XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1387
process streams and strategies were developed to improve
metallurgical outcomes.
Findings for the copper-gold refractory ore suggest that
a minimum gold deportment of around 5% is expected in
copper concentrates due to the presence of invisible gold
in chalcopyrite. This information allowed redefining the
flotation conditions to ensure that any free gold in copper
flotation was sufficiently depressed so that the CIL circuit
on flotation tailings could recover them. Care was taken to
maximize chalcopyrite recovery in copper flotation, other-
wise the invisible gold associated with chalcopyrite in flota-
tion tailings would be lost in CIL. Quantification of gold
in different species allows defining the right process strate-
gies to maximize overall gold recovery and also net smelter
returns (NSR).
One of the major challenges with some complex ore
bodies is the presence of refractory gold in iron oxides. In
the case of the copper-gold refractory ore presented in this
study, the gold losses associated with iron oxides in flota-
tion rougher tails were unusually high, around 22%. This
insight highlighted the need to recover the gold associated
with iron oxides to maximize overall gold recovery for the
deposit. A novel process was developed to maximize recov-
ery of iron oxide and the associated gold. Details of this
development are beyond the scope of this paper.
The findings of studies on the double refractory ore sug-
gested that about 23% of the total gold losses were due to
inadequate sulfide oxidation in autoclaves. In many cases,
these sulfides were in organic carbon as fine inclusions,
which resulted in poor oxidation of sulfides and the gold-
robbing behavior of carbon, thus magnifying the challenges
associated with gold recovery. A novel patented flotation
process was developed by Barrick that allowed recovery of
organic carbon and fine inclusion of sulfides in a small mass
of flotation concentrate, which could then be recovered by
roasting or other processes (Gorain and Kondos, 2012).
The findings of the studies on the triple refractory ores
suggest that pyrite was the dominant gold carrier account-
ing for 75 to 85% of total gold in flotation concentrates
whereas the flotation tailings consisted of gold losses
associated with pyrite and iron oxides. This understand-
ing allowed development of a flotation process that could
recover arsenic bearing minerals from pyrite along with
selective separation of organic carbon and pyrite. Other
flotation improvement opportunities utilizing quantita-
tive gold deportment and mineralogy information as an
important step have been discussed elsewhere (Gorain,
2016, 2013). The integrated quantitative gold mineralogy
methodology used in this study has been instrumental in
providing the much-needed insight for development of
Table 4a. Visible and Invisible Gold distribution for a Cu-Au refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %
Total Invisible
Gold, %
Total Visible
Gold, %Pyrite
Cu-
Sulphides Other Sulphides Fe-Oxides
Feed 2.46 2.64 0.04 5.54 10.7 89.3
Final Concentrate 0.47 4.53 0.09 0.02 5.1 94.9
Cleaner Scav. Tail 8.59 0.3 0.09 11.93 20.9 79.1
Rougher Tail 0.34 1.04 — 21.49 22.9 77.1
Table 4b. Invisible and Gold-robbed Surface Gold distribution for a Double refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %Total Invisible Gold,
%
Preg-robbed Surface
Gold, %Pyrite Fe-Oxides TCM
Feed 93.6 2.1 4.3 100 —
POX/CIL Residue 22.7 2.8 4.7 30.2 69.8
CIL Residue 28.2 2.4 3.8 34.4 65.6
Table 4c. Visible and Invisible Gold distribution for a triple refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %Total Invisible
Gold, %
Total Visible
Gold, %Pyrite Arsenopyrite Realgar Fe-Oxides TCM
Feed 87.5 0.4 1.6 0.2 0.2 89.9 10.1
Py Scav Ro Cone 85.4 0.2 0.6 0.2 0.1 86.5 13.5
TCM Ro Cone 75.8 8.5 5.4 0.1 0.6 90.4 9.6
Rougher Tail 37.6 0.3 1.9 25.8 0.7 66.3 33.7
process streams and strategies were developed to improve
metallurgical outcomes.
