XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1591
underground ores, and the blends were subjected to kinetic
testing. Results from the blended tests demonstrated that
acceptable levels of metal recovery could be expected in the
existing Copperton Concentrator if the ore blend were held
at 10% or less underground ore.
While the rougher kinetic testing provided recovery
estimates, they could not forecast the final concentrate
grades produced. To predict final concentrate grades result-
ing from the underground ores, the ore type (lithology)
composite samples were subjected to cleaner flotation tests.
Two types of tests were conducted. Cleaner kinetic testing
was conducted on the samples to confirm cleaner circuit
capacity was appropriate. Next, 3-stage open circuit cleaner
flotation tests were conducted. The 2nd cleaner concen-
trate was selected as a good estimate for the performance of
the installed cleaner circuit at Copperton. Second cleaner
concentrates from each lithology type were collected and
assayed via ICP so that an understanding of minor element
deportment could be developed. Cleaner results showed
that good quality concentrates (=25% Cu) could be
obtained, and that deleterious elements were not expected
to concentrate to problematic levels for smelting.
One caveat to the concentrate quality was that flotation
of the massive sulfide ore types (CMS and UMS) required
a specific reagent strategy to manage pyrite deportment.
Sodium cyanide was required as a pyrite depressant, other-
wise excessive pyrite would report to the final concentrate,
lowering the grade and the copper to sulfur ratio, which
is a key smelter quality limit. A high pyrite bleed stream
could be produced, if needed, by forcing most of the pyrite
into the cleaner circuit tailing stream. This could be accom-
plished by utilizing a strong collector in the rougher/scav-
enger circuits (which would yield a very low sulfur rougher
tail). The bulk sulfide concentrate would then be upgraded
in the cleaner circuit utilizing cyanide to split the sulfides
into a high-grade concentrate and a high pyritic tailing.
Alternatively, cyanide can simply be utilized in the rougher
circuit to drop the pyrite initially.
The final OoM scope was to conduct locked cycle
flotation testing on the lithology types, as well as surface/
underground ore blends. The locked cycle tests were able to
approximate recovery and grade predictions based on the
prior work.
Overall metallurgical projections for throughput and
recovery were applied to the mining schedule from the
underground OoM study, allowing for an assessment of the
overall project value. The results were positive enough for
the studies to advance from OoM to Prefeasibility.
Prefeasibility (PFS) Geo-metallurgical Approach
The approach to metallurgical testing in PFS (completed in
2021) was very similar to OoM with regards to the specific
comminution and flotation test procedures. Sample selec-
tion followed a very different approach, however. Rather
than targeting ore type composites that matched the geo-
logical block model averages, the PFS approach was to
measure spatial and grade variability. Considerable new
core drilling was conducted, and a “down-the-hole” sam-
pling method for core selection was used. This meant that
contiguous lengths of core were pulled and combined to
produce samples that would represent various ore depths
along any given drill hole. Composite interval lengths were
targeted to approximate underground stope sizing, so that
geo-metallurgical and mining models would have similar
granularity. Samples were generally ended at lithology type
boundaries so that the variability of the results within the
previously defined ore types could be evaluated.
The results of the variability testing demonstrated
a measurable head-grade effect on recovery predictions,
which was not unexpected based on results from the OoM
work. This allowed for recovery models to be developed
that could include head grade effects if required.
A key finding of the PFS test work was that the lithol-
ogy types were not good proxies for metallurgical ore types.
Instead, only three groupings of metallurgical response
were noticed, which led to a simplified ore type definition.
These new ore types were “high sulfur” (25% S), which
mostly included CMS and UMS lithologies, “low sulfur”
(25% S), which included Garnet and Clay rich lithology
types, and finally “magnetite skarn” ore type.
The ore response difference between low sulfur and
high sulfur was primarily driven by the observed differences
in concentrate grade with increasing sulfur content. The
mineralogy results for feed samples revealed a linear rela-
tionship between sulfur grade and pyrite grade (Figure 4).
As high sulfur samples contain higher pyrite content rela-
tive to copper sulfide minerals, it is suspected that pyrite
was out-competing copper minerals due to limited froth
capacity, reducing the ultimate grade of the concentrate.
On average, concentrate grades for high sulfur samples
were 9.1% copper, compared to an average of 24% copper
for low sulfur samples.
The magnetite skarn ore type was designated primarily
so that the magnetite content of mill feed could be esti-
mated based on the mine plan. Excessive magnetite can
cause operational issues around conveyor belt steel removal
magnets. Metallurgically, sulfur content alone could be
used to categorize the underground ore behavior. With
these ore types defined, sulfur, copper, and iron assays of a
underground ores, and the blends were subjected to kinetic
testing. Results from the blended tests demonstrated that
acceptable levels of metal recovery could be expected in the
existing Copperton Concentrator if the ore blend were held
at 10% or less underground ore.
