Geoscience Reference
In-Depth Information
Fig. 3.19
A section of a Block Model showing full size blocks and sub-blocks. Colors represent different mineralization types and full block size
is 25 × 25 × 15 m for scale
drill hole database. Open pit mine planning requires that the
block model include the ultimate pit that is often larger than
the mineralized zones.
The variables defined within a block model should be all
of those necessary for mine planning including grades and
in situ bulk density of the different geologic units. It may
commonly involve percentages, indicators, or other auxiliary
variables, such as percentage of air in the block (due to the
block being near surface or underground workings) and con-
tacts with certain geologic units that could be either waste or
contaminants.
Variables that may be included in the block model, in
addition to grid indexes and block coordinates and block
sizes (if variable) are geologic attributes such as codes for
lithology, mineralization type, degree of oxidation, altera-
tion, structural information, and estimation domains. The
estimated grades for all constituents of interest (ore and
contaminants) will be in the block model. Other variables
include the presence of clays and other consequential units,
rock hardness, bond mill indexes, crushing plant throughput
prediction, and metallurgical recoveries.
All these variables require storage. The storage require-
ments can be large for many variables in large block mod-
els. Given current computer hardware capabilities the block
model size generally is kept to a few million blocks. Clearly
this number will continue increasing.
Appropriate procedures should be in place to ensure the
quality of all the information developed and contained in the
block model, since it forms the basis of the subsequent mine
planning and economic decisions. This subject is developed
in more detail in Chap. 11.
3.5
Summary of Minimum, Good and Best
Practices
Minimum practice related to geologic mapping, logging, and
interpretation include the following aspects:
a. A series of written protocols and procedures should be
developed, clearly specifying the mappable geologic
attributes and the quality control procedures. The proto-
cols should specify the units that need to be mapped and
the general description for each unit. A physical example
(a rock chip) should be retained as a reference specimen
for the particular characteristics. In some instances, color
photographs are appropriate. The purpose is to limit the
inconsistencies that occur when different geologists map
the same rock. The protocols and procedures should be
updated on a yearly basis, based on the experience gained
in prior campaigns.
b. There should be clearly specified procedures for logging
the mapped information and entering this information
into the computerized database. At a minimum, the spe-
cifics of the procedure, supervisors involved, and timing
of the process should be included. Quality control pro-
cedures such as double-entry (if manually entering the
