document submitted 31/12/96 : note Carolyn Relf's move to
INAC 6/1/97
Approved March 14th, 1997 
1st Field Season, June-August, 1997 Simon Hanmer (Geological Survey of Canada) and Carolyn Relf (Indian and Northern Affairs)
Western Churchill NATMAP Program
The principal objective of the western Churchill NATMAP program is to
provide modern geological maps of late Archean greenstone belts in a part
of the Canadian Shield with great mineral potential, but lacking an adequate
geoscientific infrastructure. The maps will underpin an enhanced, multidisciplinary
geoscience knowledge base of the scale and scope required to formulate a
predictive framework for crustal growth, tectonic evolution and mineral
potential, and the establishment of environmental baselines for the western
Churchill Province. To that end, a set of integrated multidisciplinary objectives
are proposed:
Establish the tectonostratigraphy and tectonic settings of the late Archean
greenstone belts.
Determine the extent, nature and significance of Paleoproterozoic tectonothermal
events.
Investigate the evolution of the late Archean and Paleoproterozoic subcontinental
mantle and lower crust.
Identify the fundamental (plate?) tectonic boundaries .
Decipher the relationship of the mineral wealth to regional geology and
tectonic history.
Track the Quaternary history of the Keewatin Ice Divide.
Develop an accessible digital geoscience knowledge base and GIS.
In short, the proposed Western Churchill NATMAP Program's objectives can
be summarised as follows: To reveal the character and origin of the Archean
greenstone belts of the western Churchill, their mineral wealth, and associated
granitic continental crust, by lifting the veil of Paleoproterozoic intracontinental
tectonothermal and magmatic events"
The greatest impediment to mineral exploration in the western Churchill
Province (WCP) is the lack of modern, integrated, geological maps and an
adequate synthesis of the geological history of late Archean crustal growth
and mineralisation (VMS, Au). The importance of Paleoproterozoic events
in determining the present geological and metallogenic configuration of
the WCP has been recognised, yet we have few constraints on their distribution
in either space or time. Furthermore, although Quaternary deposits are extensive,
the glacial history of the WCP, especially that of the Keewatin Ice Divide,
is not well understood.
NATMAP serves to make the whole program greater than the sum of its parts
by fostering scientific synergy, and by permitting leveraging of funds within
the participating agencies. Four key words express the scientific difference
that NATMAP will make to this project: Collaboration: Sharing
of expertise and experience by active collaboration on all mapping projects
will re-enforce the participants (e.g. upgrading GNWT mapping, evaluation
of early Paleoproterozoic events as a team, bridging the gap between recent
INAC work and planned GSC mapping, and an end of season field meeting for
program participants and industry clients). Continuity:
Enabling a geochronologist, a lithogeochemist, a physical stratigrapher,
and a structural geologist to work at the program scale with scientists
in all of the bedrock mapping projects. Calibration: Constraints
offered by geochronology, lithogeochemistry, thermobarometry, and geophysics.
Canadians: Offering young Canadian scientists the opportunity to
undertake graduate research leading to higher degrees, and to fill the national
shortfall in geological expertise.
The Western Churchill Program brings government, university and industry
participants together and directly addresses NATMAP's themes and objectives:
By shedding new light on the Archean and Paleoproterozoic tectonic development
of the WCP, and the Laurentide Ice Sheet, it will contribute to bridging
major gaps in fundamental geoscience knowledge. In combination with mineral
deposits and metallogeny studies, the bedrock and surficial mapping will
provide an improved infrastructure for economic development, while studies
of Quaternary deposits and permafrost will provide baseline data of immediate
relevance to land use and environmental concerns. As will be clear from
the list of Outputs, this program will maximise the application of digital
technologies.
A major advance will be made in raising the level of understanding of
a huge area of the Canadian landmass toward standards adequate for mineral
exploration and sustainable resource development.
Geoscientific
Socio-Economic
(1) An integrated digital geoscience map base and GIS for the western
Churchill, incorporating all of the stand-alone products listed below. Digital
releases 2000 and 2002.
(2) Sets of new 1:50000 bedrock maps from the Kaminak (12), MacQuoid (8),
Woodburn (10), Yathkyed (3) and Angikuni (4) greenstone belts, plus a 1:125000
compilation with an upgraded stratigraphic content for Kaminak Lake. Digital
releases and upgrades commencing 1998.
(3) 1:125000 ice flow indicator maps of the Keewatin Ice Divide area (10),
sets of new 1:50000 surficial geology maps over 4 greenstone belts, locally
with terrain sensitivity components (12), and 1:125000 thematic till composition
maps integrated with new bedrock bases (3). Digital releases and upgrades
commencing 1998.
(4) Mineral deposit and metallogenic maps at various scales, plus an integrated
mineral showing/prospect/deposit/model database for the western Churchill
Province. Digital releases and upgrades commencing 1998.
