Geoscience Reference
In-Depth Information
laboratory certificate did not exist or was lost, the check
was done against the interval grade value annotated on
the log sheet. The checks also included comparing the
computerized lithology, alteration, and mineralization
type against the original log sheet. The drill hole collar
coordinates and down-the-hole survey information were
also checked. This check was done for over 30,000 inter-
vals, taking about one calendar month for three people.
2. All information related to each drill hole was placed in
a binder, and the binder catalogued and stored for future
reference. The binder also included a summary of the
drill hole's existing information, as well as the missing
information. This was done to ensure that future changes
and additions to the database could be easily tracked and
documented, also leaving the proper audit trail for future
third parties' reviews.
3. Besides checking against the original laboratory and log
sheets, other consistency checks were completed:
a. Checking that the Soluble Cu was not greater than the
Total Cu (SCu ≤ TCu, if not, SCu = TCu).
b. Checking whether duplicate intervals were present
(these are sometimes generated at the time of data input).
c. The “from” and “to” metrage of each down-the-hole
interval has to be consistent with adjacent samples.
d. The names of the drill holes have to be exactly the
same in all data tables, so that information can be cor-
rectly linked.
e. Duplicate collar coordinates are only allowed for those
drill holes that were started with one drilling method,
and were completed with another. Typically, the RC
method is used in the upper portion of the drill hole,
before entering significant mineralization, and then
converted to a diamond drill hole, thus obtaining core
in mineralized intervals.
f. Two drill holes were discarded because their collar co-
ordinates were clearly erroneous, and no information
was available to verify their exact location.
g. The coordinate system used for the drill holes was also
checked; the older drill holes were located using local
mine coordinates, while later drill holes were located
using truncated UTM coordinates.
h. The values assigned to intervals with missing Cu as-
says, non-sampled intervals, and with Cu values below
laboratory detection limit were also checked.
This checklist serves as an illustration of the type of work
involved in ensuring database integrity, which in some cases
could entail a significant amount of time. Each project will
be different, with the corresponding database will have its
own peculiarities; this list does not include all possible as-
pects that should be validated.
In addition to the validation work described above, the
database was also modified because a significant number
of older drill holes were remapped from the samples still
available in the core shack. This remapping effort was
intended to unify the logging criteria used earlier in the
project's life, thus making the geologic information more
consistent with the current geologic understanding of the
deposit. The remapping was specifically focused on the
lithology and alteration information, since they are often
difficult to map consistently.
14.1.9
Comparison of Drill Hole Types
Another aspect of the database validation relates to the dif-
ferent quality of information obtained from different drill
hole types. For any given interval, Reverse Circulation (RC)
drilling may result in a different grade than would have been
obtained from diamond drilling. This relates to the drilling
method, the sampling method, and to different drill hole di-
ameters (support) involved.
Another concern is the different drilling campaigns per-
formed at different times. The differences may result from a
combination of different factors:
4.
Changes in drill hole type
. Initial campaigns generally
use faster and cheaper drilling methods than those that
are intended for resource delineation, that require more
accurate samples. This also occasionally applies to the
laboratory techniques used in the early sampling. Exam-
ples of these differences are abundant across the mining
industry, as for example the use of percussion holes in the
San Gregorio Au vein-type deposit (Uruguay), or the use
of a rotary, open drill rig mounted on a tractor in the case
of the Michilla Mine, used to detect satellite mineraliza-
tion away from the main deposit.
5.
Differences in personnel involved
. Classically, different
geologists will see and map differently the same drill hole,
sometimes resulting in geologic descriptions that are sig-
nificantly different. This was the case at Cerro Colorado.
6. If there is a significant time lag between the different
campaigns, then the technology for drilling, sampling,
sample preparation, and assaying could change. This is
typical of projects that have been known for a number of
years, but that, for whatever reason, have not been devel-
oped in a timely manner. Again, there are many examples
in industry, including the Pueblo Viejo Au deposit (Do-
minican Republic), or CODELCO's Radomiro Tomic Cu
deposit in northern Chile, originally drilled in the 1950s,
and eventually put into production in the mid-1990s.
7. Geologic knowledge about a deposit naturally evolves
with time, as more information becomes available. This
is another common source of discrepancies between ear-
lier exploration and development geologic work and the
understanding of the deposit geology after the mine enters
production. This is also the case at Cerro Colorado, as
well as many other mines around the world.
An important issue was the systematic higher grades ob-
served from production information compared to prior re-
