XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 131
of the total throughput was affected. Crushed ore feed bins
ahead of the mills provided 12 to 24-hour surge capacity
as a buffer between the crushers and the mills to mitigate
feed upsets. High capital cost was the principal downsize of
these smaller mills with their large building footprint.
In the late 70s and early 80s the Autogenous (AG)
and Semi-Autogenous (SAG) mills were being introduced
to copper processing, first with single-pinion drives which
later switching to dual-pinion drives. The size of these early
AG mills ranged from 5.5 m (18ft) diameter installed in
Australia to 9.8 m (32 ft) installed in Canada. The con-
nected power ranging from single pinons of 932 kW
(1,250 hp) at Kanmantoo to dual pinion and 8948 kW
(12,000 hp) at Island Copper. After start-up, operators of
single AG mill circuits increased throughput by installing
Ball mills and then also adding pebble crushing, these con-
figurations were referred to as ABC circuits. Cyprus Bagdad
would be one of the first innovators with the installation of
an ABC circuit. Utah’s Island Copper operation was also an
early adaptor starling with AG mills only, then later adding
Ball mills and then converting to Sag mills or to SAB cir-
cuits. Most common today is the addition of pebble crush-
ers to the SAB circuits or now referred to as SABC circuits
(Figure 4)
Dual pinons had become more common with the larger
mills and now Gearless Motor Drives (GMD) were being
introduced. The SAG mill size would then increase over the
next period from 11 m (36 ft) to 12.2 m (40 ft) diameter.
The connected power ranging from 9 MW (12,000 hp) to
28 MW (37,550 hp). Dual pinion drives were limited to ~
9–12 MW and the GMDs 12 MW. The feed size to these
large SABC circuits was 150–200 mm (6–8 inch). The
main design variables were ore hardness and the potential
for the accumulation of critical size material in the SAG
mills. The solution was the introduction of pebble ports
to the discharge grates to relieve the AG/SAG mills. This
change led to the addition of cone crushers to crush the
pebbles, resulting to an increase the p80 transfer size of the
Ball mills.
The recent introduction of High-Pressure Grinding
Rolls (HPGR) and their higher efficiency, particularly for
harder ores has challenged the SABC circuits, however,
it still is the standard for copper process at the present.
One interesting twist has been the use of the HPGR in
the pebble crushing circuits. Goldcorp’s Penasquito Mine
and KazMinerals’ mines at Bozshakol/Aktogay have 2-stage
pebble crushing. Throughput increases have been reported
as high as 30% with the addition of the HPGR on their
hardest ore. Another group of early innovators in pebble
crushing for Gold circuits were at the Lone Tree and Jerrin
Canyon operations.
With fewer mills and more throughput per mill cir-
cuit becoming the norm, availability becomes the primary
focus. When the SAG mill is down for a liner change can
mean 100% loss of tonnage versus 10% with the smaller
multiply lines (Figure 5). Asset Management programs
have become more of a “Must Have” versus a “Nice to
Have” feature. Maintenance and Operations are shifting
towards a “Turnaround” mentality versus partial mainte-
nance based on processed tonnage/operating hours. Asset
Management is assimilating a plantwide data system that
is inclusive of all phases of Operations. The one thing that
threatens this integration is the existing “Silos” between the
various divisions, when it comes to sharing information.
Source: Tucson.com
Figure 3. Copper Processing (Magma San Manuel)
Source: R Johnson at KazMinerals Aktogay II 2021
Figure 4. SABC Circuit Copper Mine
of the total throughput was affected. Crushed ore feed bins
ahead of the mills provided 12 to 24-hour surge capacity
as a buffer between the crushers and the mills to mitigate
feed upsets. High capital cost was the principal downsize of
these smaller mills with their large building footprint.
In the late 70s and early 80s the Autogenous (AG)
and Semi-Autogenous (SAG) mills were being introduced
to copper processing, first with single-pinion drives which
later switching to dual-pinion drives. The size of these early
AG mills ranged from 5.5 m (18ft) diameter installed in
Australia to 9.8 m (32 ft) installed in Canada. The con-
nected power ranging from single pinons of 932 kW
(1,250 hp) at Kanmantoo to dual pinion and 8948 kW
(12,000 hp) at Island Copper. After start-up, operators of
single AG mill circuits increased throughput by installing
Ball mills and then also adding pebble crushing, these con-
figurations were referred to as ABC circuits. Cyprus Bagdad
would be one of the first innovators with the installation of
an ABC circuit. Utah’s Island Copper operation was also an
early adaptor starling with AG mills only, then later adding
Ball mills and then converting to Sag mills or to SAB cir-
cuits. Most common today is the addition of pebble crush-
ers to the SAB circuits or now referred to as SABC circuits
(Figure 4)
Dual pinons had become more common with the larger
mills and now Gearless Motor Drives (GMD) were being
introduced. The SAG mill size would then increase over the
next period from 11 m (36 ft) to 12.2 m (40 ft) diameter.
The connected power ranging from 9 MW (12,000 hp) to
28 MW (37,550 hp). Dual pinion drives were limited to ~
9–12 MW and the GMDs 12 MW. The feed size to these
large SABC circuits was 150–200 mm (6–8 inch). The
main design variables were ore hardness and the potential
for the accumulation of critical size material in the SAG
mills. The solution was the introduction of pebble ports
to the discharge grates to relieve the AG/SAG mills. This
change led to the addition of cone crushers to crush the
pebbles, resulting to an increase the p80 transfer size of the
Ball mills.
The recent introduction of High-Pressure Grinding
Rolls (HPGR) and their higher efficiency, particularly for
harder ores has challenged the SABC circuits, however,
it still is the standard for copper process at the present.
One interesting twist has been the use of the HPGR in
the pebble crushing circuits. Goldcorp’s Penasquito Mine
and KazMinerals’ mines at Bozshakol/Aktogay have 2-stage
pebble crushing. Throughput increases have been reported
as high as 30% with the addition of the HPGR on their
hardest ore. Another group of early innovators in pebble
crushing for Gold circuits were at the Lone Tree and Jerrin
Canyon operations.
With fewer mills and more throughput per mill cir-
cuit becoming the norm, availability becomes the primary
focus. When the SAG mill is down for a liner change can
mean 100% loss of tonnage versus 10% with the smaller
multiply lines (Figure 5). Asset Management programs
have become more of a “Must Have” versus a “Nice to
Have” feature. Maintenance and Operations are shifting
towards a “Turnaround” mentality versus partial mainte-
nance based on processed tonnage/operating hours. Asset
Management is assimilating a plantwide data system that
is inclusive of all phases of Operations. The one thing that
threatens this integration is the existing “Silos” between the
various divisions, when it comes to sharing information.
Source: Tucson.com
Figure 3. Copper Processing (Magma San Manuel)
Source: R Johnson at KazMinerals Aktogay II 2021
Figure 4. SABC Circuit Copper Mine