Further to my earlier post(1240) here is an extract which lays out a background picture to the Alberta diamond play. Something to keep in mind when reading this is that both Alberta, and Saskatchewan are part of the "Western Canadian Basin", therefore, I believe that much of the information contained within it may applicable to FALC.
____________ by APEX Geoscience Ltd. ___________
ALBERTA DIAMONDS
AN UPDATE ON THE NEWLY EMERGING DIAMONDIFEROUS
KIMBERLITE FIELD IN WESTERN CANADA
Dr. R.A. Olson, P. Geol., President and Senior Consultant, APEX
Toronto office
Mr. M.B. Dufresne, P. Geol., Principal and Consultant, APEX
Edmonton office
EXTENDED ABSTRACT
Summary
At least 15 kimberlite deposits have been discovered to date in
northern Alberta, and there are also reports of kimberlites or diamonds
in a few places in central and southern Alberta. Many, if not most, of
the northern Alberta kimberlites are diamondiferous, and a few have
carats per 100 tonne grades, micro diamond and macro diamond
counts, and stone qualities, that are similar to those reported during the
early phases of exploration of the economically important
diamondiferous kimberlites which exist near Lac de Gras, N.W.T. In
contrast to most of the N.W.T. diamondiferous kimberlite pipes, at
least some of the pipes and related pyroclastic aprons in Alberta are
quite large; in some cases, reportedly up to 15 to 20 ha in areal extent.
Thus the potential exists for a diamondiferous deposit in Alberta to
have substantial tonnages, which could impact favourably on the
economics of any discoveries, even if the carats per tonne or quality of
stones turns out to be somewhat less than that found in the N.W.T.
The economic and regulatory aspects of diamond exploration and
development in Alberta also are highly favourable because there is
excellent infrastructure im most areas, including power, water and
access via summer and winter roads and cut seismic lines, and many of
the aboriginal land claims in Alberta have already been settled. As a
result, the capital development and operating costs for a diamond mine
in Alberta may be one-third to one-half the cost of such in the N.W.T.
In conclusion, the exploration for diamondiferous kimberlites is at an
early stage in Alberta, and the potential is high for discovery of an
economically important diamond deposit.
Introduction
Diamonds were first reported in Alberta in 1958 (the "Ophdal
diamond" near Evansburg in west-central Alberta). In the early 1990's,
a kimberlitic diatreme and related pyroclastic facies were discovered
near Peace River, about 75 km northeast of Grande Prairie, Alberta
(the "Mountain Lake diatreme"). More recently, during 1997, the
Ashton Mining of Canada Ltd. - Pure Gold Ltd. - Alberta Energy
Company Ltd. joint venture have reported the discovery of 14
kimberlitic diatremes, at least 10 of which are diamondiferous, in the
Buffalo Head Hills area of north-central Alberta. At present there exist
many untested aeromagnetic anomalies and diamond indicator mineral
anomalies in both northern and southern Alberta. Therefore, because
exploration for diamondiferous kimberlites in Alberta is at a very early
stage, these positive e
arly results indicate the probability for discovery
of other important diamondiferous kimberlites in other areas of
Alberta, is high.
Regional Geology and Structure
The regional geology of Alberta is both diverse and complex (see
attached list of Selected References). In southern and north-central
Alberta the Precambrian Basement is thick (>40 km to the Moho). In
southern Alberta the basement age is Archean, whereas in
north-central Alberta the basement may be re-worked Archean or
accreted Early Proterozoic (Aphebian) terranes or, perhaps in places,
comprise Proterozoic terranes overthrust onto Archean blocks. In any
case, the basement is thick and old, hence favourable for the formation
and preservation of diamonds in the mantle. Overlying the
Precambrian rocks in Alberta is a westerly thickening wedge of
Phanerozoic strata that ranges in age from early Paleozoic to Early
Tertiary, which is up to 5 km or more total thickness in the deep basin
adjacent to the Rocky Mountain Fold and Thrust belt in westernmost
Alberta.
Present within the Phanerozoic succession there is evidence for at least
four episodes of volcanism or kimberlitic activity or both, which from
oldest to youngest are: (a) uppermost Devonian (Exshaw Fm.
bentonites - about 360 Ma); (2) mid Cretaceous (Viking and
Shaftesbury bentonites, Crowsnest Volcanics, and Buffalo Head Hills
kimberlites - ranging from about 100 to 85 Ma); (3) late Cretaceous
(Horseshoe Canyon, Belly River and Kneehills Tuff bentonites, and
the Mountain Lake kimberlitic diatreme - ranging from about 80 to 65
Ma); and lastly (4) early Tertiary (Sweetgrass Intrusions - about 54 to
49 Ma). In the past, all the bentonites in Alberta were considered to be
altered windblown volcanic debris that was entirely derived from
outside Alberta from volcanic centers active in British Columbia or the
northwestern USA However, there is some recent evidence, including
locally anomalously thick bentonites, markedly increased number of
bentonites in north-central versus east-central Alberta, and anomalous
geochemical REE signatures that indicate at least some bentonites are
or may be derived from more local volcanic centers, including possible
kimberlitic diatreme activity.
