1. -0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
G10
DICPX
G10D
G1
G3
DICR
G4
G12
Mg-ILM
G4D
G3D
G5
G5D
CPX
G9
G0
CR
Crs-ILM
G11
PC3
PCA Scaled Vectors Showing Diamondiferous KimberliteVariables
G10 DI CPX G10D G1 G3 DI CR G4 G12 Mg-ILM G4D G3D G5 G5D CPX G9 G0 CR Crs-ILM G11
Kimberlitic and Diamondiferous Crustal
Multivariate Analysis of Kimberlite Indicator Mineral Trends across Canada
Brett Ferguson1
, Bruce Eglington1
University of Saskatchewan1
Fig. 1.
Fig. 2. Fig. 3.
Fig. 4.
Fig. 5. Fig. 6.
Fig. 7.
Fig. 8.
TiO2
-MgO Kimberlitic Ilmenite Discrimination Plot (Wyatt et al., 2004) showing Mg-rich ilmenites sourced from kimberlite pipes
Cr2
O3
-MgO Chromite Diamond Inclusion and Intergrowth Plot (Fipke et al., 1995) Cr2
O3
-CaO Clinopyroxene Diamond Inclusion Field Plot (Fipke et al., 1998)
Sample Locations of microprobed indicator minerals (n=122,913) shown in blue shown with Archean cratons
PCA scaled loadings showing negative (red) correlation between more favourable kimberlitic and diamondiferous
minerals versus positive (blue) crustal correlation
PC3-PC1 analysis showing vectored trends. Positive and negative groupings can be seen
along PC3 axis between kimberlitic and crustal components
High-Potential (High scoring) PC3 samples displayed with remainder of sample locations showing
cluster following kimberlite trend
PCA Scaled Loadings Showing Diamondiferous Kimberlite Variables
The Grϋtter classification uses a variety of ranges of major oxides, as well as incorporating a
Calcium Intercept (CA_INT) where; IF CaO ≤ 3.375 + 0.25*Cr2O3
THEN CA_INT= 13.5*CaO/ (Cr2O3 + 13.5)
IF NOT CA_INT= CaO – 0.25*Cr2O3
As well as a Magnesium number (MGNUM) where;
MGNUM= (MgO/40.3)/ (MgO/40.3 + FeOt/71.85)
Incorporating the ranges, an example of the classification of G10;
Classified as G10 where; Cr2O3 [wt.%]: ≥ 1.0 to < 22.0
CA_INT [wt.%]: 0 to < 3.375
MGNUM [wt.%]: ≥0.75 to < 0.95
The suffix “D” (Diamond-facies) may also be added to minerals that show a strong compositional and
P-T association with diamond in the G10, G3, G4 and G5 classifications where;
G10D = Cr2O3 ≥ 5.0 + 0.94*CaO, or Cr2O3< 5.0 + 0.94*CaO and MnO< 0.36 (wt.%)
G3D, G4D, G5D = Na2O > 0.07 (wt.%)
(Grϋtter et al., 2004)
Garnet: Garnets were classified using the updated Grϋtter classification scheme (Grϋtter et al., 2004)
which show compositional variations in Cr, Ca, Mg, Mn, Fe and Ti. These, in turn, reflect chemical,
physical and lithological environments that can occur together with diamond (Grϋtter et al., 2004).
The microprobe analysis of major oxides (in wt.%) was used to categorize garnets as the following
(Listed in order of classification, this being of significant importance due to slight overlap between
classifications);
 G1- Low-Cr megacrysts
 G11- High-TiO2 peridotitic
 G10- Harzburgitic
 G9- Lherzolitic
 G12- Wehrlitic
 G5- Pyroxenitic, websteritic
 G4- Pyroxenitic, websteritic
 G3- Eclogitic
 G0- Unclassified
All classification diagrams and multivariate analyses were performed using the ioGAS software
package.
Principal Component Analysis: Principal component analysis (PCA) was
used in this study to analyze correlations between different variables
(classifications) of indicator minerals (i.e. G10, DI chromite, Mg-ilmenite,
etc.) in the goal of finding a ‘kimberlite sourced and potentially
diamondiferous’ trend unassociated to a more crustal sourced trend. PCA
uses orthogonal transformation to convert correlated variables
(clustered data) into a set of linearly uncorrelated values (principle
components). In order to perform PCA at the per sample level, each
sample location (n= 122,913, shown in Fig. 4.) was broken up into ratios
of percent of mineral per sample (n-mineral class/total mineral) for each
mineral analyzed (i.e. n-G10/Total Garnet = %G10).
Results: The ratios were analyzed in the PCA (per sample) resulting in two
major trends (shown in Fig. 6.) along the principle component 3 (PC3) axis.
The kimberlitic and diamondiferous is negatively loaded on PC3 while the
crustal trend is positive (Fig. 5.). PC3 scores for samples provides a single
variable (from multiple) which was used to discriminate ‘high-potential’
samples with high negative scores correlating to kimberlitic trends (Fig.
8.). Combining multiple variables into a single PC3 score decreased
sample locations dramatically (n= 23,769), with clusters of high scoring
samples becoming main areas of interest in terms of exploration
potential.
Summary: Properly classifying indicator minerals into sub-categories of
higher and lower potential for coinciding with diamond formation and
transport is an essential part to any diamond exploration program. Using
PCA on the ratios of these variables to create one new kimberlitic and
diamondiferous variable dramatically decreases the number of samples
to focus on as well as eliminates the need to layer multiple indicator
minerals on one map, which often makes for more difficult interpretation.
Even in areas where microprobe data is low in relation to total grains (i.e.
NWT), by using PCA scores basic trends can be seen correlating to high-
potential areas making this a powerful tool in any exploration program.