(5) Up to 125 new U-Pb ages, and 500 lithogeochemical analyses (+ model
ages) in supracrustal rocks and granitoids, all integrated into the integrated
digital geoscience map base. Digital release 2000 and 2002.
(6) Teleseismic and magnetotelluric crustal and lithospheric cross-sections
across the potential Archean suture and across the STZ, hung from the integrated
digital geoscience map base. Digital release 2000.
(7) Regional and targeted aeromagnetic maps incorporating industry data
and optimised for GIS integration with digital geological information, as
well as regional gravity maps and targeted profiles. Digital release commencing
1999.
(8) Annual presentation of previous field season's maps at GAC, Yellowknife
Geoscience Forum, GSC Forum, and the Nunavut Mining Symposium. Annual workshop
to present and discuss previous year's results, with book of extended abstracts,
starting 1997. Yellowknife or Ottawa. All starting 1997.
(9) A short course dealing with western Churchill NATMAP data, interpretations,
tools and techniques, (GSC Forum 2000).
(10) Symposium (GAC) of interpretations and predictive modeling of NATMAP
data, with a collection of papers in a Special Issue of CJES. Certainly
2002, possible interim Special Session (GAC) in 2000.
The western Churchill Province (WCP), one of the largest yet most poorly
known fragments of Archean crust in the world, contains an extraordinary
diversity of gold, base metal and uranium resources, and diamond prospects.
It also includes a substantial part of Nunavut. Work by government agencies
and the private sector has successfully highlighted the mineral potential
of the WCP, which is seen today as an important gold province. However,
the lack of a comprehensive geoscience knowledge infrastructure, including
modern geological maps in key areas, continues to hamper mineral exploration
and effective land use management. The absence of modern integrated maps
is exacerbated by the sheer aggregate size of the WCP, it's potential internal
complexity, and the long span of geological time during which it was subjected
to major Province-wide geological events. For example, the tectonostratigraphy
of the Archean supracrustal belts remains essentially unknown, and we have
little understanding of the Paleoproterozoic deformation and metamorphism
which affected them. Compounding the gaps in our knowledge of the bedrock
geology, the glacial history of the Quaternary sediments deposited by the
largest sector of the Laurentide Ice Sheet remain poorly known, despite
their importance for mineral exploration, and for the formulation of environmental
baselines.
The WCP has many features in common with other Archean terranes, such as
the Slave and Superior Provinces. From the crustal perspective, they contain
potentially juvenile late Archean (ca. 2.8-2.65 Ga) greenstone belts, with
variable sediment/volcanic rock ratios, now juxtaposed against possible
middle Archean cratonic nuclei. At the lithospheric scale, they are underlain
by stiff, buoyant mantle roots, which may be broadly coeval with the greenstone
belts. What sets the WCP apart from its Canadian equivalents, and many other
Archean cratons elsewhere in the world, is the extent and intensity of Proterozoic
tectonothermal events which have significantly affected the greenstone belts
and the intervening continental crust. In order to decipher the late Archean
supracrustal belts, the effects of the Paleoproterozoic tectonometamorphism
must also be understood. It is already clear that these include significant
uplift of deep crustal (granulite facies) levels along the Snowbird tectonic
zone (STZ, Chesterfield Inlet), plus high grade shear zones, migmatisation
and low grade thrusting further south. Moreover, Paleoproterozoic deformation
has significantly enhanced some Archean mineral resources, and controlled
others of Paleoproterozoic age.
It is useful to very briefly review the principal trains of thought concerning
the tectonic constitution and development of the WCP. Archean supracrustal
rocks SE of the STZ were initially treated as a large coherent greenstone
belt (Rankin-Ennadai), comparable in scale to the Abitibi belt (Superior
Province). The contrast between these and comparable supracrustal rocks
to the NW led in part to the suggestion that two "provinces" (Rae
and Hearne) were separated by a Paleoproterozoic suture, represented by
the STZ. However, further mapping and geochronology showed that the STZ
is Archean in origin, although reactivated in the Paleoproterozoic, and
questioned the suture model. Sparse, but intriguing seismic, Sm-Nd (Tdm),
U-Pb and geological data allow speculation that a fundamental cryptic boundary
may lie at an high angle to the STZ, possibly separating an older Archean
"cratonic nucleus" to the SW from late Archean crust to the NE.
Recent mapping of Paleoproterozoic supracrustal rocks suggests that the
ca. 2.45-2.1 Ga Hurwitz Group represents a large intracontinental basin,
developed on a slowly stretching late Archean supercontinent. Although Paleoproterozoic
deformation and plutonism has long been known in the WCP, only recently
has its potential extent been appreciated, and a time bracket (ca. 1.9-1.8
Ga) attributed to it. As Paleoproterozoic deformation waned, a huge volume
of intracontinental ultrapotassic volcanic rocks (Christopher Island Formation)
and dykes were emplaced onto and into the WCP.
