Lithos 76 (2004) 337 – 345
www.elsevier.com/locate/lithos
Role of geology in diamond project development
Jaroslav Jakubec *
SRK Consulting, Suite 800, 1066 West Hastings Street, Vancouver, B.C., Canada V6E 3X2
Received 25 June 2003; accepted 3 December 2003
Available online 14 July 2004
Abstract
For a mining operation to be successful, it is important to bring fundamental and applied science together. The mining
engineer needs to understand the importance of geology, mineralogy and petrography, and how projects can benefit from the
data collected during the exploration and pre-exploration stage. Geological scientists also need to understand the process of
project development from the exploration stage through mine design and operation to mine closure. Kimberlite pipe or dyke
emplacement, geology and petrology/mineralogy are three areas that illustrate how information obtained from the geological
studies could directly influence the mining method selection and the project strategy and design. Kimberlite emplacement is one
of the fundamental processes that rely on knowledge of the kimberlite body geology. Although the importance of the
emplacement model is commonly recognized in the resource geology, mining engineers do not always appreciate its importance
to the mine design. The knowledge of the orebody geometry, character of the contact zones, internal structures and distribution
of inclusions could directly influence pit wall stability (thus strip ratio), underground mining method selection, dilution,
treatability, and the dewatering strategy. Understanding the internal kimberlite geology mainly includes the geometry and
character of individual phases, and the orientation and character of internal structures that transect the rock mass. For any
mining method it is important to know ‘‘where the less and where the more competent rocks are located’’ to achieve stability.
On the other hand, the detailed facies studies may not be important for the resource and mine design if the rock types have
similar physical properties and diamond content. A good understanding of the kimberlite petrology and mineralogy could be
crucial not only to the treatability (namely diamond damage and liberation), but also to the pit wall and underground excavation
stability, support design, mine safety (mudrush risk assessment) and mine dewatering. There is no doubt that a better
understanding of the kimberlite and country rock geology has a direct impact on the safety and economics of the mining
operations. The process of mine design can start at the beginning of kimberlite discovery by incorporating the critical geological
information without necessarily increasing the exploration budget. It is important to appreciate the usefulness of fundamental
geological research and its impact on increased confidence in the mine design. Such studies should be viewed as worthwhile
investments, not as cost items.
D 2004 Published by Elsevier B.V.
Keywords: Kimberlite geology; Diamond mining; Kimberlite contact zone; Kimberlite weathering
1. Introduction
* Tel.: +1-604-681-4196; fax: +1-604-687-5532.
E-mail address: [email protected] (J. Jakubec).
0024-4937/$ - see front matter D 2004 Published by Elsevier B.V.
doi:10.1016/j.lithos.2004.03.053
For a mining operation to be successful, it is
important to bring the fundamental and applied
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J. Jakubec / Lithos 76 (2004) 337–345
sciences together. On the one hand, the mining
engineer needs to be educated about the importance
of geology, mineralogy and petrography and how he
can benefit from data collected during the exploration and pre-exploration stage; but on the other
hand, geological scientists need to be educated
about project development from the exploration
stage through mine design and operation to mine
closure.
It is not uncommon to discover significant data
gaps during the final feasibility stage or even during
the mine development stage. In many cases, such
gaps in the understanding of the nature of the
mineral deposit result in developmental delays and
cost overruns. Such ‘‘surprises’’ could be avoided if
exploration programs integrated some of the mining
and geotechnical aspects into their investigation. This
does not necessarily translate into a significant inflation of an already stretched exploration budget, if it
is done sensibly. However, it requires both parties—
mining engineers and geologists—to understand the
complete process of a project’s development. This
paper illustrates the importance of geology in the
design and development of diamond mines.
2. Project development
As soon as the resource (kimberlite pipe or
dyke) is approximately delineated to a certain
depth or lateral extent and the first indications of
values per tonne of rock are available, the question
arises: ‘‘How much will it cost to convert the
resource into a marketable product?’’. The project
is leaving the exploration stage and moving to the
feasibility process. At this point, other professions,
along with geologists, are usually invited to the
‘‘table’’.
From exploration further down the line to a focus
on environmental issues, geology remains relevant
through the entire life of the project. See the individual stages illustrated in Fig. 1.
