5
Although alkaline POX benefits from lower CAPEX
and OPEX, the reduced gold recovery results in a lower net
cash flow difference (NCFD). This NCFD value, indicat-
ing the cash flow impact at the point of CAPEX invest-
ment (year 0), is subject to factors such as operational costs
and gold price escalation. In this study, the O&M and
utilities inflation rate was conservatively set at 2%, whereas
the gold price inflation rate was set at 6% based on his-
torical data. This inflation gap caused the revenue impact
of increasing gold prices to outweigh the effect of operating
costs, leading to a sustained decrease in cash flow over time.
Consequently, the NPVD showed a significantly negative
value, indicating that alkaline POX is not economically
viable under the base case conditions, making acidic POX a
more favorable choice.
Sensitivity Analysis
To better understand the impact of the primary variables
defined in Table 2, a sensitivity analysis was conducted.
Each parameter was studied by keeping all other parameters
fixed at the base case values to isolate its specific effect. For
each variable, three to five data points were generated, and
corresponding sensitivity analysis charts were developed
and are presented in Figure 1.
The economic breakeven values (EBV, x-intercept in
the charts), detailed in Table 5, are critical points for under-
standing the feasibility of switching from acidic to alkaline
POX. These values indicate where the difference between
acidic and alkaline POX becomes negligible, effectively
meaning that alkaline POX starts to become the more eco-
nomically favorable option under those specific conditions.
The trend of the sulfide sulfur grade within this sensi-
tivity analysis is counterintuitive to conventional wisdom
regarding sulfide grade and acidic POX operation. This
result arises due to the nature of the sensitivity analysis
holding all other variables constant. Subsequently, with the
base case CO3 to SS ratio of 5 every increase of 1% sulfide
corresponds to an increase of 5% carbonate. This results in
a significant increase in carbonates which require acidula-
tion thus explaining the positive trend for sulfide grade for
alkaline POX operation. To further expand on this result an
additional sensitivity analysis was conducted by keeping the
carbonate grade constant while increasing the sulfide sulfur
grade, and the results are shown in Figure 2. The NPVD
value exhibits a complex trend as the sulfide sulfur grade
varies while the carbonate grade is fixed at 10%. In the ini-
tial range of 1–3%, as the SS grade increases, the reduc-
tion in acid demand for acidic POX outweighs the OPEX
increase driven by the steam requirement for alkaline POX,
leading to a decline in NPVD. However, in the mid-range
of 3–6%, the significant reduction in steam demand for
alkaline POX makes fuel costs dominant, resulting in an
upward trend in the NPVD curve. Beyond 6%, as the SS
grade becomes sufficiently high, no additional heat sup-
ply is required for alkaline POX, shifting the dominance
back to acid cost reductions for acidic POX and causing
the NPVD curve to decline once again. Overall, with car-
bonate fixed, the sensitivity of SS grade shows a decreasing
trend, contrary to the pattern observed in Figure 1 (a). This
change in ore parameters is considered more representative
of typical POX feed materials.
The carbonate-to-sulfide sulfur ratio had a substan-
tial impact, with higher ratios improving NPV. The EBV
for the carbonate-to-sulfide sulfur ratio was found to be
8.9, which exceeds the rule-of-thumb threshold of 5 men-
tioned earlier in POX Process Selection section. This result
aligns with the positive trend for gold prices since 1994 as
Table 4. Base Case Economic Analysis Summary
Descriptions Unit
Impacts
(Alkaline–
Acidic POX)
CAPEX Impacts
Acidulation M USD $(16.0)
Off-Gas M USD $8.7
Neutralization M USD $(16.0)
Boiler M USD $0.4
Demin M USD $0.4
Total M USD $(22.5)
OPEX Impacts
Sulfuric Acid (93%) M USD /year $(46.9)
Lime M USD /year $(1.7)
Fuel M USD /year $13.5
Total M USD /year $(35.2)
Revenue Impacts
Net Gold Difference M USD /year $(59.9)
Net Cash Flow Difference
(NCFD)
M USD /year $(24.7)
Net Present Value Difference (NPVD)
NPVD M USD $(417.8)
Table 5. Sensitivity Analysis Economic Breakeven Values
(EBV)
Parameter Base Case EBV
SS Grade ,%2.0 3.7
CO3/SS Ratio 5.0 8.9
Recovery Diff., %10.0 4.7
Gold Price, USD/oz 2,500 1,166
Gold Grade, g/t 5.0 2.3
Fuel Price, USD/L 1.0 –2.2
Although alkaline POX benefits from lower CAPEX
and OPEX, the reduced gold recovery results in a lower net
cash flow difference (NCFD). This NCFD value, indicat-
ing the cash flow impact at the point of CAPEX invest-
ment (year 0), is subject to factors such as operational costs
and gold price escalation. In this study, the O&M and
utilities inflation rate was conservatively set at 2%, whereas
the gold price inflation rate was set at 6% based on his-
torical data. This inflation gap caused the revenue impact
of increasing gold prices to outweigh the effect of operating
costs, leading to a sustained decrease in cash flow over time.