In the WCP NATMAP program, the concept of a composite "Rankin-Ennadai
greenstone belt", extending across much of the Hearne crust and comparable
to the economically important greenstone belts of the Superior Province,
will be evaluated by establishing robust stratigraphies and time lines.
The goals are to determine (i) if the individual segments of the "belt"
are related or independent, (ii) their original tectonic settings, and (iii)
their genetic relationship to the growth of the WCP as a whole. The approach
will be strategic bedrock mapping, supported by lithogeochemistry and geochronology.
Investigation of the evolution of the WCP as a whole requires additional
broad-reach tools, such as targeted lithogeochemistry, plus cost-effective
teleseismic and magnetotelluric experiments. Existing data suggest that
two end-member types of greenstone belt are represented by the ca. 2.8 Ga
Woodburn Group (Rae; continental?) and the ca. 2.7 Ga Kaminak Group (Hearne;
oceanic?), with the poorly dated, but potentially ca. 2.68-2.66 Ga MacQuoid,
Yathkyed, Angikuni and Rankin Inlet areas representing intermediate settings.
It is possible that Rae crust might extend southeast of the STZ, thereby
calling into question the nature of the latter as a fundamental structural
break. However, the foregoing is just speculation as long as the internal
stratigraphy, structure, and local tectonic setting(s) of the greenstone
belts remain unknown and potentially complex.
Bedrock mapping will focus on 5 areas, one in the Rae "province"
and four in the Hearne. GNWT and INAC will place 2-5 person mapping parties
in the Yathkyed (1997-1998) and Angikuni lakes (1997-1999) areas, respectively.
GSC will place a 4 person mapping party in the Woodburn area (1998-1999),
and focused 6-8 person mapping parties in the Tavani-Kaminak-Heninga lakes
(1997) and the MacQuoid-Gibson lakes (1998) areas. In 1999, GSC will adopt
a targeted approach to completing mapping coverage and revisiting strategic
questions raised during the earlier work.
Tavani-Kaminak-Heninga lakes (GSC)
Although parts of the greenschist facies Kaminak belt (sensu lato) have
been mapped at 1:50000 scale (parts of Tavani and Kaminak Lake areas), a
consistent belt-wide tectonostratigraphy has yet to be established. Accordingly,
the principal local objective will be to develop an upgraded tectonostratigraphy
(stratigraphy, geochronology and lithogeochemistry) from the Tavani area
in the NE, via the Kaminak Lake area to the Heninga Lake area in the SW
(Peterson, Hanmer,
Tella + 1 PDF +3 students).
The scale of work in the Tavani area will be problem dependent. The tectonostratigraphy
will be extended to the Kaminak Lake area by systematic field work in collaboration
with GNWT staff, resulting in a 1:125000 compilation map underpinning an
upgraded geoscience knowledge base. The south side of Kaminak Lake, and
the area between Kaminak and Heninga lakes, currently being explored by
INCO and others, will be systematically mapped, resulting in 12 new 1:50000
map sheets. Mapping outside of the supracrustal rocks is essential, but
must be undertaken strategically as the area is vast and outcrop highly
variable. The supracrustal rocks are cut by subvolcanic batholiths, which
could represent the heat engines for hydrothermal systems of potential economic
importance. They will also provide further petrological constraints on the
tectonic setting of the belt, the second local objective. Pre-greenstone
basement, if found, will be dealt with on an opportunistic basis. Post-greenstone
belt plutons, such as the Snow Island suite (ca. 2.65-2.55 Ga) and Nueltin
granites (ca. 1.8-1.75 Ga) are potential petrological probes of the evolving
nature of the lower crust and upper mantle (Peterson).
A limited number of type examples will be systematically mapped for this
purpose.
Several field markers can be used to discriminate between Archean and Paleoproterozoic
tectonothermal events. The ca 2.45-2.1 Ga Hurwitz Group intracontinental
sedimentary rocks outcrop within the greenstone belt. The post-Hurwitz structures
are weak in the NE part of the Archean supracrustal belt, but are strongly
developed to the SW. Metamorphic grade in the ca. 2.45 Ga NNE trending Kaminak
mafic dyke swarm increases both N and S of the greenstone belt. Taken together,
potentially Paleoproterozoic metasediments (Mackenzie Lake) north of the
greenstone belt, and the lack of perceptible deflection of associated Kaminak
dykes, are suggestive of high grade Paleoproterozoic deformation and metamorphism
much older than hitherto suspected (possibly pre-2.45 Ga). Dismemberment
of Kaminak dykes in migmatites just N of the Mackenzie Lake sediments points
to an even higher grade, post-dyke Paleoproterozoic event. Combined with
deformation of the Hurwitz Group, the implication is that multiple, potentially
unrelated, Paleoproterozoic orogenic events may have affected the WCP. In
order to evaluate these possibilities, and to strategically target the granitoid
rocks outside of the greenstone belt, a pilot mapping transect will be run
in collaboration with GNWT and INAC (Relf,
Irwin and Aspler),
from the Kaminak belt to just north of Mackenzie Lake.