Selecting the mining method starts relatively early
in the project development process, as the scramble
for input data begins. Often, at the end of the
exploration drilling program, very little is known
about the country rock or kimberlite body contact
zones, even though most of the drillholes were
Fig. 1. Stages of mining project development.
collared or terminated outside the pipe. Country rock
information is sketchy; core may be ‘‘buried’’ somewhere under the snow and useful core photographs
are not available. It is interesting to note that a set of
good core photographs could provide sufficient geotechnical information to complete the conceptual
stage design.
Fundamentally, the choice, design and operation of
mining methods depend on:
Orebody size and geometry,
Rock mass competency,
Grade distribution,
Desired production rates,
Other constraints, such as permafrost and lake
overlying deposit.
Once the mining method is selected, a conceptual
mine design is undertaken and all constraints should
be considered. Typical mine design constraints are
illustrated in Fig. 2.
Geological information is required throughout the
project development process. However, the data required should not be limited to the resource model;
J. Jakubec / Lithos 76 (2004) 337–345
Fig. 2. Typical mine design constraints.
they should include all aspects of kimberlite body and
country rock geology.
3. Geology context
In the context of the diamond mine design, the
following aspects of geology are fundamental:
Regional structural geology,
Kimberlite body geology,
Country rock geology.
3.1. Regional structural geology
Applied structural geology, in most mineral systems, is about understanding pathways. ‘Pathways’
include the crustal-scale plumbing systems that could
facilitate the emplacement of kimberlitic magmas, as
well as the pipe scale fault/fracture networks that
control syn-/post-emplacement alteration and present-day groundwater flow. Understanding these pathways can, therefore, have a profound impact on the
effective development and success of diamond projects at all stages, from exploration through mine
design and mining to mine closure.
Today’s common diamond exploration tools consist primarily of airborne geophysics and quaternary
geology (soil sampling). Both techniques used to-
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gether or in isolation have, in many cases, proven
to be highly successful means of locating kimberlite
bodies. However, in cases where kimberlites have
no distinct magnetic signature, and/or lack a traceable dispersion train, an understanding of the crustal architecture and its structural –kinematic evolution can provide valuable insights to the kimberlite
vectoring process. Using existing aeromagnetic data,
crustal scale geology and the tectonic history of a
given area, structural analysis can help identify
favourable sites for kimberlite pipe emplacement.
Integration of detailed structural analysis with ongoing geological and geotechnical studies, at the mine
scale, can potentially assist in the definition of the
geometry of a kimberlite intrusive, as well as the
geometry and distribution of its internal phases. This
approach can provide obvious benefits to geotechnical domain modeling, and could also play a major
role in the definition of the mineral resource and
reserves. Often further enhancement of existing exploration aeromagnetic data using various filtering
techniques could reveal important patterns that can
provide structural geologist with clues for the structural model development. An example of enhanced
aeromagnetic data visualization revealing potential
internal structures within a kimberlite pipe is illustrated in Fig. 3.
Effective management of ground stability and
groundwater are two of the most critical elements
that underpin the success of any mining operation.
Structural analysis and understanding of faults and
fracture systems outside and within the kimberlite can
also help with the early prediction of zones of
instability and groundwater risk. Groundwater risks
include not only the immediate impediments to
development progress, but also the progressive
strength degradation, over time, through weathering
of groundwater pathways. Structural geology can
also, therefore, make a positive contribution to the
early stages of mine design, mine planning and mine
safety, and its application to groundwater studies
further extends its relevance to mine closure and
remediation.
The maximum benefit of structural analysis is
realized when it is introduced to the project at the
earliest possible stages and carried through the life of
the project, with continuity maintained between its
different applications to each phase of development.
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Fig. 3. Enhanced processing of the aeromagnetic data reveals structural patterns transecting the kimberlite pipe.
3.2. Kimberlite orebody geology
Three main aspects of kimberlite orebody geology
that have a direct impact on the mining method
selection and design are:
Kimberlite body emplacement model,
Kimberlite body internal geology model,
Kimberlite petrology/mineralogy.
3.2.1. Kimberlite body emplacement model
This is one of the fundamental studies that can help
in understanding the kimberlite geology. Although the
significance of the emplacement model is commonly
recognized among geologists, mining engineers do
not always appreciate its importance to the mine
design. The pipe or dyke emplacement mechanism,
however, directly influences several parameters that
are fundamental to the mine method selection and
design. Those are:
Kimberlite body size and geometry,
Internal structures and rock mass competency,
Extent and competency of the kimberlite body
contact zones.