While the rougher kinetic testing provided recovery
estimates, they could not forecast the final concentrate
grades produced. To predict final concentrate grades result-
ing from the underground ores, the ore type (lithology)
composite samples were subjected to cleaner flotation tests.
Two types of tests were conducted. Cleaner kinetic testing
was conducted on the samples to confirm cleaner circuit
capacity was appropriate. Next, 3-stage open circuit cleaner
flotation tests were conducted. The 2nd cleaner concen-
trate was selected as a good estimate for the performance of
the installed cleaner circuit at Copperton. Second cleaner
concentrates from each lithology type were collected and
assayed via ICP so that an understanding of minor element
deportment could be developed. Cleaner results showed
that good quality concentrates (=25% Cu) could be
obtained, and that deleterious elements were not expected
to concentrate to problematic levels for smelting.
One caveat to the concentrate quality was that flotation
of the massive sulfide ore types (CMS and UMS) required
a specific reagent strategy to manage pyrite deportment.
Sodium cyanide was required as a pyrite depressant, other-
wise excessive pyrite would report to the final concentrate,
lowering the grade and the copper to sulfur ratio, which
is a key smelter quality limit. A high pyrite bleed stream
could be produced, if needed, by forcing most of the pyrite
into the cleaner circuit tailing stream. This could be accom-
plished by utilizing a strong collector in the rougher/scav-
enger circuits (which would yield a very low sulfur rougher
tail). The bulk sulfide concentrate would then be upgraded
in the cleaner circuit utilizing cyanide to split the sulfides
into a high-grade concentrate and a high pyritic tailing.
Alternatively, cyanide can simply be utilized in the rougher
circuit to drop the pyrite initially.
The final OoM scope was to conduct locked cycle
flotation testing on the lithology types, as well as surface/
underground ore blends. The locked cycle tests were able to
approximate recovery and grade predictions based on the
prior work.
Overall metallurgical projections for throughput and
recovery were applied to the mining schedule from the
underground OoM study, allowing for an assessment of the
overall project value. The results were positive enough for
the studies to advance from OoM to Prefeasibility.
Prefeasibility (PFS) Geo-metallurgical Approach
The approach to metallurgical testing in PFS (completed in
2021) was very similar to OoM with regards to the specific
comminution and flotation test procedures. Sample selec-
tion followed a very different approach, however. Rather
than targeting ore type composites that matched the geo-
logical block model averages, the PFS approach was to
measure spatial and grade variability. Considerable new
core drilling was conducted, and a “down-the-hole” sam-
pling method for core selection was used. This meant that
contiguous lengths of core were pulled and combined to
produce samples that would represent various ore depths
along any given drill hole. Composite interval lengths were
targeted to approximate underground stope sizing, so that
geo-metallurgical and mining models would have similar
granularity. Samples were generally ended at lithology type
boundaries so that the variability of the results within the
previously defined ore types could be evaluated.
The results of the variability testing demonstrated
a measurable head-grade effect on recovery predictions,
which was not unexpected based on results from the OoM
work. This allowed for recovery models to be developed
that could include head grade effects if required.
A key finding of the PFS test work was that the lithol-
ogy types were not good proxies for metallurgical ore types.
Instead, only three groupings of metallurgical response
were noticed, which led to a simplified ore type definition.
These new ore types were “high sulfur” (25% S), which
mostly included CMS and UMS lithologies, “low sulfur”
(25% S), which included Garnet and Clay rich lithology
types, and finally “magnetite skarn” ore type.
The ore response difference between low sulfur and
high sulfur was primarily driven by the observed differences
in concentrate grade with increasing sulfur content. The
mineralogy results for feed samples revealed a linear rela-
tionship between sulfur grade and pyrite grade (Figure 4).
As high sulfur samples contain higher pyrite content rela-
tive to copper sulfide minerals, it is suspected that pyrite
was out-competing copper minerals due to limited froth
capacity, reducing the ultimate grade of the concentrate.
On average, concentrate grades for high sulfur samples
were 9.1% copper, compared to an average of 24% copper
for low sulfur samples.
The magnetite skarn ore type was designated primarily
so that the magnetite content of mill feed could be esti-
mated based on the mine plan. Excessive magnetite can
cause operational issues around conveyor belt steel removal
magnets. Metallurgically, sulfur content alone could be
used to categorize the underground ore behavior. With
these ore types defined, sulfur, copper, and iron assays of a