Given the variability of outcrop quality and continuity, the mapping will
greatly benefit from enhancement and application of existing aeromagnetic
data, in order to more effectively extrapolate key marker horizons, such
as iron formations (Roest et
al. + 1 student). Opportunities for integration of industry data will be
actively sought, but will require funding a contract assistant. In 3D, the
boundaries of the greenstone belt may not conform to the gross orientation
of mappable structures in its interior. The only feasible way to determine
the overall 3D geometry of the greenstone belt is through gravity modeling
along carefully selected traverses (Roest
et al.). The first order questions will concern the gross symmetry of the
belt: e.g. if asymmetrical, which way does the lower boundary dip? The results
will be critical to structural interpretations of the greenstone belt, especially
if it is allochthonous.
MacQuoid(GSC), Yathkyed (GNWT), Angikuni (INAC) and
Woodburn (GSC) belts
Using the foregoing description of the investigation of the Kaminak belt
as a template, much of the scientific strategy for the work in the MacQuoid,
Yathkyed, Angikuni and Woodburn belts (sensu lato) will not be repeated
here. However, each of these projects will make its own contribution to
the broader program-scale objectives, and generate new 1:50000 scale geological
maps in each area. The Yathkyed project area straddles the boundary between
the Kaminak and Yathkyed belts. The principal local objective is to compare
the stratigraphy, tectonic setting and age of the two belts, with emphasis
on the lesser known and potentially younger Yathkyed belt (Relf,
Irwin + 4 students). The contact
between the two belts is marked by a prominent linear magnetic anomaly,
spatially coincident with Hurwitz Group sediments. The second local objective
is to evaluate the possibility that the contact is a major Paleoproterozoic
fault, and to document the tectonothermal overprint on the Archean supracrustal
belts. The Angikuni project area (Aspler,
Chiarenzelli, Cousens
+ 2 students) contains potential crystalline basement to the greenstone
belt rocks, as well as a late Archean shallow water supracrustal sequence.
The supracrustal rocks may be underlain by Rae crust, east of the STZ, and
potentially include a post-2.68 Ga unconformity within the sequence. Comparison
with recent mapping at Rankin Inlet suggests that the unconformity may be
of regional extent, and therefore of tectonic significance for any model
of formation of the WCP greenstone belts. The prime local objective is to
test these tectonostratigraphic speculations. The project area also includes
the greenschist facies Tulemalu fault and a number of satellite shear zones,
nominally parts of the STZ. A second local objective is to evaluate the
Archean and potentially Paleoproterozoic evolution of the fault array, especially
with regard to the uplift history.
The amphibolite facies MacQuoid belt is made up of a number of spatially
isolated 'belts' with different proportions of sedimentary and volcanic
rocks. Through new 1:50000 scale mapping (Tella,
Hanmer, Peterson
+ 1 PDF + 3 students), it will be determined if they are indeed contemporaneous
and/or genetically related, in order to permit comparison with the other
greenstone belts. Deformed E-W trending ca 2.2 Ga mafic dykes, which cut
the Archean structures in the greenstones, indicate that deformation is
polyphase with a strong Paleoproterozoic shear zone component developed
at the margins of the MacQuoid belt. Comaplex, Cumberland and Redfern Resources
are actively exploring for gold in the area.
The MacQuoid project area is well placed to investigate the Archean and
Paleoproterozoic tectonothermal and uplift histories of strategic parts
of the enigmatic STZ in Chesterfield Inlet, where it represents the deepest
seated, highest temperature component of the Paleoproterozoic tectonothermal
overprint on the NE Hearne "province". Once interpreted as part
of a Paleoproterozoic suture, its genetic and kinematic link to other segments
of the STZ are now in question. The fundamental problem here is how very
high temperature Paleoproterozoic gneisses were juxtaposed with Archean
rocks which accurately preserve their Archean cooling histories. This implies
very rapid Paleoproterozoic uplift and cooling soon after peak metamorphism
at ca 1.9 Ga. Field work will involve small-scale operations, probably university
based, in key areas such as the western Uvauk complex, with GSC involvement
in thermobarometric (Berman
and Gordon + 2 students) and geochronological
studies (Davis). The Paleoproterozoic
uplift history will be a key factor in understanding the northward increase
in metamorphic grade in the greenstone belts across the NE Hearne crust
as a whole. By building on a 'type section' in the STZ, where initial data
are available, there is an opportunity for comparison of coeval Paleoproterozoic
uplift histories preserved in the MacQuoid, Yathkyed and Angikuni areas
(Berman).
