4
Figure 3 illustrates that most feasibility studies relied
on the SMC (Morrell, 2004) and Bond ball mill work
index (Bond, 1961) tests to determine circuit design cri-
teria and plant performance, underscoring their status as
industry-standard tests. The “Others” category represents
projects that employed a diverse mix of SMC, JK Drop
Weight (Napier-Munn et al, 1996), and SPI tests (Starkey,
1994), along with Bond rod and ball mill work index tests,
to establish circuit design and performance parameters.
Nearly all projects conducted a Bond abrasion index test
however, this was not included in Figure 3 as it was nearly
ubiquitous across the feasibility studies analysed.
The relationship between comminution samples and
geochemical assays was assessed. Figures 4 and 5 quantify
the disparity between the two and illustrate how this rela-
tionship evolved over time. As shown in Figure 4, most
projects have fewer than 10,000 geochemical assays per
comminution sample. Projects exceeding this ratio typically
conducted multiple drilling campaigns over several years,
where geochemical sampling occurred in earlier stages, and
comminution samples were collected later. This signifi-
cantly contributed to the disparity between the two datas-
ets. Figure 5 presents a boxplot derived from the same data
as Figure 4 but breaks down the distribution by each of the
eight years analysed.
On average, projects the ratio of geochemical assays to
comminution sample tests is about 5,000:1. This illustrates
the limited number of samples dedicated to throughput
prediction compared with the much larger volume analysed
for grade prediction.
Figure 6 illustrates the trend with investment capital
by plotting the relationship between geochemical assays
and comminution samples and the number of commi-
nution tests performed per million dollars of capex on a
yearly basis. Although Table 1 shows reasonably consistent
numbers of tests and samples across the years, the ratio of
comminution tests per capex unit decreases as project capex
steadily increases. This is likely due to the resource size and
the production period’s length. However, it does indicate
that technical risk increases with project size.
RISK AND OPPORTUNITY
MANAGEMENT
The high assay sample to comminution sample ratio arises
from the inherent differences between resource-grade and
throughput risks. Geological risks, particularly resource-
grade estimation, cannot be mitigated without extensive
geochemical testing, as they directly determine the viabil-
ity of the orebody and impact long-term project planning.
In contrast, comminution risks are traditionally addressed
Figure 4. The ratio of assays to comminution samples by
number of projects
Figure 5. The ratio of geochemical to comminution samples
by year
Figure 6. Tests as a function of capital cost
Figure 3 illustrates that most feasibility studies relied
on the SMC (Morrell, 2004) and Bond ball mill work
index (Bond, 1961) tests to determine circuit design cri-
teria and plant performance, underscoring their status as
industry-standard tests. The “Others” category represents
projects that employed a diverse mix of SMC, JK Drop
Weight (Napier-Munn et al, 1996), and SPI tests (Starkey,
1994), along with Bond rod and ball mill work index tests,
to establish circuit design and performance parameters.
Nearly all projects conducted a Bond abrasion index test
however, this was not included in Figure 3 as it was nearly
ubiquitous across the feasibility studies analysed.
The relationship between comminution samples and
geochemical assays was assessed. Figures 4 and 5 quantify
the disparity between the two and illustrate how this rela-
tionship evolved over time. As shown in Figure 4, most
projects have fewer than 10,000 geochemical assays per
comminution sample. Projects exceeding this ratio typically
conducted multiple drilling campaigns over several years,
where geochemical sampling occurred in earlier stages, and
comminution samples were collected later. This signifi-
cantly contributed to the disparity between the two datas-
ets. Figure 5 presents a boxplot derived from the same data
as Figure 4 but breaks down the distribution by each of the
eight years analysed.
On average, projects the ratio of geochemical assays to
comminution sample tests is about 5,000:1. This illustrates
the limited number of samples dedicated to throughput
prediction compared with the much larger volume analysed
for grade prediction.
Figure 6 illustrates the trend with investment capital
by plotting the relationship between geochemical assays
and comminution samples and the number of commi-
nution tests performed per million dollars of capex on a
yearly basis. Although Table 1 shows reasonably consistent
numbers of tests and samples across the years, the ratio of
comminution tests per capex unit decreases as project capex
steadily increases. This is likely due to the resource size and
the production period’s length. However, it does indicate
that technical risk increases with project size.
RISK AND OPPORTUNITY
MANAGEMENT
The high assay sample to comminution sample ratio arises
from the inherent differences between resource-grade and
throughput risks. Geological risks, particularly resource-
grade estimation, cannot be mitigated without extensive
geochemical testing, as they directly determine the viabil-
ity of the orebody and impact long-term project planning.
In contrast, comminution risks are traditionally addressed
Figure 4. The ratio of assays to comminution samples by
number of projects
Figure 5. The ratio of geochemical to comminution samples
by year
Figure 6. Tests as a function of capital cost