1590 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
2 NRS (NRS2). The rationale for this subdivision is the
anticipated prevalence of unconsolidated massive sulfides
(UMS) in NRS2 that are of lower abundance in NRS1.
The anticipated mining method for the skarns is longhole
open stoping with overhand (bottom-up) mining of LCS
and NRS1 using cemented aggregate backfill for filling the
mining voids. Due to the prevalence of UMS in NRS2,
however, it is proposed that this mining area will use under-
hand (top-down) mining with flowable paste backfill to
enable filling of the mining voids.
The ore types and metallurgical responses defined for
the NRS were finalized during the NRS1 feasibility study
as: (1) low sulfur, (2) high sulfur, and (3) magnetite skarn.
It is expected that NRS2 will exhibit more high sulfur com-
pared to NRS1 due to the abundance of UMS. Due to the
relatively small size of the LCS orebody, and comparable
results across the LCS alteration types, the LCS metallurgi-
cal response has been defined within a single distinct ore
type.
The remaining skarns have much lower levels of ore-
body knowledge at this stage and metallurgical responses
are estimated at an orebody scale based on the order-of
magnitude geo-metallurgical approach.
Order of Magnitude (OoM) Geo-metallurgical
Approach
The approach in the earliest stage of study (OoM com-
pleted in 2014) focused on using the geological block
model to select core samples that would approximate the
envisioned ore types in the underground skarns. Since the
underground geology and mineralogy are quite different
than the surface ores, existing Kennecott ore type domains
could not be applied. Based on extensive core drilling and
geological logging of the resulting core, several dominate
lithologies were identified. These lithologies were adopted
as proxies for ore types during the OoM test work. The
lithology types identified were:
• Garnet dominated (“Garnet Skarn”)
• Hematite and magnetite rich (“Iron Skarn”)
• Clay rich (“Clay Skarn”)
• Consolidated massive sulfide (“CMS”)
• Unconsolidated massive sulfide (“UMS”)
The geological block models estimated the volumetric con-
tent of each lithology type and the average head grades
within each lithology. Based on these data, composite
samples of core from each lithology type were put together
for metallurgical testing. Core intervals were selected from
each lithology based mainly on head grades, so the result-
ing composite samples would average about the same head
grades as the corresponding geological block model aver-
ages. This method allowed for testing at the average condi-
tion for each lithology type. Spatial and grade variability
were not studied at OoM.
Each of the lithology composite samples was sub-
jected to metallurgical testing that included both com-
minution testing and flotation testing. These test results
allowed predictions to be applied to the mining plan of
production to model plant throughput (grind limited) and
metal recoveries. Comminution testing started with the
SAG Mill Comminution (SMC) test that was performed
to allow estimation of SAG mill throughputs for each
lithology type through the existing Kennecott Copperton
Concentrator. Similarly, the Bond Work Index (BWI) test
was subsequently run to determine ball mill throughput at
the desired grind size.
Flotation testing on the OoM lithology samples
focused primarily on rougher flotation kinetics. Standard
Denver cell batch flotation tests were conducted on each
sample at two different grind sizes (targeting ~180 µm and
~230 µm P80). This allowed for estimation of grind varia-
tion effect on recovery. From these kinetic test results, it was
possible to estimate the recovery expected in the Copperton
Concentrator’s existing flotation circuit.
Initial kinetic results on the underground ores showed
that the higher-grade underground ores required signifi-
cantly longer flotation retention time than the surface ore
types to achieve comparable metal recoveries. These results
were unsurprising due to the head grade differences, with
the underground ores ranging 2 – 4% Cu, while the surface
ores are in the range of 0.4 – 0.8%. With such an increased
head grade, the froth carrying capacity limited the rate of
metal recovery and extended the required flotation time.
The conclusion from this was that the underground ores
would either require a dedicated flotation circuit to accom-
modate the longer residence time, or these ores would need
to be co-mingled with surface mine ore prior to being fed
to the Copperton Concentrator. The latter approach was
chosen to avoid the capital cost of a new mill.
The relative tonnages of the underground and surface
mining rates allowed for underground ore to blend with
surface ores at ratios between 1:10 and 1:20. This blending
of 5–10% underground ore into the total mill feed would
reduce the overall head grade to the point that froth carrying
capacity would no longer be overloaded in the Copperton
circuit. To demonstrate this, two master composites of sur-
face ore were collected (simulating upper and lower pit ore
distributions). These surface ore samples were then sub-
jected to the same flotation kinetic testing to establish a
baseline. These ores were then blended with 5% and 10%
2 NRS (NRS2). The rationale for this subdivision is the
anticipated prevalence of unconsolidated massive sulfides
(UMS) in NRS2 that are of lower abundance in NRS1.