Recent work in the Woodburn area, in collaboration with McChip and Cumberland
Resources, suggests that the published stratigraphy of the Woodburn Group
is inverted, placing thick quartzites beneath a supracrustal succession
of komatiites, mafic to felsic volcanic rocks, and iron formations. The
revised stratigraphy invites comparison with so-called platformal greenstone
belts elsewhere (Slave and Superior), deposited on older continental basement.
The prime local objective in the Woodburn area will be to establish the
environment of deposition of the Woodburn Lake Group in order to allow comparison
with the greenstone belts to the south (Zaleski
et al.). From the sparse available data, greenstone belts in the Rae "province"
(ca. 2.8 Ga) appear to be older than those in the Hearne (ca. 2.7-2.65 Ga),
as well as being tectonically and metallogenically distinct. Resolving these
questions will contribute to testing the veracity of the Rae-Hearne dichotomy
as a fundamental break.
In all of the greenstone belt projects, the tectonostratigraphy set up during
the field work will be tested and modified by geochronology and lithogeochemistry,
which will also provide constraints on their tectonic settings. These petrological
data will be central to testing the speculation that NE part of the WCP
is late Archean crust now juxtaposed with older, middle Archean material
to the SW. Integrating bedrock mapping with U-Pb geochronology and uplift/cooling
studies, Sm-Nd isotope and igneous petrology, and geothermobarometry (Davis et al. and Berman)
will allow development of a whole-crust model for the greenstone belts.
In the WCP, a wide variety of mineral deposit types formed during the
Archean and Proterozoic, in a diverse suite of host rocks. Bedrock mapping,
lithostratigraphy pinned by geochronology, and paleotectonic setting studies,
integrated with mineral deposit research will provide the basis for understanding
metallogeny from a regional perspective. The NATMAP program represents an
opportunity to improve existing deposit models in the WCP, as well as develop
new ones. Multi-agency mineral deposit/metallogenic research (Kjarsgaard,
Kerswill, Goff,
Jenner + 3 students) will
be undertaken at three different scales (program-wide, regional or greenstone
belt, and deposit specific). A mineral showings database will initially
be developed individually for each greenstone belt under study. These databases
will form the basis for a WCP-wide database, incorporating information from
the NT-Minfile, MinSys, and Camindex databases, plus additional data from
recent assessment reports, and other non-confidential geological observations.
Regional and WCP-wide mineral occurrence and metallogenic domain maps will
be generated during the course of the project. In 1997, work will focus
on the Woodburn, Kaminak and Yathkyed belts. Work in 1998 will continue
in these belts, and include the MacQuoid and possibly Angikuni belts. Studies
in subsequent years will examine previously highlighted problems.
The principal deposit types in the WCP include: BIF hosted gold, vein gold,
volcanogenic massive sulphide, magmatic sulphides, and primary diamond deposits.
VMS deposits form in a wide variety of associations (volcanic vs sediment
vs mixed) and tectonic settings (mid-ocean ridge; island arc; back arc).
Massive sulphide deposits in sediment-dominated settings form in intracontinental
rifts, rifted continental margins, oceanic ridges near continents and back
arc basins. Metallogenic (viz. tectonic) identification of VMS deposit types
will directly contribute to developing and constraining tectonic models
for the formation of WCP greenstone belts. Similarly, gold prospects occur
in a variety of settings, including BIF-hosted syn- and epigenetic gold,
and shear zone and fault hosted vein gold. Apparent contrasts in the style
of gold (e.g. Woodburn and Meliadine) emphasises the importance of understanding
the timing of gold mineralization with respect to regional deformation and
metamorphism. Detailed mineral deposit studies will document the critical
features of the primary depositional setting for synvolcanic and synsedimentary
deposits, and the critical features of deformational/metamorphic processes
associated with deposits controlled by late tectonic events. This will allow
recognition of prospective metalliferous environments elsewhere in WCP,
and thus help guide future mineral exploration.
The Late Archean and Paleoproterozoic evolution of the subcontinental
mantle is recorded by large-scale, widespread magmatic and structural features.