With respect to the regional and more local structures in Alberta,
although the Plains region is generally considered to be much less
deformed than the Rocky Mountain Fold and Thrust Belt, and the
easterly adjacent Foothills region of Alberta, nonetheless there exists
evidence for long-lived tectonic activity that has affected the
Phanerozoic strata in the Plains region of the Western Canada
Sedimentary Basin. That is, there has been a long history of periodic
re-activation of regional structures such as (a) the Great Slave Lake
Shear Zone and the Peace River Arch in northern Alberta; (b) the
Snowbird Tectonic Zone, Thorsby Low, Western Alberta and Caroline
Arches, and Alberta Syncline in central and west-central Alberta; and
(c) the Southern Alberta Rift, and Sweetgrass and Bow Island Arches
in southern Alberta. Evidence exists for re-activation of many of these
structures periodically throughout the Phanerozoic, into possibly as
late as the early Tertiary or later. It is probable that such regional and
local structures would have played an important role in the
emplacement of diamondiferous kimberlitic magmas that resulted in
diatremes and related pyroclastic facies deposits in Alberta.
Prior Geoscientific and Exploration Work
During the mid 1990's, a compilation of scientific studies conducted
prior to and under the Canada - Alberta Mineral Development
Agreement, and in some exploration assessment reports, identified a
number of geochemically favourable diamond indicator trends in
Alberta (Dufresne et al., 1994, 1996). Subsequent exploration by the
Ashton joint venture, and by others, has discovered to end 1997: (a) at
least 14 kimberlitic diatremes in the Buffalo Head Hills region in
north-central Alberta, at least 10 of which are diamondiferous; (b
) the
Mountain Lake kimberlite near Peace River in northwest Alberta,
which is reportedly weakly diamondiferous; and (c) diamonds in
alluvium near Hinton in west-central Alberta, near Edmonton and near
Legend in southern Alberta.
The inferred ages of the currently known kimberlitic diatremes, based
on stratigraphic evidence, indicate that the Buffalo Head Hills
kimberlites may be early Turonian (i.e., about 90 to 85 Ma, existing
within the Second White Specks or Dunvegan Fm or equivalents),
whereas the Mountain Lake kimberlite is somewhat younger, late
Campanian (i.e., about 75 Ma, existing within the Wapiti Fm.). These
ages are somewhat younger than the diamondiferous kimberlites which
exist at the Fort … la Corne area, Saskatchewan (age about 101 to 94
Ma), and age equivalent to somewhat older than those at the Lac de
Gras region in the Slave Structural Province, N.W.T. (age about 74 to
52 Ma).
Current Successful Exploration Methods for Diamonds in Alberta
Exploration methods which to date have been successfully used in
Alberta include: (a) detailed to semi-detailed airborne magnetometer
surveys; (b) diamond indicator mineral sampling of selected surficial
materials (mainly stream sediment and till heavy mineral
concentrates); (c) interpretation of aerial photography and Landsat
imagery to search for ?circular' topographic or vegetation features; (d)
more recently, digital elevation modelling of topographic data and
re-interpretation of old and new seismic data are been used with
success in some places; and, finally, (e) diamond drill testing of
selected targets. The Ashton - Pure Gold - Alberta Energy joint
venture, for example, initially discovered a total of 11 kimberlites by
the drill testing of 10 selected, subtle, but definite, aeromagnetic
anomalies (1 of the kimberlites was discovered during caterpillar
tractor work while digging a drill sump).
Nonetheless, exploration in Alberta is still in its infancy, and some
exploration techniques or methodologies that have been used
elsewhere may not be applicable, or may have to be modified for the
Alberta situation. For example, thick drift occurs in many places in
northern Alberta, and this will affect both the interpretation of airborne
and ground geophysical survey results, but also the diamond indicator
mineral sampling methods and interpretation of results. That is, even
weak geophysical anomalies or a few anomalous indicator mineral
grains may be important in the Alberta situation, particularly if they
correlate with a ?roughly circular' topographic or vegetation anomaly.