Consequently, the NPVD showed a significantly negative
value, indicating that alkaline POX is not economically
viable under the base case conditions, making acidic POX a
more favorable choice.
Sensitivity Analysis
To better understand the impact of the primary variables
defined in Table 2, a sensitivity analysis was conducted.
Each parameter was studied by keeping all other parameters
fixed at the base case values to isolate its specific effect. For
each variable, three to five data points were generated, and
corresponding sensitivity analysis charts were developed
and are presented in Figure 1.
The economic breakeven values (EBV, x-intercept in
the charts), detailed in Table 5, are critical points for under-
standing the feasibility of switching from acidic to alkaline
POX. These values indicate where the difference between
acidic and alkaline POX becomes negligible, effectively
meaning that alkaline POX starts to become the more eco-
nomically favorable option under those specific conditions.
The trend of the sulfide sulfur grade within this sensi-
tivity analysis is counterintuitive to conventional wisdom
regarding sulfide grade and acidic POX operation. This
result arises due to the nature of the sensitivity analysis
holding all other variables constant. Subsequently, with the
base case CO3 to SS ratio of 5 every increase of 1% sulfide
corresponds to an increase of 5% carbonate. This results in
a significant increase in carbonates which require acidula-
tion thus explaining the positive trend for sulfide grade for
alkaline POX operation. To further expand on this result an
additional sensitivity analysis was conducted by keeping the
carbonate grade constant while increasing the sulfide sulfur
grade, and the results are shown in Figure 2. The NPVD
value exhibits a complex trend as the sulfide sulfur grade
varies while the carbonate grade is fixed at 10%. In the ini-
tial range of 1–3%, as the SS grade increases, the reduc-
tion in acid demand for acidic POX outweighs the OPEX
increase driven by the steam requirement for alkaline POX,
leading to a decline in NPVD. However, in the mid-range
of 3–6%, the significant reduction in steam demand for
alkaline POX makes fuel costs dominant, resulting in an
upward trend in the NPVD curve. Beyond 6%, as the SS
grade becomes sufficiently high, no additional heat sup-
ply is required for alkaline POX, shifting the dominance
back to acid cost reductions for acidic POX and causing
the NPVD curve to decline once again. Overall, with car-
bonate fixed, the sensitivity of SS grade shows a decreasing
trend, contrary to the pattern observed in Figure 1 (a). This
change in ore parameters is considered more representative
of typical POX feed materials.
The carbonate-to-sulfide sulfur ratio had a substan-
tial impact, with higher ratios improving NPV. The EBV
for the carbonate-to-sulfide sulfur ratio was found to be
8.9, which exceeds the rule-of-thumb threshold of 5 men-
tioned earlier in POX Process Selection section. This result
aligns with the positive trend for gold prices since 1994 as
Table 4. Base Case Economic Analysis Summary
Descriptions Unit
Impacts
(Alkaline–
Acidic POX)
CAPEX Impacts
Acidulation M USD $(16.0)
Off-Gas M USD $8.7
Neutralization M USD $(16.0)
Boiler M USD $0.4
Demin M USD $0.4
Total M USD $(22.5)
OPEX Impacts
Sulfuric Acid (93%) M USD /year $(46.9)
Lime M USD /year $(1.7)
Fuel M USD /year $13.5
Total M USD /year $(35.2)
Revenue Impacts
Net Gold Difference M USD /year $(59.9)
Net Cash Flow Difference
(NCFD)
M USD /year $(24.7)
Net Present Value Difference (NPVD)
NPVD M USD $(417.8)
Table 5. Sensitivity Analysis Economic Breakeven Values
(EBV)
Parameter Base Case EBV
SS Grade ,%2.0 3.7
CO3/SS Ratio 5.0 8.9
Recovery Diff., %10.0 4.7
Gold Price, USD/oz 2,500 1,166
Gold Grade, g/t 5.0 2.3
Fuel Price, USD/L 1.0 –2.2