These may include a cryptic tectonic suture, lithospheric folds, a crustal-scale
fault (STZ), at least two granite "blooms" (Snow Island and Nueltin),
several diabase dyke swarms, and a giant ultrapotassic magma field. They
can only be effectively investigated by incorporating integrated broad-reach
techniques, such as petrological and isotopic research (Peterson,
Cousens and Davis),
long wavelength gravity data (Roest
et al.), and teleseismic and magnetotelluric experiments (White
et al. and Eaton). As in other
Archean cratons world-wide, the WCP is thought to be underlain by a refractory,
buoyant mantle root, extending down to ca. 400 km depth. Although the root,
as established from seismic data, is apparently remote from crustal features
targeted by the bedrock mapping projects, its existence places significant
constraints on crust-mantle interaction and crustal melting in models derived
for other components of the WCP NATMAP program. Because lithospheric roots
are classically interpreted to result from massive basalt and komatiite
extraction from the upper mantle, the assumed late Archean age for the WCP
mantle root may have implications for the tectonic setting of the penecontemporaneous
greenstone belts. It may also present a hurdle to the application of delamination
models, formulated in younger settings, to explain the widespread nature
of crustal and mantle-derived magmatic suites (ca. 2.6 Ga Snow Island and
ca. 1.8-1.7 Ga Nueltin granitoids). Furthermore, a huge volume of ultrapotassic
material (Christopher Island Formation) was erupted at ca. 1.85-1.80 Ga,
derived by melting of strongly metasomatized upper mantle. Although Province-wide
upper mantle enrichment could be related to shallowly dipping Paleoproterozoic
subduction beneath the WCP (ca. 2.0-1.8 Ga), it is not obvious how a late
Archean mantle root would be preserved. Nevertheless, given the presence
of diamonds in ultrapotassic dykes, the timing and distribution of upper
mantle metasomatism has implications for mineral exploration.
The age and nature of the root are tentatively predicated on sparse seismic
data for the upper mantle. Spatial variation of seismic shear wave velocity
for the WCP grossly outlines a deep seated boundary between faster lithosphere
to the SW and slower lithosphere to the NE. This suggestion derives some
support from the distribution of a limited number of Sm-Nd model and U-Pb
magmatic ages in both the Rae and Hearne "provinces" (Middle to
Late Archean in the southwest vs Late Archean in the northeast). This raises
the possibility that the major tectonic boundary in the WCP is cryptic and
lies at a high angle to the STZ, separating a middle Archean crust to the
SW from younger late Archean crust to the NE. Such a boundary might also
be reflected in variations in crustal thickness, presence/absence of a high
velocity zone at the base of the crust, distribution of electrical resistivity
within the crust and upper mantle, as well as differences in seismic and
electrical anisotropy, and degree of mantle metasomatism. Similar characteristics
could enable the STZ at to be imaged at depth to determine its gross orientation,
and whether it is an intra-crustal fault or a fundamental lithospheric-scale
structure.
The proposed teleseismic - magnetotelluric experiment (1998-1999) would
deploy 8 geophysical instruments along profiles parallel and perpendicular
to the STZ. Complete analysis of the data would include anisotropy measurements,
as well as mapping of sub-horizontal lithospheric boundaries and the seismic
and conductivity structure of the lithosphere. According to existing criteria,
the test of the age of the lithosphere is as follows: if it is indeed late
Archean, then mantle structure should reflect the penetrative nature and
orientation of the late Archean crustal structure. Otherwise it may reflect
the discontinuous nature of Paleoproterozoic crustal deformation, or show
no geometrical correlation with crustal structure at all.
The lithogeochemistry of granitoids is a powerful, broad-reach, petrotectonic
tool. Strategically upgrading the distribution of well constrained Sm-Nd
model ages across the WCP, and obtaining new Pb isotope data, will contribute
to testing the possible existence of an older cratonic nucleus to the SW,
and the postulated differences between Rae and Hearne "provinces"
(Peterson and Cousens;
1997 and ongoing). The principal gap in the existing data set lies in the
NE Hearne, where NATMAP bedrock mapping will be focused. The widespread
distribution of ca. 2.6 Ga Snow Island suite granitoids across the WCP does
not correspond to the belt-like configuration expected for classical subduction-related
magmatic arcs, and their genesis remains a fundamental problem in the crustal
evolution of the WCP. By exploiting them as crustal and mantle probes, one
can test for contemporaneous basaltic underplating, with direct repercussions
for the age of the inferred mantle root. Mafic and ultrapotassic dyke swarms
intruded from ca. 2.45 Ga to ca. 1.8 Ga, represent further probes into the
evolving lithospheric mantle through the Paleoproterozoic.
The salient point here is that these broad-scale crustal and lithospheric
features reflect the boundary conditions determining the late Archean and
Paleoproterozoic tectonic evolution of the WCP. Without constraints, interpretations
of the NATMAP geological mapping will remain inherently equivocal.
The Keewatin Ice Divide is the last centre of the Keewatin Sector of
the Laurentide Ice Sheet. The sequence of ice flow events and the migration
of the divide with time have influenced the entire sector, yet they are
not well understood. Nonetheless, it is known that the ice divide was spatially
coincident with the STZ, and that it migrated generally eastwards from ca.
11000-8000 years ago. Establishing the ice flow history will impact on bedrock-related
mineral exploration across the WCP. This will be achieved through upgrading
existing surficial maps, including glacial landform and ice flow indicator
datasets, by regional field work throughout the NATMAP program area (McMartin, geologist + 2 students).
Combined with regional ice flow mapping, stratigraphic sections and available
drill core datasets will be used to identify changes in till provenance
and associated shifts in ice flow.
