document submitted 31/12/96 : note Carolyn Relf's move to
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
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.
(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
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,
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
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