Kimberlite orebody size and geometry are key
aspects of resource estimating. They are also fundamental for selecting the mine method and design. Pipe
shape and dimension, together with rock mass competency, determine cavability and pipe or dyke contact
geometry helps determine dilution estimates.
The simplistic pipe geometry model developed
during the exploration stage is often followed
throughout the feasibility study, when it should be
refined. It is not uncommon to find the pipe contacts
in the ‘‘wrong’’ location only when pre-production
development starts. Pipe shapes can be quite variable
even within close clusters of kimberlites, as documented, for example, at Gahcho Kué (Hetman et al.,
2003). Without sufficient drilling data, it is impossible
to predict such geometry with any degree of certainty.
This problem could be even worse when dealing with
‘‘2D’’ deposits such as kimberlite dykes. Because of
the relatively large lateral extent of the kimberlite
dykes, the drillholes are widely spaced. Simplistic
dyke geometry models from the exploration stage
could prove to be insufficient for mine design in later
stages of the project development.
Often, during the kimberlite pipe delineation process, holes are terminated as soon as they leave the
J. Jakubec / Lithos 76 (2004) 337–345
kimberlite. This could (and does) lead to erroneous
interpretations of pipe geometries, in some cases
because the ‘‘country rock contact’’ is only a xenolith.
It is often found that poor quality rock mass adjacent to
the kimberlite body contacts create mining difficulties
in both open pit and underground operations. From the
geotechnical point of view, two types of contact zone
can be recognized: the internal contact zone within the
kimberlite body and the external contact zone developed in the country rocks. Their character depends
largely on the kimberlite emplacement mechanism and
could be further affected by kimberlite weathering (and
associated volumetric change) and by groundwater
movement along the contact. Typically, internal contact zones consist of series of shear zones sub-parallel
to the kimberlite body contacts. The external contact
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zones are often represented by highly jointed rocks
mass where existing fabric was enhanced by alteration
and in some cases new fractures were created. An
example of a highly jointed external contact zone is
illustrated in Figs. 4 and 5.
3.2.2. Kimberlite body internal geology model
Understanding the internal geology of the pipe or
dyke in the context of mine design involves understanding the geometry and character of individual
phases, and the orientation and character of internal
structures that transect the rock mass. For any mining
method it is important to know ‘‘where the less and
where the more competent rocks are located’’. However, from the mine design point of view, the detailed
internal geology studies may not be important if the
Fig. 4. Example of well-developed external contact zones outside the kimberlite pipe. The contact zone geometry and rock mass competency
will impact on physical mine stability and dilution.
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domain model. This domain model could be used for
the mine layout and infrastructure location or, as
illustrated in Fig. 6, for the geotechnical block model
used in numerical stability analysis.
The xenolith content and character are not only
important for the kimberlite emplacement model; they
are of prime interest to both mining and metallurgical
engineers. The engineers need to take xenoliths into
consideration for blast design, ground support design,
kimberlite cutability and crusher design. This is especially valid where kimberlite pipes intrude into hard
competent rocks such as granitoids and basalts.
Fig. 5. Extensive external contact zones (several metres wide)
identified in the drill core. Notice a higher fracture frequency and
broken core within the contact zone developed in the granite. In this
case there is no apparent internal contact zone developed in
kimberlite.
rock types have similar physical properties and diamond content.
Because the various kimberlite phases often have
different physical properties, the kimberlite geology
model is typically used as a basis for the geotechnical
3.2.3. Kimberlite petrology and mineralogy
Forming a good understanding of the kimberlite
petrology and mineralogy could be crucial not only to
the ore treatability (namely, diamond damage and
liberation), but also to stability of the pit wall and
underground excavation, the support design, mine
safety (mudrush risk assessment) and mine dewatering. Clay characterization could provide important
clues to the weathering susceptibility of the individual
kimberlite rock types and could help delineate geotechnical domains.
Fig. 6. Example of a geotechnical domain model based on the internal kimberlite pipe geology (left). This domain model was used to create a
geotechnical block model (right) used in numerical stability analyses. Each block has attached series of geotechnical parameters used in
calculations.