The anticipated mining method for the skarns is longhole
open stoping with overhand (bottom-up) mining of LCS
and NRS1 using cemented aggregate backfill for filling the
mining voids. Due to the prevalence of UMS in NRS2,
however, it is proposed that this mining area will use under-
hand (top-down) mining with flowable paste backfill to
enable filling of the mining voids.
The ore types and metallurgical responses defined for
the NRS were finalized during the NRS1 feasibility study
as: (1) low sulfur, (2) high sulfur, and (3) magnetite skarn.
It is expected that NRS2 will exhibit more high sulfur com-
pared to NRS1 due to the abundance of UMS. Due to the
relatively small size of the LCS orebody, and comparable
results across the LCS alteration types, the LCS metallurgi-
cal response has been defined within a single distinct ore
type.
The remaining skarns have much lower levels of ore-
body knowledge at this stage and metallurgical responses
are estimated at an orebody scale based on the order-of
magnitude geo-metallurgical approach.
Order of Magnitude (OoM) Geo-metallurgical
Approach
The approach in the earliest stage of study (OoM com-
pleted in 2014) focused on using the geological block
model to select core samples that would approximate the
envisioned ore types in the underground skarns. Since the
underground geology and mineralogy are quite different
than the surface ores, existing Kennecott ore type domains
could not be applied. Based on extensive core drilling and
geological logging of the resulting core, several dominate
lithologies were identified. These lithologies were adopted
as proxies for ore types during the OoM test work. The
lithology types identified were:
• Garnet dominated (“Garnet Skarn”)
• Hematite and magnetite rich (“Iron Skarn”)
• Clay rich (“Clay Skarn”)
• Consolidated massive sulfide (“CMS”)
• Unconsolidated massive sulfide (“UMS”)
The geological block models estimated the volumetric con-
tent of each lithology type and the average head grades
within each lithology. Based on these data, composite
samples of core from each lithology type were put together
for metallurgical testing. Core intervals were selected from
each lithology based mainly on head grades, so the result-
ing composite samples would average about the same head
grades as the corresponding geological block model aver-
ages. This method allowed for testing at the average condi-
tion for each lithology type. Spatial and grade variability
were not studied at OoM.
Each of the lithology composite samples was sub-
jected to metallurgical testing that included both com-
minution testing and flotation testing. These test results
allowed predictions to be applied to the mining plan of
production to model plant throughput (grind limited) and
metal recoveries. Comminution testing started with the
SAG Mill Comminution (SMC) test that was performed
to allow estimation of SAG mill throughputs for each
lithology type through the existing Kennecott Copperton
Concentrator. Similarly, the Bond Work Index (BWI) test
was subsequently run to determine ball mill throughput at
the desired grind size.
Flotation testing on the OoM lithology samples
focused primarily on rougher flotation kinetics. Standard
Denver cell batch flotation tests were conducted on each
sample at two different grind sizes (targeting ~180 µm and
~230 µm P80). This allowed for estimation of grind varia-
tion effect on recovery. From these kinetic test results, it was
possible to estimate the recovery expected in the Copperton
Concentrator’s existing flotation circuit.
Initial kinetic results on the underground ores showed
that the higher-grade underground ores required signifi-
cantly longer flotation retention time than the surface ore
types to achieve comparable metal recoveries. These results
were unsurprising due to the head grade differences, with
the underground ores ranging 2 – 4% Cu, while the surface
ores are in the range of 0.4 – 0.8%. With such an increased
head grade, the froth carrying capacity limited the rate of
metal recovery and extended the required flotation time.
The conclusion from this was that the underground ores
would either require a dedicated flotation circuit to accom-
modate the longer residence time, or these ores would need
to be co-mingled with surface mine ore prior to being fed
to the Copperton Concentrator. The latter approach was
chosen to avoid the capital cost of a new mill.
The relative tonnages of the underground and surface
mining rates allowed for underground ore to blend with
surface ores at ratios between 1:10 and 1:20. This blending
of 5–10% underground ore into the total mill feed would
reduce the overall head grade to the point that froth carrying
capacity would no longer be overloaded in the Copperton
circuit. To demonstrate this, two master composites of sur-
face ore were collected (simulating upper and lower pit ore
distributions). These surface ore samples were then sub-
jected to the same flotation kinetic testing to establish a
baseline. These ores were then blended with 5% and 10%