulfosalts 0.04 0.2 0.14 0.41 0.01 0.06 0.01 0.001
Other Sulfide and Sulfosalts 0.03 0.01 0.01 0.00 0.05 0.03 0.02 0.01
Non-Sulfide Gangue 90.40 86.74 86.26 87.67 94.29 91.08 92.65 94.49
Total 99.99 100.00 100.00 100.00 99.99 100.00 99.99 100.00
Table 3. Gold distribution, relative carbon content and gold robbing classification of the eight selected head samples
Sample ID Visible Gold, %Solid Solution Gold, %Carbon Content
Gold Robbing
Classification
1 79.5 20.5 Low Non
2 87.8 12.2 Low Non
3 63.6 36.4 Low Non
4 95.1 4.9 Low Non
5 37.5 62.5 High Highly
6 64.1 35.9 High Highly
7 16.2 83.8 High Highly
8 33.3 66.7 High Highly

1480 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
mill. The concentrate samples were re-ground with a labo-
ratory Vertimill containing ceramic media to a target grind
size P80 of 25 µm prior to leaching.
It is important to note that the leach tests were con-
ducted on the pyrite concentrate while other analysis such
as the gold-rob #and mineralogical analyses presented in
the following sections were conducted on head samples. A
carbon depressant was utilize for CM grades above 0.05%
during the flotation stages, with about 20% of the CM
reporting to the pyrite concentrate. Given the mass pull and
recovery of the flotation stages, no enrichment of the CM
was observed, therefore it was assumed that the CM pres-
ent in the pyrite concentrate samples is representative of the
CM present in the head samples, as seen in Figure 3. The
degree of particle size reduction from the original sample
to the pyrite concentrate, represents one of the limitations
for a comprehensive mineral characterization of the leach
feed samples. Particularly, sample preparation for spectros-
copy based methods can be difficult due to the fine-grained
nature of the pyrite concentrate.
Two rounds of cyanidation leach testwork were com-
pleted on 83 pyrite concentrate samples to determine the
leachable gold content that remained in concentrate gen-
erated from the sequential rougher flotation tests. Leach
testwork for all samples was completed with and without
the presence of activated carbon to assess the impact of the
carbon-in-leach (CIL) process on the gold extractions and
its ability to overcome the gold robbing produced by the
presence of CM in the samples.
Analysis of the results of the tests on both leach con-
figurations, did not show a strong correlation between the
gold recoveries and the CM content or the gold-rob #,indi-
cating that other factors are influencing the metallurgical
response. Gold robbing by various sulfides minerals as well
as clays has been reported in the literature (Miller, Wan and
Diaz 2016), given that the leach feed samples considered in
this study have variable concentration of sulfides, this could
be a factor affecting the extent of gold extraction.
To reduce the impact of other factors on the analysis of
the leach response and how it depends on the CM content,
the difference between CIL tests and leach without carbon
was examined. The delta gold extractions were calculated
using both leach tests for each sample. Figure 4 shows the
delta gold extractions plotted against the CM concentra-
tion of the pyrite concentrate samples with a dotted vertical
Figure 2. High level flowsheet of sequential rougher flotation
Figure 3. Percent of CM in the head samples vs the pyrite concentrate

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Extracted Text (may have errors)

1480 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
mill. The concentrate samples were re-ground with a labo-
ratory Vertimill containing ceramic media to a target grind
size P80 of 25 µm prior to leaching.
It is important to note that the leach tests were con-
ducted on the pyrite concentrate while other analysis such
as the gold-rob #and mineralogical analyses presented in
the following sections were conducted on head samples. A
carbon depressant was utilize for CM grades above 0.05%
during the flotation stages, with about 20% of the CM
reporting to the pyrite concentrate. Given the mass pull and
recovery of the flotation stages, no enrichment of the CM
was observed, therefore it was assumed that the CM pres-
ent in the pyrite concentrate samples is representative of the
CM present in the head samples, as seen in Figure 3. The
degree of particle size reduction from the original sample
to the pyrite concentrate, represents one of the limitations
for a comprehensive mineral characterization of the leach
feed samples. Particularly, sample preparation for spectros-
copy based methods can be difficult due to the fine-grained
nature of the pyrite concentrate.
Two rounds of cyanidation leach testwork were com-
pleted on 83 pyrite concentrate samples to determine the
leachable gold content that remained in concentrate gen-
erated from the sequential rougher flotation tests. Leach
testwork for all samples was completed with and without
the presence of activated carbon to assess the impact of the
carbon-in-leach (CIL) process on the gold extractions and
its ability to overcome the gold robbing produced by the
presence of CM in the samples.
Analysis of the results of the tests on both leach con-
figurations, did not show a strong correlation between the
gold recoveries and the CM content or the gold-rob #,indi-
cating that other factors are influencing the metallurgical
response. Gold robbing by various sulfides minerals as well
as clays has been reported in the literature (Miller, Wan and
Diaz 2016), given that the leach feed samples considered in
this study have variable concentration of sulfides, this could
be a factor affecting the extent of gold extraction.
To reduce the impact of other factors on the analysis of
the leach response and how it depends on the CM content,
the difference between CIL tests and leach without carbon
was examined. The delta gold extractions were calculated
using both leach tests for each sample. Figure 4 shows the
delta gold extractions plotted against the CM concentra-
tion of the pyrite concentrate samples with a dotted vertical
Figure 2. High level flowsheet of sequential rougher flotation
Figure 3. Percent of CM in the head samples vs the pyrite concentrate