Interestingly, one difference between the topographic expression of
kimberlites in the Lac de Gras region, N.W.T. and Alberta, is that in
Alberta several of the diatremes which have been found to date
comprise low, but distinct positive topographic features, which is
contrast to the majority of the Lac de Gras kimberlites that typically
occur beneath lakes or in similar, covered depressions. The reason for
this probably is that in the N.W.T. situation, the kimberlites are less
resistant to glacial erosion compared to the surrounding Precambrian
rocks, whereas in Alberta the kimberlites are more resistant in
comparison to the typically surrounding Mesozoic shales and other
thin-bedded sedimentary rocks.
As well, another difference may be the types and chemical signatures
of indicator grains in Alberta. For example, although pyropic garnets
have been found in several places in Alberta, G10 pyropic garnets are,
to date, relatively rare; the reason for this is uncertain. Some of the
indicator minerals which have been found to be useful in Alberta to
indicate kimberlitic or other ultramafic diatremes, and particularly
those that are potentially diamondiferous, include: chrome diopsides,
eclogitic and pyropic garnets, omphacitic pyroxenes, chrome-rich
picro chromites, picro ilmenites and chromian olivines. In short, the
diamond indicator mineral chemistry data that currently are in the
public domain are largely deriv
ed from South Africa or Australian
kimberlitic or lamproitic diamondiferous diatreme fields, and these
data may or may not be directly applicable to the Alberta situation, or
there may exist some differences with respect to mineral grain
chemistries in Alberta that still are favourably indicative of
diamondiferous eclogitic or peridotitic mantle and kimberlitic or
lamproitic diatremes.
Economic and Regulatory Considerations
One comparison of interest is the number of micro and macro
diamonds which have been reported to have been discovered to date in
Alberta, compared with some of the preliminary early-stage data from
pipes discovered at the Lac de Gras region. That is, for the initial 10
pipes which were discovered at Lac de Gras, 6 pipes had micro
diamond counts of 25 or more (ranging from 28 to 132 micro
diamonds) in core samples ranging from 23.2 kg to 161.4 kg in weight,
and macro diamond counts ranging from 8 to 55 stones. In Alberta, of
the first 14 pipes discovered by the Ashton joint venture, 10 are
diamondiferous, and of these the initial recoveries from core samples
include at least 4 pipes with micro diamond counts ranging from 31 to
270 stones, and macro diamond counts ranging up to 90 stones,
although both counts include some broken stones. In short, the initial
Alberta micro and macro diamond counts compare favourably with the
initial results from the Lac de Gras region. Another difference
between Alberta and the N.W.T. is that the initial Lac de Gras
discoveries resulted from initial drilling of targets with favourable
diamond indicator mineral chemistries that followed the culmination
of years of indicator mineral sampling by Mr. Fipke and others. In
contrast, the Alberta discoveries resulted from the initial recognition of
unusual, relatively low amplitude, circular magnetic anomalies in
wide-spaced fixed-wing aeromagnetic data flown essentially for oil
and gas exploration purposes in northern Alberta, followed by drill
testing of targets that had not been further prioritized by use of
diamond indicator mineral sampling.
The size of the currently known Alberta diamondiferous kimberlitic
diatremes compares very favourably with those in the N.W.T. In the
N.W.T. because of erosion of the upper parts of the N.W.T.
diamondiferous diatremes, both BHP/Diamet and Aber/Kennecott
have to put 4 or 5 higher grade pipes together in order to get sufficient
tonnes of economically viable kimberlite. In contrast, in Alberta many
of the diatremes have a diamondiferous crater pyroclastic facies
preserved, and some of the Alberta pipes encompass an areal extent of
15 ha to 20+ ha. Hence, the tonnage potential of some of the
diamondiferous kimberlites in Alberta is huge, even if the diamond
grades and quantities turn out to be less than those in the N.W.T.
Lastly, turning to the economic and regulatory aspects of diamond
exploration and development in Alberta, these are also favourable. For
example, during the 1980's and early 1990's the government of
Alberta promulgated significantly revised staking, exploitation and
environmental regulatory regimes that compare favourably to other
provincial and territorial jurisdictions of Canada. As well, many of the
aboriginal land claims have been settled in Alberta. Finally, in most
parts of Alberta there is excellent infrastructure, including power,
water, and communities for logistical support, and there is good all-
year access via summer and winter roads and cut seismic lines. As a
result, the exploration for, and capital development and operating costs
for a diamond mine in Alberta may be one-third to one-half the cost of
such in the N.W.T.