Given the extent of Quaternary deposits in the WCP, it is only by combining
complementary bedrock and surficial studies that the knowledge base essential
for successful mineral exploration will be obtained. By combining surficial
and geochemical mapping over the greenstone belts, Quaternary studies will
be applied directly to mineral exploration, integrated at a more detailed
scale with mineral deposit studies and bedrock mapping. Mapping of till
composition will also aid bedrock mapping in areas of poor outcrop; petrologically
distinctive marker horizons can be located to within a few km's of their
position beneath the Quaternary cover. Detailed field studies with WMC in
the Meliadine belt, north of Rankin Inlet (McMartin 1997-1998) will demonstrate
the ability to map concealed bedrock, and to locate sources of mineralized
drift. In addition to surficial mapping, till geochemistry and permafrost
studies will form the basis for establishing environmental baselines. Such
data will be required for resource development activities, ranging from
the construction of access roads, to the assessment of the potential impact
of mine development. An initial permafrost study is planned for the WMC
Meliadine gold development (Wolfe
and Dyke 1997). Similar work
in the Yathkyed (McMartin
1997-1998), MacQuoid and Angikuni lakes areas (geologist 1997-1999) will
focus on the ice divide itself where indications of both NW and SE flow
are present. However, without NATMAP funding for the geologist, it will
not be possible for McMartin alone to undertake the MacQuoid and Angikuni
work.
In an undertaking of the scope of the western Churchill NATMAP program,
it is essential to maintain a common perspective among all the participants.
Diverse sets of existing bedrock, mineral deposit, surficial and geophysical
data can be rendered most useful if they are first collated and housed in
uniform digital format, in a common projection. New information stemming
from the on-going mapping program can be directly integrated with minimal
delay. In light of the diversity of geoscientific activities and client
needs, and the variety of computer platforms in use, the most efficient
vehicle for ensuring coordination and easy access to the evolving data sets
is a central GIS database, with access
via the Internet. As an analytical resource, this form of database management
will encourage communication between geoscientific disciplines and participating
agencies, and enhance the multidisciplinary interpretation and visualization
of geoscience problems (Wilkinson
and Broome).
The principal product of the western Churchill NATMAP program will be new
sets of maps (bedrock, metallogenic, surficial and geophysical) at a variety
of scales (1:50000, 1:125000 and 1:250000) of spatially discontinuous areas.
However, the integrated product must be coherent, and of greater value than
the individual components. Accordingly, 1:500000 compilations of large segments
of the WCP in both the Rae and Hearne "provinces" will be combined
in a common base into which the NATMAP data will be integrated. This will
place the new work in a regional context, as well as enhancing the predictive
value of current information.
Geological and processed potential field data can be readily overlain, mutually
enhancing their utility. More than data management and visualisation, GIS
offers analytical capabilities for the treatment of point information (e.g.
lithogeochemistry) in testing correlations with the bedrock geology, for
example within and between greenstone belts, or plutonic suites. Predictive
economic mineral favourability maps can be constructed from knowledge-based
modeling of bedrock, surficial and geophysical data. Combining multiple
remotely sensed parameters by using a trained classifier (e.g. artificial
neural network) can provide reconnaissance-level predictive geological maps
(Brodaric et al.), and assist
in filling gaps in mapping coverage between bedrock project areas where
outcrop is poor and/or access is difficult, as is commonly the case in the
WCP.
NATMAP funding will provide the opportunity to build scientific bridges
by fostering interaction between the agencies and projects, by funding personnel
who will bring much needed expertise and knowledge to the research team,
and by ensuring high quality work throughout the program.
Collaboration: Each agency could operate independently,
but active collaboration makes the whole greater than the sum of its parts.
Sharing of knowledge in the field in the form of personnel exchange, and
active collaboration on key mapping actions will re-enforce all of the participants.
Targets for 1997 include (a) GSC-GNWT collaboration to upgrade the tectonostratigraphy
of the 1:50000 mapping recently completed by GNWT along the north side of
Kaminak Lake; (b) GSC-GNWT-INAC pilot transect to the Mackenzie Lake sediments
north of the Kaminak greenstone belt to evaluate the potential for pre-2.45
Ga Paleoproterozoic deformation and metamorphism; (c) GSC-INAC collaboration
to bridge the poorly exposed gap between recent INAC coverage and the SW
extent of planned GSC mapping SW of Heninga Lake; (d) an end of season field
workshop for NATMAP and industry participants in the Kaminak (1997) and
MacQuoid (1998) project areas. Calibration and Continuity:
Calibration offered by good geochronology and lithogeochemistry is essential
for stratigraphic correlations and tectonic settings, as is the depth control
offered by geothermobarometry and geophysics for larger scale extrapolations
and tectonic models. All bedrock projects, including GNWT and INAC, will
be looking to the GSC for isotope support (from absolute dating to petrological
tracers). The workload implied by the stratigraphic and tectonic studies
of all bedrock projects, and the general lack of expert stratigraphic skills
throughout the NATMAP teams (INAC excepted), require the involvement of
an additional geochronologist/lithogeochemist and a physical stratigrapher.
