Geoscience Reference
In-Depth Information
Fig. 3.1
Geologic Log used by BHP Billiton at their Spence deposit, northern Chile. Courtesy of BHP Billiton
obtain a reliable model of spatial continuity for each domain, as
well as sufficient drill hole data to obtain a robust grade estimate.
Specifying too many geological factors/domains does
not help with estimation. One such case was the Chuqui-
camata copper mine. During the mid-1990s there were 64
estimation domains defined in the sulphide zone in support
of the resource model. Many of these units, although clearly
distinguishable and properly characterized from a geologic
standpoint, were only weak mineralization controls and in
some cases did not have sufficient data support to allow for
robust inference. Thus, they were poorly estimated. In the
late 1990s, after a review of the production data against the
predicted data, the estimation domains used in the resource
model were reduced to less than 30. There were other im-
provements to the overall resource modeling process; how-
ever, it was recognized that reducing the number of estima-
tion domains resulted in an improved resource model.
As the project moves from early exploration into resource
definition and pre-feasibility, the gathering of geologic in-
formation for exploration and resource delineation requires
more planning and control (Hartman
1992
, p. 30). Some as-
pects to be considered include:
a. Development of detailed written protocols for data collec-
tion and geologic work. While they need to be constantly
updated, they are to be used throughout the project. The
protocols should describe the procedures used by the field
geologist to control drilling; the sampling protocol and
equipment to be used at the drill rig; the corresponding
mapping and logging protocols; procedures for using and
maintaining hand-held logging devices used (if avail-
able); quality control and quality assurance (QA/QC)
programs for laboratory assay controls; and proper chain
of custody for all samples. The consistent use of protocols
and procedures will help create more reliable databases.
b. Active supervision and continued training of all personnel
involved, ensuring correct and consistent application of
procedures and protocols. Protocols are of little value if
there is no training and supervision.
c. Correct management of logged and mapped geologic in-
formation including handling, storage, electronic input,
and interpretation/evaluation. This may include a descrip-
tion of drill hole information according to prescribed
conventions; adequate documentation of the work done;
adequate storage of the same documentation, and specific
descriptions as a documentation trail for future audits.
d. Working sections with (hand) drawn interpretations allow
for a dynamic understanding of geologic controls, and
better management of future data gathering campaigns.
e. It is critical to properly store and retain half cores, field
sample rejects, coarse and pulp rejects from the sample
preparation and assaying processes. Sufficient and proper
storage of the excess sample material from drilling should
be planned for early in the project's life. Storage areas
should be covered, clean, and well organized.
f. Information loss because of bad quality control or lack
of quality assurance procedures is serious. One often-