Findings for the copper-gold refractory ore suggest that
a minimum gold deportment of around 5% is expected in
copper concentrates due to the presence of invisible gold
in chalcopyrite. This information allowed redefining the
flotation conditions to ensure that any free gold in copper
flotation was sufficiently depressed so that the CIL circuit
on flotation tailings could recover them. Care was taken to
maximize chalcopyrite recovery in copper flotation, other-
wise the invisible gold associated with chalcopyrite in flota-
tion tailings would be lost in CIL. Quantification of gold
in different species allows defining the right process strate-
gies to maximize overall gold recovery and also net smelter
returns (NSR).
One of the major challenges with some complex ore
bodies is the presence of refractory gold in iron oxides. In
the case of the copper-gold refractory ore presented in this
study, the gold losses associated with iron oxides in flota-
tion rougher tails were unusually high, around 22%. This
insight highlighted the need to recover the gold associated
with iron oxides to maximize overall gold recovery for the
deposit. A novel process was developed to maximize recov-
ery of iron oxide and the associated gold. Details of this
development are beyond the scope of this paper.
The findings of studies on the double refractory ore sug-
gested that about 23% of the total gold losses were due to
inadequate sulfide oxidation in autoclaves. In many cases,
these sulfides were in organic carbon as fine inclusions,
which resulted in poor oxidation of sulfides and the gold-
robbing behavior of carbon, thus magnifying the challenges
associated with gold recovery. A novel patented flotation
process was developed by Barrick that allowed recovery of
organic carbon and fine inclusion of sulfides in a small mass
of flotation concentrate, which could then be recovered by
roasting or other processes (Gorain and Kondos, 2012).
The findings of the studies on the triple refractory ores
suggest that pyrite was the dominant gold carrier account-
ing for 75 to 85% of total gold in flotation concentrates
whereas the flotation tailings consisted of gold losses
associated with pyrite and iron oxides. This understand-
ing allowed development of a flotation process that could
recover arsenic bearing minerals from pyrite along with
selective separation of organic carbon and pyrite. Other
flotation improvement opportunities utilizing quantita-
tive gold deportment and mineralogy information as an
important step have been discussed elsewhere (Gorain,
2016, 2013). The integrated quantitative gold mineralogy
methodology used in this study has been instrumental in
providing the much-needed insight for development of
Table 4a. Visible and Invisible Gold distribution for a Cu-Au refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %
Total Invisible
Gold, %
Total Visible
Gold, %Pyrite
Cu-
Sulphides Other Sulphides Fe-Oxides
Feed 2.46 2.64 0.04 5.54 10.7 89.3
Final Concentrate 0.47 4.53 0.09 0.02 5.1 94.9
Cleaner Scav. Tail 8.59 0.3 0.09 11.93 20.9 79.1
Rougher Tail 0.34 1.04 — 21.49 22.9 77.1
Table 4b. Invisible and Gold-robbed Surface Gold distribution for a Double refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %Total Invisible Gold,
%
Preg-robbed Surface
Gold, %Pyrite Fe-Oxides TCM
Feed 93.6 2.1 4.3 100 —
POX/CIL Residue 22.7 2.8 4.7 30.2 69.8
CIL Residue 28.2 2.4 3.8 34.4 65.6
Table 4c. Visible and Invisible Gold distribution for a triple refractory ore
Sample ID
Invisible/Sub-Microscopic Gold, %Total Invisible
Gold, %
Total Visible
Gold, %Pyrite Arsenopyrite Realgar Fe-Oxides TCM
Feed 87.5 0.4 1.6 0.2 0.2 89.9 10.1
Py Scav Ro Cone 85.4 0.2 0.6 0.2 0.1 86.5 13.5
TCM Ro Cone 75.8 8.5 5.4 0.1 0.6 90.4 9.6
Rougher Tail 37.6 0.3 1.9 25.8 0.7 66.3 33.7