Geoscience Reference
In-Depth Information
Table 14.6 Relative percentage
comparison in drill holes vs.
interpreted model, mineralization
type
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done because of the importance of mineralization type
as mineralization control.
4. For alteration and lithology, the bench polygons result-
ing from cutting the E-W solids were re-interpreted using
the 10 m composite intercepts available. Additionally,
where available, pit and blast hole was used to refine
in detail the interpreted polygons. These final polygons
were then extruded in the vertical direction to produce
the final solids.
5. The last step of the interpretation of mineralization type
was similar to Step 4 above, obtaining the final inter-
preted solids from refined mid-bench polygons, in turn
obtained from the polygons cut from N-S sections, and
refined using drill hole composites and production map-
ping for the final interpretation.
The upper portion of the Leach unit was not explicitly mod-
eled. It was left as the by-default unit, and then overprinted
with the other modeled units. There were, however, a num-
ber of leached bodies internal to other units that had to be
modeled explicitly.
the arithmetic average of the density values for each unit
described, which approximately coincides with the esti-
mation domains defined above. Using arithmetic averages
by geologic unit is a standard procedure in mining, par-
ticularly in circumstances where there are relatively few
density values available. Also, density should not vary
abruptly in space. Spatial coverage of the density values
has to be fairly uniform and different grade ranges need to
be sampled to capture the variations in density values as
a function of grade. Additional density data would allow
proper domaining and estimation using Ordinary Kriging,
for example.
14.1.13
Geologic Interpretation and Modeling
Some of the considerations that affected the choice of mod-
eling methodology included:
a) The software used in the modeling, which required the
use of solids, obtained through either wireframing tech-
niques or extrusions of sectional polygons.
b) The bench height, set at 10 m, which is also the height of
the blocks of the resource model.
c) The time and human resources available to execute the
work, which led to simplifying the methodology for the
least important geologic variables.
Only those geologic variables with significant potential im-
pact on the resource model and volumetric representation in
the database were modeled. Considering the lesser impor-
tance of lithology and alteration, compared to mineralization
type, as mineralization controls, a more detailed modeling
process was used for the latter. The following steps were
used to build the geologic model:
1. Development of E-W cross sections, spaced 50 m apart,
and posting all available drill hole samples that exist
within ± 25 m of the section plane. This was done for
each variable separately.
2. Interpretation of the drill hole intercepts as sectional
polygons.
3. Extrusion of the interpreted alteration and lithology
polygons to obtain solids, and then cutting these solids
with orthogonal constant-elevation planes, correspond-
ing to mid-bench elevations. In the case of mineral-
ization type, the orthogonal planes used corresponded
to N-S longitudinal sections every 50 m, again with a
± 25 m tolerance. This added interpretation step was
14.1.14
Volumetric and Other Checks
Two different comparisons were made to check whether the
interpreted volumes were globally unbiased.
The block model assignments of each geologic variable
were checked on screen and on paper (sections and plan
views plotted at a 1:500 scale) against the interpreted solids.
The second check is a comparison between the volume of
the solids and the representation (relative percentage) in the
database of each unit. There should be no significant volu-
metric bias after interpretation. Drill hole clustering and sub-
jectiveness in the mapping and logging process may render
the geologic data less reliable.
Table 14.6 shows, as an example, the relative percentage
in drill holes (logged meters vs. total meters) for each miner-
alization type (main mineralized units), compared to the total
and relative percentages of the corresponding interpretation.
Results are quite satisfactory.
The 2003 interpretation was compared to the previous
geologic model. Figure 14.9 shows the interpreted mineral-
ization type for Section 82230N, where the different units
are color-coded (brown = leached; green = oxide; red = sul-
fide; yellow = MSH, and purple = hypogene). The 2003
model units are represented with the dotted fill, while the
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