Introduction: The goal of this study was to reduce the dimensionality of
a Kimberlite Indicator Mineral database in regard to microprobe data
from grains across Canada, so as to identify prospective diamond districts.
Principle component analysis (PCA) was applied for this purpose.
Approximately 200,000+ indicator minerals were compiled and
categorized into sub-classifications, some of which reflect their potential
co-derivation and transport with diamonds via kimberlites. The study
looked at ratios between these classifications (per sample) in the theory
that the more ‘kimberlitic’ and ‘diamondiferous’ indicator minerals
would occur together more frequently compared to the more crustal
indicator minerals. PCA facilitated identification of a new variable based
on a combination of mineral categories, creating an easier, more robust,
way of selecting higher potential targets in lieu of looking at individual
mineral categories. Indicator minerals assessed in this study were garnet,
chromite, ilmenite and cr-diopside (clinopyroxene).
Methods: The kimberlite indicator minerals analyzed in this study include garnet, ilmenite, chromite
and clinopyroxene. These are considered to be some of the more favorable mantle sourced minerals
associated with diamond. Classifying these indicator minerals into various diamond potential sub-
categories is key in aiding with any exploration program in the search for diamond-bearing kimberlite.
The following methods were used in classifying the aforementioned indicator minerals of focus:
High-potential PC3 samples (n=23,769) displyed in pink, Archean cratons displayed in blue
Map Interpretation: Analyzing the high-scoring PC3 samples (Fig. 8.),
several promising clusters (see attached figures below) are displayed with
additional detail. Two trends in northern Alberta and one in northeastern
Manitoba that cluster well in the PC3 variable show high abundances of
diamond facies garnets, G10 Harzburgitic garnet, Mg-ilmenite
(kimberlitic), DI chromite as well as DI clinopyroxenes.
This application can also be used in areas of high density clusters with
many high-scoring samples. The NWT exhibits this, and using a larger
scale map to look at the spatial distribution of high-scoring samples
compared to the remainder (Fig. 7.) shows a definitive cluster of high-
scores following the same trend as known kimberlites.
Note the correlation between the high-scoring samples with Archean
craton. Typically diamond-bearing kimberlites are found on-craton,
which is promising to see majority of high-potential samples plot on-
craton or near craton margins.
References: Grütter, H.S., Gurney, J.J., Menzies, A.H. and Winter, F. (2004): An updated classification scheme for mantle-derived garnet,
for use by diamond explorers; Lithos, 77, pages 841-857.
Fipke, C.E., Gurney, J.J. and Moore (1995): Diamond exploration techniques emphasising indicator mineral geochemistry and
Canadian examples; Geological Survey of Canada, Bulletin 423, 86 pages.
Wyatt, B.A., Baumgartner, M., Ancar, E. and Grütter, H. (2004): Compositional classification of "kimberlitic" and "non-
kimberlitic" ilmenite; Lithos, 77, pages 819- 840.
Simandl, G.J., Ferbey, T., Levson, V.M., Robinson, N.D., Lane, R., Smith, R., Demchuk, T.E., Raudsepp, I.M., and Hickin, A.S.
(2005): Kimberlite and Diamond Indicator Minerals in Northeast British Columbia, Canada - A Reconnaissance Survey, British
Columbia Ministry of Energy, Mines Petroleum Resources GeoFile 2005-25, 25 pages.
Harvey, S.E, Kjarsgaard, B.A., and Kelley, L.I. (2001): Kimberlites of central Saskatchewan: Compilation and significance of
indicator mineral geochemistry with respect to diamond potential; in Summary of Investigations 2001, Volume 2,
Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2001-4.2.
Acknowledgements: This study would not have been possible without generous contributions of
time and data from the following people: Barrett Elliot, Doug Irwin and Kelly Pierce (Northwest
Territories Geological Survey), Colin Card (Saskatchewan Geological Survey), Shawn Harvey (Cameco)
and Levi Kalinsky (Cameco).
Ilmenite: Ilmenite is an important indicator of kimberlite due to its Mg-rich species (picroilmenite)
often being sourced from kimberlite pipes. The MgO-TiO2 Kimberlitic Ilmenite Discrimination Plot (Fig.
1.) pictured left was used to discriminate between ilmenites sourced from kimberlite (shown in red)
versus those having formed in a crustal origin (shown in blue) (Wyatt et al., 2004). The ‘undefined’
region prevents any overlap between those of kimberlitic or crustal sources.
Chromite: 98% of worldwide chromite inclusions in diamond fall into the High-Cr, moderate to high
MgO diamond inclusion and diamond intergrowth fields in Cr2O3-MgO plots (Harvey et al., 2001;
Fipke et al., 1995). This is an important pathfinder to peridotite sourced diamonds. The same Cr2O3-
MgO plot (Fig. 2.) was applied in classifying chromites for this study, with chromites that fall into the
diamond inclusion and diamond intergrowth field being displayed in red on the Cr2O3 vs MgO in
Chromites plot.
Clinopyroxene: Clinopyroxene (cr-diopside) found in association with other mantle-sourced minerals
can be used as an indicator for kimberlite, and also provide proximity to source as clinopyroxenes
typically are destroyed after relatively short transport. Cr2O3-CaO plots representing the
compositions of CPX found as inclusions in diamonds (Simandl et al., 2005; Fipke et al., 1998) can
also show potential for coinciding with diamond in the diamond stability field. The plot displayed
below (Fig. 3.) shows CPX in this study that fall into the diamond inclusion field, highlighted in pink.
Identifying diamond districts, one can then apply geological
interpretations, such as glacial transport, to find the source of indicator
minerals.