J. Jakubec / Lithos 76 (2004) 337–345
One of the fundamental geotechnical issues to
consider in selecting the mining method and design
is the strength and deformation characteristic of the
rock mass in which mining takes place. Not only can
various kimberlite rock types have variable properties,
such properties can change rapidly with time. Most
kimberlites fall into the category of weak to moderately strong rocks (see Fig. 7). In the context of mine
design, this would not pose a challenge. The problem
arises if the kimberlite loses it strength within days of
exposure. This can happen if the ‘‘wrong’’ clays are
present in the rock matrix. If clays from the smectite
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group are exposed to moisture or, even worse, to wet
and dry cycles, they swell and disintegrate the rock
matrix, dramatically reducing the strength of the rock
mass. This can have major consequences for the
stability of excavations (Fig. 8), supportability of the
rock mass, driving conditions, risk of mudrush, etc.
To combat kimberlite deterioration, many underground diamond operations apply sealant to prevent
moisture from entering the exposed rock. Failure to do
so can result in rapid tunnel deterioration. Preventing
kimberlite weathering could pose particular challenges in the Arctic where low temperatures or con-
Fig. 7. Comparison of typical ranges of unconfined compressive strength of major kimberlite and country rock types encountered on various
diamond mining projects worldwide. Note that the strength of various kimberlites ranges from very weak (less than 5 MPa) to very strong (over
200 MPa).
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J. Jakubec / Lithos 76 (2004) 337–345
densation could prevent effective application of most
sealants.
The environmental effects of kimberlite weathering
and leaching also recently came under the microscope
with the successful development of diamond mines in
northern Canada. According to Day (2003) through
detailed investigation, it was determined that coarse
kimberlite rejects from the process plant are leached
by contact with natural, strongly acidic soils.
It is important, therefore, to characterize the weathering susceptibility of the various kimberlite rock
types in the early stages of the project so these factors
can be built into the mine design to forestall a
‘‘surprise’’ during development. A simple qualitative
‘‘accelerated’’ weathering test could be used to establish the degree of weathering of various kimberlites
(see Fig. 9).
3.3. Country rock geology
In the context of mine design, the knowledge of
country rock geology is at least as important as the
geology of the kimberlite itself. Pit slopes, underground access development and mining infrastructure
are mainly located in the country rock. The knowl-
Fig. 9. An accelerated drill core weathering test reveals variable
weathering susceptibility of the individual kimberlite rock types.
This simple test could provide a relative comparison of the various
units. The rate of deterioration could be calibrated for the clay types
and could be used as a predictive mine design tool.
edge of country rock types could also be crucial for
the kimberlite emplacement model. The country rock
xenoliths could provide important evidence of the
volcanic sequence and timing of the kimberlite
formation.
4. Conclusions
Fig. 8. High weathering susceptibility of a clay-rich kimberlite
causes severe deterioration of the open pit benches. This
significantly increases safety risks of the operation and could lead
to slope failures.
There is no doubt that a better understanding of
both kimberlite and country rock geology has a direct
impact on the safety and economics of the mining
operations. The process of mine design could start
right at the beginning of the discovery without necessarily significantly increasing the exploration budget. Even simple issues such as using drill core
photography during the exploration stage could potentially save hundreds of thousands of dollars on
drilling during the subsequent stages of the conceptual
and pre-feasibility study. Several rock strength estimates performed on the exploration core can provide,
at very low cost, invaluable information for a ‘‘first
pass’’ mine design.
J. Jakubec / Lithos 76 (2004) 337–345
It is important to appreciate fundamental geological research and its impact on the increased confidence in mine design. Such studies must not be
viewed as cost items but as an investment. However,
the investment can only be made efficiently if one
understands the whole process, the data requirements
down the line, and risks and uncertainties associated
with the project.
345
References
Day, S., 2003. Coarse kimberlite rejects at Ekati Diamond Minek.
SRK Newsletter, vol. 31, p. 6.
Hetman, C.M., Scott Smith, B.H., Paul, J.L., Winter, F.W., 2003.
Geology of the Gahcho Kué kimberlite pipes, NWT, Canada:
root to diatreme transition zones. 8th International Kimberlite
Conference, British Columbia. Extended Abstracts.