These scientists are required to ensure scientific continuity between the
various bedrock projects by working with scientists in all of the projects
participating in the program. Similarly, a structural geologist (post-doctoral
fellow) will be essential to enable Hanmer to dedicate 35% of the field
season to building scientific bridges between the different WCP NATMAP projects,
and providing scientific leadership at the program scale. Canadians:
NATMAP support will make the difference between simply hiring student mapping
assistants, and offering young Canadian scientists the opportunity to undertake
graduate research leading to higher degrees, and ensuring them multi-year
continuity, even when the bedrock mapping priorities change from year to
year. Examples: students working independently on specific topics in the
Kaminak belt (stratigraphy), Whitehills-Meadowbank belt (metallogeny) and
the STZ (Paleoproterozoic deformation and metamorphism).
Aspler, L. INAC Sedimentology,
stratigraphy, bedrock mapping, leader Angikuni.
Berman, R. GSC/CGD Geothermobarometry.
Broome, J. GSC/CGD GIS, geological
integration.
Brodaric, B. GSC/CGD Virtual
reconnaissance mapping from remotely sensed data.
Buchan, K. GSC/CGD Proterozoic
dyke swarms, paleomagnetism.
Chiarenzelli, J. SUNY Oswego
Lithogeochemistry, bedrock mapping, Angikuni.
Cousens, B. Carleton U. Lithogeochemistry,
Angikuni.
Davis, B. GSC/CGD Geochronology.
Dyke, L. GSC/TSD Permafrost,
Quaternary.
Eaton, D. UWO Teleseismic, crustal
and upper mantle geophysics.
Goff, S. INAC Regional metallogeny.
Gordon, T. Calgary U. Geothermobarometry,
STZ, thesis supervisor
Hanmer, S. GSC/CGD NATMAP co-leader,
structural geology, bedrock mapping Kaminak and MacQuoid, scientific continuity.
Irwin, D. GNWT Bedrock mapping, Yathkyed.
James, D. Laurentian U. Mineral deposits, gold, Whitehills-Meadowbank
Jenner, G. MUN Metallogeny,
VMS-Ni deposit studies.
Jones, A. GSC/CGD Magnetotelluric,
crustal and upper mantle geophysics.
Kjarsgaard, B. GSC/MRD Metallogeny,
VMS-Ni deposit studies.
Kerswill, J. GSC/MRD Metallogeny,
gold, iron formations.
LeCheminant, A. GSC/CGD
Proterozoic dyke swarms, lithogeochemistry
McMartin, I. GSC/TSD Ice flow,
till deposits, Quaternary, Keewatin Ice Divide.
Peterson, T. GSC/CGD Lithogeochemistry,
bedrock mapping, Kaminak.
Relf, C. INAC NATMAP co-leader, bedrock
mapping, leader Yathkyed.
Roest, W. GSC/CGD Potential fields,
magnetics.
Tella, S. GSC/CGD Bedrock mapping,
leader MacQuoid.
Waldron, J. St Mary's U.
Sedimentology and structural geology, thesis supervisor.
White, D. GSC/CGD Teleseismic,
crustal and upper mantle geophysics.
Wilkinson, L. GSC/CGD GIS,
geological integration.
Wolfe, S. GSC/TSD Permafrost,
Quaternary.
Zaleski, E. GSC/CGD Bedrock
mapping, leader Whitehills-Meadowbank.
Unnamed* GSC/CGD Sedimentology, stratigraphy, physical volcanology, scientific
continuity at program scale, bedrock mapping Kaminak.
Unnamed* GSC/CGD Lithogeochemistry, isotopic to tracer petrology with emphasis
on the supracrustal sequences, scientific coordination and continuity at
program scale.
Unnamed* GSC/CGD Contract assistant, integration of industry aeromagnetic
data.
Unnamed* GSC/TSD Quaternary geologist, MacQuoid and Angikuni.
PDF* GSC/CGD Structural geology, bedrock mapping, Kaminak and MacQuoid.
12 thesis students* Universities Bedrock mapping, field-oriented stratigraphic
and geochemistry studies, structure and thermobarometry, metallogeny, potential
fields and Quaternary studies (all projects).
6 student assistants Universities Bedrock and surficvial mapping, aeromagnetics.
Comaplex Industry Logistical support, Kaminak
INCO Industry Logistical support, Kaminak
Cumberland Industry Logistical support, Whitehills-Meadowbank
McChip Industry Logistical support, Whitehills-Meadowbank
WMC Industry Logistical support, Meliadine
* = require direct NATMAP funding support
Western Churchill NATMAP
Simon Hanmer's Home Page