Conclusion
In conclusion, there are several reasons for believing Alberta is
geologically favourable for the existence of important diamondiferous
kimberlitic diatremes, including: (1) thick Precambrian continental
crust is present in both north-central and southern Alberta; (2) a
complex regional and local structural setting exists in places in both
the
southern and northern parts of the province, which include
numerous long-lived faults and faulted zones that may have facilitated
access of kimberlitic magmas from the deep mantle to the surface; (3)
there are stratigraphically and geochemically anomalous bentonites
which may be derived from local volcanic or kimberlitic extrusive
centers; (4) there are several areas within Alberta which have been
identified by widely spaced sampling to contain anomalous diamond
indicator grains that in some places include micro or macro diamonds
that have not, as yet, been traced to a bedrock source; and most
importantly, (5) there are at least 15 kimberlitic diatremes in north-
central and northwest Alberta, of which 10 are known to be
diamondiferous and several are reported to have micro diamond and
macro diamond counts which are similar to the early phases of
sampling of the diamondiferous kimberlites which exist at the
economically important Lac de Gras region, N.W.T. In short, we
conclude that, at present, ALBERTA IS INADEQUATELY EXPLORED FOR
DIAMONDIFEROUS DEPOSITS.
SELECTED REFERENCES
Dufresne, M.B., Leckie, D.A. and Eccles, D.R., In Press. Study of the
geochemical and stratigraphic setting of the Shaftesbury
Formation in northern Alberta and its potential to host ore
deposits; Geological Survey of Canada Open File Report.
Dufresne, M.B., Eccles, D.R., McKinstry, B., Schmitt, D.R., Fenton,
M.M., Pawlowicz, J.G. and Edwards, W.A.D., 1996. The
Diamond Potential of Alberta; Alberta Geological Survey
Bulletin No. 63, 158 p.
Dufresne, M.B., Olson, R.A., Schmitt, D.R., McKinstry, B., Eccles,
D.R., Fenton, M.M., Pawlowicz, J.G., Edwards, W.A.D. and
Richardson, R.J.H., 1994. The Diamond Potential of Alberta: A
regional synthesis of the structural and stratigraphic setting,
and other preliminary indications of diamond potential;
Alberta Research Council Open File Report, 1994-10, 349 p.
Dufresne, M.B., Henderson, B.A., Fenton, M.M., Pawlowicz, J.G. and
Richardson, R.J.H., 1994. The mineral deposits potential of
the Marguerite River and Fort McKay areas, Northeast
Alberta; Alberta Research Council Open File Report, 1994-9,
67 p.
Eccles, D.R., Dufresne, M.B. and Kjarsgaard, B.A., 1997. Heavy
mineral geochemical analysis of the Mountain Lake Diatreme;
In Geology of a Late Cretaceous possible kimberlite at
Mountain Lake, Alberta - chemistry, petrology, indicator
minerals, aeromagnetic signature, age, stratigraphic position
and setting; Geological Survey of Canada Open File 3441, p.
159-174.
Eccles, D.R., Dufresne, M.B. and Lywood, P., In Press.
Reconnaissance study of diamond and metallic mineral
potential for the Kakwa/Wapiti area, west-central Alberta;
Alberta Geological Survey Open File 1997-04.
Fenton, M.M., Pawlowicz, J.G., Andriashek, L.D., Dufresne, M.B.,
Chao, D., Price, M. and Goulet, D., In Press. Wapiti Map
Sheet 83L: Quaternary geology, till mineralogy and
geochemistry, preliminary report; Alberta Geological Survey
Open File Report.
Fenton, M.M., Pawlowicz, J.G. and Dufresne, M.B., 1994.
Reconnaissance mineral and geochemical survey with
emphasis on northern Alberta; MDA Project M92-04-006, year
2; Alberta Research Council Open File Report 1994-21.
Fenton, M.M., Pawlowicz, J.G. and Dufresne, M.B., 1996.
Reconnaissance mineral and geochemical survey with
emphasis on northern Alberta: project final report: MDA
Project M92-04-006; Alberta Geological Survey Open File
Report 1996-07.
Hamilton, W.N. and Olson, R.A. 1994. Mineral resources of the
Western Canada Sedimentary Basin; in G.M. Mossop and I.
Shetsen (eds.), Atlas of the Western Canada Sedimentary
Basin, Alberta Geological Survey of the Alberta Research
Council, and Canadian Society of Petroleum Geologists, pp.
483-501.
Olson, R.A. on behalf of the Alberta Chamber of Resources, 1987.
Alberta - Opportunities for Metallic Minerals; a
document
jointly prepared by Trigg, Woollett, Olson Consulting Ltd., and
the Alberta Geological Survey of the Alberta Research
Council, and subsequently published and distributed by the
Alberta Chamber of Resources.
Olson, R.A., Dufresne, M.B., Freeman, M.E., Richardson, R.J.H. and
Eccles, R.E. 1994. Regional metallogenic evaluation of
Alberta; Alberta Research Council Open File Report 1994-8.
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